Merge remote-tracking branch 'origin/release-v1.106' into matrix-org-hotfixes

2024-09-17 18:55:10 +00:00 · 2024-04-25 16:01:00 +01:00 · 2024-04-25 16:01:00 +01:00 · b9639065eb
commit b9639065eb
parent 31ac8b745c 30c50e0240
50 changed files with 1712 additions and 217 deletions
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@ -30,7 +30,7 @@ jobs:
        run: docker buildx inspect

      - name: Install Cosign
-        uses: sigstore/cosign-installer@v3.4.0
+        uses: sigstore/cosign-installer@v3.5.0

      - name: Checkout repository
        uses: actions/checkout@v4
--- a/.github/workflows/docs-pr.yaml
+++ b/.github/workflows/docs-pr.yaml
@ -19,7 +19,7 @@ jobs:
          fetch-depth: 0

      - name: Setup mdbook
-        uses: peaceiris/actions-mdbook@adeb05db28a0c0004681db83893d56c0388ea9ea # v1.2.0
+        uses: peaceiris/actions-mdbook@ee69d230fe19748b7abf22df32acaa93833fad08 # v2.0.0
        with:
          mdbook-version: '0.4.17'

@ -53,7 +53,7 @@ jobs:
      - uses: actions/checkout@v4

      - name: Setup mdbook
-        uses: peaceiris/actions-mdbook@adeb05db28a0c0004681db83893d56c0388ea9ea # v1.2.0
+        uses: peaceiris/actions-mdbook@ee69d230fe19748b7abf22df32acaa93833fad08 # v2.0.0
        with:
          mdbook-version: '0.4.17'

--- a/.github/workflows/docs.yaml
+++ b/.github/workflows/docs.yaml
@ -56,7 +56,7 @@ jobs:
          fetch-depth: 0

      - name: Setup mdbook
-        uses: peaceiris/actions-mdbook@adeb05db28a0c0004681db83893d56c0388ea9ea # v1.2.0
+        uses: peaceiris/actions-mdbook@ee69d230fe19748b7abf22df32acaa93833fad08 # v2.0.0
        with:
          mdbook-version: '0.4.17'

@ -80,7 +80,7 @@ jobs:

      # Deploy to the target directory.
      - name: Deploy to gh pages
-        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3.9.3
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e # v4.0.0
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          publish_dir: ./book
@ -110,7 +110,7 @@ jobs:

      # Deploy to the target directory.
      - name: Deploy to gh pages
-        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3.9.3
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e # v4.0.0
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          publish_dir: ./dev-docs/_build/html
--- a/CHANGES.md
+++ b/CHANGES.md
@ -1,3 +1,59 @@
+# Synapse 1.106.0rc1 (2024-04-25)
+
+### Features
+
+- Send an email if the address is already bound to an user account. ([\#16819](https://github.com/element-hq/synapse/issues/16819))
+- Implement the rendezvous mechanism described by [MSC4108](https://github.com/matrix-org/matrix-spec-proposals/issues/4108). ([\#17056](https://github.com/element-hq/synapse/issues/17056))
+- Support delegating the rendezvous mechanism described [MSC4108](https://github.com/matrix-org/matrix-spec-proposals/issues/4108) to an external implementation. ([\#17086](https://github.com/element-hq/synapse/issues/17086))
+
+### Bugfixes
+
+- Add validation to ensure that the `limit` parameter on `/publicRooms` is non-negative. ([\#16920](https://github.com/element-hq/synapse/issues/16920))
+- Return `400 M_NOT_JSON` upon receiving invalid JSON in query parameters across various client and admin endpoints, rather than an internal server error. ([\#16923](https://github.com/element-hq/synapse/issues/16923))
+- Make the CSAPI endpoint `/keys/device_signing/upload` idempotent. ([\#16943](https://github.com/element-hq/synapse/issues/16943))
+- Redact membership events if the user requested erasure upon deactivating. ([\#17076](https://github.com/element-hq/synapse/issues/17076))
+
+### Improved Documentation
+
+- Add a prompt in the contributing guide to manually configure icu4c. ([\#17069](https://github.com/element-hq/synapse/issues/17069))
+- Clarify what part of message retention is still experimental. ([\#17099](https://github.com/element-hq/synapse/issues/17099))
+
+### Internal Changes
+
+- Use new receipts column to optimise receipt and push action SQL queries. Contributed by Nick @ Beeper (@fizzadar). ([\#17032](https://github.com/element-hq/synapse/issues/17032), [\#17096](https://github.com/element-hq/synapse/issues/17096))
+- Fix mypy with latest Twisted release. ([\#17036](https://github.com/element-hq/synapse/issues/17036))
+- Bump minimum supported Rust version to 1.66.0. ([\#17079](https://github.com/element-hq/synapse/issues/17079))
+- Add helpers to transform Twisted requests to Rust http Requests/Responses. ([\#17081](https://github.com/element-hq/synapse/issues/17081))
+- Fix type annotation for `visited_chains` after `mypy` upgrade. ([\#17125](https://github.com/element-hq/synapse/issues/17125))
+
+
+
+### Updates to locked dependencies
+
+* Bump anyhow from 1.0.81 to 1.0.82. ([\#17095](https://github.com/element-hq/synapse/issues/17095))
+* Bump peaceiris/actions-gh-pages from 3.9.3 to 4.0.0. ([\#17087](https://github.com/element-hq/synapse/issues/17087))
+* Bump peaceiris/actions-mdbook from 1.2.0 to 2.0.0. ([\#17089](https://github.com/element-hq/synapse/issues/17089))
+* Bump pyasn1-modules from 0.3.0 to 0.4.0. ([\#17093](https://github.com/element-hq/synapse/issues/17093))
+* Bump pygithub from 2.2.0 to 2.3.0. ([\#17092](https://github.com/element-hq/synapse/issues/17092))
+* Bump ruff from 0.3.5 to 0.3.7. ([\#17094](https://github.com/element-hq/synapse/issues/17094))
+* Bump sigstore/cosign-installer from 3.4.0 to 3.5.0. ([\#17088](https://github.com/element-hq/synapse/issues/17088))
+* Bump twine from 4.0.2 to 5.0.0. ([\#17091](https://github.com/element-hq/synapse/issues/17091))
+* Bump types-pillow from 10.2.0.20240406 to 10.2.0.20240415. ([\#17090](https://github.com/element-hq/synapse/issues/17090))
+
+# Synapse 1.105.1 (2024-04-23)
+
+## Security advisory
+
+The following issues are fixed in 1.105.1.
+
+- [GHSA-3h7q-rfh9-xm4v](https://github.com/element-hq/synapse/security/advisories/GHSA-3h7q-rfh9-xm4v) / [CVE-2024-31208](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-31208) — High Severity
+
+  Weakness in auth chain indexing allows DoS from remote room members through disk fill and high CPU usage.
+
+See the advisories for more details. If you have any questions, email security@element.io.
+
+
+
 # Synapse 1.105.0 (2024-04-16)

 No significant changes since 1.105.0rc1.
--- a/Cargo.lock
+++ b/Cargo.lock
@ -13,9 +13,9 @@ dependencies = [

 [[package]]
 name = "anyhow"
-version = "1.0.81"
+version = "1.0.82"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0952808a6c2afd1aa8947271f3a60f1a6763c7b912d210184c5149b5cf147247"
+checksum = "f538837af36e6f6a9be0faa67f9a314f8119e4e4b5867c6ab40ed60360142519"

 [[package]]
 name = "arc-swap"
@ -59,6 +59,12 @@ dependencies = [
 "generic-array",
 ]

+[[package]]
+name = "bumpalo"
+version = "3.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "79296716171880943b8470b5f8d03aa55eb2e645a4874bdbb28adb49162e012c"
+
 [[package]]
 name = "bytes"
 version = "1.6.0"
@ -92,9 +98,9 @@ dependencies = [

 [[package]]
 name = "digest"
-version = "0.10.5"
+version = "0.10.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "adfbc57365a37acbd2ebf2b64d7e69bb766e2fea813521ed536f5d0520dcf86c"
+checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
 dependencies = [
 "block-buffer",
 "crypto-common",
@ -117,6 +123,19 @@ dependencies = [
 "version_check",
 ]

+[[package]]
+name = "getrandom"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94b22e06ecb0110981051723910cbf0b5f5e09a2062dd7663334ee79a9d1286c"
+dependencies = [
+ "cfg-if",
+ "js-sys",
+ "libc",
+ "wasi",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "headers"
 version = "0.4.0"
@ -182,6 +201,15 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4217ad341ebadf8d8e724e264f13e593e0648f5b3e94b3896a5df283be015ecc"

+[[package]]
+name = "js-sys"
+version = "0.3.69"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29c15563dc2726973df627357ce0c9ddddbea194836909d655df6a75d2cf296d"
+dependencies = [
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "lazy_static"
 version = "1.4.0"
@ -266,6 +294,12 @@ version = "1.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7170ef9988bc169ba16dd36a7fa041e5c4cbeb6a35b76d4c03daded371eae7c0"

+[[package]]
+name = "ppv-lite86"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.76"
@ -369,6 +403,36 @@ dependencies = [
 "proc-macro2",
 ]

+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.2.16"
@ -461,6 +525,17 @@ dependencies = [
 "digest",
 ]

+[[package]]
+name = "sha2"
+version = "0.10.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "793db75ad2bcafc3ffa7c68b215fee268f537982cd901d132f89c6343f3a3dc8"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
 [[package]]
 name = "smallvec"
 version = "1.10.0"
@ -489,6 +564,7 @@ name = "synapse"
 version = "0.1.0"
 dependencies = [
 "anyhow",
+ "base64",
 "blake2",
 "bytes",
 "headers",
@ -496,12 +572,15 @@ dependencies = [
 "http",
 "lazy_static",
 "log",
+ "mime",
 "pyo3",
 "pyo3-log",
 "pythonize",
 "regex",
 "serde",
 "serde_json",
+ "sha2",
+ "ulid",
 ]

 [[package]]
@ -516,6 +595,17 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dcf81ac59edc17cc8697ff311e8f5ef2d99fcbd9817b34cec66f90b6c3dfd987"

+[[package]]
+name = "ulid"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34778c17965aa2a08913b57e1f34db9b4a63f5de31768b55bf20d2795f921259"
+dependencies = [
+ "getrandom",
+ "rand",
+ "web-time",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.5"
@ -534,6 +624,76 @@ version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"

+[[package]]
+name = "wasi"
+version = "0.11.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
+
+[[package]]
+name = "wasm-bindgen"
+version = "0.2.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4be2531df63900aeb2bca0daaaddec08491ee64ceecbee5076636a3b026795a8"
+dependencies = [
+ "cfg-if",
+ "wasm-bindgen-macro",
+]
+
+[[package]]
+name = "wasm-bindgen-backend"
+version = "0.2.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "614d787b966d3989fa7bb98a654e369c762374fd3213d212cfc0251257e747da"
+dependencies = [
+ "bumpalo",
+ "log",
+ "once_cell",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1f8823de937b71b9460c0c34e25f3da88250760bec0ebac694b49997550d726"
+dependencies = [
+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
+name = "wasm-bindgen-macro-support"
+version = "0.2.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e94f17b526d0a461a191c78ea52bbce64071ed5c04c9ffe424dcb38f74171bb7"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-backend",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.2.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af190c94f2773fdb3729c55b007a722abb5384da03bc0986df4c289bf5567e96"
+
+[[package]]
+name = "web-time"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a6580f308b1fad9207618087a65c04e7a10bc77e02c8e84e9b00dd4b12fa0bb"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.36.1"
--- a/changelog.d/16920.bugfix
+++ b/changelog.d/16920.bugfix
@ -1 +0,0 @@
-Adds validation to ensure that the `limit` parameter on `/publicRooms` is non-negative.
--- a/changelog.d/16943.bugfix
+++ b/changelog.d/16943.bugfix
@ -1 +0,0 @@
-Make the CSAPI endpoint `/keys/device_signing/upload` idempotent.
--- a/changelog.d/17032.misc
+++ b/changelog.d/17032.misc
@ -1 +0,0 @@
-Use new receipts column to optimise receipt and push action SQL queries. Contributed by Nick @ Beeper (@fizzadar).
--- a/changelog.d/17036.misc
+++ b/changelog.d/17036.misc
@ -1 +0,0 @@
-Fix mypy with latest Twisted release.
--- a/changelog.d/17079.misc
+++ b/changelog.d/17079.misc
@ -1 +0,0 @@
-Bump minimum supported Rust version to 1.66.0.
--- a/changelog.d/17081.misc
+++ b/changelog.d/17081.misc
@ -1 +0,0 @@
-Add helpers to transform Twisted requests to Rust http Requests/Responses.
--- a/changelog.d/17086.feature
+++ b/changelog.d/17086.feature
@ -1 +0,0 @@
-Support delegating the rendezvous mechanism described MSC4108 to an external implementation.
--- a/changelog.d/17096.misc
+++ b/changelog.d/17096.misc
@ -1 +0,0 @@
-Use new receipts column to optimise receipt and push action SQL queries. Contributed by Nick @ Beeper (@fizzadar).
--- a/debian/changelog
+++ b/debian/changelog
@ -1,3 +1,15 @@
+matrix-synapse-py3 (1.106.0~rc1) stable; urgency=medium
+
+  * New Synapse release 1.106.0rc1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Thu, 25 Apr 2024 15:54:59 +0100
+
+matrix-synapse-py3 (1.105.1) stable; urgency=medium
+
+  * New Synapse release 1.105.1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 23 Apr 2024 15:56:18 +0100
+
 matrix-synapse-py3 (1.105.0) stable; urgency=medium

  * New Synapse release 1.105.0.
--- a/docs/development/contributing_guide.md
+++ b/docs/development/contributing_guide.md
@ -86,6 +86,8 @@ poetry install --extras all
 This will install the runtime and developer dependencies for the project.  Be sure to check
 that the `poetry install` step completed cleanly.

+For OSX users, be sure to set `PKG_CONFIG_PATH` to support `icu4c`. Run `brew info icu4c` for more details.
+
 ## Running Synapse via poetry

 To start a local instance of Synapse in the locked poetry environment, create a config file:
--- a/docs/message_retention_policies.md
+++ b/docs/message_retention_policies.md
@ -7,8 +7,10 @@ follow the semantics described in
 and allow server and room admins to configure how long messages should
 be kept in a homeserver's database before being purged from it.
 **Please note that, as this feature isn't part of the Matrix
-specification yet, this implementation is to be considered as
-experimental.**
+specification yet, the use of `m.room.retention` events for per-room
+retention policies is to be considered as experimental. However, the use
+of a default message retention policy is considered a stable feature
+in Synapse.**

 A message retention policy is mainly defined by its `max_lifetime`
 parameter, which defines how long a message can be kept around after
--- a/poetry.lock
+++ b/poetry.lock
@ -1848,17 +1848,17 @@ files = [

 [[package]]
 name = "pyasn1-modules"
-version = "0.3.0"
+version = "0.4.0"
 description = "A collection of ASN.1-based protocols modules"
 optional = false
-python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,>=2.7"
+python-versions = ">=3.8"
 files = [
-    {file = "pyasn1_modules-0.3.0-py2.py3-none-any.whl", hash = "sha256:d3ccd6ed470d9ffbc716be08bd90efbd44d0734bc9303818f7336070984a162d"},
-    {file = "pyasn1_modules-0.3.0.tar.gz", hash = "sha256:5bd01446b736eb9d31512a30d46c1ac3395d676c6f3cafa4c03eb54b9925631c"},
+    {file = "pyasn1_modules-0.4.0-py3-none-any.whl", hash = "sha256:be04f15b66c206eed667e0bb5ab27e2b1855ea54a842e5037738099e8ca4ae0b"},
+    {file = "pyasn1_modules-0.4.0.tar.gz", hash = "sha256:831dbcea1b177b28c9baddf4c6d1013c24c3accd14a1873fffaa6a2e905f17b6"},
 ]

 [package.dependencies]
-pyasn1 = ">=0.4.6,<0.6.0"
+pyasn1 = ">=0.4.6,<0.7.0"

 [[package]]
 name = "pycparser"
@ -1983,13 +1983,13 @@ typing-extensions = ">=4.6.0,<4.7.0 || >4.7.0"

 [[package]]
 name = "pygithub"
-version = "2.2.0"
+version = "2.3.0"
 description = "Use the full Github API v3"
 optional = false
 python-versions = ">=3.7"
 files = [
-    {file = "PyGithub-2.2.0-py3-none-any.whl", hash = "sha256:41042ea53e4c372219db708c38d2ca1fd4fadab75475bac27d89d339596cfad1"},
-    {file = "PyGithub-2.2.0.tar.gz", hash = "sha256:e39be7c4dc39418bdd6e3ecab5931c636170b8b21b4d26f9ecf7e6102a3b51c3"},
+    {file = "PyGithub-2.3.0-py3-none-any.whl", hash = "sha256:65b499728be3ce7b0cd2cd760da3b32f0f4d7bc55e5e0677617f90f6564e793e"},
+    {file = "PyGithub-2.3.0.tar.gz", hash = "sha256:0148d7347a1cdeed99af905077010aef81a4dad988b0ba51d4108bf66b443f7e"},
 ]

 [package.dependencies]
@ -2444,28 +2444,28 @@ files = [

 [[package]]
 name = "ruff"
-version = "0.3.5"
+version = "0.3.7"
 description = "An extremely fast Python linter and code formatter, written in Rust."
 optional = false
 python-versions = ">=3.7"
 files = [
-    {file = "ruff-0.3.5-py3-none-macosx_10_12_x86_64.macosx_11_0_arm64.macosx_10_12_universal2.whl", hash = "sha256:aef5bd3b89e657007e1be6b16553c8813b221ff6d92c7526b7e0227450981eac"},
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+    {file = "ruff-0.3.7-py3-none-win_amd64.whl", hash = "sha256:5ef0e501e1e39f35e03c2acb1d1238c595b8bb36cf7a170e7c1df1b73da00e74"},
+    {file = "ruff-0.3.7-py3-none-win_arm64.whl", hash = "sha256:789e144f6dc7019d1f92a812891c645274ed08af6037d11fc65fcbc183b7d59f"},
+    {file = "ruff-0.3.7.tar.gz", hash = "sha256:d5c1aebee5162c2226784800ae031f660c350e7a3402c4d1f8ea4e97e232e3ba"},
 ]

 [[package]]
@ -2954,13 +2954,13 @@ docs = ["sphinx (<7.0.0)"]

 [[package]]
 name = "twine"
-version = "4.0.2"
+version = "5.0.0"
 description = "Collection of utilities for publishing packages on PyPI"
 optional = false
-python-versions = ">=3.7"
+python-versions = ">=3.8"
 files = [
-    {file = "twine-4.0.2-py3-none-any.whl", hash = "sha256:929bc3c280033347a00f847236564d1c52a3e61b1ac2516c97c48f3ceab756d8"},
-    {file = "twine-4.0.2.tar.gz", hash = "sha256:9e102ef5fdd5a20661eb88fad46338806c3bd32cf1db729603fe3697b1bc83c8"},
+    {file = "twine-5.0.0-py3-none-any.whl", hash = "sha256:a262933de0b484c53408f9edae2e7821c1c45a3314ff2df9bdd343aa7ab8edc0"},
+    {file = "twine-5.0.0.tar.gz", hash = "sha256:89b0cc7d370a4b66421cc6102f269aa910fe0f1861c124f573cf2ddedbc10cf4"},
 ]

 [package.dependencies]
@ -3109,13 +3109,13 @@ files = [

 [[package]]
 name = "types-pillow"
-version = "10.2.0.20240406"
+version = "10.2.0.20240415"
 description = "Typing stubs for Pillow"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "types-Pillow-10.2.0.20240406.tar.gz", hash = "sha256:62e0cc1f17caba40e72e7154a483f4c7f3bea0e1c34c0ebba9de3c7745bc306d"},
-    {file = "types_Pillow-10.2.0.20240406-py3-none-any.whl", hash = "sha256:5ac182e8afce53de30abca2fdf9cbec7b2500e549d0be84da035a729a84c7c47"},
+    {file = "types-Pillow-10.2.0.20240415.tar.gz", hash = "sha256:dd6058027639bcdc66ba78b228cc25fdae42524c2150c78c804da427e7e76e70"},
+    {file = "types_Pillow-10.2.0.20240415-py3-none-any.whl", hash = "sha256:f933332b7e96010bae9b9cf82a4c9979ff0c270d63f5c5bbffb2d789b85cd00b"},
 ]

 [[package]]
@ -3451,4 +3451,4 @@ user-search = ["pyicu"]
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.8.0"
-content-hash = "4abda113a01f162bb3978b0372956d569364533aa39f57863c234363f8449a4f"
+content-hash = "1951f2b4623138d47db08a405edd970e67599d05804bb459af21a085e1665f69"
--- a/pyproject.toml
+++ b/pyproject.toml
@ -96,7 +96,7 @@ module-name = "synapse.synapse_rust"

 [tool.poetry]
 name = "matrix-synapse"
-version = "1.105.0"
+version = "1.106.0rc1"
 description = "Homeserver for the Matrix decentralised comms protocol"
 authors = ["Matrix.org Team and Contributors <packages@matrix.org>"]
 license = "AGPL-3.0-or-later"
@ -321,7 +321,7 @@ all = [
 # This helps prevents merge conflicts when running a batch of dependabot updates.
 isort = ">=5.10.1"
 black = ">=22.7.0"
-ruff = "0.3.5"
+ruff = "0.3.7"
 # Type checking only works with the pydantic.v1 compat module from pydantic v2
 pydantic = "^2"

--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@ -23,11 +23,13 @@ name = "synapse.synapse_rust"

 [dependencies]
 anyhow = "1.0.63"
+base64 = "0.21.7"
 bytes = "1.6.0"
 headers = "0.4.0"
 http = "1.1.0"
 lazy_static = "1.4.0"
 log = "0.4.17"
+mime = "0.3.17"
 pyo3 = { version = "0.20.0", features = [
    "macros",
    "anyhow",
@ -37,8 +39,10 @@ pyo3 = { version = "0.20.0", features = [
 pyo3-log = "0.9.0"
 pythonize = "0.20.0"
 regex = "1.6.0"
+sha2 = "0.10.8"
 serde = { version = "1.0.144", features = ["derive"] }
 serde_json = "1.0.85"
+ulid = "1.1.2"

 [features]
 extension-module = ["pyo3/extension-module"]
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@ -7,6 +7,7 @@ pub mod errors;
 pub mod events;
 pub mod http;
 pub mod push;
+pub mod rendezvous;

 lazy_static! {
    static ref LOGGING_HANDLE: ResetHandle = pyo3_log::init();
@ -45,6 +46,7 @@ fn synapse_rust(py: Python<'_>, m: &PyModule) -> PyResult<()> {
    acl::register_module(py, m)?;
    push::register_module(py, m)?;
    events::register_module(py, m)?;
+    rendezvous::register_module(py, m)?;

    Ok(())
 }
--- a/rust/src/rendezvous/mod.rs
+++ b/rust/src/rendezvous/mod.rs
@ -0,0 +1,315 @@
+/*
+ * This file is licensed under the Affero General Public License (AGPL) version 3.
+ *
+ * Copyright (C) 2024 New Vector, Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * See the GNU Affero General Public License for more details:
+ * <https://www.gnu.org/licenses/agpl-3.0.html>.
+ *
+ */
+
+use std::{
+    collections::{BTreeMap, HashMap},
+    time::{Duration, SystemTime},
+};
+
+use bytes::Bytes;
+use headers::{
+    AccessControlAllowOrigin, AccessControlExposeHeaders, CacheControl, ContentLength, ContentType,
+    HeaderMapExt, IfMatch, IfNoneMatch, Pragma,
+};
+use http::{header::ETAG, HeaderMap, Response, StatusCode, Uri};
+use mime::Mime;
+use pyo3::{
+    exceptions::PyValueError, pyclass, pymethods, types::PyModule, Py, PyAny, PyObject, PyResult,
+    Python, ToPyObject,
+};
+use ulid::Ulid;
+
+use self::session::Session;
+use crate::{
+    errors::{NotFoundError, SynapseError},
+    http::{http_request_from_twisted, http_response_to_twisted, HeaderMapPyExt},
+};
+
+mod session;
+
+// n.b. Because OPTIONS requests are handled by the Python code, we don't need to set Access-Control-Allow-Headers.
+fn prepare_headers(headers: &mut HeaderMap, session: &Session) {
+    headers.typed_insert(AccessControlAllowOrigin::ANY);
+    headers.typed_insert(AccessControlExposeHeaders::from_iter([ETAG]));
+    headers.typed_insert(Pragma::no_cache());
+    headers.typed_insert(CacheControl::new().with_no_store());
+    headers.typed_insert(session.etag());
+    headers.typed_insert(session.expires());
+    headers.typed_insert(session.last_modified());
+}
+
+#[pyclass]
+struct RendezvousHandler {
+    base: Uri,
+    clock: PyObject,
+    sessions: BTreeMap<Ulid, Session>,
+    capacity: usize,
+    max_content_length: u64,
+    ttl: Duration,
+}
+
+impl RendezvousHandler {
+    /// Check the input headers of a request which sets data for a session, and return the content type.
+    fn check_input_headers(&self, headers: &HeaderMap) -> PyResult<Mime> {
+        let ContentLength(content_length) = headers.typed_get_required()?;
+
+        if content_length > self.max_content_length {
+            return Err(SynapseError::new(
+                StatusCode::PAYLOAD_TOO_LARGE,
+                "Payload too large".to_owned(),
+                "M_TOO_LARGE",
+                None,
+                None,
+            ));
+        }
+
+        let content_type: ContentType = headers.typed_get_required()?;
+
+        // Content-Type must be text/plain
+        if content_type != ContentType::text() {
+            return Err(SynapseError::new(
+                StatusCode::BAD_REQUEST,
+                "Content-Type must be text/plain".to_owned(),
+                "M_INVALID_PARAM",
+                None,
+                None,
+            ));
+        }
+
+        Ok(content_type.into())
+    }
+
+    /// Evict expired sessions and remove the oldest sessions until we're under the capacity.
+    fn evict(&mut self, now: SystemTime) {
+        // First remove all the entries which expired
+        self.sessions.retain(|_, session| !session.expired(now));
+
+        // Then we remove the oldest entires until we're under the limit
+        while self.sessions.len() > self.capacity {
+            self.sessions.pop_first();
+        }
+    }
+}
+
+#[pymethods]
+impl RendezvousHandler {
+    #[new]
+    #[pyo3(signature = (homeserver, /, capacity=100, max_content_length=4*1024, eviction_interval=60*1000, ttl=60*1000))]
+    fn new(
+        py: Python<'_>,
+        homeserver: &PyAny,
+        capacity: usize,
+        max_content_length: u64,
+        eviction_interval: u64,
+        ttl: u64,
+    ) -> PyResult<Py<Self>> {
+        let base: String = homeserver
+            .getattr("config")?
+            .getattr("server")?
+            .getattr("public_baseurl")?
+            .extract()?;
+        let base = Uri::try_from(format!("{base}_synapse/client/rendezvous"))
+            .map_err(|_| PyValueError::new_err("Invalid base URI"))?;
+
+        let clock = homeserver.call_method0("get_clock")?.to_object(py);
+
+        // Construct a Python object so that we can get a reference to the
+        // evict method and schedule it to run.
+        let self_ = Py::new(
+            py,
+            Self {
+                base,
+                clock,
+                sessions: BTreeMap::new(),
+                capacity,
+                max_content_length,
+                ttl: Duration::from_millis(ttl),
+            },
+        )?;
+
+        let evict = self_.getattr(py, "_evict")?;
+        homeserver.call_method0("get_clock")?.call_method(
+            "looping_call",
+            (evict, eviction_interval),
+            None,
+        )?;
+
+        Ok(self_)
+    }
+
+    fn _evict(&mut self, py: Python<'_>) -> PyResult<()> {
+        let clock = self.clock.as_ref(py);
+        let now: u64 = clock.call_method0("time_msec")?.extract()?;
+        let now = SystemTime::UNIX_EPOCH + Duration::from_millis(now);
+        self.evict(now);
+
+        Ok(())
+    }
+
+    fn handle_post(&mut self, py: Python<'_>, twisted_request: &PyAny) -> PyResult<()> {
+        let request = http_request_from_twisted(twisted_request)?;
+
+        let content_type = self.check_input_headers(request.headers())?;
+
+        let clock = self.clock.as_ref(py);
+        let now: u64 = clock.call_method0("time_msec")?.extract()?;
+        let now = SystemTime::UNIX_EPOCH + Duration::from_millis(now);
+
+        // We trigger an immediate eviction if we're at 2x the capacity
+        if self.sessions.len() >= self.capacity * 2 {
+            self.evict(now);
+        }
+
+        // Generate a new ULID for the session from the current time.
+        let id = Ulid::from_datetime(now);
+
+        let uri = format!("{base}/{id}", base = self.base);
+
+        let body = request.into_body();
+
+        let session = Session::new(body, content_type, now, self.ttl);
+
+        let response = serde_json::json!({
+            "url": uri,
+        })
+        .to_string();
+
+        let mut response = Response::new(response.as_bytes());
+        *response.status_mut() = StatusCode::CREATED;
+        response.headers_mut().typed_insert(ContentType::json());
+        prepare_headers(response.headers_mut(), &session);
+        http_response_to_twisted(twisted_request, response)?;
+
+        self.sessions.insert(id, session);
+
+        Ok(())
+    }
+
+    fn handle_get(&mut self, py: Python<'_>, twisted_request: &PyAny, id: &str) -> PyResult<()> {
+        let request = http_request_from_twisted(twisted_request)?;
+
+        let if_none_match: Option<IfNoneMatch> = request.headers().typed_get_optional()?;
+
+        let now: u64 = self.clock.call_method0(py, "time_msec")?.extract(py)?;
+        let now = SystemTime::UNIX_EPOCH + Duration::from_millis(now);
+
+        let id: Ulid = id.parse().map_err(|_| NotFoundError::new())?;
+        let session = self
+            .sessions
+            .get(&id)
+            .filter(|s| !s.expired(now))
+            .ok_or_else(NotFoundError::new)?;
+
+        if let Some(if_none_match) = if_none_match {
+            if !if_none_match.precondition_passes(&session.etag()) {
+                let mut response = Response::new(Bytes::new());
+                *response.status_mut() = StatusCode::NOT_MODIFIED;
+                prepare_headers(response.headers_mut(), session);
+                http_response_to_twisted(twisted_request, response)?;
+                return Ok(());
+            }
+        }
+
+        let mut response = Response::new(session.data());
+        *response.status_mut() = StatusCode::OK;
+        let headers = response.headers_mut();
+        prepare_headers(headers, session);
+        headers.typed_insert(session.content_type());
+        headers.typed_insert(session.content_length());
+        http_response_to_twisted(twisted_request, response)?;
+
+        Ok(())
+    }
+
+    fn handle_put(&mut self, py: Python<'_>, twisted_request: &PyAny, id: &str) -> PyResult<()> {
+        let request = http_request_from_twisted(twisted_request)?;
+
+        let content_type = self.check_input_headers(request.headers())?;
+
+        let if_match: IfMatch = request.headers().typed_get_required()?;
+
+        let data = request.into_body();
+
+        let now: u64 = self.clock.call_method0(py, "time_msec")?.extract(py)?;
+        let now = SystemTime::UNIX_EPOCH + Duration::from_millis(now);
+
+        let id: Ulid = id.parse().map_err(|_| NotFoundError::new())?;
+        let session = self
+            .sessions
+            .get_mut(&id)
+            .filter(|s| !s.expired(now))
+            .ok_or_else(NotFoundError::new)?;
+
+        if !if_match.precondition_passes(&session.etag()) {
+            let mut headers = HeaderMap::new();
+            prepare_headers(&mut headers, session);
+
+            let mut additional_fields = HashMap::with_capacity(1);
+            additional_fields.insert(
+                String::from("org.matrix.msc4108.errcode"),
+                String::from("M_CONCURRENT_WRITE"),
+            );
+
+            return Err(SynapseError::new(
+                StatusCode::PRECONDITION_FAILED,
+                "ETag does not match".to_owned(),
+                "M_UNKNOWN", // Would be M_CONCURRENT_WRITE
+                Some(additional_fields),
+                Some(headers),
+            ));
+        }
+
+        session.update(data, content_type, now);
+
+        let mut response = Response::new(Bytes::new());
+        *response.status_mut() = StatusCode::ACCEPTED;
+        prepare_headers(response.headers_mut(), session);
+        http_response_to_twisted(twisted_request, response)?;
+
+        Ok(())
+    }
+
+    fn handle_delete(&mut self, twisted_request: &PyAny, id: &str) -> PyResult<()> {
+        let _request = http_request_from_twisted(twisted_request)?;
+
+        let id: Ulid = id.parse().map_err(|_| NotFoundError::new())?;
+        let _session = self.sessions.remove(&id).ok_or_else(NotFoundError::new)?;
+
+        let mut response = Response::new(Bytes::new());
+        *response.status_mut() = StatusCode::NO_CONTENT;
+        response
+            .headers_mut()
+            .typed_insert(AccessControlAllowOrigin::ANY);
+        http_response_to_twisted(twisted_request, response)?;
+
+        Ok(())
+    }
+}
+
+pub fn register_module(py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    let child_module = PyModule::new(py, "rendezvous")?;
+
+    child_module.add_class::<RendezvousHandler>()?;
+
+    m.add_submodule(child_module)?;
+
+    // We need to manually add the module to sys.modules to make `from
+    // synapse.synapse_rust import rendezvous` work.
+    py.import("sys")?
+        .getattr("modules")?
+        .set_item("synapse.synapse_rust.rendezvous", child_module)?;
+
+    Ok(())
+}
--- a/rust/src/rendezvous/session.rs
+++ b/rust/src/rendezvous/session.rs
@ -0,0 +1,91 @@
+/*
+ * This file is licensed under the Affero General Public License (AGPL) version 3.
+ *
+ * Copyright (C) 2024 New Vector, Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * See the GNU Affero General Public License for more details:
+ * <https://www.gnu.org/licenses/agpl-3.0.html>.
+ */
+
+use std::time::{Duration, SystemTime};
+
+use base64::{engine::general_purpose::URL_SAFE_NO_PAD, Engine as _};
+use bytes::Bytes;
+use headers::{ContentLength, ContentType, ETag, Expires, LastModified};
+use mime::Mime;
+use sha2::{Digest, Sha256};
+
+/// A single session, containing data, metadata, and expiry information.
+pub struct Session {
+    hash: [u8; 32],
+    data: Bytes,
+    content_type: Mime,
+    last_modified: SystemTime,
+    expires: SystemTime,
+}
+
+impl Session {
+    /// Create a new session with the given data, content type, and time-to-live.
+    pub fn new(data: Bytes, content_type: Mime, now: SystemTime, ttl: Duration) -> Self {
+        let hash = Sha256::digest(&data).into();
+        Self {
+            hash,
+            data,
+            content_type,
+            expires: now + ttl,
+            last_modified: now,
+        }
+    }
+
+    /// Returns true if the session has expired at the given time.
+    pub fn expired(&self, now: SystemTime) -> bool {
+        self.expires <= now
+    }
+
+    /// Update the session with new data, content type, and last modified time.
+    pub fn update(&mut self, data: Bytes, content_type: Mime, now: SystemTime) {
+        self.hash = Sha256::digest(&data).into();
+        self.data = data;
+        self.content_type = content_type;
+        self.last_modified = now;
+    }
+
+    /// Returns the Content-Type header of the session.
+    pub fn content_type(&self) -> ContentType {
+        self.content_type.clone().into()
+    }
+
+    /// Returns the Content-Length header of the session.
+    pub fn content_length(&self) -> ContentLength {
+        ContentLength(self.data.len() as _)
+    }
+
+    /// Returns the ETag header of the session.
+    pub fn etag(&self) -> ETag {
+        let encoded = URL_SAFE_NO_PAD.encode(self.hash);
+        // SAFETY: Base64 encoding is URL-safe, so ETag-safe
+        format!("\"{encoded}\"")
+            .parse()
+            .expect("base64-encoded hash should be URL-safe")
+    }
+
+    /// Returns the Last-Modified header of the session.
+    pub fn last_modified(&self) -> LastModified {
+        self.last_modified.into()
+    }
+
+    /// Returns the Expires header of the session.
+    pub fn expires(&self) -> Expires {
+        self.expires.into()
+    }
+
+    /// Returns the current data stored in the session.
+    pub fn data(&self) -> Bytes {
+        self.data.clone()
+    }
+}
--- a/synapse/config/emailconfig.py
+++ b/synapse/config/emailconfig.py
@ -52,6 +52,7 @@ DEFAULT_SUBJECTS = {
    "invite_from_person_to_space": "[%(app)s] %(person)s has invited you to join the %(space)s space on %(app)s...",
    "password_reset": "[%(server_name)s] Password reset",
    "email_validation": "[%(server_name)s] Validate your email",
+    "email_already_in_use": "[%(server_name)s] Email already in use",
 }

 LEGACY_TEMPLATE_DIR_WARNING = """
@ -76,6 +77,7 @@ class EmailSubjectConfig:
    invite_from_person_to_space: str
    password_reset: str
    email_validation: str
+    email_already_in_use: str


 class EmailConfig(Config):
@ -180,6 +182,12 @@ class EmailConfig(Config):
            registration_template_text = email_config.get(
                "registration_template_text", "registration.txt"
            )
+            already_in_use_template_html = email_config.get(
+                "already_in_use_template_html", "already_in_use.html"
+            )
+            already_in_use_template_text = email_config.get(
+                "already_in_use_template_html", "already_in_use.txt"
+            )
            add_threepid_template_html = email_config.get(
                "add_threepid_template_html", "add_threepid.html"
            )
@ -215,6 +223,8 @@ class EmailConfig(Config):
                self.email_password_reset_template_text,
                self.email_registration_template_html,
                self.email_registration_template_text,
+                self.email_already_in_use_template_html,
+                self.email_already_in_use_template_text,
                self.email_add_threepid_template_html,
                self.email_add_threepid_template_text,
                self.email_password_reset_template_confirmation_html,
@ -230,6 +240,8 @@ class EmailConfig(Config):
                    password_reset_template_text,
                    registration_template_html,
                    registration_template_text,
+                    already_in_use_template_html,
+                    already_in_use_template_text,
                    add_threepid_template_html,
                    add_threepid_template_text,
                    "password_reset_confirmation.html",
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@ -413,12 +413,22 @@ class ExperimentalConfig(Config):
        )

        # MSC4108: Mechanism to allow OIDC sign in and E2EE set up via QR code
+        self.msc4108_enabled = experimental.get("msc4108_enabled", False)
+
        self.msc4108_delegation_endpoint: Optional[str] = experimental.get(
            "msc4108_delegation_endpoint", None
        )

-        if self.msc4108_delegation_endpoint is not None and not self.msc3861.enabled:
+        if (
+            self.msc4108_enabled or self.msc4108_delegation_endpoint is not None
+        ) and not self.msc3861.enabled:
            raise ConfigError(
                "MSC4108 requires MSC3861 to be enabled",
                ("experimental", "msc4108_delegation_endpoint"),
            )
+
+        if self.msc4108_delegation_endpoint is not None and self.msc4108_enabled:
+            raise ConfigError(
+                "You cannot have MSC4108 both enabled and delegated at the same time",
+                ("experimental", "msc4108_delegation_endpoint"),
+            )
--- a/synapse/handlers/deactivate_account.py
+++ b/synapse/handlers/deactivate_account.py
@ -261,11 +261,22 @@ class DeactivateAccountHandler:
        user = UserID.from_string(user_id)

        rooms_for_user = await self.store.get_rooms_for_user(user_id)
+        requester = create_requester(user, authenticated_entity=self._server_name)
+        should_erase = await self.store.is_user_erased(user_id)
+
        for room_id in rooms_for_user:
            logger.info("User parter parting %r from %r", user_id, room_id)
            try:
+                # Before parting the user, redact all membership events if requested
+                if should_erase:
+                    event_ids = await self.store.get_membership_event_ids_for_user(
+                        user_id, room_id
+                    )
+                    for event_id in event_ids:
+                        await self.store.expire_event(event_id)
+
                await self._room_member_handler.update_membership(
-                    create_requester(user, authenticated_entity=self._server_name),
+                    requester,
                    user,
                    room_id,
                    "leave",
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@ -909,8 +909,9 @@ def set_cors_headers(request: "SynapseRequest") -> None:
    request.setHeader(
        b"Access-Control-Allow-Methods", b"GET, HEAD, POST, PUT, DELETE, OPTIONS"
    )
-    if request.path is not None and request.path.startswith(
-        b"/_matrix/client/unstable/org.matrix.msc4108/rendezvous"
+    if request.path is not None and (
+        request.path == b"/_matrix/client/unstable/org.matrix.msc4108/rendezvous"
+        or request.path.startswith(b"/_synapse/client/rendezvous")
    ):
        request.setHeader(
            b"Access-Control-Allow-Headers",
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@ -23,6 +23,7 @@

 import enum
 import logging
+import urllib.parse as urlparse
 from http import HTTPStatus
 from typing import (
    TYPE_CHECKING,
@ -450,6 +451,87 @@ def parse_string(
    )


+def parse_json(
+    request: Request,
+    name: str,
+    default: Optional[dict] = None,
+    required: bool = False,
+    encoding: str = "ascii",
+) -> Optional[JsonDict]:
+    """
+    Parse a JSON parameter from the request query string.
+
+    Args:
+        request: the twisted HTTP request.
+        name: the name of the query parameter.
+        default: value to use if the parameter is absent,
+            defaults to None.
+        required: whether to raise a 400 SynapseError if the
+           parameter is absent, defaults to False.
+        encoding: The encoding to decode the string content with.
+
+    Returns:
+        A JSON value, or `default` if the named query parameter was not found
+        and `required` was False.
+
+    Raises:
+        SynapseError if the parameter is absent and required, or if the
+            parameter is present and not a JSON object.
+    """
+    args: Mapping[bytes, Sequence[bytes]] = request.args  # type: ignore
+    return parse_json_from_args(
+        args,
+        name,
+        default,
+        required=required,
+        encoding=encoding,
+    )
+
+
+def parse_json_from_args(
+    args: Mapping[bytes, Sequence[bytes]],
+    name: str,
+    default: Optional[dict] = None,
+    required: bool = False,
+    encoding: str = "ascii",
+) -> Optional[JsonDict]:
+    """
+    Parse a JSON parameter from the request query string.
+
+    Args:
+        args: a mapping of request args as bytes to a list of bytes (e.g. request.args).
+        name: the name of the query parameter.
+        default: value to use if the parameter is absent,
+            defaults to None.
+        required: whether to raise a 400 SynapseError if the
+            parameter is absent, defaults to False.
+        encoding: the encoding to decode the string content with.
+
+        A JSON value, or `default` if the named query parameter was not found
+        and `required` was False.
+
+    Raises:
+        SynapseError if the parameter is absent and required, or if the
+            parameter is present and not a JSON object.
+    """
+    name_bytes = name.encode("ascii")
+
+    if name_bytes not in args:
+        if not required:
+            return default
+
+        message = f"Missing required integer query parameter {name}"
+        raise SynapseError(HTTPStatus.BAD_REQUEST, message, errcode=Codes.MISSING_PARAM)
+
+    json_str = parse_string_from_args(args, name, required=True, encoding=encoding)
+
+    try:
+        return json_decoder.decode(urlparse.unquote(json_str))
+    except Exception:
+        message = f"Query parameter {name} must be a valid JSON object"
+        raise SynapseError(HTTPStatus.BAD_REQUEST, message, errcode=Codes.NOT_JSON)
+
+
 EnumT = TypeVar("EnumT", bound=enum.Enum)


--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@ -205,6 +205,22 @@ class Mailer:
            template_vars,
        )

+    emails_sent_counter.labels("already_in_use")
+
+    async def send_already_in_use_mail(self, email_address: str) -> None:
+        """Send an email if the address is already bound to an user account
+
+        Args:
+            email_address: Email address we're sending to the "already in use" mail
+        """
+
+        await self.send_email(
+            email_address,
+            self.email_subjects.email_already_in_use
+            % {"server_name": self.hs.config.server.server_name, "app": self.app_name},
+            {},
+        )
+
    emails_sent_counter.labels("add_threepid")

    async def send_add_threepid_mail(
--- a/synapse/res/templates/already_in_use.html
+++ b/synapse/res/templates/already_in_use.html
@ -0,0 +1,12 @@
+{% extends "_base.html" %}
+{% block title %}Email already in use{% endblock %}
+
+{% block body %}
+<p>You have asked us to register this email with a new Matrix account, but this email is already registered with an existing account.</p>
+
+<p>Please reset your password if needed.</p>
+
+<p>If this was not you, you can safely disregard this email.</p>
+
+<p>Thank you.</p>
+{% endblock %}
--- a/synapse/res/templates/already_in_use.txt
+++ b/synapse/res/templates/already_in_use.txt
@ -0,0 +1,10 @@
+Hello there,
+
+You have asked us to register this email with a new Matrix account,
+but this email is already registered with an existing account.
+
+Please reset your password if needed.
+
+If this was not you, you can safely disregard this email.
+
+Thank you.
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@ -21,7 +21,6 @@
 import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, List, Optional, Tuple, cast
-from urllib import parse as urlparse

 import attr

@ -38,6 +37,7 @@ from synapse.http.servlet import (
    assert_params_in_dict,
    parse_enum,
    parse_integer,
+    parse_json,
    parse_json_object_from_request,
    parse_string,
 )
@ -51,7 +51,6 @@ from synapse.storage.databases.main.room import RoomSortOrder
 from synapse.streams.config import PaginationConfig
 from synapse.types import JsonDict, RoomID, ScheduledTask, UserID, create_requester
 from synapse.types.state import StateFilter
-from synapse.util import json_decoder

 if TYPE_CHECKING:
    from synapse.api.auth import Auth
@ -776,14 +775,8 @@ class RoomEventContextServlet(RestServlet):
        limit = parse_integer(request, "limit", default=10)

        # picking the API shape for symmetry with /messages
-        filter_str = parse_string(request, "filter", encoding="utf-8")
-        if filter_str:
-            filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(
-                self._hs, json_decoder.decode(filter_json)
-            )
-        else:
-            event_filter = None
+        filter_json = parse_json(request, "filter", encoding="utf-8")
+        event_filter = Filter(self._hs, filter_json) if filter_json else None

        event_context = await self.room_context_handler.get_event_context(
            requester,
@ -914,21 +907,16 @@ class RoomMessagesRestServlet(RestServlet):
        )
        # Twisted will have processed the args by now.
        assert request.args is not None
+
+        filter_json = parse_json(request, "filter", encoding="utf-8")
+        event_filter = Filter(self._hs, filter_json) if filter_json else None
+
        as_client_event = b"raw" not in request.args
-        filter_str = parse_string(request, "filter", encoding="utf-8")
-        if filter_str:
-            filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(
-                self._hs, json_decoder.decode(filter_json)
-            )
-            if (
-                event_filter
-                and event_filter.filter_json.get("event_format", "client")
-                == "federation"
-            ):
-                as_client_event = False
-        else:
-            event_filter = None
+        if (
+            event_filter
+            and event_filter.filter_json.get("event_format", "client") == "federation"
+        ):
+            as_client_event = False

        msgs = await self._pagination_handler.get_messages(
            room_id=room_id,
--- a/synapse/rest/client/register.py
+++ b/synapse/rest/client/register.py
@ -86,12 +86,18 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
        self.config = hs.config

        if self.hs.config.email.can_verify_email:
-            self.mailer = Mailer(
+            self.registration_mailer = Mailer(
                hs=self.hs,
                app_name=self.config.email.email_app_name,
                template_html=self.config.email.email_registration_template_html,
                template_text=self.config.email.email_registration_template_text,
            )
+            self.already_in_use_mailer = Mailer(
+                hs=self.hs,
+                app_name=self.config.email.email_app_name,
+                template_html=self.config.email.email_already_in_use_template_html,
+                template_text=self.config.email.email_already_in_use_template_text,
+            )

    async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
        if not self.hs.config.email.can_verify_email:
@ -139,8 +145,10 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
            if self.hs.config.server.request_token_inhibit_3pid_errors:
                # Make the client think the operation succeeded. See the rationale in the
                # comments for request_token_inhibit_3pid_errors.
+                # Still send an email to warn the user that an account already exists.
                # Also wait for some random amount of time between 100ms and 1s to make it
                # look like we did something.
+                await self.already_in_use_mailer.send_already_in_use_mail(email)
                await self.hs.get_clock().sleep(random.randint(1, 10) / 10)
                return 200, {"sid": random_string(16)}

@ -151,7 +159,7 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
            email,
            client_secret,
            send_attempt,
-            self.mailer.send_registration_mail,
+            self.registration_mailer.send_registration_mail,
            next_link,
        )

--- a/synapse/rest/client/rendezvous.py
+++ b/synapse/rest/client/rendezvous.py
@ -97,9 +97,25 @@ class MSC4108DelegationRendezvousServlet(RestServlet):
        )


+class MSC4108RendezvousServlet(RestServlet):
+    PATTERNS = client_patterns(
+        "/org.matrix.msc4108/rendezvous$", releases=[], v1=False, unstable=True
+    )
+
+    def __init__(self, hs: "HomeServer") -> None:
+        super().__init__()
+        self._handler = hs.get_rendezvous_handler()
+
+    def on_POST(self, request: SynapseRequest) -> None:
+        self._handler.handle_post(request)
+
+
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
    if hs.config.experimental.msc3886_endpoint is not None:
        MSC3886RendezvousServlet(hs).register(http_server)

+    if hs.config.experimental.msc4108_enabled:
+        MSC4108RendezvousServlet(hs).register(http_server)
+
    if hs.config.experimental.msc4108_delegation_endpoint is not None:
        MSC4108DelegationRendezvousServlet(hs).register(http_server)
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@ -52,6 +52,7 @@ from synapse.http.servlet import (
    parse_boolean,
    parse_enum,
    parse_integer,
+    parse_json,
    parse_json_object_from_request,
    parse_string,
    parse_strings_from_args,
@ -65,7 +66,6 @@ from synapse.rest.client.transactions import HttpTransactionCache
 from synapse.streams.config import PaginationConfig
 from synapse.types import JsonDict, Requester, StreamToken, ThirdPartyInstanceID, UserID
 from synapse.types.state import StateFilter
-from synapse.util import json_decoder
 from synapse.util.cancellation import cancellable
 from synapse.util.stringutils import parse_and_validate_server_name, random_string

@ -703,21 +703,16 @@ class RoomMessageListRestServlet(RestServlet):
        )
        # Twisted will have processed the args by now.
        assert request.args is not None
+
+        filter_json = parse_json(request, "filter", encoding="utf-8")
+        event_filter = Filter(self._hs, filter_json) if filter_json else None
+
        as_client_event = b"raw" not in request.args
-        filter_str = parse_string(request, "filter", encoding="utf-8")
-        if filter_str:
-            filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(
-                self._hs, json_decoder.decode(filter_json)
-            )
-            if (
-                event_filter
-                and event_filter.filter_json.get("event_format", "client")
-                == "federation"
-            ):
-                as_client_event = False
-        else:
-            event_filter = None
+        if (
+            event_filter
+            and event_filter.filter_json.get("event_format", "client") == "federation"
+        ):
+            as_client_event = False

        msgs = await self.pagination_handler.get_messages(
            room_id=room_id,
@ -898,14 +893,8 @@ class RoomEventContextServlet(RestServlet):
        limit = parse_integer(request, "limit", default=10)

        # picking the API shape for symmetry with /messages
-        filter_str = parse_string(request, "filter", encoding="utf-8")
-        if filter_str:
-            filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(
-                self._hs, json_decoder.decode(filter_json)
-            )
-        else:
-            event_filter = None
+        filter_json = parse_json(request, "filter", encoding="utf-8")
+        event_filter = Filter(self._hs, filter_json) if filter_json else None

        event_context = await self.room_context_handler.get_event_context(
            requester, room_id, event_id, limit, event_filter
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@ -141,8 +141,13 @@ class VersionsRestServlet(RestServlet):
                    # Allows clients to handle push for encrypted events.
                    "org.matrix.msc4028": self.config.experimental.msc4028_push_encrypted_events,
                    # MSC4108: Mechanism to allow OIDC sign in and E2EE set up via QR code
-                    "org.matrix.msc4108": self.config.experimental.msc4108_delegation_endpoint
-                    is not None,
+                    "org.matrix.msc4108": (
+                        self.config.experimental.msc4108_enabled
+                        or (
+                            self.config.experimental.msc4108_delegation_endpoint
+                            is not None
+                        )
+                    ),
                },
            },
        )
--- a/synapse/rest/synapse/client/init.py
+++ b/synapse/rest/synapse/client/init.py
@ -26,6 +26,7 @@ from twisted.web.resource import Resource
 from synapse.rest.synapse.client.new_user_consent import NewUserConsentResource
 from synapse.rest.synapse.client.pick_idp import PickIdpResource
 from synapse.rest.synapse.client.pick_username import pick_username_resource
+from synapse.rest.synapse.client.rendezvous import MSC4108RendezvousSessionResource
 from synapse.rest.synapse.client.sso_register import SsoRegisterResource
 from synapse.rest.synapse.client.unsubscribe import UnsubscribeResource

@ -76,6 +77,9 @@ def build_synapse_client_resource_tree(hs: "HomeServer") -> Mapping[str, Resourc
        # To be removed in Synapse v1.32.0.
        resources["/_matrix/saml2"] = res

+    if hs.config.experimental.msc4108_enabled:
+        resources["/_synapse/client/rendezvous"] = MSC4108RendezvousSessionResource(hs)
+
    return resources


--- a/synapse/rest/synapse/client/rendezvous.py
+++ b/synapse/rest/synapse/client/rendezvous.py
@ -0,0 +1,58 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+#
+
+import logging
+from typing import TYPE_CHECKING, List
+
+from synapse.api.errors import UnrecognizedRequestError
+from synapse.http.server import DirectServeJsonResource
+from synapse.http.site import SynapseRequest
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class MSC4108RendezvousSessionResource(DirectServeJsonResource):
+    isLeaf = True
+
+    def __init__(self, hs: "HomeServer") -> None:
+        super().__init__()
+        self._handler = hs.get_rendezvous_handler()
+
+    async def _async_render_GET(self, request: SynapseRequest) -> None:
+        postpath: List[bytes] = request.postpath  # type: ignore
+        if len(postpath) != 1:
+            raise UnrecognizedRequestError()
+        session_id = postpath[0].decode("ascii")
+
+        self._handler.handle_get(request, session_id)
+
+    def _async_render_PUT(self, request: SynapseRequest) -> None:
+        postpath: List[bytes] = request.postpath  # type: ignore
+        if len(postpath) != 1:
+            raise UnrecognizedRequestError()
+        session_id = postpath[0].decode("ascii")
+
+        self._handler.handle_put(request, session_id)
+
+    def _async_render_DELETE(self, request: SynapseRequest) -> None:
+        postpath: List[bytes] = request.postpath  # type: ignore
+        if len(postpath) != 1:
+            raise UnrecognizedRequestError()
+        session_id = postpath[0].decode("ascii")
+
+        self._handler.handle_delete(request, session_id)
--- a/synapse/server.py
+++ b/synapse/server.py
@ -143,6 +143,7 @@ from synapse.state import StateHandler, StateResolutionHandler
 from synapse.storage import Databases
 from synapse.storage.controllers import StorageControllers
 from synapse.streams.events import EventSources
+from synapse.synapse_rust.rendezvous import RendezvousHandler
 from synapse.types import DomainSpecificString, ISynapseReactor
 from synapse.util import Clock
 from synapse.util.distributor import Distributor
@ -859,6 +860,10 @@ class HomeServer(metaclass=abc.ABCMeta):
    def get_room_forgetter_handler(self) -> RoomForgetterHandler:
        return RoomForgetterHandler(self)

+    @cache_in_self
+    def get_rendezvous_handler(self) -> RendezvousHandler:
+        return RendezvousHandler(self)
+
    @cache_in_self
    def get_outbound_redis_connection(self) -> "ConnectionHandler":
        """
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@ -19,6 +19,7 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
+import collections
 import itertools
 import logging
 from collections import OrderedDict
@ -53,6 +54,7 @@ from synapse.storage.database import (
    LoggingDatabaseConnection,
    LoggingTransaction,
 )
+from synapse.storage.databases.main.event_federation import EventFederationStore
 from synapse.storage.databases.main.events_worker import EventCacheEntry
 from synapse.storage.databases.main.search import SearchEntry
 from synapse.storage.engines import PostgresEngine
@ -768,40 +770,26 @@ class PersistEventsStore:
        #      that have the same chain ID as the event.
        #   2. For each retained auth event we:
        #       a. Add a link from the event's to the auth event's chain
-        #          ID/sequence number; and
-        #       b. Add a link from the event to every chain reachable by the
-        #          auth event.
+        #          ID/sequence number

        # Step 1, fetch all existing links from all the chains we've seen
        # referenced.
        chain_links = _LinkMap()
-        auth_chain_rows = cast(
-            List[Tuple[int, int, int, int]],
-            db_pool.simple_select_many_txn(
-                txn,
-                table="event_auth_chain_links",
-                column="origin_chain_id",
-                iterable={chain_id for chain_id, _ in chain_map.values()},
-                keyvalues={},
-                retcols=(
-                    "origin_chain_id",
-                    "origin_sequence_number",
-                    "target_chain_id",
-                    "target_sequence_number",
-                ),
-            ),
-        )
-        for (
-            origin_chain_id,
-            origin_sequence_number,
-            target_chain_id,
-            target_sequence_number,
-        ) in auth_chain_rows:
-            chain_links.add_link(
-                (origin_chain_id, origin_sequence_number),
-                (target_chain_id, target_sequence_number),
-                new=False,
-            )
+
+        for links in EventFederationStore._get_chain_links(
+            txn, {chain_id for chain_id, _ in chain_map.values()}
+        ):
+            for origin_chain_id, inner_links in links.items():
+                for (
+                    origin_sequence_number,
+                    target_chain_id,
+                    target_sequence_number,
+                ) in inner_links:
+                    chain_links.add_link(
+                        (origin_chain_id, origin_sequence_number),
+                        (target_chain_id, target_sequence_number),
+                        new=False,
+                    )

        # We do this in toplogical order to avoid adding redundant links.
        for event_id in sorted_topologically(
@ -836,18 +824,6 @@ class PersistEventsStore:
                    (chain_id, sequence_number), (auth_chain_id, auth_sequence_number)
                )

-                # Step 2b, add a link to chains reachable from the auth
-                # event.
-                for target_id, target_seq in chain_links.get_links_from(
-                    (auth_chain_id, auth_sequence_number)
-                ):
-                    if target_id == chain_id:
-                        continue
-
-                    chain_links.add_link(
-                        (chain_id, sequence_number), (target_id, target_seq)
-                    )
-
        db_pool.simple_insert_many_txn(
            txn,
            table="event_auth_chain_links",
@ -2451,31 +2427,6 @@ class _LinkMap:
        current_links[src_seq] = target_seq
        return True

-    def get_links_from(
-        self, src_tuple: Tuple[int, int]
-    ) -> Generator[Tuple[int, int], None, None]:
-        """Gets the chains reachable from the given chain/sequence number.
-
-        Yields:
-            The chain ID and sequence number the link points to.
-        """
-        src_chain, src_seq = src_tuple
-        for target_id, sequence_numbers in self.maps.get(src_chain, {}).items():
-            for link_src_seq, target_seq in sequence_numbers.items():
-                if link_src_seq <= src_seq:
-                    yield target_id, target_seq
-
-    def get_links_between(
-        self, source_chain: int, target_chain: int
-    ) -> Generator[Tuple[int, int], None, None]:
-        """Gets the links between two chains.
-
-        Yields:
-            The source and target sequence numbers.
-        """
-
-        yield from self.maps.get(source_chain, {}).get(target_chain, {}).items()
-
    def get_additions(self) -> Generator[Tuple[int, int, int, int], None, None]:
        """Gets any newly added links.

@ -2502,9 +2453,24 @@ class _LinkMap:
        if src_chain == target_chain:
            return target_seq <= src_seq

-        links = self.get_links_between(src_chain, target_chain)
-        for link_start_seq, link_end_seq in links:
-            if link_start_seq <= src_seq and target_seq <= link_end_seq:
-                return True
+        # We have to graph traverse the links to check for indirect paths.
+        visited_chains: Dict[int, int] = collections.Counter()
+        search = [(src_chain, src_seq)]
+        while search:
+            chain, seq = search.pop()
+            visited_chains[chain] = max(seq, visited_chains[chain])
+            for tc, links in self.maps.get(chain, {}).items():
+                for ss, ts in links.items():
+                    # Don't revisit chains we've already seen, unless the target
+                    # sequence number is higher than last time.
+                    if ts <= visited_chains.get(tc, 0):
+                        continue
+
+                    if ss <= seq:
+                        if tc == target_chain:
+                            if target_seq <= ts:
+                                return True
+                        else:
+                            search.append((tc, ts))

        return False
--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@ -1234,6 +1234,28 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):

        return set(room_ids)

+    async def get_membership_event_ids_for_user(
+        self, user_id: str, room_id: str
+    ) -> Set[str]:
+        """Get all event_ids for the given user and room.
+
+        Args:
+            user_id: The user ID to get the event IDs for.
+            room_id: The room ID to look up events for.
+
+        Returns:
+            Set of event IDs
+        """
+
+        event_ids = await self.db_pool.simple_select_onecol(
+            table="room_memberships",
+            keyvalues={"user_id": user_id, "room_id": room_id},
+            retcol="event_id",
+            desc="get_membership_event_ids_for_user",
+        )
+
+        return set(event_ids)
+
    @cached(max_entries=5000)
    async def _get_membership_from_event_id(
        self, member_event_id: str
--- a/synapse/storage/schema/init.py
+++ b/synapse/storage/schema/init.py
@ -132,12 +132,16 @@ Changes in SCHEMA_VERSION = 82

 Changes in SCHEMA_VERSION = 83
    - The event_txn_id is no longer used.
+
+Changes in SCHEMA_VERSION = 84
+    - No longer assumes that `event_auth_chain_links` holds transitive links, and
+      so read operations must do graph traversal.
 """


 SCHEMA_COMPAT_VERSION = (
-    # The event_txn_id table and tables from MSC2716 no longer exist.
-    83
+    # Transitive links are no longer written to `event_auth_chain_links`
+    84
 )
 """Limit on how far the synapse codebase can be rolled back without breaking db compat

--- a/synapse/synapse_rust/rendezvous.pyi
+++ b/synapse/synapse_rust/rendezvous.pyi
@ -0,0 +1,30 @@
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+
+from twisted.web.iweb import IRequest
+
+from synapse.server import HomeServer
+
+class RendezvousHandler:
+    def __init__(
+        self,
+        homeserver: HomeServer,
+        /,
+        capacity: int = 100,
+        max_content_length: int = 4 * 1024,  # MSC4108 specifies 4KB
+        eviction_interval: int = 60 * 1000,
+        ttl: int = 60 * 1000,
+    ) -> None: ...
+    def handle_post(self, request: IRequest) -> None: ...
+    def handle_get(self, request: IRequest, session_id: str) -> None: ...
+    def handle_put(self, request: IRequest, session_id: str) -> None: ...
+    def handle_delete(self, request: IRequest, session_id: str) -> None: ...
--- a/tests/handlers/test_deactivate_account.py
+++ b/tests/handlers/test_deactivate_account.py
@ -424,3 +424,40 @@ class DeactivateAccountTestCase(HomeserverTestCase):
            self._store.get_knocked_at_rooms_for_local_user(self.user)
        )
        self.assertEqual(len(after_deactivate_knocks), 0)
+
+    def test_membership_is_redacted_upon_deactivation(self) -> None:
+        """
+        Tests that room membership events are redacted if erasure is requested.
+        """
+        # Create a room
+        room_id = self.helper.create_room_as(
+            self.user,
+            is_public=True,
+            tok=self.token,
+        )
+
+        # Change the displayname
+        membership_event, _ = self.get_success(
+            self.handler.update_membership(
+                requester=create_requester(self.user),
+                target=UserID.from_string(self.user),
+                room_id=room_id,
+                action=Membership.JOIN,
+                content={"displayname": "Hello World!"},
+            )
+        )
+
+        # Deactivate the account
+        self._deactivate_my_account()
+
+        # Get the all membership event IDs
+        membership_event_ids = self.get_success(
+            self._store.get_membership_event_ids_for_user(self.user, room_id=room_id)
+        )
+
+        # Get the events incl. JSON
+        events = self.get_success(self._store.get_events_as_list(membership_event_ids))
+
+        # Validate that there is no displayname in any of the events
+        for event in events:
+            self.assertTrue("displayname" not in event.content)
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@ -21,6 +21,7 @@
 import json
 import time
 import urllib.parse
+from http import HTTPStatus
 from typing import List, Optional
 from unittest.mock import AsyncMock, Mock

@ -2190,6 +2191,33 @@ class RoomMessagesTestCase(unittest.HomeserverTestCase):
        chunk = channel.json_body["chunk"]
        self.assertEqual(len(chunk), 0, [event["content"] for event in chunk])

+    def test_room_message_filter_query_validation(self) -> None:
+        # Test json validation in (filter) query parameter.
+        # Does not test the validity of the filter, only the json validation.
+
+        # Check Get with valid json filter parameter, expect 200.
+        valid_filter_str = '{"types": ["m.room.message"]}'
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{self.room_id}/messages?dir=b&filter={valid_filter_str}",
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.json_body)
+
+        # Check Get with invalid json filter parameter, expect 400 NOT_JSON.
+        invalid_filter_str = "}}}{}"
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{self.room_id}/messages?dir=b&filter={invalid_filter_str}",
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.BAD_REQUEST, channel.json_body)
+        self.assertEqual(
+            channel.json_body["errcode"], Codes.NOT_JSON, channel.json_body
+        )
+

 class JoinAliasRoomTestCase(unittest.HomeserverTestCase):
    servlets = [
@ -2522,6 +2550,39 @@ class JoinAliasRoomTestCase(unittest.HomeserverTestCase):
            else:
                self.fail("Event %s from events_after not found" % j)

+    def test_room_event_context_filter_query_validation(self) -> None:
+        # Test json validation in (filter) query parameter.
+        # Does not test the validity of the filter, only the json validation.
+
+        # Create a user with room and event_id.
+        user_id = self.register_user("test", "test")
+        user_tok = self.login("test", "test")
+        room_id = self.helper.create_room_as(user_id, tok=user_tok)
+        event_id = self.helper.send(room_id, "message 1", tok=user_tok)["event_id"]
+
+        # Check Get with valid json filter parameter, expect 200.
+        valid_filter_str = '{"types": ["m.room.message"]}'
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{room_id}/context/{event_id}?filter={valid_filter_str}",
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.json_body)
+
+        # Check Get with invalid json filter parameter, expect 400 NOT_JSON.
+        invalid_filter_str = "}}}{}"
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{room_id}/context/{event_id}?filter={invalid_filter_str}",
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.BAD_REQUEST, channel.json_body)
+        self.assertEqual(
+            channel.json_body["errcode"], Codes.NOT_JSON, channel.json_body
+        )
+

 class MakeRoomAdminTestCase(unittest.HomeserverTestCase):
    servlets = [
--- a/tests/rest/client/test_register.py
+++ b/tests/rest/client/test_register.py
@ -22,6 +22,7 @@
 import datetime
 import os
 from typing import Any, Dict, List, Tuple
+from unittest.mock import AsyncMock

 import pkg_resources

@ -42,6 +43,7 @@ from synapse.types import JsonDict
 from synapse.util import Clock

 from tests import unittest
+from tests.server import ThreadedMemoryReactorClock
 from tests.unittest import override_config


@ -58,6 +60,13 @@ class RegisterRestServletTestCase(unittest.HomeserverTestCase):
        config["allow_guest_access"] = True
        return config

+    def make_homeserver(
+        self, reactor: ThreadedMemoryReactorClock, clock: Clock
+    ) -> HomeServer:
+        hs = super().make_homeserver(reactor, clock)
+        hs.get_send_email_handler()._sendmail = AsyncMock()
+        return hs
+
    def test_POST_appservice_registration_valid(self) -> None:
        user_id = "@as_user_kermit:test"
        as_token = "i_am_an_app_service"
--- a/tests/rest/client/test_rendezvous.py
+++ b/tests/rest/client/test_rendezvous.py
@ -2,7 +2,7 @@
 # This file is licensed under the Affero General Public License (AGPL) version 3.
 #
 # Copyright 2022 The Matrix.org Foundation C.I.C.
-# Copyright (C) 2023 New Vector, Ltd
+# Copyright (C) 2023-2024 New Vector, Ltd
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as
@ -19,9 +19,14 @@
 #
 #

+from typing import Dict
+from urllib.parse import urlparse
+
 from twisted.test.proto_helpers import MemoryReactor
+from twisted.web.resource import Resource

 from synapse.rest.client import rendezvous
+from synapse.rest.synapse.client.rendezvous import MSC4108RendezvousSessionResource
 from synapse.server import HomeServer
 from synapse.util import Clock

@ -42,6 +47,12 @@ class RendezvousServletTestCase(unittest.HomeserverTestCase):
        self.hs = self.setup_test_homeserver()
        return self.hs

+    def create_resource_dict(self) -> Dict[str, Resource]:
+        return {
+            **super().create_resource_dict(),
+            "/_synapse/client/rendezvous": MSC4108RendezvousSessionResource(self.hs),
+        }
+
    def test_disabled(self) -> None:
        channel = self.make_request("POST", msc3886_endpoint, {}, access_token=None)
        self.assertEqual(channel.code, 404)
@ -75,3 +86,391 @@ class RendezvousServletTestCase(unittest.HomeserverTestCase):
        channel = self.make_request("POST", msc4108_endpoint, {}, access_token=None)
        self.assertEqual(channel.code, 307)
        self.assertEqual(channel.headers.getRawHeaders("Location"), ["https://asd"])
+
+    @unittest.skip_unless(HAS_AUTHLIB, "requires authlib")
+    @override_config(
+        {
+            "disable_registration": True,
+            "experimental_features": {
+                "msc4108_enabled": True,
+                "msc3861": {
+                    "enabled": True,
+                    "issuer": "https://issuer",
+                    "client_id": "client_id",
+                    "client_auth_method": "client_secret_post",
+                    "client_secret": "client_secret",
+                    "admin_token": "admin_token_value",
+                },
+            },
+        }
+    )
+    def test_msc4108(self) -> None:
+        """
+        Test the MSC4108 rendezvous endpoint, including:
+            - Creating a session
+            - Getting the data back
+            - Updating the data
+            - Deleting the data
+            - ETag handling
+        """
+        # We can post arbitrary data to the endpoint
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_type=b"text/plain",
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 201)
+        self.assertSubstring("/_synapse/client/rendezvous/", channel.json_body["url"])
+        headers = dict(channel.headers.getAllRawHeaders())
+        self.assertIn(b"ETag", headers)
+        self.assertIn(b"Expires", headers)
+        self.assertEqual(headers[b"Content-Type"], [b"application/json"])
+        self.assertEqual(headers[b"Access-Control-Allow-Origin"], [b"*"])
+        self.assertEqual(headers[b"Access-Control-Expose-Headers"], [b"etag"])
+        self.assertEqual(headers[b"Cache-Control"], [b"no-store"])
+        self.assertEqual(headers[b"Pragma"], [b"no-cache"])
+        self.assertIn("url", channel.json_body)
+        self.assertTrue(channel.json_body["url"].startswith("https://"))
+
+        url = urlparse(channel.json_body["url"])
+        session_endpoint = url.path
+        etag = headers[b"ETag"][0]
+
+        # We can get the data back
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+
+        self.assertEqual(channel.code, 200)
+        headers = dict(channel.headers.getAllRawHeaders())
+        self.assertEqual(headers[b"ETag"], [etag])
+        self.assertIn(b"Expires", headers)
+        self.assertEqual(headers[b"Content-Type"], [b"text/plain"])
+        self.assertEqual(headers[b"Access-Control-Allow-Origin"], [b"*"])
+        self.assertEqual(headers[b"Access-Control-Expose-Headers"], [b"etag"])
+        self.assertEqual(headers[b"Cache-Control"], [b"no-store"])
+        self.assertEqual(headers[b"Pragma"], [b"no-cache"])
+        self.assertEqual(channel.text_body, "foo=bar")
+
+        # We can make sure the data hasn't changed
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+            custom_headers=[("If-None-Match", etag)],
+        )
+
+        self.assertEqual(channel.code, 304)
+
+        # We can update the data
+        channel = self.make_request(
+            "PUT",
+            session_endpoint,
+            "foo=baz",
+            content_type=b"text/plain",
+            access_token=None,
+            custom_headers=[("If-Match", etag)],
+        )
+
+        self.assertEqual(channel.code, 202)
+        headers = dict(channel.headers.getAllRawHeaders())
+        old_etag = etag
+        new_etag = headers[b"ETag"][0]
+
+        # If we try to update it again with the old etag, it should fail
+        channel = self.make_request(
+            "PUT",
+            session_endpoint,
+            "bar=baz",
+            content_type=b"text/plain",
+            access_token=None,
+            custom_headers=[("If-Match", old_etag)],
+        )
+
+        self.assertEqual(channel.code, 412)
+        self.assertEqual(channel.json_body["errcode"], "M_UNKNOWN")
+        self.assertEqual(
+            channel.json_body["org.matrix.msc4108.errcode"], "M_CONCURRENT_WRITE"
+        )
+
+        # If we try to get with the old etag, we should get the updated data
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+            custom_headers=[("If-None-Match", old_etag)],
+        )
+
+        self.assertEqual(channel.code, 200)
+        headers = dict(channel.headers.getAllRawHeaders())
+        self.assertEqual(headers[b"ETag"], [new_etag])
+        self.assertEqual(channel.text_body, "foo=baz")
+
+        # We can delete the data
+        channel = self.make_request(
+            "DELETE",
+            session_endpoint,
+            access_token=None,
+        )
+
+        self.assertEqual(channel.code, 204)
+
+        # If we try to get the data again, it should fail
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+
+        self.assertEqual(channel.code, 404)
+        self.assertEqual(channel.json_body["errcode"], "M_NOT_FOUND")
+
+    @unittest.skip_unless(HAS_AUTHLIB, "requires authlib")
+    @override_config(
+        {
+            "disable_registration": True,
+            "experimental_features": {
+                "msc4108_enabled": True,
+                "msc3861": {
+                    "enabled": True,
+                    "issuer": "https://issuer",
+                    "client_id": "client_id",
+                    "client_auth_method": "client_secret_post",
+                    "client_secret": "client_secret",
+                    "admin_token": "admin_token_value",
+                },
+            },
+        }
+    )
+    def test_msc4108_expiration(self) -> None:
+        """
+        Test that entries are evicted after a TTL.
+        """
+        # Start a new session
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_type=b"text/plain",
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 201)
+        session_endpoint = urlparse(channel.json_body["url"]).path
+
+        # Sanity check that we can get the data back
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.text_body, "foo=bar")
+
+        # Advance the clock, TTL of entries is 1 minute
+        self.reactor.advance(60)
+
+        # Get the data back, it should be gone
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 404)
+
+    @unittest.skip_unless(HAS_AUTHLIB, "requires authlib")
+    @override_config(
+        {
+            "disable_registration": True,
+            "experimental_features": {
+                "msc4108_enabled": True,
+                "msc3861": {
+                    "enabled": True,
+                    "issuer": "https://issuer",
+                    "client_id": "client_id",
+                    "client_auth_method": "client_secret_post",
+                    "client_secret": "client_secret",
+                    "admin_token": "admin_token_value",
+                },
+            },
+        }
+    )
+    def test_msc4108_capacity(self) -> None:
+        """
+        Test that a capacity limit is enforced on the rendezvous sessions, as old
+        entries are evicted at an interval when the limit is reached.
+        """
+        # Start a new session
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_type=b"text/plain",
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 201)
+        session_endpoint = urlparse(channel.json_body["url"]).path
+
+        # Sanity check that we can get the data back
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.text_body, "foo=bar")
+
+        # Start a lot of new sessions
+        for _ in range(100):
+            channel = self.make_request(
+                "POST",
+                msc4108_endpoint,
+                "foo=bar",
+                content_type=b"text/plain",
+                access_token=None,
+            )
+            self.assertEqual(channel.code, 201)
+
+        # Get the data back, it should still be there, as the eviction hasn't run yet
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+
+        self.assertEqual(channel.code, 200)
+
+        # Advance the clock, as it will trigger the eviction
+        self.reactor.advance(1)
+
+        # Get the data back, it should be gone
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+
+    @unittest.skip_unless(HAS_AUTHLIB, "requires authlib")
+    @override_config(
+        {
+            "disable_registration": True,
+            "experimental_features": {
+                "msc4108_enabled": True,
+                "msc3861": {
+                    "enabled": True,
+                    "issuer": "https://issuer",
+                    "client_id": "client_id",
+                    "client_auth_method": "client_secret_post",
+                    "client_secret": "client_secret",
+                    "admin_token": "admin_token_value",
+                },
+            },
+        }
+    )
+    def test_msc4108_hard_capacity(self) -> None:
+        """
+        Test that a hard capacity limit is enforced on the rendezvous sessions, as old
+        entries are evicted immediately when the limit is reached.
+        """
+        # Start a new session
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_type=b"text/plain",
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 201)
+        session_endpoint = urlparse(channel.json_body["url"]).path
+        # We advance the clock to make sure that this entry is the "lowest" in the session list
+        self.reactor.advance(1)
+
+        # Sanity check that we can get the data back
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.text_body, "foo=bar")
+
+        # Start a lot of new sessions
+        for _ in range(200):
+            channel = self.make_request(
+                "POST",
+                msc4108_endpoint,
+                "foo=bar",
+                content_type=b"text/plain",
+                access_token=None,
+            )
+            self.assertEqual(channel.code, 201)
+
+        # Get the data back, it should already be gone as we hit the hard limit
+        channel = self.make_request(
+            "GET",
+            session_endpoint,
+            access_token=None,
+        )
+
+        self.assertEqual(channel.code, 404)
+
+    @unittest.skip_unless(HAS_AUTHLIB, "requires authlib")
+    @override_config(
+        {
+            "disable_registration": True,
+            "experimental_features": {
+                "msc4108_enabled": True,
+                "msc3861": {
+                    "enabled": True,
+                    "issuer": "https://issuer",
+                    "client_id": "client_id",
+                    "client_auth_method": "client_secret_post",
+                    "client_secret": "client_secret",
+                    "admin_token": "admin_token_value",
+                },
+            },
+        }
+    )
+    def test_msc4108_content_type(self) -> None:
+        """
+        Test that the content-type is restricted to text/plain.
+        """
+        # We cannot post invalid content-type arbitrary data to the endpoint
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_is_form=True,
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 400)
+        self.assertEqual(channel.json_body["errcode"], "M_INVALID_PARAM")
+
+        # Make a valid request
+        channel = self.make_request(
+            "POST",
+            msc4108_endpoint,
+            "foo=bar",
+            content_type=b"text/plain",
+            access_token=None,
+        )
+        self.assertEqual(channel.code, 201)
+        url = urlparse(channel.json_body["url"])
+        session_endpoint = url.path
+        headers = dict(channel.headers.getAllRawHeaders())
+        etag = headers[b"ETag"][0]
+
+        # We can't update the data with invalid content-type
+        channel = self.make_request(
+            "PUT",
+            session_endpoint,
+            "foo=baz",
+            content_is_form=True,
+            access_token=None,
+            custom_headers=[("If-Match", etag)],
+        )
+        self.assertEqual(channel.code, 400)
+        self.assertEqual(channel.json_body["errcode"], "M_INVALID_PARAM")
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@ -2175,6 +2175,31 @@ class RoomMessageListTestCase(RoomBase):
        chunk = channel.json_body["chunk"]
        self.assertEqual(len(chunk), 0, [event["content"] for event in chunk])

+    def test_room_message_filter_query_validation(self) -> None:
+        # Test json validation in (filter) query parameter.
+        # Does not test the validity of the filter, only the json validation.
+
+        # Check Get with valid json filter parameter, expect 200.
+        valid_filter_str = '{"types": ["m.room.message"]}'
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/messages?access_token=x&dir=b&filter={valid_filter_str}",
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.json_body)
+
+        # Check Get with invalid json filter parameter, expect 400 NOT_JSON.
+        invalid_filter_str = "}}}{}"
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/messages?access_token=x&dir=b&filter={invalid_filter_str}",
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.BAD_REQUEST, channel.json_body)
+        self.assertEqual(
+            channel.json_body["errcode"], Codes.NOT_JSON, channel.json_body
+        )
+

 class RoomMessageFilterTestCase(RoomBase):
    """Tests /rooms/$room_id/messages REST events."""
@ -3213,6 +3238,33 @@ class ContextTestCase(unittest.HomeserverTestCase):
        self.assertDictEqual(events_after[0].get("content"), {}, events_after[0])
        self.assertEqual(events_after[1].get("content"), {}, events_after[1])

+    def test_room_event_context_filter_query_validation(self) -> None:
+        # Test json validation in (filter) query parameter.
+        # Does not test the validity of the filter, only the json validation.
+        event_id = self.helper.send(self.room_id, "message 7", tok=self.tok)["event_id"]
+
+        # Check Get with valid json filter parameter, expect 200.
+        valid_filter_str = '{"types": ["m.room.message"]}'
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/context/{event_id}?filter={valid_filter_str}",
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.json_body)
+
+        # Check Get with invalid json filter parameter, expect 400 NOT_JSON.
+        invalid_filter_str = "}}}{}"
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/context/{event_id}?filter={invalid_filter_str}",
+            access_token=self.tok,
+        )
+
+        self.assertEqual(channel.code, HTTPStatus.BAD_REQUEST, channel.json_body)
+        self.assertEqual(
+            channel.json_body["errcode"], Codes.NOT_JSON, channel.json_body
+        )
+

 class RoomAliasListTestCase(unittest.HomeserverTestCase):
    servlets = [
--- a/tests/server.py
+++ b/tests/server.py
@ -351,6 +351,7 @@ def make_request(
    request: Type[Request] = SynapseRequest,
    shorthand: bool = True,
    federation_auth_origin: Optional[bytes] = None,
+    content_type: Optional[bytes] = None,
    content_is_form: bool = False,
    await_result: bool = True,
    custom_headers: Optional[Iterable[CustomHeaderType]] = None,
@ -373,6 +374,8 @@ def make_request(
            with the usual REST API path, if it doesn't contain it.
        federation_auth_origin: if set to not-None, we will add a fake
            Authorization header pretenting to be the given server name.
+        content_type: The content-type to use for the request. If not set then will default to
+            application/json unless content_is_form is true.
        content_is_form: Whether the content is URL encoded form data. Adds the
            'Content-Type': 'application/x-www-form-urlencoded' header.
        await_result: whether to wait for the request to complete rendering. If true,
@ -436,7 +439,9 @@ def make_request(
        )

    if content:
-        if content_is_form:
+        if content_type is not None:
+            req.requestHeaders.addRawHeader(b"Content-Type", content_type)
+        elif content_is_form:
            req.requestHeaders.addRawHeader(
                b"Content-Type", b"application/x-www-form-urlencoded"
            )
--- a/tests/storage/test_event_chain.py
+++ b/tests/storage/test_event_chain.py
@ -21,6 +21,8 @@

 from typing import Dict, List, Set, Tuple, cast

+from parameterized import parameterized
+
 from twisted.test.proto_helpers import MemoryReactor
 from twisted.trial import unittest

@ -45,7 +47,8 @@ class EventChainStoreTestCase(HomeserverTestCase):
        self.store = hs.get_datastores().main
        self._next_stream_ordering = 1

-    def test_simple(self) -> None:
+    @parameterized.expand([(False,), (True,)])
+    def test_simple(self, batched: bool) -> None:
        """Test that the example in `docs/auth_chain_difference_algorithm.md`
        works.
        """
@ -53,6 +56,7 @@ class EventChainStoreTestCase(HomeserverTestCase):
        event_factory = self.hs.get_event_builder_factory()
        bob = "@creator:test"
        alice = "@alice:test"
+        charlie = "@charlie:test"
        room_id = "!room:test"

        # Ensure that we have a rooms entry so that we generate the chain index.
@ -191,6 +195,26 @@ class EventChainStoreTestCase(HomeserverTestCase):
            )
        )

+        charlie_invite = self.get_success(
+            event_factory.for_room_version(
+                RoomVersions.V6,
+                {
+                    "type": EventTypes.Member,
+                    "state_key": charlie,
+                    "sender": alice,
+                    "room_id": room_id,
+                    "content": {"tag": "charlie_invite"},
+                },
+            ).build(
+                prev_event_ids=[],
+                auth_event_ids=[
+                    create.event_id,
+                    alice_join2.event_id,
+                    power_2.event_id,
+                ],
+            )
+        )
+
        events = [
            create,
            bob_join,
@ -200,33 +224,41 @@ class EventChainStoreTestCase(HomeserverTestCase):
            bob_join_2,
            power_2,
            alice_join2,
+            charlie_invite,
        ]

        expected_links = [
            (bob_join, create),
-            (power, create),
            (power, bob_join),
-            (alice_invite, create),
            (alice_invite, power),
-            (alice_invite, bob_join),
            (bob_join_2, power),
            (alice_join2, power_2),
+            (charlie_invite, alice_join2),
        ]

-        self.persist(events)
+        # We either persist as a batch or one-by-one depending on test
+        # parameter.
+        if batched:
+            self.persist(events)
+        else:
+            for event in events:
+                self.persist([event])
+
        chain_map, link_map = self.fetch_chains(events)

        # Check that the expected links and only the expected links have been
        # added.
-        self.assertEqual(len(expected_links), len(list(link_map.get_additions())))
+        event_map = {e.event_id: e for e in events}
+        reverse_chain_map = {v: event_map[k] for k, v in chain_map.items()}

-        for start, end in expected_links:
-            start_id, start_seq = chain_map[start.event_id]
-            end_id, end_seq = chain_map[end.event_id]
-
-            self.assertIn(
-                (start_seq, end_seq), list(link_map.get_links_between(start_id, end_id))
-            )
+        self.maxDiff = None
+        self.assertCountEqual(
+            expected_links,
+            [
+                (reverse_chain_map[(s1, s2)], reverse_chain_map[(t1, t2)])
+                for s1, s2, t1, t2 in link_map.get_additions()
+            ],
+        )

        # Test that everything can reach the create event, but the create event
        # can't reach anything.
@ -368,24 +400,23 @@ class EventChainStoreTestCase(HomeserverTestCase):

        expected_links = [
            (bob_join, create),
-            (power, create),
            (power, bob_join),
-            (alice_invite, create),
            (alice_invite, power),
-            (alice_invite, bob_join),
        ]

        # Check that the expected links and only the expected links have been
        # added.
-        self.assertEqual(len(expected_links), len(list(link_map.get_additions())))
+        event_map = {e.event_id: e for e in events}
+        reverse_chain_map = {v: event_map[k] for k, v in chain_map.items()}

-        for start, end in expected_links:
-            start_id, start_seq = chain_map[start.event_id]
-            end_id, end_seq = chain_map[end.event_id]
-
-            self.assertIn(
-                (start_seq, end_seq), list(link_map.get_links_between(start_id, end_id))
-            )
+        self.maxDiff = None
+        self.assertCountEqual(
+            expected_links,
+            [
+                (reverse_chain_map[(s1, s2)], reverse_chain_map[(t1, t2)])
+                for s1, s2, t1, t2 in link_map.get_additions()
+            ],
+        )

    def persist(
        self,
@ -489,8 +520,6 @@ class LinkMapTestCase(unittest.TestCase):
        link_map = _LinkMap()

        link_map.add_link((1, 1), (2, 1), new=False)
-        self.assertCountEqual(link_map.get_links_between(1, 2), [(1, 1)])
-        self.assertCountEqual(link_map.get_links_from((1, 1)), [(2, 1)])
        self.assertCountEqual(link_map.get_additions(), [])
        self.assertTrue(link_map.exists_path_from((1, 5), (2, 1)))
        self.assertFalse(link_map.exists_path_from((1, 5), (2, 2)))
@ -499,18 +528,31 @@ class LinkMapTestCase(unittest.TestCase):

        # Attempting to add a redundant link is ignored.
        self.assertFalse(link_map.add_link((1, 4), (2, 1)))
-        self.assertCountEqual(link_map.get_links_between(1, 2), [(1, 1)])
+        self.assertCountEqual(link_map.get_additions(), [])

        # Adding new non-redundant links works
        self.assertTrue(link_map.add_link((1, 3), (2, 3)))
-        self.assertCountEqual(link_map.get_links_between(1, 2), [(1, 1), (3, 3)])
+        self.assertCountEqual(link_map.get_additions(), [(1, 3, 2, 3)])

        self.assertTrue(link_map.add_link((2, 5), (1, 3)))
-        self.assertCountEqual(link_map.get_links_between(2, 1), [(5, 3)])
-        self.assertCountEqual(link_map.get_links_between(1, 2), [(1, 1), (3, 3)])
-
        self.assertCountEqual(link_map.get_additions(), [(1, 3, 2, 3), (2, 5, 1, 3)])

+    def test_exists_path_from(self) -> None:
+        "Check that `exists_path_from` can handle non-direct links"
+        link_map = _LinkMap()
+
+        link_map.add_link((1, 1), (2, 1), new=False)
+        link_map.add_link((2, 1), (3, 1), new=False)
+
+        self.assertTrue(link_map.exists_path_from((1, 4), (3, 1)))
+        self.assertFalse(link_map.exists_path_from((1, 4), (3, 2)))
+
+        link_map.add_link((1, 5), (2, 3), new=False)
+        link_map.add_link((2, 2), (3, 3), new=False)
+
+        self.assertTrue(link_map.exists_path_from((1, 6), (3, 2)))
+        self.assertFalse(link_map.exists_path_from((1, 4), (3, 2)))
+

 class EventChainBackgroundUpdateTestCase(HomeserverTestCase):
    servlets = [
--- a/tests/unittest.py
+++ b/tests/unittest.py
@ -523,6 +523,7 @@ class HomeserverTestCase(TestCase):
        request: Type[Request] = SynapseRequest,
        shorthand: bool = True,
        federation_auth_origin: Optional[bytes] = None,
+        content_type: Optional[bytes] = None,
        content_is_form: bool = False,
        await_result: bool = True,
        custom_headers: Optional[Iterable[CustomHeaderType]] = None,
@ -541,6 +542,9 @@ class HomeserverTestCase(TestCase):
            with the usual REST API path, if it doesn't contain it.
            federation_auth_origin: if set to not-None, we will add a fake
                Authorization header pretenting to be the given server name.
+
+            content_type: The content-type to use for the request. If not set then will default to
+                application/json unless content_is_form is true.
            content_is_form: Whether the content is URL encoded form data. Adds the
                'Content-Type': 'application/x-www-form-urlencoded' header.

@ -566,6 +570,7 @@ class HomeserverTestCase(TestCase):
            request,
            shorthand,
            federation_auth_origin,
+            content_type,
            content_is_form,
            await_result,
            custom_headers,
				`@ -1 +0,0 @@`
				Adds validation to ensure that the `limit` parameter on `/publicRooms` is non-negative.
				`@ -1 +0,0 @@`
				Make the CSAPI endpoint `/keys/device_signing/upload` idempotent.
				`@ -1 +0,0 @@`
				`Use new receipts column to optimise receipt and push action SQL queries. Contributed by Nick @ Beeper (@fizzadar).`
				`@ -1 +0,0 @@`
				`Bump minimum supported Rust version to 1.66.0.`
				`@ -1 +0,0 @@`
				`Add helpers to transform Twisted requests to Rust http Requests/Responses.`
				`@ -1 +0,0 @@`
				`Support delegating the rendezvous mechanism described MSC4108 to an external implementation.`