Merge commit 'c9c544cda' into anoa/dinsic_release_1_21_x

* commit 'c9c544cda':
  Remove `ChainedIdGenerator`. (#8123)
  Switch the JSON byte producer from a pull to a push producer. (#8116)
  Updated docs: Added note about missing 308 redirect support. (#8120)
  Be stricter about JSON that is accepted by Synapse (#8106)
  Convert runWithConnection to async. (#8121)
  Remove the unused inlineCallbacks code-paths in the caching code (#8119)
  Separate `get_current_token` into two. (#8113)
  Convert events worker database to async/await. (#8071)
  Add a link to the matrix-synapse-rest-password-provider. (#8111)

Author: anoadragon453

changelog.d/8071.misc

@@ -0,0 +1 @@
+Convert various parts of the codebase to async/await.

changelog.d/8106.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug where invalid JSON would be accepted by Synapse.

changelog.d/8111.doc

@@ -0,0 +1 @@
+Link to matrix-synapse-rest-password-provider in the password provider documentation.

changelog.d/8113.misc

@@ -0,0 +1 @@
+Separate `get_current_token` into two since there are two different use cases for it.

changelog.d/8116.feature

@@ -0,0 +1 @@
+Iteratively encode JSON to avoid blocking the reactor.

changelog.d/8119.misc

@@ -0,0 +1 @@
+Convert various parts of the codebase to async/await.

changelog.d/8120.doc

@@ -0,0 +1 @@
+Updated documentation to note that Synapse does not follow `HTTP 308` redirects due to an upstream library not supporting them. Contributed by Ryan Cole.

changelog.d/8121.misc

@@ -0,0 +1 @@
+Convert various parts of the codebase to async/await.

changelog.d/8123.misc

@@ -0,0 +1 @@
+Remove `ChainedIdGenerator`.

docs/federate.md

@@ -47,6 +47,18 @@ you invite them to. This can be caused by an incorrectly-configured reverse
 proxy: see [reverse_proxy.md](<reverse_proxy.md>) for instructions on how to correctly
 configure a reverse proxy.
 
+### Known issues
+
+**HTTP `308 Permanent Redirect` redirects are not followed**: Due to missing features
+in the HTTP library used by Synapse, 308 redirects are currently not followed by
+federating servers, which can cause `M_UNKNOWN` or `401 Unauthorized` errors. This
+may affect users who are redirecting apex-to-www (e.g. `example.com` -> `www.example.com`),
+and especially users of the Kubernetes *Nginx Ingress* module, which uses 308 redirect
+codes by default. For those Kubernetes users, [this Stackoverflow post](https://stackoverflow.com/a/52617528/5096871) 
+might be helpful. For other users, switching to a `301 Moved Permanently` code may be
+an option. 308 redirect codes will be supported properly in a future
+release of Synapse.
+
 ## Running a demo federation of Synapses
 
 If you want to get up and running quickly with a trio of homeservers in a