docs: release notes for 10.2.5 (#3884)

docs/src/main/paradox/release-notes/10.2.x.md

@@ -1,5 +1,104 @@
 # 10.2.x Release Notes
 
+## 10.2.5
+
+This release includes a set of performance improvements in the HTTP/2 infrastructure. Aside from internal improvements,
+some performance-related changes introduce new APIs or settings:
+
+#### HTTP/2: Trailers on messages with Strict entities
+
+HTTP/2 server and client can now send `Strict` entities to completely avoid stream materialization overhead for common
+use cases that require no streaming. This required providing a new way to attach trailing headers to a message also for
+messages with `Strict` entities. For that purpose the new attribute `AttributeKeys.trailer` of type @apidoc[Trailer] can be
+attached to a message. This is a common scenario for gRPC which uses trailing headers to transmit the status code in a response.
+
+Streaming entities using `Chunked` entities can still use the `LastChunk` to provide trailing headers.
+
+See @ref[Trailing Headers](../server-side/http2.md#trailing-headers) for more information.
+
+#### HTTP/2: Collect Strict entities
+
+HTTP/2 servers can request to produce `Strict` entities also for incoming requests by using the new
+`akka.http.server.http2.min-collect-strict-entity-size` setting. With that setting, the server can be instructed to
+hold back an incoming request to collect more data until either the request has been fully received (`Strict` entity is
+dispatched) or the given limit of collected data has been reached (`Chunked` entity is dispatched as before).
+This is another optimization to avoid stream materialization overhead where possible for small requests (also common with
+simple gRPC requests).
+
+The setting is still disabled by default. See the accompanying comments in the @ref[reference.conf](../configuration.md#configuration)
+for more information.
+
+#### Other notable improvements
+
+ * Client connection pool has a new `keep-alive-timeout` to avoid race conditions with server-side timeouts.
+   See @ref[Keep Alive Timeout](../common/timeouts.md#keep-alive-timeout).
+
+### Changes since 10.2.4
+
+#### akka-http-core
+
+##### Features
+
+* Add pool keep-alive-timeout [#3816](https://github.com/akka/akka-http/pull/3816)
+* Add flag to log WebSocket frame traffic [#3739](https://github.com/akka/akka-http/pull/3739)
+* Move `isStrict` up a level to ws.Message [#3847](https://github.com/akka/akka-http/pull/3847)
+* Add setting to automatically collect HTTP/2 request entity data into strict entities [#3829](https://github.com/akka/akka-http/pull/3829)
+* Allow trailing HTTP/2 headers on strict responses [#3820](https://github.com/akka/akka-http/pull/3820)
+
+##### Improvements / Fixes
+
+* Include port in HTTP/2 binding warning [#3793](https://github.com/akka/akka-http/pull/3793)
+* Don't send '100 Continue' if 'Content-Length' header is 0, doesn't exist or data got sent early [#3786](https://github.com/akka/akka-http/pull/3786)
+* Preserve original response headers during server termination [#3819](https://github.com/akka/akka-http/pull/3819)
+* Remove the requirement of max-open-requests being a power of two [#3827](https://github.com/akka/akka-http/pull/3827)
+* Add detail to onBadProtocol [#2877](https://github.com/akka/akka-http/pull/2877)
+* Back off on HTTP/2 client persistent connection failure [#3857](https://github.com/akka/akka-http/pull/3857)
+* Block demux stage completion until in-flight ops complete [#3734](https://github.com/akka/akka-http/pull/3734)
+* Ensure unhandled error ultimately get translated into GOAWAY frames [#3839](https://github.com/akka/akka-http/pull/3839)
+* Properly propagate completion through PersistentConnection [#3855](https://github.com/akka/akka-http/pull/3855)
+* Remove Http2FrameRendering stage [#3838](https://github.com/akka/akka-http/pull/3838)
+* Remove reflective access to alpn classes (JDK16 support) [#3811](https://github.com/akka/akka-http/pull/3811)
+
+##### Optimizations
+
+* Cache ContentType rendering [#3830](https://github.com/akka/akka-http/pull/3830)
+* Cache ModeledHeader.value [#3846](https://github.com/akka/akka-http/pull/3846)
+* Cache lowercaseName in `ModeledCustomHeaderCompanion` [#3851](https://github.com/akka/akka-http/pull/3851)
+* Only render date-header once per second [#3832](https://github.com/akka/akka-http/pull/3832)
+* Don't include RequestTimeoutSupport if disabled [#3862](https://github.com/akka/akka-http/pull/3862)
+* Fix UriParser constructor performance [#3813](https://github.com/akka/akka-http/pull/3813)
+* Increase some default buffer sizes [#3863](https://github.com/akka/akka-http/pull/3863)
+* A few simple microoptimizations that turned up in profiling [#3872](https://github.com/akka/akka-http/pull/3872)
+* Append new trailing headers at the end [#3821](https://github.com/akka/akka-http/pull/3821)
+* Avoid async boundary in ProtocolSwitch [#3831](https://github.com/akka/akka-http/pull/3831)
+* Avoid calling LoggingAdapter.isDebugEnabled in multiplexer [#3869](https://github.com/akka/akka-http/pull/3869)
+* Avoid creating GenericOutlet for every out element [#3848](https://github.com/akka/akka-http/pull/3848)
+* Avoid extra allocations in frame renderer [#3823](https://github.com/akka/akka-http/pull/3823)
+* Cache expensive `isDebugEnabled` call [#3850](https://github.com/akka/akka-http/pull/3850)
+* Convert stream handling map to LongMap [#3845](https://github.com/akka/akka-http/pull/3845)
+* Don't recordStateChange when debug logging is disabled [#3842](https://github.com/akka/akka-http/pull/3842)
+* Fix window management while CollectingIncomingData [#3837](https://github.com/akka/akka-http/pull/3837)
+* Provide missing handling logic in CollectingIncomingData state + tests [#3837](https://github.com/akka/akka-http/pull/3837)
+* Import shaded twitter hpack library (APL2) [#3849](https://github.com/akka/akka-http/pull/3849)
+* Never create Default entity [#3841](https://github.com/akka/akka-http/pull/3841)
+* Optimize header parsing by caching headers in HPACK tables [#3861](https://github.com/akka/akka-http/pull/3861)
+* Support Strict entities in Http2SubStream [#3824](https://github.com/akka/akka-http/pull/3824)
+* Use ByteString.length instead of ByteString.size [#3853](https://github.com/akka/akka-http/pull/3853)
+* Use cached ContentType.value instead of toString [#3865](https://github.com/akka/akka-http/pull/3865)
+* Use mutable.Queue for state in multiplexer [#3873](https://github.com/akka/akka-http/pull/3873)
+
+#### Build
+
+* Update caffeine from 2.8.8 to 2.9.0 [#3768](https://github.com/akka/akka-http/pull/3768)
+* Update github-api from 1.122 to 1.123 [#3777](https://github.com/akka/akka-http/pull/3777)
+* Update to Scala 2.13.5, 2.12.13 and scalafix 0.9.26 [#3780](https://github.com/akka/akka-http/pull/3780)
+* Finally update to sbt 1.4.7 [#3781](https://github.com/akka/akka-http/pull/3781)
+* Publish to sonatype directly [#3792](https://github.com/akka/akka-http/pull/3792)
+* Import shaded twitter hpack library (APL2) [#3849](https://github.com/akka/akka-http/pull/3849)
+* Update dependencies [#3870](https://github.com/akka/akka-http/pull/3870)
+* Disable parallel test execution during Github Actions runs [#3866](https://github.com/akka/akka-http/pull/3866)
+* Run full validation when workflow definition has changed [#3881](https://github.com/akka/akka-http/pull/3881)
+
 ## 10.2.4
 
 This release fixes [CVE-2021-23339](https://nvd.nist.gov/vuln/detail/CVE-2021-23339), a vulnerability regarding interpretation of `Transfer-Encoding` headers. See