Add server-side WebSocket compression#1114
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* Negotiate RFC 7692 permessage-deflate for server-side WebSockets. * Add compression settings, documentation, release notes, and MiMa filters. * Cover negotiation, compression, fragmentation, context takeover, max allocation, and low-level frame handling.
* Add WebSocketUpgrade overloads that accept a compressionEnabled flag. * Wire accepted WebSockets to decline negotiated compression per request. * Document and test per-upgrade compression disabling.
This was referenced Jun 30, 2026
pjfanning
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Jun 30, 2026
| @@ -0,0 +1,341 @@ | |||
| /* | |||
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the source header should be the standard Apache header - see https://github.com/apache/pekko/blob/main/CONTRIBUTING.md#pull-request-requirements - unless this code is largely a copy/paste of 3rd party code (in which case, the existing source header in that code would be used)
pjfanning
reviewed
Jun 30, 2026
| * use the given handlerFlow to handle WebSocket messages from the client. The given subprotocol must be one | ||
| * of the ones offered by the client. | ||
| * | ||
| * The compressionEnabled flag allows declining negotiated WebSocket compression for this accepted WebSocket. |
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can you add @since 2.0.0 on new public API methods?
pjfanning
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Jun 30, 2026
| * Dependency versions have been updated | ||
| * Jackson3 is supported in a new pekko-http-jackson3 lib | ||
| * Changed Java DSL methods that return Scala Durations to return Java Durations ([PR788](https://github.com/apache/pekko-http/pull/788)) | ||
| * Server-side WebSocket connections can now negotiate RFC 7692 `permessage-deflate` compression when requested by the client. |
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2.0.0-M1 is already released. Just revert this and we will form 2.0.0-M2 release notes when that release is ready, hopefully in a month or 2.
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I see netty have many compression support, should we do that too? |
He-Pin
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Jul 1, 2026
| # Whether the server should support WebSocket compression using the RFC 7692 | ||
| # permessage-deflate extension. Compression is negotiated during the | ||
| # WebSocket handshake and is only used when the client requests it. | ||
| enabled = true |
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Should we do adaptive compression?
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What changed
Adds server-side support for RFC 7692
permessage-deflateWebSocket compression.Compression is negotiated during the WebSocket handshake when the client offers
permessage-deflateinSec-WebSocket-Extensions. It is enabled by default and can be disabled globally through configuration.Also adds an API option to decline negotiated compression for a single accepted WebSocket upgrade.
Details
This PR adds:
permessage-deflatenegotiation for server-side WebSocketsclient_max_window_bitsWebSocketUpgradeoverloadsNetty comparison
The implementation follows Netty’s
permessage-deflatebehavior where it makes sense for Pekko HTTP:server_no_context_takeoverandclient_no_context_takeovercan be negotiatedclient_max_window_bitscan be negotiatedmax-allocationOne deliberate difference is zlib implementation scope. Netty also uses the JDK
DeflaterandInflaterAPIs for the default zlib settings, and only switches to JZlib when non-default zlibwindowBitsormemLevelsupport is needed. Pekko HTTP currently uses only the JDKDeflaterandInflaterAPIs, like Tomcat and Jetty. The JDK API does not expose zlibwindowBitsormemLevel, so Pekko HTTP does not acceptserver_max_window_bitsvalues below15and does not provide server window-size or memory-level settings.Clients may still request
client_max_window_bits; when they do, Pekko HTTP can include the configuredpreferred-client-window-sizein the handshake response to ask the client to use that window size for client-to-server messages.Security notes
WebSocket compression can increase CPU and memory usage.
The default context takeover settings match common server defaults and favor compression efficiency. Applications that need a more conservative setup can configure no-context-takeover behavior or disable compression globally/per accepted WebSocket.
max-allocationlimits decompressed message size. If the limit is exceeded while inflating a compressed message, Pekko HTTP closes the connection with a WebSocket protocol error.Testing
Ran:
sbt "http-core / Test / testOnly org.apache.pekko.http.impl.engine.ws.WebSocketServerSpec" sbt +mimaReportBinaryIssuesAlso verified Play Framework integration against the locally published Pekko HTTP artifact:
(This is a WIP pull request for Play which I will submit tomorrow - I will you ping you then)
References