Merge pull request #5362 from cloudflare/harris/EW-9632-increase-web-socket-max-message-size-32m

EW-9632 Increase max WebSocket message size limit to 32MiB

Author: harrishancock

src/workerd/api/web-socket.c++

@@ -13,6 +13,7 @@
 #include <workerd/io/worker.h>
 #include <workerd/jsg/jsg.h>
 #include <workerd/jsg/ser.h>
+#include <workerd/util/autogate.h>
 #include <workerd/util/sentry.h>
 
 #include <kj/compat/url.h>
@@ -475,10 +476,24 @@ WebSocket::Accepted::~Accepted() noexcept(false) {
   }
 }
 
+// Default max WebSocket message size limit. Note that kj-http's own default is 1MiB
+// (`kj::WebSocket::SUGGESTED_MAX_MESSAGE_SIZE`). We've found this to be too small for many commmon
+// use cases, such as proxying Chrome Devtools Protocol messages.
+//
+// JS-RPC messages are size-limited to 32MiB, and it seems to be working well, so we're setting the
+// WebSocket default max message size to match that.
+//
+// TODO(soon): This is currently autogated, so that we can enable the change in production before
+//   enabling it by default in local development. This is so that people do not inadvertently deploy
+//   something that works locally but breaks when deployed.
+static constexpr size_t WEBSOCKET_MAX_MESSAGE_SIZE = 32u << 20;
+
 void WebSocket::startReadLoop(jsg::Lock& js, kj::Maybe<kj::Own<InputGate::CriticalSection>> cs) {
   size_t maxMessageSize = kj::WebSocket::SUGGESTED_MAX_MESSAGE_SIZE;
   if (FeatureFlags::get(js).getIncreaseWebsocketMessageSize()) {
     maxMessageSize = 128u << 20;
+  } else if (util::Autogate::isEnabled(util::AutogateKey::WEBSOCKET_MAX_MESSAGE_SIZE_32M)) {
+    maxMessageSize = WEBSOCKET_MAX_MESSAGE_SIZE;
   }
 
   // If the kj::WebSocket happens to be an AbortableWebSocket (see util/abortable.h), then

src/workerd/util/autogate.c++

@@ -25,6 +25,8 @@ kj::StringPtr KJ_STRINGIFY(AutogateKey key) {
       return "streaming-tail-worker"_kj;
     case AutogateKey::TAIL_STREAM_REFACTOR:
       return "tail-stream-refactor"_kj;
+    case AutogateKey::WEBSOCKET_MAX_MESSAGE_SIZE_32M:
+      return "websocket-max-message-size-32m"_kj;
     case AutogateKey::NumOfKeys:
       KJ_FAIL_ASSERT("NumOfKeys should not be used in getName");
   }

src/workerd/util/autogate.h

@@ -20,6 +20,8 @@ enum class AutogateKey {
   STREAMING_TAIL_WORKER,
   // Enable refactor used to consolidate the different tail worker stream implementations.
   TAIL_STREAM_REFACTOR,
+  // Increase max WebSocket message size to 32MiB.
+  WEBSOCKET_MAX_MESSAGE_SIZE_32M,
   NumOfKeys  // Reserved for iteration.
 };