grpc-js: handle multiple messages in single 'data' event

This commit adds support for receiving multiple messages in a
single 'data' event from the underlying HTTP2 stream. It also
handles potential out of order messages due to asynchronous
deserialization of messages.

packages/grpc-js/src/server-call.ts

@@ -117,6 +117,10 @@ export class ServerReadableStreamImpl<RequestType, ResponseType>
   }
 
   _read(size: number) {
+    if (!this.call.consumeUnpushedMessages(this)) {
+      return;
+    }
+
     this.call.resume();
   }
 
@@ -324,6 +328,10 @@ export class Http2ServerCallStream<
   deadline: NodeJS.Timer = noopTimer;
   private wantTrailers = false;
   private metadataSent = false;
+  private canPush = false;
+  private isPushPending = false;
+  private bufferedMessages: Array<Buffer | null> = [];
+  private messagesToPush: Array<RequestType | null> = [];
 
   constructor(
     private stream: http2.ServerHttp2Stream,
@@ -531,38 +539,98 @@ export class Http2ServerCallStream<
   ) {
     const decoder = new StreamDecoder();
 
-    /* This code here is wrong but getting the client working is the priority
-     * right now and I'm not going to block that on fixing what is currently
-     * unused code. If multiple messages come in with a single frame, this will
-     * keep calling readable.push after it has returned false, which should not
-     * happen. Independent of that, deserializeMessage is asynchronous, which
-     * means that incoming messages could be reordered when emitted to the
-     * application. That effect will become more pronounced when compression
-     * support is added and deserializeMessage takes longer by an amount of
-     * time dependent on the size of the message. A system like the one in
-     * call-stream.ts should be added to buffer incoming messages and
-     * preserve ordering more strongly */
-
     this.stream.on('data', async (data: Buffer) => {
       const messages = decoder.write(data);
-      for (const message of messages) {
-        try {
-          const deserialized = await this.deserializeMessage(message);
 
-          if (!readable.push(deserialized)) {
+      for (const message of messages) {
-            this.stream.pause();
+        this.pushOrBufferMessage(readable, message);
-          }
-        } catch (err) {
-          err.code = Status.INTERNAL;
-          readable.emit('error', err);
-        }
       }
     });
 
     this.stream.once('end', () => {
-      readable.push(null);
+      this.pushOrBufferMessage(readable, null);
     });
   }
+
+  consumeUnpushedMessages(
+    readable:
+      | ServerReadableStream<RequestType, ResponseType>
+      | ServerDuplexStream<RequestType, ResponseType>
+  ): boolean {
+    this.canPush = true;
+
+    while (this.messagesToPush.length > 0) {
+      const nextMessage = this.messagesToPush.shift();
+      const canPush = readable.push(nextMessage);
+
+      if (nextMessage === null || canPush === false) {
+        this.canPush = false;
+        break;
+      }
+    }
+
+    return this.canPush;
+  }
+
+  private pushOrBufferMessage(
+    readable:
+      | ServerReadableStream<RequestType, ResponseType>
+      | ServerDuplexStream<RequestType, ResponseType>,
+    messageBytes: Buffer | null
+  ): void {
+    if (this.isPushPending) {
+      this.bufferedMessages.push(messageBytes);
+    } else {
+      this.pushMessage(readable, messageBytes);
+    }
+  }
+
+  private async pushMessage(
+    readable:
+      | ServerReadableStream<RequestType, ResponseType>
+      | ServerDuplexStream<RequestType, ResponseType>,
+    messageBytes: Buffer | null
+  ) {
+    if (messageBytes === null) {
+      if (this.canPush) {
+        readable.push(null);
+      } else {
+        this.messagesToPush.push(null);
+      }
+
+      return;
+    }
+
+    this.isPushPending = true;
+
+    try {
+      const deserialized = await this.deserializeMessage(messageBytes);
+
+      if (this.canPush) {
+        if (!readable.push(deserialized)) {
+          this.canPush = false;
+          this.stream.pause();
+        }
+      } else {
+        this.messagesToPush.push(deserialized);
+      }
+    } catch (err) {
+      // Ignore any remaining messages when errors occur.
+      this.bufferedMessages.length = 0;
+
+      err.code = Status.INTERNAL;
+      readable.emit('error', err);
+    }
+
+    this.isPushPending = false;
+
+    if (this.bufferedMessages.length > 0) {
+      this.pushMessage(
+        readable,
+        this.bufferedMessages.shift() as Buffer | null
+      );
+    }
+  }
 }
 
 // tslint:disable:no-any