http2: add diagnostics channel 'http2.server.stream.finish'

Signed-off-by: Darshan Sen <raisinten@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/58560
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

doc/api/diagnostics_channel.md

@@ -1259,6 +1259,14 @@ Emitted when a stream is started on the server.
 
 Emitted when an error occurs during the processing of a stream on the server.
 
+`http2.server.stream.finish`
+
+* `stream` {ServerHttp2Stream}
+* `headers` {HTTP/2 Headers Object}
+* `flags` {number}
+
+Emitted when a stream is sent on the server.
+
 #### Modules
 
 > Stability: 1 - Experimental

lib/internal/http2/core.js

@@ -198,6 +198,7 @@ const onClientStreamCloseChannel = dc.channel('http2.client.stream.close');
 const onServerStreamCreatedChannel = dc.channel('http2.server.stream.created');
 const onServerStreamStartChannel = dc.channel('http2.server.stream.start');
 const onServerStreamErrorChannel = dc.channel('http2.server.stream.error');
+const onServerStreamFinishChannel = dc.channel('http2.server.stream.finish');
 
 let debug = require('internal/util/debuglog').debuglog('http2', (fn) => {
   debug = fn;
@@ -2919,8 +2920,17 @@ class ServerHttp2Stream extends Http2Stream {
     }
 
     const ret = this[kHandle].respond(headersList, streamOptions);
-    if (ret < 0)
+    if (ret < 0) {
       this.destroy(new NghttpError(ret));
+    } else if (onServerStreamFinishChannel.hasSubscribers) {
+      // No point in running this if the respond() call above fails because
+      // that would mean that it is an invalid call.
+      onServerStreamFinishChannel.publish({
+        stream: this,
+        headers,
+        flags: state.flags,
+      });
+    }
   }
 
   // Initiate a response using an open FD. Note that there are fewer

test/parallel/test-diagnostics-channel-http2-server-stream-finish.js

@@ -0,0 +1,61 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+// This test ensures that the built-in HTTP/2 diagnostics channels are reporting
+// the diagnostics messages for the 'http2.server.stream.finish' channel when
+// ServerHttp2Streams#respond() sends a regular stream as well as a push stream.
+
+const Countdown = require('../common/countdown');
+const assert = require('assert');
+const dc = require('diagnostics_channel');
+const http2 = require('http2');
+const { Duplex } = require('stream');
+
+const serverHttp2StreamFinishCount = 2;
+
+dc.subscribe('http2.server.stream.finish', common.mustCall(({ stream, headers, flags }) => {
+  // Since ServerHttp2Stream is not exported from any module, this just checks
+  // if the stream is an instance of Duplex and the constructor name is
+  // 'ServerHttp2Stream'.
+  assert.ok(stream instanceof Duplex);
+  assert.strictEqual(stream.constructor.name, 'ServerHttp2Stream');
+
+  assert.ok(headers && !Array.isArray(headers) && typeof headers === 'object');
+
+  assert.strictEqual(typeof flags, 'number');
+}, serverHttp2StreamFinishCount));
+
+const server = http2.createServer();
+server.on('stream', common.mustCall((stream) => {
+  stream.respond();
+  stream.end();
+
+  stream.pushStream({}, common.mustSucceed((pushStream) => {
+    pushStream.respond();
+    pushStream.end();
+  }));
+}));
+
+server.listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  const client = http2.connect(`http://localhost:${port}`);
+
+  const countdown = new Countdown(serverHttp2StreamFinishCount, () => {
+    client.close();
+    server.close();
+  });
+
+  const stream = client.request({});
+  stream.on('response', common.mustCall(() => {
+    countdown.dec();
+  }));
+
+  client.on('stream', common.mustCall((pushStream) => {
+    pushStream.on('push', common.mustCall(() => {
+      countdown.dec();
+    }));
+  }));
+}));