http2: add diagnostics channel 'http2.client.stream.start'

Signed-off-by: Darshan Sen <raisinten@gmail.com>
PR-URL: #58292
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

Author: RaisinTen

doc/api/diagnostics_channel.md

@@ -1210,6 +1210,13 @@ Emitted when server sends a response.
 
 Emitted when a stream is created on the client.
 
+`http2.client.stream.start`
+
+* `stream` {ClientHttp2Stream}
+* `headers` {HTTP/2 Headers Object}
+
+Emitted when a stream is started on the client.
+
 #### Modules
 
 > Stability: 1 - Experimental

lib/internal/http2/core.js

@@ -186,6 +186,7 @@ const { _connectionListener: httpConnectionListener } = http;
 
 const dc = require('diagnostics_channel');
 const onClientStreamCreatedChannel = dc.channel('http2.client.stream.created');
+const onClientStreamStartChannel = dc.channel('http2.client.stream.start');
 
 let debug = require('internal/util/debuglog').debuglog('http2', (fn) => {
   debug = fn;
@@ -381,6 +382,12 @@ function onSessionHeaders(handle, id, cat, flags, headers, sensitiveHeaders) {
           headers: obj,
         });
       }
+      if (onClientStreamStartChannel.hasSubscribers) {
+        onClientStreamStartChannel.publish({
+          stream,
+          headers: obj,
+        });
+      }
       if (endOfStream) {
         stream.push(null);
       }
@@ -717,7 +724,7 @@ function onGoawayData(code, lastStreamID, buf) {
 // When a ClientHttp2Session is first created, the socket may not yet be
 // connected. If request() is called during this time, the actual request
 // will be deferred until the socket is ready to go.
-function requestOnConnect(headers, options) {
+function requestOnConnect(headersList, headersParam, options) {
   const session = this[kSession];
 
   // At this point, the stream should have already been destroyed during
@@ -744,7 +751,7 @@ function requestOnConnect(headers, options) {
 
   // `ret` will be either the reserved stream ID (if positive)
   // or an error code (if negative)
-  const ret = session[kHandle].request(headers,
+  const ret = session[kHandle].request(headersList,
                                        streamOptions,
                                        options.parent | 0,
                                        options.weight | 0,
@@ -776,6 +783,12 @@ function requestOnConnect(headers, options) {
     return;
   }
   this[kInit](ret.id(), ret);
+  if (onClientStreamStartChannel.hasSubscribers) {
+    onClientStreamStartChannel.publish({
+      stream: this,
+      headers: headersParam,
+    });
+  }
 }
 
 // Validates that priority options are correct, specifically:
@@ -1859,7 +1872,7 @@ class ClientHttp2Session extends Http2Session {
       }
     }
 
-    const onConnect = reqAsync.bind(requestOnConnect.bind(stream, headersList, options));
+    const onConnect = reqAsync.bind(requestOnConnect.bind(stream, headersList, headersParam, options));
     if (this.connecting) {
       if (this[kPendingRequestCalls] !== null) {
         this[kPendingRequestCalls].push(onConnect);

test/parallel/test-diagnostics-channel-http2-client-stream-start.js

@@ -0,0 +1,59 @@
+'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.client.stream.start' channel when
+// ClientHttp2Streams are started by both:
+// - the client calling ClientHttp2Session#request()
+// - in response to an incoming 'push' event from the server
+
+const Countdown = require('../common/countdown');
+const assert = require('assert');
+const dc = require('diagnostics_channel');
+const http2 = require('http2');
+const { Duplex } = require('stream');
+
+const clientHttp2StreamStartCount = 2;
+
+dc.subscribe('http2.client.stream.start', common.mustCall(({ stream, headers }) => {
+  // Since ClientHttp2Stream is not exported from any module, this just checks
+  // if the stream is an instance of Duplex.
+  assert.ok(stream instanceof Duplex);
+  assert.strictEqual(stream.constructor.name, 'ClientHttp2Stream');
+  assert.ok(headers && !Array.isArray(headers) && typeof headers === 'object');
+}, clientHttp2StreamStartCount));
+
+const server = http2.createServer();
+server.on('stream', common.mustCall((stream) => {
+  stream.respond();
+  stream.end();
+
+  stream.pushStream({}, common.mustSucceed((pushStream) => {
+    pushStream.respond();
+    pushStream.end();
+  }, 1));
+}, 1));
+
+server.listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  const client = http2.connect(`http://localhost:${port}`);
+
+  const countdown = new Countdown(clientHttp2StreamStartCount, () => {
+    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();
+    }, 1));
+  }, 1));
+}, 1));