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

doc/api/diagnostics_channel.md

@@ -1246,6 +1246,13 @@ closing the stream can be retrieved using the `stream.rstCode` property.
 
 Emitted when a stream is created on the server.
 
+`http2.server.stream.start`
+
+* `stream` {ServerHttp2Stream}
+* `headers` {HTTP/2 Headers Object}
+
+Emitted when a stream is started on the server.
+
 #### Modules
 
 > Stability: 1 - Experimental

lib/internal/http2/core.js

@@ -191,6 +191,7 @@ const onClientStreamErrorChannel = dc.channel('http2.client.stream.error');
 const onClientStreamFinishChannel = dc.channel('http2.client.stream.finish');
 const onClientStreamCloseChannel = dc.channel('http2.client.stream.close');
 const onServerStreamCreatedChannel = dc.channel('http2.server.stream.created');
+const onServerStreamStartChannel = dc.channel('http2.server.stream.start');
 
 let debug = require('internal/util/debuglog').debuglog('http2', (fn) => {
   debug = fn;
@@ -374,6 +375,12 @@ function onSessionHeaders(handle, id, cat, flags, headers, sensitiveHeaders) {
           headers: obj,
         });
       }
+      if (onServerStreamStartChannel.hasSubscribers) {
+        onServerStreamStartChannel.publish({
+          stream,
+          headers: obj,
+        });
+      }
       if (endOfStream) {
         stream.push(null);
       }
@@ -2841,7 +2848,16 @@ class ServerHttp2Stream extends Http2Stream {
     if (headRequest)
       stream[kState].flags |= STREAM_FLAGS_HEAD_REQUEST;
 
-    process.nextTick(callback, null, stream, headers, 0);
+    process.nextTick(() => {
+      if (onServerStreamStartChannel.hasSubscribers) {
+        onServerStreamStartChannel.publish({
+          stream,
+          headers,
+        });
+      }
+
+      callback(null, stream, headers, 0);
+    });
 
     if (onServerStreamCreatedChannel.hasSubscribers) {
       onServerStreamCreatedChannel.publish({

test/parallel/test-diagnostics-channel-http2-server-stream-created-start-timing.js

@@ -0,0 +1,65 @@
+'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.start' channel only
+// after the 'http2.server.stream.created' channel.
+
+const Countdown = require('../common/countdown');
+const assert = require('assert');
+const dc = require('diagnostics_channel');
+const http2 = require('http2');
+
+const serverHttp2StreamCreationCount = 2;
+
+const map = {};
+
+dc.subscribe('http2.server.stream.created', common.mustCall(({ stream, headers }) => {
+  map[stream.id] = { ...map[stream.id], 'createdTime': process.hrtime.bigint() };
+}, serverHttp2StreamCreationCount));
+
+dc.subscribe('http2.server.stream.start', common.mustCall(({ stream, headers }) => {
+  map[stream.id] = { ...map[stream.id], 'startTime': process.hrtime.bigint() };
+}, serverHttp2StreamCreationCount));
+
+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(serverHttp2StreamCreationCount, () => {
+    client.close();
+    server.close();
+
+    const timings = Object.values(map);
+    assert.strictEqual(timings.length, serverHttp2StreamCreationCount);
+
+    for (const { createdTime, startTime } of timings) {
+      assert.ok(createdTime < startTime);
+    }
+  });
+
+  const stream = client.request({});
+  stream.on('response', common.mustCall(() => {
+    countdown.dec();
+  }));
+
+  client.on('stream', common.mustCall((pushStream) => {
+    pushStream.on('push', common.mustCall(() => {
+      countdown.dec();
+    }));
+  }));
+}));

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

@@ -0,0 +1,60 @@
+'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.start' channel when
+// ServerHttp2Streams are started by both:
+// - in response to an incoming 'stream' event from the client
+// - the server calling ServerHttp2Stream#pushStream()
+
+const Countdown = require('../common/countdown');
+const assert = require('assert');
+const dc = require('diagnostics_channel');
+const http2 = require('http2');
+const { Duplex } = require('stream');
+
+const serverHttp2StreamCreationCount = 2;
+
+dc.subscribe('http2.server.stream.start', common.mustCall(({ stream, headers }) => {
+  // 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');
+}, serverHttp2StreamCreationCount));
+
+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(serverHttp2StreamCreationCount, () => {
+    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();
+    }));
+  }));
+}));