http2: add writable* properties to compat api

added writableHighWaterMark, writableLength, and writableFinished
properties with test.

Refs: #29829

PR-URL: #33506
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/internal/http2/compat.js

@@ -519,6 +519,18 @@ class Http2ServerResponse extends Stream {
     return this[kStream].writableCorked;
   }
 
+  get writableHighWaterMark() {
+    return this[kStream].writableHighWaterMark;
+  }
+
+  get writableFinished() {
+    return this[kStream].writableFinished;
+  }
+
+  get writableLength() {
+    return this[kStream].writableLength;
+  }
+
   set statusCode(code) {
     code |= 0;
     if (code >= 100 && code < 200)

test/parallel/test-http2-res-writable-properties.js

@@ -0,0 +1,30 @@
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto) { common.skip('missing crypto'); }
+const assert = require('assert');
+const http2 = require('http2');
+
+const server = http2.createServer(common.mustCall((req, res) => {
+  const hwm = req.socket.writableHighWaterMark;
+  assert.strictEqual(res.writableHighWaterMark, hwm);
+  assert.strictEqual(res.writableLength, 0);
+  res.write('');
+  const len = res.writableLength;
+  res.write('asd');
+  assert.strictEqual(res.writableLength, len + 3);
+  res.end();
+  res.on('finish', common.mustCall(() => {
+    assert.strictEqual(res.writableLength, 0);
+    assert.ok(res.writableFinished, 'writableFinished is not truthy');
+    server.close();
+  }));
+}));
+
+server.listen(0, common.mustCall(() => {
+  const client = http2.connect(`http://localhost:${server.address().port}`);
+  const request = client.request();
+  request.on('data', common.mustCall());
+  request.on('end', common.mustCall(() => {
+    client.close();
+  }));
+}));