http2: verify that a dependency cycle may exist

Backport-PR-URL: #18050
Backport-PR-URL: #20456
PR-URL: #17968
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/parallel/test-http2-priority-cycle-.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const assert = require('assert');
+const http2 = require('http2');
+const Countdown = require('../common/countdown');
+
+const server = http2.createServer();
+const largeBuffer = Buffer.alloc(1e4);
+
+// Verify that a dependency cycle may exist, but that it doesn't crash anything
+
+server.on('stream', common.mustCall((stream) => {
+  stream.respond();
+  setImmediate(() => {
+    stream.end(largeBuffer);
+  });
+}, 3));
+server.on('session', common.mustCall((session) => {
+  session.on('priority', (id, parent, weight, exclusive) => {
+    assert.strictEqual(weight, 16);
+    assert.strictEqual(exclusive, false);
+    switch (id) {
+      case 1:
+        assert.strictEqual(parent, 5);
+        break;
+      case 3:
+        assert.strictEqual(parent, 1);
+        break;
+      case 5:
+        assert.strictEqual(parent, 3);
+        break;
+      default:
+        assert.fail('should not happen');
+    }
+  });
+}));
+
+server.listen(0, common.mustCall(() => {
+  const client = http2.connect(`http://localhost:${server.address().port}`);
+
+  const countdown = new Countdown(3, () => {
+    client.close();
+    server.close();
+  });
+
+  {
+    const req = client.request();
+    req.priority({ parent: 5 });
+    req.resume();
+    req.on('close', () => countdown.dec());
+  }
+
+  {
+    const req = client.request();
+    req.priority({ parent: 1 });
+    req.resume();
+    req.on('close', () => countdown.dec());
+  }
+
+  {
+    const req = client.request();
+    req.priority({ parent: 3 });
+    req.resume();
+    req.on('close', () => countdown.dec());
+  }
+}));