http2: fix endless loop when writing empty string

src/node_http2.cc

@@ -2184,6 +2184,17 @@ ssize_t Http2Stream::Provider::Stream::OnRead(nghttp2_session* handle,
 
   size_t amount = 0;          // amount of data being sent in this data frame.
 
+  // Remove all empty chunks from the head of the queue.
+  // This is done here so that .write('', cb) is still a meaningful way to
+  // find out when the HTTP2 stream wants to consume data, and because the
+  // StreamBase API allows empty input chunks.
+  while (!stream->queue_.empty() && stream->queue_.front().buf.len == 0) {
+    WriteWrap* finished = stream->queue_.front().req_wrap;
+    stream->queue_.pop();
+    if (finished != nullptr)
+      finished->Done(0);
+  }
+
   if (!stream->queue_.empty()) {
     DEBUG_HTTP2SESSION2(session, "stream %d has pending outbound data", id);
     amount = std::min(stream->available_outbound_length_, length);
@@ -2197,7 +2208,8 @@ ssize_t Http2Stream::Provider::Stream::OnRead(nghttp2_session* handle,
     }
   }
 
-  if (amount == 0 && stream->IsWritable() && stream->queue_.empty()) {
+  if (amount == 0 && stream->IsWritable()) {
+    CHECK(stream->queue_.empty());
     DEBUG_HTTP2SESSION2(session, "deferring stream %d", id);
     return NGHTTP2_ERR_DEFERRED;
   }

test/parallel/test-http2-client-write-empty-string.js

@@ -0,0 +1,54 @@
+'use strict';
+
+const assert = require('assert');
+const http2 = require('http2');
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+for (const chunkSequence of [
+  [ '' ],
+  [ '', '' ]
+]) {
+  const server = http2.createServer();
+  server.on('stream', common.mustCall((stream, headers, flags) => {
+    stream.respond({ 'content-type': 'text/html' });
+
+    let data = '';
+    stream.on('data', common.mustNotCall((chunk) => {
+      data += chunk.toString();
+    }));
+    stream.on('end', common.mustCall(() => {
+      stream.end(`"${data}"`);
+    }));
+  }));
+
+  server.listen(0, common.mustCall(() => {
+    const port = server.address().port;
+    const client = http2.connect(`http://localhost:${port}`);
+
+    const req = client.request({
+      ':method': 'POST',
+      ':path': '/'
+    });
+
+    req.on('response', common.mustCall((headers) => {
+      assert.strictEqual(headers[':status'], 200);
+      assert.strictEqual(headers['content-type'], 'text/html');
+    }));
+
+    let data = '';
+    req.setEncoding('utf8');
+    req.on('data', common.mustCallAtLeast((d) => data += d));
+    req.on('end', common.mustCall(() => {
+      assert.strictEqual(data, '""');
+      server.close();
+      client.close();
+    }));
+
+    for (const chunk of chunkSequence)
+      req.write(chunk);
+    req.end();
+  }));
+}