net/quic: Add support for HTTP/3 CONNECT Fast Open

SpdyProxyClientSocket uses read_callback_ for both Connect() and
Read(), and its OnIOComplete() calls read_callback_, thus its fast
connect code checks read_callback_. The code was ported to
QuicProxyClientSocket without much change.

But QuicProxyClientSocket uses a separate connect_callback_ apart from
read_callback_, and its OnIOComplete() calls connect_callback_, thus
when headers are received after Connect() it doesn't need to check
read_callback_ and should always avoid calling connect_callback_.

src/net/quic/quic_proxy_client_socket.cc

@@ -42,6 +42,8 @@ QuicProxyClientSocket::QuicProxyClientSocket(
       proxy_chain_index_(proxy_chain_index),
       proxy_delegate_(proxy_delegate),
       user_agent_(user_agent),
+      use_fastopen_(false),
+      read_headers_pending_(false),
       net_log_(net_log) {
   DCHECK(stream_->IsOpen());
 
@@ -304,6 +306,16 @@ int QuicProxyClientSocket::DoLoop(int last_io_result) {
         rv = DoReadReplyComplete(rv);
         net_log_.EndEventWithNetErrorCode(
             NetLogEventType::HTTP_TRANSACTION_TUNNEL_READ_HEADERS, rv);
+        if (use_fastopen_ && read_headers_pending_) {
+          read_headers_pending_ = false;
+          if (rv < 0) {
+            // read_callback_ will be called with this error and be reset.
+            // Further data after that will be ignored.
+            next_state_ = STATE_DISCONNECTED;
+          }
+          // Prevents calling connect_callback_.
+          rv = ERR_IO_PENDING;
+        }
         break;
       default:
         NOTREACHED_IN_MIGRATION() << "bad state";
@@ -347,6 +359,11 @@ int QuicProxyClientSocket::DoSendRequest() {
     if (result < 0) {
       return result;
     }
+    if (proxy_delegate_headers.HasHeader("fastopen")) {
+      proxy_delegate_headers.RemoveHeader("fastopen");
+      // TODO(klzgrad): look into why Fast Open does not work.
+      use_fastopen_ = true;
+    }
     request_.extra_headers.MergeFrom(proxy_delegate_headers);
   }
 
@@ -387,6 +404,11 @@ int QuicProxyClientSocket::DoReadReply() {
       &response_header_block_,
       base::BindOnce(&QuicProxyClientSocket::OnReadResponseHeadersComplete,
                      weak_factory_.GetWeakPtr()));
+  if (use_fastopen_ && rv == ERR_IO_PENDING) {
+    read_headers_pending_ = true;
+    next_state_ = STATE_CONNECT_COMPLETE;
+    return OK;
+  }
   if (rv == ERR_IO_PENDING)
     return ERR_IO_PENDING;
   if (rv < 0)
@@ -435,6 +457,13 @@ int QuicProxyClientSocket::DoReadReplyComplete(int result) {
 
 void QuicProxyClientSocket::OnReadResponseHeadersComplete(int result) {
   // Convert the now-populated quiche::HttpHeaderBlock to HttpResponseInfo
+  if (use_fastopen_ && read_headers_pending_) {
+    if (next_state_ == STATE_DISCONNECTED)
+      return;
+    if (next_state_ == STATE_CONNECT_COMPLETE)
+      next_state_ = STATE_READ_REPLY_COMPLETE;
+  }
+
   if (result > 0)
     result = ProcessResponseHeaders(response_header_block_);
 

src/net/quic/quic_proxy_client_socket.h

@@ -146,6 +146,12 @@ class NET_EXPORT_PRIVATE QuicProxyClientSocket : public ProxyClientSocket {
 
   std::string user_agent_;
 
+  // Session connect timing info.
+  LoadTimingInfo::ConnectTiming connect_timing_;
+
+  bool use_fastopen_;
+  bool read_headers_pending_;
+
   const NetLogWithSource net_log_;
 
   // The default weak pointer factory.