From 1503e362f61ca8c55adebcce802a724ae375debe Mon Sep 17 00:00:00 2001
From: jwilson <jwilson@squareup.com>
Date: Sun, 22 May 2016 10:16:13 -0400
Subject: [PATCH] Flush streams if the window size is zero.

Otherwise we can deadlock, with OkHttp waiting for the server to send a larger
window and the server not knowing that there's a stream that even wants it.
---
 .../internal/framed/Http2ConnectionTest.java  | 44 +++++++++++++++++++
 .../internal/framed/FramedConnection.java     |  4 +-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/okhttp-tests/src/test/java/okhttp3/internal/framed/Http2ConnectionTest.java b/okhttp-tests/src/test/java/okhttp3/internal/framed/Http2ConnectionTest.java
index b2a583857..67d6964d7 100644
--- a/okhttp-tests/src/test/java/okhttp3/internal/framed/Http2ConnectionTest.java
+++ b/okhttp-tests/src/test/java/okhttp3/internal/framed/Http2ConnectionTest.java
@@ -177,6 +177,50 @@ public final class Http2ConnectionTest {
     assertEquals(newMaxFrameSize, connection.frameWriter.maxDataLength());
   }
 
+  /**
+   * Webservers may set the initial window size to zero, which is a special case because it means
+   * that we have to flush headers immediately before any request body can be sent.
+   * https://github.com/square/okhttp/issues/2543
+   */
+  @Test public void peerSetsZeroFlowControl() throws Exception {
+    peer.setVariantAndClient(HTTP_2, true);
+
+    // Write the mocking script.
+    peer.sendFrame().settings(new Settings().set(INITIAL_WINDOW_SIZE, 0, 0));
+    peer.sendFrame().windowUpdate(0, 10); // Increase the connection window size.
+    peer.acceptFrame(); // PING or SETTINGS ACK
+    peer.acceptFrame(); // PING or SETTINGS ACK
+    peer.sendFrame().ping(true, 1, 0);
+    peer.acceptFrame(); // HEADERS STREAM 3
+    peer.sendFrame().windowUpdate(3, 5);
+    peer.acceptFrame(); // DATA STREAM 3 "abcde"
+    peer.sendFrame().windowUpdate(3, 5);
+    peer.acceptFrame(); // DATA STREAM 3 "fghi"
+    peer.play();
+
+    // Play it back.
+    FramedConnection connection = connection(peer, HTTP_2);
+    connection.ping().roundTripTime(); // Ensure the SETTINGS have been received.
+    FramedStream stream = connection.newStream(headerEntries("a", "android"), true, true);
+    BufferedSink sink = Okio.buffer(stream.getSink());
+    sink.writeUtf8("abcdefghi");
+    sink.flush();
+
+    // Verify the peer received what was expected.
+    peer.takeFrame(); // PING or SETTINGS ACK
+    peer.takeFrame(); // PING or SETTINGS ACK
+    MockSpdyPeer.InFrame headers = peer.takeFrame();
+    assertEquals(TYPE_HEADERS, headers.type);
+    MockSpdyPeer.InFrame data1 = peer.takeFrame();
+    assertEquals(TYPE_DATA, data1.type);
+    assertEquals(3, data1.streamId);
+    assertTrue(Arrays.equals("abcde".getBytes("UTF-8"), data1.data));
+    MockSpdyPeer.InFrame data2 = peer.takeFrame();
+    assertEquals(TYPE_DATA, data2.type);
+    assertEquals(3, data2.streamId);
+    assertTrue(Arrays.equals("fghi".getBytes("UTF-8"), data2.data));
+  }
+
   @Test public void receiveGoAwayHttp2() throws Exception {
     peer.setVariantAndClient(HTTP_2, false);
 
diff --git a/okhttp/src/main/java/okhttp3/internal/framed/FramedConnection.java b/okhttp/src/main/java/okhttp3/internal/framed/FramedConnection.java
index 7e1a582be..90c8e3805 100644
--- a/okhttp/src/main/java/okhttp3/internal/framed/FramedConnection.java
+++ b/okhttp/src/main/java/okhttp3/internal/framed/FramedConnection.java
@@ -249,6 +249,7 @@ public final class FramedConnection implements Closeable {
       boolean in) throws IOException {
     boolean outFinished = !out;
     boolean inFinished = !in;
+    boolean flushHeaders;
     FramedStream stream;
     int streamId;
 
@@ -260,6 +261,7 @@ public final class FramedConnection implements Closeable {
         streamId = nextStreamId;
         nextStreamId += 2;
         stream = new FramedStream(streamId, this, outFinished, inFinished, requestHeaders);
+        flushHeaders = !out || bytesLeftInWriteWindow == 0L || stream.bytesLeftInWriteWindow == 0L;
         if (stream.isOpen()) {
           streams.put(streamId, stream);
           setIdle(false);
@@ -275,7 +277,7 @@ public final class FramedConnection implements Closeable {
       }
     }
 
-    if (!out) {
+    if (flushHeaders) {
       frameWriter.flush();
     }