http2: make pausing/unpausing set/clear local stream window

This reduces the HTTP/2 window size to 32 MB since libcurl might have to
buffer up to this amount of data in memory and yet we don't want it set
lower to potentially impact tranfer performance on high speed networks.

Requires nghttp2 commit b3f85e2daa629
(https://github.com/nghttp2/nghttp2/pull/1444) to work properly, to end
up in the next release after 1.40.0.

Fixes #4939
Closes #4940

1 files changed, 53 insertions, 4 deletions

diff --git a/lib/http2.c b/lib/http2.c
index dffc7a254..72b38a3f6 100644
--- a/lib/http2.c
+++ b/lib/http2.c
@@ -55,7 +55,7 @@
 #define NGHTTP2_HAS_SET_LOCAL_WINDOW_SIZE 1
 #endif
 
-#define HTTP2_HUGE_WINDOW_SIZE (1 << 30)
+#define HTTP2_HUGE_WINDOW_SIZE (32 * 1024 * 1024) /* 32 MB */
 
 #ifdef DEBUG_HTTP2
 #define H2BUGF(x) x
@@ -1118,6 +1118,7 @@ static void populate_settings(struct connectdata *conn,
                               struct http_conn *httpc)
 {
   nghttp2_settings_entry *iv = httpc->local_settings;
+  DEBUGASSERT(conn->data);
 
   iv[0].settings_id = NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS;
   iv[0].value = Curl_multi_max_concurrent_streams(conn->data->multi);
@@ -1554,8 +1555,12 @@ static ssize_t http2_recv(struct connectdata *conn, int sockindex,
     return ncopy;
   }
 
-  H2BUGF(infof(data, "http2_recv: easy %p (stream %u)\n",
-               data, stream->stream_id));
+  H2BUGF(infof(data, "http2_recv: easy %p (stream %u) win %u/%u\n",
+               data, stream->stream_id,
+               nghttp2_session_get_local_window_size(httpc->h2),
+               nghttp2_session_get_stream_local_window_size(httpc->h2,
+                                                            stream->stream_id)
+           ));
 
   if((data->state.drain) && stream->memlen) {
     H2BUGF(infof(data, "http2_recv: DRAIN %zu bytes stream %u!! (%p => %p)\n",
@@ -1586,7 +1591,6 @@ static ssize_t http2_recv(struct connectdata *conn, int sockindex,
     stream->pausedata += nread;
     stream->pauselen -= nread;
 
-    infof(data, "%zd data bytes written\n", nread);
     if(stream->pauselen == 0) {
       H2BUGF(infof(data, "Unpaused by stream %u\n", stream->stream_id));
       DEBUGASSERT(httpc->pause_stream_id == stream->stream_id);
@@ -2288,6 +2292,51 @@ CURLcode Curl_http2_switched(struct connectdata *conn,
   return CURLE_OK;
 }
 
+CURLcode Curl_http2_stream_pause(struct Curl_easy *data, bool pause)
+{
+  DEBUGASSERT(data);
+  DEBUGASSERT(data->conn);
+  /* if it isn't HTTP/2, we're done */
+  if(!data->conn->proto.httpc.h2)
+    return CURLE_OK;
+#ifdef NGHTTP2_HAS_SET_LOCAL_WINDOW_SIZE
+  else {
+    struct HTTP *stream = data->req.protop;
+    struct http_conn *httpc = &data->conn->proto.httpc;
+    uint32_t window = !pause * HTTP2_HUGE_WINDOW_SIZE;
+    int rv = nghttp2_session_set_local_window_size(httpc->h2,
+                                                   NGHTTP2_FLAG_NONE,
+                                                   stream->stream_id,
+                                                   window);
+    if(rv) {
+      failf(data, "nghttp2_session_set_local_window_size() failed: %s(%d)",
+            nghttp2_strerror(rv), rv);
+      return CURLE_HTTP2;
+    }
+
+    /* make sure the window update gets sent */
+    rv = h2_session_send(data, httpc->h2);
+    if(rv)
+      return CURLE_SEND_ERROR;
+
+    DEBUGF(infof(data, "Set HTTP/2 window size to %u for stream %u\n",
+                 window, stream->stream_id));
+
+#ifdef DEBUGBUILD
+    {
+      /* read out the stream local window again */
+      uint32_t window2 =
+        nghttp2_session_get_stream_local_window_size(httpc->h2,
+                                                     stream->stream_id);
+      DEBUGF(infof(data, "HTTP/2 window size is now %u for stream %u\n",
+                   window2, stream->stream_id));
+    }
+#endif
+  }
+#endif
+  return CURLE_OK;
+}
+
 CURLcode Curl_http2_add_child(struct Curl_easy *parent,
                               struct Curl_easy *child,
                               bool exclusive)