Initial support for HTTP/2 dependencies and weights

net/spdy/spdy_framer.cc

Index: net/spdy/spdy_framer.cc
diff --git a/net/spdy/spdy_framer.cc b/net/spdy/spdy_framer.cc
index 79a529f5724f172ffb4d9e07718dbd3087f8582c..48923244af7e54bd67157540558adf964d885800 100644
--- a/net/spdy/spdy_framer.cc
+++ b/net/spdy/spdy_framer.cc
@@ -184,8 +184,8 @@ size_t SpdyFramer::GetSynStreamMinimumSize() const {
     return GetControlFrameHeaderSize() + 10;
   } else {
     // Calculated as:
-    // frame prefix + 4 (priority)
-    return GetControlFrameHeaderSize() + 4;
+    // frame prefix + 5 (priority)
+    return GetControlFrameHeaderSize() + 5;

[Ryan Hamilton, 2014/05/19 22:56:41]

I'm not terribly in love with the magic number here. Any chance you can extract
this to a constant? Perhaps that's not super important, though I do think it'd
be a bit more readable.

Perhaps it should be 2 constants, actually... one for weight size, and one for
dependency size?

[Johnny, 2014/05/19 23:27:17]

Done. Though, now this particularly calls attention to all of the /other/ places
that should do this in spdy_framer.cc :)

   }
 }
 
@@ -1047,7 +1047,7 @@ void SpdyFramer::ProcessControlFrameHeader(uint16 control_frame_type_field) {
       frame_size_without_variable_data = GetHeadersMinimumSize();
       if (protocol_version() > SPDY3 &&
           current_frame_flags_ & HEADERS_FLAG_PRIORITY) {
-        frame_size_without_variable_data += 4;  // priority
+        frame_size_without_variable_data += 5;  // priority
       }
       break;
     case PUSH_PROMISE:
@@ -1414,8 +1414,13 @@ size_t SpdyFramer::ProcessControlFrameBeforeHeaderBlock(const char* data,
               (current_frame_flags_ & HEADERS_FLAG_PRIORITY) != 0;
           uint32 priority = 0;
           if (protocol_version() > SPDY3 && has_priority) {
-            successful_read = reader.ReadUInt31(&priority);
-            DCHECK(successful_read);
+            // TODO(jgraettinger): Process dependency rather than ignoring it.
+            reader.Seek(4);
+            uint8 weight = 0;
+            successful_read = reader.ReadUInt8(&weight);
+            if (successful_read) {
+              priority = MapWeightToPriority(weight);
+            }
           }
           DCHECK(reader.IsDoneReading());
           if (debug_visitor_) {
@@ -2376,7 +2381,9 @@ SpdySerializedFrame* SpdyFramer::SerializeSynStream(
                           HEADERS,
                           flags,
                           syn_stream.stream_id());
-    builder.WriteUInt32(priority);
+    // TODO(jgraettinger): Plumb priorities and stream dependencies.
+    builder.WriteUInt32(0);  // Non-exclusive bit and root stream ID.
+    builder.WriteUInt8(MapPriorityToWeight(priority));
   }
   DCHECK_EQ(GetSynStreamMinimumSize(), builder.length());
   if (protocol_version() > SPDY3) {
@@ -2664,7 +2671,9 @@ SpdySerializedFrame* SpdyFramer::SerializeHeaders(
                           flags,
                           headers.stream_id());
     if (headers.has_priority()) {
-      builder.WriteUInt32(priority);
+      // TODO(jgraettinger): Plumb priorities and stream dependencies.
+      builder.WriteUInt32(0);  // Non-exclusive bit and root stream ID.
+      builder.WriteUInt8(MapPriorityToWeight(priority));
     }
   }
   if (protocol_version() <= SPDY2) {
@@ -3055,6 +3064,16 @@ HpackDecoder* SpdyFramer::GetHpackDecoder() {
   return hpack_decoder_.get();
 }
 
+uint8 SpdyFramer::MapPriorityToWeight(SpdyPriority priority) {
+  const float kSteps = 255.9f / 7.f;
+  return static_cast<uint8>(kSteps * (7.f - priority));
+}
+
+SpdyPriority SpdyFramer::MapWeightToPriority(uint8 weight) {
+  const float kSteps = 255.9f / 7.f;
+  return static_cast<SpdyPriority>(7.f - weight / kSteps);
+}
+
 // Incrementally decompress the control frame's header block, feeding the
 // result to the visitor in chunks. Continue this until the visitor
 // indicates that it cannot process any more data, or (more commonly) we