http2: adjust stream buffer size

Adjust stream buffer size to allow full 4 default-sized frames
including their frame headers to allow more efficient sending
of data to the socket.

PR-URL: #16445
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: apapirovski

src/node_http2.cc

@@ -824,7 +824,7 @@ int Http2Session::DoWrite(WriteWrap* req_wrap,
   return 0;
 }
 
-void Http2Session::AllocateSend(size_t recommended, uv_buf_t* buf) {
+void Http2Session::AllocateSend(uv_buf_t* buf) {
   buf->base = stream_alloc();
   buf->len = kAllocBufferSize;
 }

src/node_http2.h

@@ -331,7 +331,8 @@ class Http2Options {
   padding_strategy_type padding_strategy_ = PADDING_STRATEGY_NONE;
 };
 
-static const size_t kAllocBufferSize = 64 * 1024;
+// This allows for 4 default-sized frames with their frame headers
+static const size_t kAllocBufferSize = 4 * (16384 + 9);
 
 typedef uint32_t(*get_setting)(nghttp2_session* session,
                                nghttp2_settings_id id);
@@ -414,7 +415,7 @@ class Http2Session : public AsyncWrap,
   void OnFrameError(int32_t id, uint8_t type, int error_code) override;
   void OnTrailers(Nghttp2Stream* stream,
                   const SubmitTrailers& submit_trailers) override;
-  void AllocateSend(size_t recommended, uv_buf_t* buf) override;
+  void AllocateSend(uv_buf_t* buf) override;
 
   int DoWrite(WriteWrap* w, uv_buf_t* bufs, size_t count,
               uv_stream_t* send_handle) override;

src/node_http2_core-inl.h

@@ -490,7 +490,7 @@ inline void Nghttp2Session::SendPendingData() {
     return;
 
   uv_buf_t dest;
-  AllocateSend(SEND_BUFFER_RECOMMENDED_SIZE, &dest);
+  AllocateSend(&dest);
   size_t destLength = 0;             // amount of data stored in dest
   size_t destRemaining = dest.len;   // amount space remaining in dest
   size_t destOffset = 0;             // current write offset of dest

src/node_http2_core.h

@@ -42,7 +42,6 @@ class Nghttp2Stream;
 struct nghttp2_stream_write_t;
 
 #define MAX_BUFFER_COUNT 16
-#define SEND_BUFFER_RECOMMENDED_SIZE 4096
 
 enum nghttp2_session_type {
   NGHTTP2_SESSION_SERVER,
@@ -178,7 +177,7 @@ class Nghttp2Session {
   virtual ssize_t GetPadding(size_t frameLength,
                              size_t maxFrameLength) { return 0; }
   virtual void OnFreeSession() {}
-  virtual void AllocateSend(size_t suggested_size, uv_buf_t* buf) = 0;
+  virtual void AllocateSend(uv_buf_t* buf) = 0;
 
   virtual bool HasGetPaddingCallback() { return false; }