http2: shrink memory to match read data

Perform a shrinking `Realloc()` so that less data is used for HTTP2 reads. PR-URL: nodejs#26201 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: addaleax

src/node_http2.cc

@@ -1774,17 +1774,8 @@ void Http2Session::OnStreamRead(ssize_t nread, const uv_buf_t& buf) {
  Http2Scope h2scope(this);
  CHECK_NOT_NULL(stream_);
  Debug(this, "receiving %d bytes", nread);
- IncrementCurrentSessionMemory(buf.len);
  CHECK(stream_buf_ab_.IsEmpty());
 
- OnScopeLeave on_scope_leave([&]() {
- // Once finished handling this write, reset the stream buffer.
- // The memory has either been free()d or was handed over to V8.
- DecrementCurrentSessionMemory(buf.len);
- stream_buf_ab_ = Local<ArrayBuffer>();
- stream_buf_ = uv_buf_init(nullptr, 0);
- });
-
  // Only pass data on if nread > 0
  if (nread <= 0) {
  free(buf.base);
@@ -1794,29 +1785,35 @@ void Http2Session::OnStreamRead(ssize_t nread, const uv_buf_t& buf) {
  return;
  }
 
+ // Shrink to the actual amount of used data.
+ char* base = Realloc(buf.base, nread);
+
+ IncrementCurrentSessionMemory(nread);
+ OnScopeLeave on_scope_leave([&]() {
+ // Once finished handling this write, reset the stream buffer.
+ // The memory has either been free()d or was handed over to V8.
+ DecrementCurrentSessionMemory(nread);
+ stream_buf_ab_ = Local<ArrayBuffer>();
+ stream_buf_ = uv_buf_init(nullptr, 0);
+ });
+
  // Make sure that there was no read previously active.
  CHECK_NULL(stream_buf_.base);
  CHECK_EQ(stream_buf_.len, 0);
 
  // Remember the current buffer, so that OnDataChunkReceived knows the
  // offset of a DATA frame's data into the socket read buffer.
- stream_buf_ = uv_buf_init(buf.base, nread);
-
- // Verify that currently: There is memory allocated into which
- // the data has been read, and that memory buffer is at least as large
- // as the amount of data we have read, but we have not yet made an
- // ArrayBuffer out of it.
- CHECK_LE(static_cast<size_t>(nread), stream_buf_.len);
+ stream_buf_ = uv_buf_init(base, nread);
 
  Isolate* isolate = env()->isolate();
 
  // Create an array buffer for the read data. DATA frames will be emitted
  // as slices of this array buffer to avoid having to copy memory.
  stream_buf_ab_ =
  ArrayBuffer::New(isolate,
-  buf.base,
-  nread,
-  ArrayBufferCreationMode::kInternalized);
+ base,
+ nread,
+ ArrayBufferCreationMode::kInternalized);
 
  statistics_.data_received += nread;
  ssize_t ret = Write(&stream_buf_, 1);

test/sequential/test-http2-max-session-memory.js

@@ -8,7 +8,7 @@ const http2 = require('http2');
 
 // Test that maxSessionMemory Caps work
 
-const largeBuffer = Buffer.alloc(1e6);
+const largeBuffer = Buffer.alloc(2e6);
 
 const server = http2.createServer({ maxSessionMemory: 1 });