tranport: Reduce heap allocs by setting BufferSlice capacity

internal/transport/transport.go

@@ -378,12 +378,28 @@ func (s *Stream) ReadMessageHeader(header []byte) (err error) {
 	return nil
 }
 
+// ceil returns the ceil after dividing the numerator and denominator while
+// avoiding integer overflows.
+func ceil(numerator, denominator int) int {
+	if numerator == 0 {
+		return 0
+	}
+	return (numerator-1)/denominator + 1
+}
+
 // Read reads n bytes from the wire for this stream.
 func (s *Stream) read(n int) (data mem.BufferSlice, err error) {
 	// Don't request a read if there was an error earlier
 	if er := s.trReader.er; er != nil {
 		return nil, er
 	}
+	// gRPC Go accepts data frames with a maximum length of 16KB. Larger
+	// messages must be split into multiple frames. We pre-allocate the
+	// buffer to avoid resizing during the read loop, but cap the initial
+	// capacity to 128 frames (2MB) to prevent over-allocation or panics
+	// when reading extremely large streams.
+	allocCap := min(ceil(n, http2MaxFrameLen), 128)
+	data = make(mem.BufferSlice, 0, allocCap)
 	s.readRequester.requestRead(n)
 	for n != 0 {
 		buf, err := s.trReader.Read(n)