mem: ensure Reader buffers are reused on early return (grpc#8886)

If there was an error, e.g. while decompressing the data, we still want
to return all buffers to the pool.

RELEASE NOTES: None

Author: ash2k

rpc_util.go

@@ -961,24 +961,32 @@ func recvAndDecompress(p *parser, s recvCompressor, dc Decompressor, maxReceiveM
 	return out, nil
 }
 
-// decompress processes the given data by decompressing it using either a custom decompressor or a standard compressor.
-// If a custom decompressor is provided, it takes precedence. The function validates that the decompressed data
-// does not exceed the specified maximum size and returns an error if this limit is exceeded.
-// On success, it returns the decompressed data. Otherwise, it returns an error if decompression fails or the data exceeds the size limit.
+// decompress processes the given data by decompressing it using either
+// a custom decompressor or a standard compressor. If a custom decompressor
+// is provided, it takes precedence. The function validates that
+// the decompressed data does not exceed the specified maximum size and returns
+// an error if this limit is exceeded. On success, it returns the decompressed
+// data. Otherwise, it returns an error if decompression fails or the data
+// exceeds the size limit.
 func decompress(compressor encoding.Compressor, d mem.BufferSlice, dc Decompressor, maxReceiveMessageSize int, pool mem.BufferPool) (mem.BufferSlice, error) {
 	if dc != nil {
-		uncompressed, err := dc.Do(d.Reader())
+		r := d.Reader()
+		uncompressed, err := dc.Do(r)
 		if err != nil {
+			r.Close() // ensure buffers are reused
 			return nil, status.Errorf(codes.Internal, "grpc: failed to decompress the received message: %v", err)
 		}
 		if len(uncompressed) > maxReceiveMessageSize {
+			r.Close() // ensure buffers are reused
 			return nil, status.Errorf(codes.ResourceExhausted, "grpc: message after decompression larger than max (%d vs. %d)", len(uncompressed), maxReceiveMessageSize)
 		}
 		return mem.BufferSlice{mem.SliceBuffer(uncompressed)}, nil
 	}
 	if compressor != nil {
-		dcReader, err := compressor.Decompress(d.Reader())
+		r := d.Reader()
+		dcReader, err := compressor.Decompress(r)
 		if err != nil {
+			r.Close() // ensure buffers are reused
 			return nil, status.Errorf(codes.Internal, "grpc: failed to decompress the message: %v", err)
 		}
 
@@ -990,11 +998,13 @@ func decompress(compressor encoding.Compressor, d mem.BufferSlice, dc Decompress
 		}
 		out, err := mem.ReadAll(dcReader, pool)
 		if err != nil {
+			r.Close() // ensure buffers are reused
 			out.Free()
 			return nil, status.Errorf(codes.Internal, "grpc: failed to read decompressed data: %v", err)
 		}
 
 		if out.Len() > maxReceiveMessageSize {
+			r.Close() // ensure buffers are reused
 			out.Free()
 			return nil, status.Errorf(codes.ResourceExhausted, "grpc: received message after decompression larger than max %d", maxReceiveMessageSize)
 		}