Class MessageFramer

core/src/main/java/io/grpc/internal/MessageFramer.java:45–445

Encodes gRPC messages to be delivered via the transport layer which implements MessageFramer.Sink.

 * MessageFramer.Sink}.
 */
public class MessageFramer implements Framer {

  private static final int NO_MAX_OUTBOUND_MESSAGE_SIZE = -1;

  /**
   * Sink implemented by the transport layer to receive frames and forward them to their
   * destination.
   */
  public interface Sink {
    /**
     * Delivers a frame via the transport.
     *
     * @param frame a non-empty buffer to deliver or {@code null} if the framer is being
     *              closed and there is no data to deliver.
     * @param endOfStream whether the frame is the last one for the GRPC stream
     * @param flush {@code true} if more data may not be arriving soon
     * @param numMessages the number of messages that this series of frames represents
     */
    void deliverFrame(
        @Nullable WritableBuffer frame,
        boolean endOfStream,
        boolean flush,
        int numMessages);
  }

  private static final int HEADER_LENGTH = 5;
  private static final byte UNCOMPRESSED = 0;
  private static final byte COMPRESSED = 1;

  private final Sink sink;
  // effectively final.  Can only be set once.
  private int maxOutboundMessageSize = NO_MAX_OUTBOUND_MESSAGE_SIZE;
  private WritableBuffer buffer;
  /**
   * if > 0 - the number of bytes to allocate for the current known-length message.
   */
  private int knownLengthPendingAllocation;
  private Compressor compressor = Codec.Identity.NONE;
  private boolean messageCompression = true;
  private final OutputStreamAdapter outputStreamAdapter = new OutputStreamAdapter();
  private final ByteBuffer headerScratch = ByteBuffer.allocate(HEADER_LENGTH);
  private final WritableBufferAllocator bufferAllocator;
  private final StatsTraceContext statsTraceCtx;
  // transportTracer is nullable until it is integrated with client transports
  private boolean closed;

  // Tracing and stats-related states
  private int messagesBuffered;
  private int currentMessageSeqNo = -1;
  private long currentMessageWireSize;

  /**
   * Creates a {@code MessageFramer}.
   *
   * @param sink the sink used to deliver frames to the transport
   * @param bufferAllocator allocates buffers that the transport can commit to the wire.
   */
  public MessageFramer(