protobuf-nano/src/main/java/io/grpc/protobuf/nano/DeferredNanoProtoInputStream.java

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package io.grpc.protobuf.nano;

import com.google.common.io.ByteStreams;
import com.google.protobuf.nano.CodedOutputByteBufferNano;
import com.google.protobuf.nano.MessageNano;

import io.grpc.DeferredInputStream;
import io.grpc.KnownLength;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.annotation.Nullable;

/**
 * Implementation of {@link DeferredInputStream} backed by a nano proto.
 */
public class DeferredNanoProtoInputStream extends DeferredInputStream<MessageNano>
    implements KnownLength {

  // DeferredNanoProtoInputStream is first initialized with a *message*. *partial* is initially
  // null.
  // Once there has been a read operation on this stream, *message* is serialized to *partial* and
  // set to null.
  @Nullable private MessageNano message;
  @Nullable private ByteArrayInputStream partial;

  public DeferredNanoProtoInputStream(MessageNano message) {
    this.message = message;
  }

  private void toPartial() {
    if (message != null) {
      partial = new ByteArrayInputStream(MessageNano.toByteArray(message));
      message = null;
    }
  }

  @Override
  public int flushTo(OutputStream target) throws IOException {
    // TODO(simonma): flushTo is an optimization of DeferredInputStream, for the implementations
    // that can write data directly to OutputStream, if we don't support flushTo (by not extending
    // DeferredInputStream), the caller will use ByteStreams.copy anyway. So consider extends
    // InputStream directly or make a real optimization here (like save the byte[] and use it for a
    // single target.write()).
    int written = 0;
    toPartial();
    if (partial != null) {
      written = (int) ByteStreams.copy(partial, target);
      partial = null;
    }
    return written;
  }

  @Override
  public int read() throws IOException {
    toPartial();
    if (partial != null) {
      return partial.read();
    }
    return -1;
  }

  @Override
  public int read(byte[] b, int off, int len) throws IOException {
    if (message != null) {
      int size = message.getSerializedSize();
      if (size == 0) {
        message = null;
        partial = null;
        return -1;
      }
      if (len >= size) {
        // This is the only case that is zero-copy.
        CodedOutputByteBufferNano output = CodedOutputByteBufferNano.newInstance(b, off, size);
        message.writeTo(output);
        output.checkNoSpaceLeft();

        message = null;
        partial = null;
        return size;
      }

      toPartial();
    }
    if (partial != null) {
      return partial.read(b, off, len);
    }
    return -1;
  }

  @Override
  public int available() throws IOException {
    if (message != null) {
      return message.getSerializedSize();
    } else if (partial != null) {
      return partial.available();
    }
    return 0;
  }
}