NanoProtoInputStream.java

/*
 * Copyright 2014, Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *    * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above
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 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package io.grpc.protobuf.nano;

import com.google.protobuf.nano.CodedOutputByteBufferNano;
import com.google.protobuf.nano.MessageNano;
import io.grpc.KnownLength;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.annotation.Nullable;

/**
 * An {@link InputStream} backed by a nano proto.
 */
class NanoProtoInputStream extends InputStream implements KnownLength {

  // NanoProtoInputStream 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 NanoProtoInputStream(MessageNano message) {
    this.message = message;
  }

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

  @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;
  }
}