Hooking up Cipher to Okio’s new UnsafeCursor.

OkioCipher.java

/*
 * Copyright 2018 Square Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okio;

import java.io.IOException;
import java.security.GeneralSecurityException;
import javax.crypto.Cipher;

public final class OkioCipher {
  static final byte[] EMPTY_ARRAY = new byte[0];

  final Cipher cipher;
  final Buffer.UnsafeCursor sourceCursor = new Buffer.UnsafeCursor();
  final Buffer.UnsafeCursor sinkCursor = new Buffer.UnsafeCursor();

  OkioCipher(Cipher cipher) {
    this.cipher = cipher;
  }

  /**
   * Encrypts or decrypts {@code byteCount} bytes from {@code source} to {@code sink}, ending with
   * {@link Cipher#doFinal} or its overloads. Returns the total number of bytes emitted to {@code
   * sink}.
   */
  public int cipherUntilDoFinal(BufferedSource source, BufferedSink sink, long byteCount)
      throws IOException, GeneralSecurityException {
    int result = 0;
    boolean callDoFinal = false;

    while (byteCount > 0) {
      // Encrypt up to byteCount bytes from the source.
      Buffer sourceBuffer = source.buffer();
      sourceBuffer.require(1L);

      try (Buffer.UnsafeCursor ic = sourceBuffer.readUnsafe(sourceCursor)) {
        ic.seek(0L);
        int segmentByteCount = ic.end - ic.start;
        int inputByteCount = (int) Math.min(byteCount, segmentByteCount);
        callDoFinal = (inputByteCount == byteCount);
        int outputByteCount = updateOrDoFinal(ic, sink, inputByteCount, callDoFinal);
        source.skip(inputByteCount);
        result += outputByteCount;
        byteCount -= inputByteCount;
      }
    }

    if (!callDoFinal) {
      result += updateOrDoFinal(null, sink, 0, true);
    }

    return result;
  }

  /**
   * Encrypts/decrypts {@code byteCount} bytes from {@code source} to {@code sink}. Returns the
   * number of bytes written to {@code sink}.
   */
  private int updateOrDoFinal(Buffer.UnsafeCursor source, BufferedSink sink,
      int byteCount, boolean doFinal) throws GeneralSecurityException, IOException {
    int outputByteCount = cipher.getOutputSize(byteCount);
    if (outputByteCount == 0) {
      // When we're writing 0 bytes emit into an empty array.
      int resultByteCount = updateOrDoFinalNoOutput(source, byteCount, doFinal);
      if (resultByteCount != 0) throw new AssertionError();
      return 0;

    } else if (outputByteCount <= Segment.SIZE) {
      // When what we're writing fits in a segment write directly do the sink cursor.
      Buffer sinkBuffer = sink.buffer();
      long sinkBufferSize = sinkBuffer.size();
      try (Buffer.UnsafeCursor oc = sinkBuffer.readAndWriteUnsafe(sinkCursor)) {
        oc.expandBuffer(outputByteCount);
        oc.seek(sinkBufferSize);
        int resultByteCount = updateOrDoFinalToCursor(source, byteCount, doFinal, oc);
        oc.resizeBuffer(sinkBufferSize + resultByteCount);
        sink.emitCompleteSegments();
        return resultByteCount;
      }

    } else {
      // Write to a temporary array and then write that to the sink.
      byte[] bytes = updateOrDoFinalToByteArray(source, byteCount, doFinal);
      sink.write(bytes);
      return bytes.length;
    }
  }

  /** Crypts {@code byteCount} bytes of {@code source} and produces no output. */
  private int updateOrDoFinalNoOutput(Buffer.UnsafeCursor source, int byteCount, boolean doFinal)
      throws GeneralSecurityException {
    if (doFinal) {
      return byteCount > 0
          ? cipher.doFinal(source.data, source.start, byteCount, EMPTY_ARRAY, 0)
          : cipher.doFinal(EMPTY_ARRAY, 0);
    } else {
      return cipher.update(source.data, source.start, byteCount, EMPTY_ARRAY, 0);
    }
  }

  /** Crypts {@code byteCount} bytes of {@code source} and writes to {@code sink}. */
  private int updateOrDoFinalToCursor(Buffer.UnsafeCursor source, int byteCount, boolean doFinal,
      Buffer.UnsafeCursor sink) throws GeneralSecurityException {
    if (doFinal) {
      return byteCount > 0
          ? cipher.doFinal(source.data, source.start, byteCount, sink.data, sink.start)
          : cipher.doFinal(sink.data, sink.start);
    } else {
      return cipher.update(source.data, source.start, byteCount, sink.data, sink.start);
    }
  }

  /** Crypts {@code byteCount} bytes of {@code source} and returns them. */
  private byte[] updateOrDoFinalToByteArray(Buffer.UnsafeCursor source, int byteCount,
      boolean doFinal) throws GeneralSecurityException {
    if (doFinal) {
      return byteCount > 0
          ? cipher.doFinal(source.data, source.start, byteCount)
          : cipher.doFinal();
    } else {
      return cipher.update(source.data, source.start, byteCount);
    }
  }
}