pw_hdlc/java/test/dev/pigweed/pw_hdlc/EncoderTest.java - pigweed/pigweed - Git at Google

 // Copyright 2022 The Pigweed Authors
 //
 // 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
 //
 //     https://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 dev.pigweed.pw_hdlc;

 import static com.google.common.truth.Truth.assertThat;
 import static java.nio.charset.StandardCharsets.US_ASCII;

 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import org.junit.Test;
 import org.junit.runner.RunWith;

 public class EncoderTest {
   private static final int OUTPUT_SIZE = 1024;
   private static final byte UNNUMBERED_CONTROL = 0x03;
   private static final byte ADDRESS = 0x7B;
   private static final byte ENCODED_ADDRESS = (byte) ((ADDRESS << 1) | 1);
   private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream(OUTPUT_SIZE);

   @Test
   public void emptyPayload() throws IOException {
     ByteBuffer emptyPayload = ByteBuffer.allocate(0);
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .writeCrc(0x832d343f)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, emptyPayload, outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void oneBytePayload() throws IOException {
     byte[] payload = {'A'};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write((byte) 'A')
                                 .writeCrc(0x653c9e82)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void oneBytePayload_escape0x7d() throws IOException {
     byte[] payload = {0x7d};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(Protocol.ESCAPE)
                                 .write((byte) (0x7d ^ 0x20))
                                 .writeCrc(0x4a53e205)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void oneBytePayload_escape0x7e() throws IOException {
     byte[] payload = {0x7e};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(Protocol.ESCAPE)
                                 .write((byte) (0x7e ^ 0x20))
                                 .writeCrc(0xd35ab3bf)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void addressNeedsEscaping() throws IOException {
     byte address = 0x7d >> 1;
     byte[] payload = {'A'};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(Protocol.ESCAPE)
                                 .write((byte) 0x5d)
                                 .write(UNNUMBERED_CONTROL)
                                 .write((byte) 'A')
                                 .writeCrc(0x899E00D4)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(address, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void crcNeedsEscaping() throws IOException {
     byte[] payload = {'a', 'a'};
     // The CRC-32 of {ENCODED_ADDRESS, UNNUMBERED_CONTROL, "aa"} is 0x7ee04473, so
     // the 0x7e must be escaped.
     byte[] expectedCrc = {0x73, 0x44, (byte) 0xe0, 0x7d, 0x5e};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(payload)
                                 .write(expectedCrc)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void multiplePayloads() throws IOException {
     byte[] payload1 = {'A', 'B', 'C'};
     byte[] payload2 = {'D', 'E', 'F'};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(payload1)
                                 .writeCrc(0x72410ee4)
                                 .writeFlag()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(payload2)
                                 .writeCrc(0x4ba1ae47)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload1), outputStream);
     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload2), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void payloadWithNoEscapes() throws IOException {
     byte[] payload = "1995 toyota corolla".getBytes(US_ASCII);
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(payload)
                                 .writeCrc(0x53ee911c)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void multiByteAddress() throws IOException {
     long address = 0x3fff;
     byte[] encodedAddress = {(byte) 0xfe, (byte) 0xff};
     byte[] payload = "abc".getBytes(US_ASCII);
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(encodedAddress)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(payload)
                                 .writeCrc(0x8cee2978)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(address, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void payloadWithMultipleEscapes() throws IOException {
     byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};
     byte[] escapedPayload = {0x7D, 0x5E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x5D, 0x7D, 0x5E};
     byte[] expectedResult = new ExpectedValueBuilder()
                                 .writeFlag()
                                 .write(ENCODED_ADDRESS)
                                 .write(UNNUMBERED_CONTROL)
                                 .write(escapedPayload)
                                 .writeCrc(0x1563a4e6)
                                 .writeFlag()
                                 .build();

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void writeFrame() throws IOException {
     byte[] payload = {5, (byte) 0xab, 0x42, 0x24, (byte) 0xf9, 0x54, (byte) 0xfb, 0x3d};
     byte[] expectedResult =
         new ExpectedValueBuilder().writeFlag().write(payload).writeFlag().build();
     Frame frame = Frame.parse(ByteBuffer.wrap(payload));

     Encoder.writeFrame(frame, outputStream);

     assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
   }

   @Test
   public void getUiFrameEncodedSize_empty() throws IOException {
     byte[] payload = {};

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
   }

   @Test
   public void getUiFrameEncodedSize_oneByte() throws IOException {
     byte[] payload = {0x61};

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
   }

   @Test
   public void getUiFrameEncodedSize_multipleEscapes() throws IOException {
     byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
   }

   @Test
   public void getMaxPayloadBytesInUiFrameOfSize_emptyPayload() {
     byte[] payload = {};

     assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 1000)).isEqualTo(0);
   }

   @Test
   public void getMaxPayloadBytesInUiFrameOfSize_emptyFrame() {
     byte[] payload = {1, 2, 3, 4};

     assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 0)).isEqualTo(0);
   }

   @Test
   public void getMaxPayloadBytesInUiFrameOfSize_exactFit() throws IOException {
     byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};
     final int requiredReservedSize = Encoder.getUiFrameEncodedSize(ADDRESS, payload);

     Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

     assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize))
         .isEqualTo(payload.length);
     // Not enough room for the last payload byte, which is escaped, so needs two bytes.
     assertThat(
         Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize - 1))
         .isEqualTo(payload.length - 1);
     assertThat(
         Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize - 2))
         .isEqualTo(payload.length - 1);
   }

   @Test
   public void maxPayloadBytesInUiFrameOfSize_extraRoom() {
     byte[] payload = {1, 2, 3, 4};

     assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 1000))
         .isEqualTo(payload.length);
   }

   private static class ExpectedValueBuilder {
     private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream(OUTPUT_SIZE);

     public ExpectedValueBuilder writeFlag() throws IOException {
       outputStream.write(Protocol.FLAG);
       return this;
     }

     public ExpectedValueBuilder write(byte b) throws IOException {
       outputStream.write(b);
       return this;
     }

     public ExpectedValueBuilder write(byte[] buffer) throws IOException {
       outputStream.write(buffer);
       return this;
     }

     public ExpectedValueBuilder writeCrc(int crc) throws IOException {
       outputStream.write(0xFF & crc);
       outputStream.write(0xFF & (crc >> 8));
       outputStream.write(0xFF & (crc >> 16));
       outputStream.write(0xFF & (crc >> 24));
       return this;
     }

     byte[] build() {
       return outputStream.toByteArray();
     }
   }
 }
	// Copyright 2022 The Pigweed Authors
	//
	// 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
	//
	// https://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 dev.pigweed.pw_hdlc;

	import static com.google.common.truth.Truth.assertThat;
	import static java.nio.charset.StandardCharsets.US_ASCII;

	import java.io.ByteArrayOutputStream;
	import java.io.IOException;
	import java.nio.ByteBuffer;
	import org.junit.Test;
	import org.junit.runner.RunWith;

	public class EncoderTest {
	private static final int OUTPUT_SIZE = 1024;
	private static final byte UNNUMBERED_CONTROL = 0x03;
	private static final byte ADDRESS = 0x7B;
	private static final byte ENCODED_ADDRESS = (byte) ((ADDRESS << 1) \| 1);
	private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream(OUTPUT_SIZE);

	@Test
	public void emptyPayload() throws IOException {
	ByteBuffer emptyPayload = ByteBuffer.allocate(0);
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.writeCrc(0x832d343f)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, emptyPayload, outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void oneBytePayload() throws IOException {
	byte[] payload = {'A'};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write((byte) 'A')
	.writeCrc(0x653c9e82)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void oneBytePayload_escape0x7d() throws IOException {
	byte[] payload = {0x7d};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(Protocol.ESCAPE)
	.write((byte) (0x7d ^ 0x20))
	.writeCrc(0x4a53e205)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void oneBytePayload_escape0x7e() throws IOException {
	byte[] payload = {0x7e};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(Protocol.ESCAPE)
	.write((byte) (0x7e ^ 0x20))
	.writeCrc(0xd35ab3bf)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void addressNeedsEscaping() throws IOException {
	byte address = 0x7d >> 1;
	byte[] payload = {'A'};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(Protocol.ESCAPE)
	.write((byte) 0x5d)
	.write(UNNUMBERED_CONTROL)
	.write((byte) 'A')
	.writeCrc(0x899E00D4)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(address, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void crcNeedsEscaping() throws IOException {
	byte[] payload = {'a', 'a'};
	// The CRC-32 of {ENCODED_ADDRESS, UNNUMBERED_CONTROL, "aa"} is 0x7ee04473, so
	// the 0x7e must be escaped.
	byte[] expectedCrc = {0x73, 0x44, (byte) 0xe0, 0x7d, 0x5e};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(payload)
	.write(expectedCrc)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void multiplePayloads() throws IOException {
	byte[] payload1 = {'A', 'B', 'C'};
	byte[] payload2 = {'D', 'E', 'F'};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(payload1)
	.writeCrc(0x72410ee4)
	.writeFlag()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(payload2)
	.writeCrc(0x4ba1ae47)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload1), outputStream);
	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload2), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void payloadWithNoEscapes() throws IOException {
	byte[] payload = "1995 toyota corolla".getBytes(US_ASCII);
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(payload)
	.writeCrc(0x53ee911c)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void multiByteAddress() throws IOException {
	long address = 0x3fff;
	byte[] encodedAddress = {(byte) 0xfe, (byte) 0xff};
	byte[] payload = "abc".getBytes(US_ASCII);
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(encodedAddress)
	.write(UNNUMBERED_CONTROL)
	.write(payload)
	.writeCrc(0x8cee2978)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(address, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void payloadWithMultipleEscapes() throws IOException {
	byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};
	byte[] escapedPayload = {0x7D, 0x5E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x5D, 0x7D, 0x5E};
	byte[] expectedResult = new ExpectedValueBuilder()
	.writeFlag()
	.write(ENCODED_ADDRESS)
	.write(UNNUMBERED_CONTROL)
	.write(escapedPayload)
	.writeCrc(0x1563a4e6)
	.writeFlag()
	.build();

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void writeFrame() throws IOException {
	byte[] payload = {5, (byte) 0xab, 0x42, 0x24, (byte) 0xf9, 0x54, (byte) 0xfb, 0x3d};
	byte[] expectedResult =
	new ExpectedValueBuilder().writeFlag().write(payload).writeFlag().build();
	Frame frame = Frame.parse(ByteBuffer.wrap(payload));

	Encoder.writeFrame(frame, outputStream);

	assertThat(outputStream.toByteArray()).isEqualTo(expectedResult);
	}

	@Test
	public void getUiFrameEncodedSize_empty() throws IOException {
	byte[] payload = {};

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
	}

	@Test
	public void getUiFrameEncodedSize_oneByte() throws IOException {
	byte[] payload = {0x61};

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
	}

	@Test
	public void getUiFrameEncodedSize_multipleEscapes() throws IOException {
	byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(Encoder.getUiFrameEncodedSize(ADDRESS, payload)).isEqualTo(outputStream.size());
	}

	@Test
	public void getMaxPayloadBytesInUiFrameOfSize_emptyPayload() {
	byte[] payload = {};

	assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 1000)).isEqualTo(0);
	}

	@Test
	public void getMaxPayloadBytesInUiFrameOfSize_emptyFrame() {
	byte[] payload = {1, 2, 3, 4};

	assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 0)).isEqualTo(0);
	}

	@Test
	public void getMaxPayloadBytesInUiFrameOfSize_exactFit() throws IOException {
	byte[] payload = {0x7E, 0x7B, 0x61, 0x62, 0x63, 0x7D, 0x7E};
	final int requiredReservedSize = Encoder.getUiFrameEncodedSize(ADDRESS, payload);

	Encoder.writeUiFrame(ADDRESS, ByteBuffer.wrap(payload), outputStream);

	assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize))
	.isEqualTo(payload.length);
	// Not enough room for the last payload byte, which is escaped, so needs two bytes.
	assertThat(
	Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize - 1))
	.isEqualTo(payload.length - 1);
	assertThat(
	Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, requiredReservedSize - 2))
	.isEqualTo(payload.length - 1);
	}

	@Test
	public void maxPayloadBytesInUiFrameOfSize_extraRoom() {
	byte[] payload = {1, 2, 3, 4};

	assertThat(Encoder.getMaxPayloadBytesInUiFrameOfSize(ADDRESS, payload, 1000))
	.isEqualTo(payload.length);
	}

	private static class ExpectedValueBuilder {
	private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream(OUTPUT_SIZE);

	public ExpectedValueBuilder writeFlag() throws IOException {
	outputStream.write(Protocol.FLAG);
	return this;
	}

	public ExpectedValueBuilder write(byte b) throws IOException {
	outputStream.write(b);
	return this;
	}

	public ExpectedValueBuilder write(byte[] buffer) throws IOException {
	outputStream.write(buffer);
	return this;
	}

	public ExpectedValueBuilder writeCrc(int crc) throws IOException {
	outputStream.write(0xFF & crc);
	outputStream.write(0xFF & (crc >> 8));
	outputStream.write(0xFF & (crc >> 16));
	outputStream.write(0xFF & (crc >> 24));
	return this;
	}

	byte[] build() {
	return outputStream.toByteArray();
	}
	}
	}