/// <summary>
/// Decode messages from a payload and assign it a given kafka offset.
/// </summary>
/// <param name="offset">The offset represting the log entry from kafka of this message.</param>
/// <param name="payload">The byte[] encode as a message from kafka.</param>
/// <returns>Enumerable representing stream of messages decoded from byte[].</returns>
/// <remarks>The return type is an Enumerable as the message could be a compressed message set.</remarks>
public static IEnumerable<Message> DecodeMessage(long offset, byte[] payload)
{
var crc = payload.Take(4);
var stream = new ReadByteStream(payload.Skip(4));
if (crc.SequenceEqual(Crc32.ComputeHash(stream.Payload)) == false)
throw new FailCrcCheckException("Payload did not match CRC validation.");
var message = new Message
{
Meta = new MessageMetadata { Offset = offset },
MagicNumber = stream.ReadByte(),
Attribute = stream.ReadByte(),
Key = stream.ReadIntString()
};
var codec = (MessageCodec)(ProtocolConstants.AttributeCodeMask & message.Attribute);
switch (codec)
{
case MessageCodec.CodecNone:
message.BinaryValue = stream.ReadIntPrefixedBytes();
yield return message;
break;
case MessageCodec.CodecGzip:
var gZipData = stream.ReadIntPrefixedBytes();
foreach (var m in DecodeMessageSet(Compression.Unzip(gZipData)))
{
yield return m;
}
break;
default:
throw new NotSupportedException(string.Format("Codec type of {0} is not supported.", codec));
}
}
