Frame enumeration

The following C# code snippets demonstrate how to enumerate vehicle data frames from a received data batch:

internal readonly struct PubSubFrame
{
    public int Version { get; init; }

    public string VehicleId { get; init; }

    public int Length { get; init; }

    public ReadOnlyMemory<byte> Data { get; init; }
}

internal readonly struct PubSubBatch(ReadOnlyMemory<byte> data) : IEnumerable<PubSubFrame>
{
    public ReadOnlyMemory<byte> Data { get; } = data;

    public IEnumerator<PubSubFrame> GetEnumerator()
    {
        const int VEHICLE_ID_LENGTH = 16;
        const char HEADER_CHAR = 'F';
        const int VERSION_V1 = 0x01;

        for (int idx = 0; idx < Data.Length;)
        {
            byte header = Data.Span[idx++];
            if (header != HEADER_CHAR)
            {
                throw new Exception("Invalid frame header");
            }

            byte version = Data.Span[idx++];
            if (version != VERSION_V1)
            {
                throw new Exception("Unsupported version");
            }

            ReadOnlyMemory<byte> vId = Data.Slice(idx, VEHICLE_ID_LENGTH);
            Guid vGuid = new(vId.ToArray());
            string vehicleId = vGuid.ToString();
            idx += VEHICLE_ID_LENGTH;
      
            int length = BinaryPrimitives.ReadInt32LittleEndian(Data.Span[idx..]);
            idx += sizeof(int);

            ReadOnlyMemory<byte> data = Data.Slice(idx, length);
            idx += length;

            yield return new PubSubFrame()
            {
                Version = version,
                VehicleId = vehicleId,
                Length = length,
                Data = data
            };
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

Usage Example

The following example shows how to process incoming messages and iterate through the vehicle data frames contained in each batch:

Task startTask = subscriber.StartAsync((PubsubMessage message, CancellationToken cancel) =>
{
    Console.WriteLine($"Received message - length: {message.Data.Length}");

    try
    {
        // Process received message here
        foreach (PubSubFrame frame in new PubSubBatch(message.Data.Memory))
        {
            // Processing vehicle data frames
        }
    }
    catch (Exception e)
    {
        Console.WriteLine($"ERROR: {e.Message}");
    }

    return Task.FromResult(SubscriberClient.Reply.Ack);
});