internal static async Task WriteSubscribeAsync(this Stream stream, Subscribe subscribe)
{
// Determine packet size
var variableHeaderSize = WordSize;
var payloadSize = subscribe.GetPayloadSize();
var(remainingLength, remainingLengthBuffer) = EncodeRemainingLength(variableHeaderSize + payloadSize);
var fixedHeaderSize = 1 + remainingLength; // 1 => holds packet type in high nibble, reserved in low
var bufferSize = fixedHeaderSize + variableHeaderSize + payloadSize;
var buffer = new byte[bufferSize];
var index = 0;
// Fixed header
// - Packet type
buffer[index++] = CombineNibbles(Subscribe.PacketType, Bit1);
// - Remaining length
Buffer.BlockCopy(remainingLengthBuffer, 0, buffer, index, remainingLength);
index += remainingLength;
// Variable header
// - Message Id
Buffer.BlockCopy(subscribe.PacketId.GetBigEndianBytes(), 0, buffer, index, WordSize);
index += WordSize;
// Payload
// - Subscriptions
subscribe.Subscriptions.ForEach(subscription =>
{
index = EncodeString(subscription.TopicFilter, buffer, index);
buffer[index++] = (byte)subscription.RequestedQoS;
});
await stream.WriteAsync(buffer, 0, index).ConfigureAwait(false);
await stream.FlushAsync().ConfigureAwait(false);
}
private static int GetPayloadSize(this Subscribe subscribe) => subscribe.Subscriptions.Select(subscription => subscription.TopicFilter).Aggregate(0, (count, topicFilter) => count + topicFilter.TryGetUTF8ByteCount()) + subscribe.Subscriptions.Count;