Dns_mirage.MakeSourcemodule S : Tcpip.Stack.V4V6A 2byte-length per message flow abstraction, the embedding of DNS frames via TCP.
of_flow flow is f.
flow f is the underlying flow.
read_tcp f returns either a buffer or an error (logs actual error).
send_tcp flow buf sends the buffer, either succeeds or fails (logs actual error).
send_tcp_multiple flow bufs sends the buffers, either succeeds or fails (logs actual error).