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ed2ba5b07a
In the DNS TCP code, there are a couple of places where we have a buffer containing a message which we need to send via TCP. The DNS protocol is that this is sent as <16-bit length in network order><message> Making two write calls, one for the length and one for the message causes the TCP stack to send two packets, one for each. A single packet containing both is preferable from a performance POV. Implement a scatter-gather version of our read_write() wrapper and use it where necessary to send TCP DNS messages.