CODEWITHSUNDEEP
csocketssend
JoeManiaci
JoeManiaci

Reputation: 475

Two TCP/IP socket send() requests were actually handled in one TCP Message

I had two send()s in my C program and looking at wireshark, I realized they were sent out as one TCP/IP message. I am assuming this is some sort of TCP/IP optimization that determined they were small enough that they could be sent out together. However, I am rebuilding an old program from scratch and I am building my tool based on it's TCP/IP traffic: MTU limitations, internal protocol design, etc. So if the old tool sends out two separate messages, I need to send out two separate messages.

So does anyone know what specifically it is doing in the background(besides simple optimization) and if there is a flag or something that needs to be enabled/disabled so that I get a 1 to 1 ratio of C send()s and TCP/IP transmission? For now all I can do to keep them separated is to put a sleep(1) after every send().

Thanks.

Upvotes: 4

Views: 2554

Answers (1)

Sneftel
Sneftel

Reputation: 41513

You can set TCP_NODELAY in setsockopt to disable Nagle's algorithm, to prevent your OS from combining small packets. However, it's important for you to realize that TCP is a stream-oriented protocol, and individual "packets" are not intended to be meaningfully separated. Routers along the way are free to combine or split TCP packets (though this is uncommon, due to the extra processing required), and the receiving OS will not necessarily read exactly one sent packet per recv(). If you want to delineate packets of information in TCP, you'll need to use a header structure to report how many of the following bytes belong to that packet.

Upvotes: 9

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