[EBook] [C++] Socket programming - Linux Unix.PDF

Beej's Guide to Network Programming

Using Internet Sockets

Version 1.5.4 (17-May-1998)

[http://www.ecst.csuchico.edu/~beej/guide/net]

Intro

Hey! Socket programming got you down? Is this stuff just a little too difficult to figure out from the

man pages? You want to do cool Internet programming, but you don't have time to wade through a

gob of structs trying to figure out if you have to call bind() before you connect(), etc., etc.

Hopefully, though, it'll be just enough for those man pages to start making sense... :-)

Platform and Compiler

gcc

compiler. It was also found to compile on HPUX using gcc. Note that every code snippet was not

individually tested.

listen()--Will somebody please call me?

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accept()--"Thank you for calling port 3490."

send() and recv()--Talk to me, baby!

sendto() and recvfrom()--Talk to me, DGRAM-style

close() and shutdown()--Get outta my face!

getpeername()--Who are you?

gethostname()--Who am I?

DNS--You say "whitehouse.gov", I say "198.137.240.100"

Disclaimer and Call for Help

What is a socket?

You hear talk of "sockets" all the time, and perhaps you are wondering just what they are exactly.

by reading or writing to a file descriptor. A file descriptor is simply an integer associated with an open

file. But (and here's the catch), that file can be a network connection, a FIFO, a pipe, a terminal, a real

is, "You can!" The longer answer is, "You can, but send() and recv() offer much greater control

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What's this? There are two types of Internet sockets? Yes. Well, no. I'm lying. There are more, but I

Cool. What about Datagram sockets? Why are they called connectionless? What is the deal, here,

may arrive out of order. If it arrives, the data within the packet will be error-free.

Datagram sockets also use IP for routing, but they don't use TCP; they use the "User Datagram

Protocol", or "UDP" (see RFC-768.)

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born, the packet is wrapped ("encapsulated") in a header (and maybe footer) by the first protocol (say,

the TFTP protocol), then the whole thing (TFTP header included) is encapsulated again by the next

(serial, thin Ethernet, AUI, whatever) because programs on lower levels deal with it for you. The

Application

Session

Transport

Network

and sendto() it out. The kernel builds the Transport Layer and Internet Layer on for you and the

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