Beej's 网络编程

Beej’s Guide to Network Programming

Using Internet Sockets

Brian "Beej" Hall

beej@piratehaven.org

Copyright © 1995-2001 by Brian "Beej" Hall

Revision History

Revision Version 1.0.0 August, 1995 Revised by: beej

Initial version.

Revision Version 1.5.5 January 13, 1999 Revised by: beej

1. Intro............................................................................................................................................................................3

1.1. Audience.........................................................................................................................................................3

1.2. Platform and Compiler...................................................................................................................................3

1.3. Official Homepage .........................................................................................................................................3

1.4. Note for Solaris/SunOS Programmers ...........................................................................................................3

1.5. Note for Windows Programmers....................................................................................................................4

1.6. Email Policy...................................................................................................................................................5

1.7. Mirroring........................................................................................................................................................5

1.8. Note for Translators........................................................................................................................................5

1.9. Copyright and Distribution.............................................................................................................................5

4. System Calls or Bust...............................................................................................................................................12

4.1. socket()–Get the File Descriptor!.............................................................................................................12

4.2. bind()–What port am I on?........................................................................................................................13

4.3. connect()–Hey, you!.................................................................................................................................15

4.4. listen()–Will somebody please call me?.................................................................................................16

4.5. accept()–"Thank you for calling port 3490."...........................................................................................16

4.6. send() and recv()–Talk to me, baby!......................................................................................................18

4.7. sendto() and recvfrom()–Talk to me, DGRAM-style ..........................................................................19

4.8. close() and shutdown()–Get outta my face!..........................................................................................19

4.9. getpeername()–Who are you? .................................................................................................................20

6. Slightly Advanced Techniques...............................................................................................................................29

6.1. Blocking .......................................................................................................................................................29

6.2. select()–Synchronous I/O Multiplexing..................................................................................................30

6.3. Handling Partial send()s............................................................................................................................35

6.4. Son of Data Encapsulation...........................................................................................................................36

7. More References......................................................................................................................................................38

7.1. man Pages....................................................................................................................................................38

7.2. Books............................................................................................................................................................39

7.3. Web References............................................................................................................................................40

7.4. RFCs.............................................................................................................................................................40

Well, guess what! I’ve already done this nasty business, and I’m dying to share the information with everyone!

You’ve come to the right place. This document should give the average competent C programmer the edge s/he needs

to get a grip on this networking noise.

1.1. Audience

This document has been written as a tutorial, not a reference. It is probably at its best when read by individuals who

are just starting out with socket programming and are looking for a foothold. It is certainly not the complete guide to

sockets programming, by any means.

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

1.2. Platform and Compiler

The code contained within this document was compiled on a Linux PC using Gnu’s gcc compiler. It should, however,

1.4. Note for Solaris/SunOS Programmers

When compiling for Solaris or SunOS, you need to specify some extra command-line switches for linking in the

proper libraries. In order to do this, simply add "-lnsl -lsocket -lresolv" to the end of the compile command,

like so:

If you still get errors, you could try further adding a "-lxnet" to the end of that command line. I don’t know what

that does, exactly, but some people seem to need it.

Another place that you might find problems is in the call to setsockopt(). The prototype differs from that on my

Linux box, so instead of:

enter this:

I have a particular dislike for Windows, and encourage you to try Linux, BSD, or Unix instead. That being said, you

can still use this stuff under Windows.

First, ignore pretty much all of the system header files I mention in here. All you need to include is:

Wait! You also have to make a call to WSAStartup() before doing anything else with the sockets library. The code

to do that looks something like this:

and look for the box titled "Object/library modules". Add "wsock32.lib" to that list.

Or so I hear.

Finally, you need to call WSACleanup() when you’re all through with the sockets library. See your online help for

details.

Once you do that, the rest of the examples in this tutorial should generally apply, with a few exceptions. For one

thing, you can’t use close() to close a socket–you need to use closesocket(), instead. Also, select() only

works with socket descriptors, not file descriptors (like 0 for stdin).

There is also a socket class that you can use, CSocket. Check your compilers help pages for more information.

To get more information about Winsock, read the Winsock FAQ

and go from there.

that, the CreateThread() is a little easier to digest...unfortunately a discussion about multithreading is beyond the

scope of this document. I can only talk about so much, you know!

a pretty busy life and there are times when I just can’t answer a question you have. When that’s the case, I usually

just delete the message. It’s nothing personal; I just won’t ever have the time to give the detailed answer you require.

As a rule, the more complex the question, the less likely I am to respond. If you can narrow down your question

before mailing it and be sure to include any pertinent information (like platform, compiler, error messages you’re

getting, and anything else you think might help me troubleshoot), you’re much more likely to get a response. For

more pointers, read ESR’s document, How To Ask Questions The Smart Way

.

If you don’t get a response, hack on it some more, try to find the answer, and if it’s still elusive, then write me again

with the information you’ve found and hopefully it will be enough for me to help out.

Now that I’ve badgered you about how to write and not write me, I’d just like to let you know that I fully appreciate

If you want to translate the guide into another language, write me at <beej@piratehaven.org> and I’ll link to

your translation from the main page.

Feel free to add your name and email address to the translation.

Sorry, but due to space constraints, I cannot host the translations myself.

1.9. Copyright and Distribution

Beej’s Guide to Network Programming is Copyright © 1995-2001 Brian "Beej" Hall.

This guide may be freely reprinted in any medium provided that its content is not altered, it is presented in its

entirety, and this copyright notice remains intact.

Educators are especially encouraged to recommend or supply copies of this guide to their students.