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<HTML><HEAD>  <TITLE>BBS水木清华站∶精华区</TITLE></HEAD><BODY><CENTER><H1>BBS水木清华站∶精华区</H1></CENTER>发信人:&nbsp;mry&nbsp;(木日),&nbsp;信区:&nbsp;Linux&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<BR>标&nbsp;&nbsp;题:&nbsp;Beej's&nbsp;Guide&nbsp;to&nbsp;Network&nbsp;Programming&nbsp;<BR>发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Tue&nbsp;Nov&nbsp;16&nbsp;19:31:29&nbsp;1999)&nbsp;<BR>&nbsp;<BR>《Unix&nbsp;Network&nbsp;Programming》虽然经典，不过太长了&nbsp;<BR>初学者可以现读读这篇简单的，估计一天就差不多&nbsp;<BR>========================================================&nbsp;<BR>&nbsp;<BR><A HREF="http://www.ecst.csuchico.edu/~beej/guide/net/">http://www.ecst.csuchico.edu/~beej/guide/net/</A>&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Beej's&nbsp;Guide&nbsp;to&nbsp;Network&nbsp;Programming&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Using&nbsp;Internet&nbsp;Sockets&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Version&nbsp;1.5.3&nbsp;(01-Nov-1997)&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[<A HREF="http://www.ecst.csuchico.edu/~beej/guide/net]">http://www.ecst.csuchico.edu/~beej/guide/net]</A>&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>Intro&nbsp;<BR>Hey!&nbsp;Socket&nbsp;programming&nbsp;got&nbsp;you&nbsp;down?&nbsp;Is&nbsp;this&nbsp;stuff&nbsp;just&nbsp;a&nbsp;little&nbsp;too&nbsp;<BR>difficult&nbsp;to&nbsp;figure&nbsp;out&nbsp;from&nbsp;the&nbsp;man&nbsp;pages?&nbsp;You&nbsp;want&nbsp;to&nbsp;do&nbsp;cool&nbsp;Internet&nbsp;<BR>programming,&nbsp;but&nbsp;you&nbsp;don't&nbsp;have&nbsp;time&nbsp;to&nbsp;wade&nbsp;through&nbsp;a&nbsp;gob&nbsp;of&nbsp;structs&nbsp;trying&nbsp;<BR>&nbsp;<BR>to&nbsp;figure&nbsp;out&nbsp;if&nbsp;you&nbsp;have&nbsp;to&nbsp;call&nbsp;bind()&nbsp;before&nbsp;you&nbsp;connect(),&nbsp;etc.,&nbsp;etc.&nbsp;<BR>Well,&nbsp;guess&nbsp;what!&nbsp;I've&nbsp;already&nbsp;done&nbsp;this&nbsp;nasty&nbsp;business,&nbsp;and&nbsp;I'm&nbsp;dying&nbsp;to&nbsp;<BR>share&nbsp;the&nbsp;information&nbsp;with&nbsp;everyone!&nbsp;You've&nbsp;come&nbsp;to&nbsp;the&nbsp;right&nbsp;place.&nbsp;This&nbsp;<BR>document&nbsp;should&nbsp;give&nbsp;the&nbsp;average&nbsp;competent&nbsp;C&nbsp;programmer&nbsp;the&nbsp;edge&nbsp;s/he&nbsp;needs&nbsp;<BR>to&nbsp;get&nbsp;a&nbsp;grip&nbsp;on&nbsp;this&nbsp;networking&nbsp;noise.&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>Audience&nbsp;<BR>This&nbsp;document&nbsp;has&nbsp;been&nbsp;written&nbsp;as&nbsp;a&nbsp;tutorial,&nbsp;not&nbsp;a&nbsp;reference.&nbsp;It&nbsp;is&nbsp;<BR>probably&nbsp;at&nbsp;its&nbsp;best&nbsp;when&nbsp;read&nbsp;by&nbsp;individuals&nbsp;who&nbsp;are&nbsp;just&nbsp;starting&nbsp;out&nbsp;with&nbsp;<BR>&nbsp;<BR>socket&nbsp;programming&nbsp;and&nbsp;are&nbsp;looking&nbsp;for&nbsp;a&nbsp;foothold.&nbsp;It&nbsp;is&nbsp;certainly&nbsp;not&nbsp;the&nbsp;<BR>complete&nbsp;guide&nbsp;to&nbsp;sockets&nbsp;programming,&nbsp;by&nbsp;any&nbsp;means.&nbsp;<BR>Hopefully,&nbsp;though,&nbsp;it'll&nbsp;be&nbsp;just&nbsp;enough&nbsp;for&nbsp;those&nbsp;man&nbsp;pages&nbsp;to&nbsp;start&nbsp;making&nbsp;<BR>sense...&nbsp;:-)&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>Platform&nbsp;and&nbsp;Compiler&nbsp;<BR>Most&nbsp;of&nbsp;the&nbsp;code&nbsp;contained&nbsp;within&nbsp;this&nbsp;document&nbsp;was&nbsp;compiled&nbsp;on&nbsp;a&nbsp;Linux&nbsp;PC&nbsp;<BR>using&nbsp;Gnu's&nbsp;gcc&nbsp;compiler.&nbsp;It&nbsp;was&nbsp;also&nbsp;found&nbsp;to&nbsp;compile&nbsp;on&nbsp;HPUX&nbsp;using&nbsp;gcc.&nbsp;<BR>Note&nbsp;that&nbsp;every&nbsp;code&nbsp;snippet&nbsp;was&nbsp;not&nbsp;individually&nbsp;tested.&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>Contents:&nbsp;<BR>&nbsp;&nbsp;&nbsp;1&nbsp;What&nbsp;is&nbsp;a&nbsp;socket?&nbsp;<BR>&nbsp;&nbsp;&nbsp;2&nbsp;Two&nbsp;Types&nbsp;of&nbsp;Internet&nbsp;Sockets&nbsp;<BR>&nbsp;&nbsp;&nbsp;3&nbsp;Low&nbsp;level&nbsp;Nonsense&nbsp;and&nbsp;Network&nbsp;Theory&nbsp;<BR>&nbsp;&nbsp;&nbsp;4&nbsp;structs--Know&nbsp;these,&nbsp;or&nbsp;aliens&nbsp;will&nbsp;destroy&nbsp;the&nbsp;planet!&nbsp;<BR>&nbsp;&nbsp;&nbsp;5&nbsp;Convert&nbsp;the&nbsp;Natives!&nbsp;<BR>&nbsp;&nbsp;&nbsp;6&nbsp;IP&nbsp;Addresses&nbsp;and&nbsp;How&nbsp;to&nbsp;Deal&nbsp;With&nbsp;Them&nbsp;<BR>&nbsp;&nbsp;&nbsp;7&nbsp;socket()--Get&nbsp;the&nbsp;File&nbsp;Descriptor!&nbsp;<BR>&nbsp;&nbsp;&nbsp;8&nbsp;bind()--What&nbsp;port&nbsp;am&nbsp;I&nbsp;on?&nbsp;<BR>&nbsp;&nbsp;&nbsp;9&nbsp;connect()--Hey,&nbsp;you!&nbsp;<BR>&nbsp;&nbsp;10&nbsp;listen()--Will&nbsp;somebody&nbsp;please&nbsp;call&nbsp;me?&nbsp;<BR>&nbsp;&nbsp;11&nbsp;accept()--&quot;Thank&nbsp;you&nbsp;for&nbsp;calling&nbsp;port&nbsp;3490.&quot;&nbsp;<BR>&nbsp;&nbsp;12&nbsp;send()&nbsp;and&nbsp;recv()--Talk&nbsp;to&nbsp;me,&nbsp;baby!&nbsp;<BR>&nbsp;&nbsp;13&nbsp;sendto()&nbsp;and&nbsp;recvfrom()--Talk&nbsp;to&nbsp;me,&nbsp;DGRAM-style&nbsp;<BR>&nbsp;&nbsp;14&nbsp;close()&nbsp;and&nbsp;shutdown()--Get&nbsp;outta&nbsp;my&nbsp;face!&nbsp;<BR>&nbsp;&nbsp;15&nbsp;getpeername()--Who&nbsp;are&nbsp;you?&nbsp;<BR>&nbsp;&nbsp;16&nbsp;gethostname()--Who&nbsp;am&nbsp;I?&nbsp;<BR>&nbsp;&nbsp;17&nbsp;DNS--You&nbsp;say&nbsp;&quot;whitehouse.gov&quot;,&nbsp;I&nbsp;say&nbsp;&quot;198.137.240.100&quot;&nbsp;<BR>&nbsp;&nbsp;18&nbsp;Client-Server&nbsp;Background&nbsp;<BR>&nbsp;&nbsp;19&nbsp;A&nbsp;Simple&nbsp;Stream&nbsp;Server&nbsp;<BR>&nbsp;&nbsp;20&nbsp;A&nbsp;Simple&nbsp;Stream&nbsp;Client&nbsp;<BR>&nbsp;&nbsp;21&nbsp;Datagram&nbsp;Sockets&nbsp;<BR>&nbsp;&nbsp;22&nbsp;Blocking&nbsp;<BR>&nbsp;&nbsp;23&nbsp;select()--Synchronous&nbsp;I/O&nbsp;Multiplexing.&nbsp;Cool!&nbsp;<BR>&nbsp;&nbsp;24&nbsp;More&nbsp;references&nbsp;<BR>&nbsp;&nbsp;25&nbsp;Disclaimer&nbsp;and&nbsp;Call&nbsp;for&nbsp;Help&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>1.&nbsp;What&nbsp;is&nbsp;a&nbsp;socket?&nbsp;<BR>You&nbsp;hear&nbsp;talk&nbsp;of&nbsp;&quot;sockets&quot;&nbsp;all&nbsp;the&nbsp;time,&nbsp;and&nbsp;perhaps&nbsp;you&nbsp;are&nbsp;wondering&nbsp;just&nbsp;<BR>what&nbsp;they&nbsp;are&nbsp;exactly.&nbsp;Well,&nbsp;they're&nbsp;this:&nbsp;a&nbsp;way&nbsp;to&nbsp;speak&nbsp;to&nbsp;other&nbsp;programs&nbsp;<BR>using&nbsp;standard&nbsp;Unix&nbsp;file&nbsp;descriptors.&nbsp;<BR>What?&nbsp;<BR>Ok--you&nbsp;may&nbsp;have&nbsp;heard&nbsp;some&nbsp;Unix&nbsp;hacker&nbsp;state,&nbsp;&quot;Jeez,&nbsp;everything&nbsp;in&nbsp;Unix&nbsp;is&nbsp;<BR>a&nbsp;file!&quot;&nbsp;What&nbsp;that&nbsp;person&nbsp;may&nbsp;have&nbsp;been&nbsp;talking&nbsp;about&nbsp;is&nbsp;the&nbsp;fact&nbsp;that&nbsp;when&nbsp;<BR>Unix&nbsp;programs&nbsp;do&nbsp;any&nbsp;sort&nbsp;of&nbsp;I/O,&nbsp;they&nbsp;do&nbsp;it&nbsp;by&nbsp;reading&nbsp;or&nbsp;writing&nbsp;to&nbsp;a&nbsp;file&nbsp;<BR>&nbsp;<BR>descriptor.&nbsp;A&nbsp;file&nbsp;descriptor&nbsp;is&nbsp;simply&nbsp;an&nbsp;integer&nbsp;associated&nbsp;with&nbsp;an&nbsp;open&nbsp;<BR>file.&nbsp;But&nbsp;(and&nbsp;here's&nbsp;the&nbsp;catch),&nbsp;that&nbsp;file&nbsp;can&nbsp;be&nbsp;a&nbsp;network&nbsp;connection,&nbsp;a&nbsp;<BR>FIFO,&nbsp;a&nbsp;pipe,&nbsp;a&nbsp;terminal,&nbsp;a&nbsp;real&nbsp;on-the-disk&nbsp;file,&nbsp;or&nbsp;just&nbsp;about&nbsp;anything&nbsp;<BR>else.&nbsp;Everything&nbsp;in&nbsp;Unix&nbsp;is&nbsp;a&nbsp;file!&nbsp;So&nbsp;when&nbsp;you&nbsp;want&nbsp;to&nbsp;communicate&nbsp;with&nbsp;<BR>another&nbsp;program&nbsp;over&nbsp;the&nbsp;Internet&nbsp;you're&nbsp;gonna&nbsp;do&nbsp;it&nbsp;through&nbsp;a&nbsp;file&nbsp;<BR>descriptor,&nbsp;you'd&nbsp;better&nbsp;believe&nbsp;it.&nbsp;<BR>&quot;Where&nbsp;do&nbsp;I&nbsp;get&nbsp;this&nbsp;file&nbsp;descriptor&nbsp;for&nbsp;network&nbsp;communication,&nbsp;Mr.&nbsp;<BR>Smarty-Pants?&quot;&nbsp;is&nbsp;probably&nbsp;the&nbsp;last&nbsp;question&nbsp;on&nbsp;your&nbsp;mind&nbsp;right&nbsp;now,&nbsp;but&nbsp;I'm&nbsp;<BR>&nbsp;<BR>going&nbsp;to&nbsp;answer&nbsp;it&nbsp;anyway:&nbsp;You&nbsp;make&nbsp;a&nbsp;call&nbsp;to&nbsp;the&nbsp;socket()&nbsp;system&nbsp;routine.&nbsp;<BR>It&nbsp;returns&nbsp;the&nbsp;socket&nbsp;descriptor,&nbsp;and&nbsp;you&nbsp;communicate&nbsp;through&nbsp;it&nbsp;using&nbsp;the&nbsp;<BR>specialized&nbsp;send()&nbsp;and&nbsp;recv()&nbsp;(&quot;man&nbsp;send&quot;,&nbsp;&quot;man&nbsp;recv&quot;)&nbsp;socket&nbsp;calls.&nbsp;<BR>&quot;But,&nbsp;hey!&quot;&nbsp;you&nbsp;might&nbsp;be&nbsp;exclaiming&nbsp;right&nbsp;about&nbsp;now.&nbsp;&quot;If&nbsp;it's&nbsp;a&nbsp;file&nbsp;<BR>descriptor,&nbsp;why&nbsp;in&nbsp;the&nbsp;hell&nbsp;can't&nbsp;I&nbsp;just&nbsp;use&nbsp;the&nbsp;normal&nbsp;read()&nbsp;and&nbsp;write()&nbsp;<BR>calls&nbsp;to&nbsp;communicate&nbsp;through&nbsp;the&nbsp;socket?&quot;&nbsp;The&nbsp;short&nbsp;answer&nbsp;is,&nbsp;&quot;You&nbsp;can!&quot;&nbsp;<BR>The&nbsp;longer&nbsp;answer&nbsp;is,&nbsp;&quot;You&nbsp;can,&nbsp;but&nbsp;send()&nbsp;and&nbsp;recv()&nbsp;offer&nbsp;much&nbsp;greater&nbsp;<BR>control&nbsp;over&nbsp;your&nbsp;data&nbsp;transmission.&quot;&nbsp;<BR>What&nbsp;next?&nbsp;How&nbsp;about&nbsp;this:&nbsp;there&nbsp;are&nbsp;all&nbsp;kinds&nbsp;of&nbsp;sockets.&nbsp;There&nbsp;are&nbsp;DARPA&nbsp;<BR>Internet&nbsp;addresses&nbsp;(Internet&nbsp;Sockets),&nbsp;path&nbsp;names&nbsp;on&nbsp;a&nbsp;local&nbsp;node&nbsp;(Unix&nbsp;<BR>Sockets),&nbsp;CCITT&nbsp;X.25&nbsp;addresses&nbsp;(X.25&nbsp;Sockets&nbsp;that&nbsp;you&nbsp;can&nbsp;safely&nbsp;ignore),&nbsp;<BR>and&nbsp;probably&nbsp;many&nbsp;others&nbsp;depending&nbsp;on&nbsp;which&nbsp;Unix&nbsp;flavor&nbsp;you&nbsp;run.&nbsp;This&nbsp;<BR>document&nbsp;deals&nbsp;only&nbsp;with&nbsp;the&nbsp;first:&nbsp;Internet&nbsp;Sockets.&nbsp;<BR>----------------------------------------------------------------------------&nbsp;<BR>&nbsp;<BR>2.&nbsp;Two&nbsp;Types&nbsp;of&nbsp;Internet&nbsp;Sockets&nbsp;<BR>What's&nbsp;this?&nbsp;There&nbsp;are&nbsp;two&nbsp;types&nbsp;of&nbsp;Internet&nbsp;sockets?&nbsp;Yes.&nbsp;Well,&nbsp;no.&nbsp;I'm&nbsp;<BR>lying.&nbsp;There&nbsp;are&nbsp;more,&nbsp;but&nbsp;I&nbsp;didn't&nbsp;want&nbsp;to&nbsp;scare&nbsp;you.&nbsp;I'm&nbsp;only&nbsp;going&nbsp;to&nbsp;<BR>talk&nbsp;about&nbsp;two&nbsp;types&nbsp;here.&nbsp;Except&nbsp;for&nbsp;this&nbsp;sentence,&nbsp;where&nbsp;I'm&nbsp;going&nbsp;to&nbsp;tell&nbsp;<BR>&nbsp;<BR>you&nbsp;that&nbsp;&quot;Raw&nbsp;Sockets&quot;&nbsp;are&nbsp;also&nbsp;very&nbsp;powerful&nbsp;and&nbsp;you&nbsp;should&nbsp;look&nbsp;them&nbsp;up.&nbsp;<BR>All&nbsp;right,&nbsp;already.&nbsp;What&nbsp;are&nbsp;the&nbsp;two&nbsp;types?&nbsp;One&nbsp;is&nbsp;&quot;Stream&nbsp;Sockets&quot;;&nbsp;the&nbsp;<BR>other&nbsp;is&nbsp;&quot;Datagram&nbsp;Sockets&quot;,&nbsp;which&nbsp;may&nbsp;hereafter&nbsp;be&nbsp;referred&nbsp;to&nbsp;as&nbsp;<BR>&quot;SOCK_STREAM&quot;&nbsp;and&nbsp;&quot;SOCK_DGRAM&quot;,&nbsp;respectively.&nbsp;Datagram&nbsp;sockets&nbsp;are&nbsp;sometimes&nbsp;<BR>&nbsp;<BR>called&nbsp;&quot;connectionless&nbsp;sockets&quot;&nbsp;(though&nbsp;they&nbsp;can&nbsp;be&nbsp;connect()'d&nbsp;if&nbsp;you&nbsp;<BR>really&nbsp;want.&nbsp;See&nbsp;connect(),&nbsp;below.&nbsp;<BR>Stream&nbsp;sockets&nbsp;are&nbsp;reliable&nbsp;two-way&nbsp;connected&nbsp;communication&nbsp;streams.&nbsp;If&nbsp;you&nbsp;<BR>output&nbsp;two&nbsp;items&nbsp;into&nbsp;the&nbsp;socket&nbsp;in&nbsp;the&nbsp;order&nbsp;&quot;1,&nbsp;2&quot;,&nbsp;they&nbsp;will&nbsp;arrive&nbsp;in&nbsp;<BR>
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