00000004.htm

一份很好的linux入门资料

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bzero(&amp;(dest_addr.sin_zero),&nbsp;8);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;zero&nbsp;the&nbsp;rest&nbsp;of&nbsp;the&nbsp;struc&nbsp;<BR>
t&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;don't&nbsp;forget&nbsp;to&nbsp;error&nbsp;check&nbsp;the&nbsp;connect()!&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;connect(sockfd,&nbsp;(struct&nbsp;sockaddr&nbsp;*)&amp;dest_addr,&nbsp;sizeof(struct&nbsp;sockadd&nbsp;<BR>
r));&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
Again,&nbsp;be&nbsp;sure&nbsp;to&nbsp;check&nbsp;the&nbsp;return&nbsp;value&nbsp;from&nbsp;connect()--it'll&nbsp;return&nbsp;-1&nbsp;on&nbsp;<BR>
error&nbsp;and&nbsp;set&nbsp;the&nbsp;variable&nbsp;errno.&nbsp;<BR>
Also,&nbsp;notice&nbsp;that&nbsp;we&nbsp;didn't&nbsp;call&nbsp;bind().&nbsp;Basically,&nbsp;we&nbsp;don't&nbsp;care&nbsp;about&nbsp;our&nbsp;<BR>
local&nbsp;port&nbsp;number;&nbsp;we&nbsp;only&nbsp;care&nbsp;where&nbsp;we're&nbsp;going.&nbsp;The&nbsp;kernel&nbsp;will&nbsp;choose&nbsp;a&nbsp;<BR>
local&nbsp;port&nbsp;for&nbsp;us,&nbsp;and&nbsp;the&nbsp;site&nbsp;we&nbsp;connect&nbsp;to&nbsp;will&nbsp;automatically&nbsp;get&nbsp;this&nbsp;<BR>
information&nbsp;from&nbsp;us.&nbsp;No&nbsp;worries.&nbsp;<BR>
----------------------------------------------------------------------------&nbsp;<BR>
&nbsp;<BR>
10.&nbsp;listen()--Will&nbsp;somebody&nbsp;please&nbsp;call&nbsp;me?&nbsp;<BR>
Ok,&nbsp;time&nbsp;for&nbsp;a&nbsp;change&nbsp;of&nbsp;pace.&nbsp;What&nbsp;if&nbsp;you&nbsp;don't&nbsp;want&nbsp;to&nbsp;connect&nbsp;to&nbsp;a&nbsp;remote&nbsp;<BR>
&nbsp;<BR>
host.&nbsp;Say,&nbsp;just&nbsp;for&nbsp;kicks,&nbsp;that&nbsp;you&nbsp;want&nbsp;to&nbsp;wait&nbsp;for&nbsp;incoming&nbsp;connections&nbsp;<BR>
and&nbsp;handle&nbsp;them&nbsp;in&nbsp;some&nbsp;way.&nbsp;The&nbsp;process&nbsp;is&nbsp;two&nbsp;step:&nbsp;first&nbsp;you&nbsp;listen(),&nbsp;<BR>
then&nbsp;you&nbsp;accept()&nbsp;(see&nbsp;below.)&nbsp;<BR>
The&nbsp;listen&nbsp;call&nbsp;is&nbsp;fairly&nbsp;simple,&nbsp;but&nbsp;requires&nbsp;a&nbsp;bit&nbsp;of&nbsp;explanation:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;listen(int&nbsp;sockfd,&nbsp;int&nbsp;backlog);&nbsp;<BR>
sockfd&nbsp;is&nbsp;the&nbsp;usual&nbsp;socket&nbsp;file&nbsp;descriptor&nbsp;from&nbsp;the&nbsp;socket()&nbsp;system&nbsp;call.&nbsp;<BR>
backlog&nbsp;is&nbsp;the&nbsp;number&nbsp;of&nbsp;connections&nbsp;allowed&nbsp;on&nbsp;the&nbsp;incoming&nbsp;queue.&nbsp;What&nbsp;<BR>
does&nbsp;that&nbsp;mean?&nbsp;Well,&nbsp;incoming&nbsp;connections&nbsp;are&nbsp;going&nbsp;to&nbsp;wait&nbsp;in&nbsp;this&nbsp;queue&nbsp;<BR>
until&nbsp;you&nbsp;accept()&nbsp;them&nbsp;(see&nbsp;below)&nbsp;and&nbsp;this&nbsp;is&nbsp;the&nbsp;limit&nbsp;on&nbsp;how&nbsp;many&nbsp;can&nbsp;<BR>
queue&nbsp;up.&nbsp;Most&nbsp;systems&nbsp;silently&nbsp;limit&nbsp;this&nbsp;number&nbsp;to&nbsp;about&nbsp;20;&nbsp;you&nbsp;can&nbsp;<BR>
probably&nbsp;get&nbsp;away&nbsp;with&nbsp;setting&nbsp;it&nbsp;to&nbsp;5&nbsp;or&nbsp;10.&nbsp;<BR>
Again,&nbsp;as&nbsp;per&nbsp;usual,&nbsp;listen()&nbsp;returns&nbsp;-1&nbsp;and&nbsp;sets&nbsp;errno&nbsp;on&nbsp;error.&nbsp;<BR>
Well,&nbsp;as&nbsp;you&nbsp;can&nbsp;probably&nbsp;imagine,&nbsp;we&nbsp;need&nbsp;to&nbsp;call&nbsp;bind()&nbsp;before&nbsp;we&nbsp;call&nbsp;<BR>
listen()&nbsp;or&nbsp;the&nbsp;kernel&nbsp;will&nbsp;have&nbsp;us&nbsp;listening&nbsp;on&nbsp;a&nbsp;random&nbsp;port.&nbsp;Bleah!&nbsp;So&nbsp;if&nbsp;<BR>
&nbsp;<BR>
you're&nbsp;going&nbsp;to&nbsp;be&nbsp;listening&nbsp;for&nbsp;incoming&nbsp;connections,&nbsp;the&nbsp;sequence&nbsp;of&nbsp;<BR>
system&nbsp;calls&nbsp;you'll&nbsp;make&nbsp;is:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;socket();&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;bind();&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;listen();&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;accept()&nbsp;goes&nbsp;here&nbsp;*/&nbsp;<BR>
I'll&nbsp;just&nbsp;leave&nbsp;that&nbsp;in&nbsp;the&nbsp;place&nbsp;of&nbsp;sample&nbsp;code,&nbsp;since&nbsp;it's&nbsp;fairly&nbsp;<BR>
self-explanatory.&nbsp;(The&nbsp;code&nbsp;in&nbsp;the&nbsp;accept()&nbsp;section,&nbsp;below,&nbsp;is&nbsp;more&nbsp;<BR>
complete.)&nbsp;The&nbsp;really&nbsp;tricky&nbsp;part&nbsp;of&nbsp;this&nbsp;whole&nbsp;sha-bang&nbsp;is&nbsp;the&nbsp;call&nbsp;to&nbsp;<BR>
accept().&nbsp;<BR>
----------------------------------------------------------------------------&nbsp;<BR>
&nbsp;<BR>
11.&nbsp;accept()--&quot;Thank&nbsp;you&nbsp;for&nbsp;calling&nbsp;port&nbsp;3490.&quot;&nbsp;<BR>
Get&nbsp;ready--the&nbsp;accept()&nbsp;call&nbsp;is&nbsp;kinda&nbsp;weird!&nbsp;What's&nbsp;going&nbsp;to&nbsp;happen&nbsp;is&nbsp;this:&nbsp;<BR>
&nbsp;<BR>
someone&nbsp;far&nbsp;far&nbsp;away&nbsp;will&nbsp;try&nbsp;to&nbsp;connect()&nbsp;to&nbsp;your&nbsp;machine&nbsp;on&nbsp;a&nbsp;port&nbsp;that&nbsp;<BR>
you&nbsp;are&nbsp;listen()'ing&nbsp;on.&nbsp;Their&nbsp;connection&nbsp;will&nbsp;be&nbsp;queued&nbsp;up&nbsp;waiting&nbsp;to&nbsp;be&nbsp;<BR>
accept()'ed.&nbsp;You&nbsp;call&nbsp;accept()&nbsp;and&nbsp;you&nbsp;tell&nbsp;it&nbsp;to&nbsp;get&nbsp;the&nbsp;pending&nbsp;<BR>
connection.&nbsp;It'll&nbsp;return&nbsp;to&nbsp;you&nbsp;a&nbsp;brand&nbsp;new&nbsp;socket&nbsp;file&nbsp;descriptor&nbsp;to&nbsp;use&nbsp;<BR>
for&nbsp;this&nbsp;single&nbsp;connection!&nbsp;That's&nbsp;right,&nbsp;suddenly&nbsp;you&nbsp;have&nbsp;two&nbsp;socket&nbsp;file&nbsp;<BR>
descriptors&nbsp;for&nbsp;the&nbsp;price&nbsp;of&nbsp;one!&nbsp;The&nbsp;original&nbsp;one&nbsp;is&nbsp;still&nbsp;listening&nbsp;on&nbsp;<BR>
your&nbsp;port&nbsp;and&nbsp;the&nbsp;newly&nbsp;created&nbsp;one&nbsp;is&nbsp;finally&nbsp;ready&nbsp;to&nbsp;send()&nbsp;and&nbsp;recv().&nbsp;<BR>
We're&nbsp;there!&nbsp;<BR>
The&nbsp;call&nbsp;is&nbsp;as&nbsp;follows:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#include&nbsp;&lt;sys/socket.h&gt;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;accept(int&nbsp;sockfd,&nbsp;void&nbsp;*addr,&nbsp;int&nbsp;*addrlen);&nbsp;<BR>
sockfd&nbsp;is&nbsp;the&nbsp;listen()'ing&nbsp;socket&nbsp;descriptor.&nbsp;Easy&nbsp;enough.&nbsp;addr&nbsp;will&nbsp;usually&nbsp;<BR>
&nbsp;<BR>
be&nbsp;a&nbsp;pointer&nbsp;to&nbsp;a&nbsp;local&nbsp;struct&nbsp;sockaddr_in.&nbsp;This&nbsp;is&nbsp;where&nbsp;the&nbsp;information&nbsp;<BR>
about&nbsp;the&nbsp;incoming&nbsp;connection&nbsp;will&nbsp;go&nbsp;(and&nbsp;you&nbsp;can&nbsp;determine&nbsp;which&nbsp;host&nbsp;is&nbsp;<BR>
calling&nbsp;you&nbsp;from&nbsp;which&nbsp;port).&nbsp;addrlen&nbsp;is&nbsp;a&nbsp;local&nbsp;integer&nbsp;variable&nbsp;that&nbsp;<BR>
should&nbsp;be&nbsp;set&nbsp;to&nbsp;sizeof(struct&nbsp;sockaddr_in)&nbsp;before&nbsp;its&nbsp;address&nbsp;is&nbsp;passed&nbsp;to&nbsp;<BR>
accept().&nbsp;Accept&nbsp;will&nbsp;not&nbsp;put&nbsp;more&nbsp;than&nbsp;that&nbsp;many&nbsp;bytes&nbsp;into&nbsp;addr.&nbsp;If&nbsp;it&nbsp;<BR>
puts&nbsp;fewer&nbsp;in,&nbsp;it'll&nbsp;change&nbsp;the&nbsp;value&nbsp;of&nbsp;addrlen&nbsp;to&nbsp;reflect&nbsp;that.&nbsp;<BR>
Guess&nbsp;what?&nbsp;accept()&nbsp;returns&nbsp;-1&nbsp;and&nbsp;sets&nbsp;errno&nbsp;if&nbsp;an&nbsp;error&nbsp;occurs.&nbsp;Betcha&nbsp;<BR>
didn't&nbsp;figure&nbsp;that.&nbsp;<BR>
Like&nbsp;before,&nbsp;this&nbsp;is&nbsp;a&nbsp;bunch&nbsp;to&nbsp;absorb&nbsp;in&nbsp;one&nbsp;chunk,&nbsp;so&nbsp;here's&nbsp;a&nbsp;sample&nbsp;code&nbsp;<BR>
&nbsp;<BR>
fragment&nbsp;for&nbsp;your&nbsp;perusal:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;#include&nbsp;&lt;string.h&gt;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;#include&nbsp;&lt;sys/types.h&gt;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;#include&nbsp;&lt;sys/socket.h&gt;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;#define&nbsp;MYPORT&nbsp;3490&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;the&nbsp;port&nbsp;users&nbsp;will&nbsp;be&nbsp;connecting&nbsp;to&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;#define&nbsp;BACKLOG&nbsp;10&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;how&nbsp;many&nbsp;pending&nbsp;connections&nbsp;queue&nbsp;will&nbsp;hold&nbsp;*&nbsp;<BR>
/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;main()&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;sockfd,&nbsp;new_fd;&nbsp;&nbsp;/*&nbsp;listen&nbsp;on&nbsp;sock_fd,&nbsp;new&nbsp;connection&nbsp;on&nbsp;new_fd&nbsp;&nbsp;<BR>
*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;sockaddr_in&nbsp;my_addr;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;my&nbsp;address&nbsp;information&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;sockaddr_in&nbsp;their_addr;&nbsp;/*&nbsp;connector's&nbsp;address&nbsp;information&nbsp;*/&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;sin_size;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sockfd&nbsp;=&nbsp;socket(AF_INET,&nbsp;SOCK_STREAM,&nbsp;0);&nbsp;/*&nbsp;do&nbsp;some&nbsp;error&nbsp;checking!&nbsp;<BR>
&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;my_addr.sin_family&nbsp;=&nbsp;AF_INET;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;host&nbsp;byte&nbsp;order&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;my_addr.sin_port&nbsp;=&nbsp;htons(MYPORT);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;short,&nbsp;network&nbsp;byte&nbsp;order&nbsp;*&nbsp;<BR>
/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;my_addr.sin_addr.s_addr&nbsp;=&nbsp;INADDR_ANY;&nbsp;/*&nbsp;auto-fill&nbsp;with&nbsp;my&nbsp;IP&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bzero(&amp;(my_addr.sin_zero),&nbsp;8);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;zero&nbsp;the&nbsp;rest&nbsp;of&nbsp;the&nbsp;struct&nbsp;<BR>
&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/*&nbsp;don't&nbsp;forget&nbsp;your&nbsp;error&nbsp;checking&nbsp;for&nbsp;these&nbsp;calls:&nbsp;*/&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;bind(sockfd,&nbsp;(struct&nbsp;sockaddr&nbsp;*)&amp;my_addr,&nbsp;sizeof(struct&nbsp;sockaddr));&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;listen(sockfd,&nbsp;BACKLOG);&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sin_size&nbsp;=&nbsp;sizeof(struct&nbsp;sockaddr_in);&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new_fd&nbsp;=&nbsp;accept(sockfd,&nbsp;&amp;their_addr,&nbsp;&amp;sin_size);&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
Again,&nbsp;note&nbsp;that&nbsp;we&nbsp;will&nbsp;use&nbsp;the&nbsp;socket&nbsp;descriptor&nbsp;new_fd&nbsp;for&nbsp;all&nbsp;send()&nbsp;and&nbsp;<BR>
&nbsp;<BR>
recv()&nbsp;calls.&nbsp;If&nbsp;you're&nbsp;only&nbsp;getting&nbsp;one&nbsp;single&nbsp;connection&nbsp;ever,&nbsp;you&nbsp;can&nbsp;<BR>
close()&nbsp;the&nbsp;original&nbsp;sockfd&nbsp;in&nbsp;order&nbsp;to&nbsp;prevent&nbsp;more&nbsp;incoming&nbsp;connections&nbsp;on&nbsp;<BR>
the&nbsp;same&nbsp;port,&nbsp;if&nbsp;you&nbsp;so&nbsp;desire.&nbsp;<BR>
&nbsp;<BR>
---------------------------------------------------------------------------&nbsp;<BR>
-&nbsp;<BR>
12.&nbsp;send()&nbsp;and&nbsp;recv()--Talk&nbsp;to&nbsp;me,&nbsp;baby!&nbsp;<BR>
These&nbsp;two&nbsp;functions&nbsp;are&nbsp;for&nbsp;communicating&nbsp;over&nbsp;stream&nbsp;sockets&nbsp;or&nbsp;connected&nbsp;<BR>
datagram&nbsp;sockets.&nbsp;If&nbsp;you&nbsp;want&nbsp;to&nbsp;use&nbsp;regular&nbsp;unconnected&nbsp;datagram&nbsp;sockets,&nbsp;<BR>
you'll&nbsp;need&nbsp;to&nbsp;see&nbsp;the&nbsp;section&nbsp;on&nbsp;sendto()&nbsp;and&nbsp;recvfrom(),&nbsp;below.&nbsp;<BR>
The&nbsp;send()&nbsp;call:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;send(int&nbsp;sockfd,&nbsp;const&nbsp;void&nbsp;*msg,&nbsp;int&nbsp;len,&nbsp;int&nbsp;flags);&nbsp;<BR>
sockfd&nbsp;is&nbsp;the&nbsp;socket&nbsp;descriptor&nbsp;you&nbsp;want&nbsp;to&nbsp;send&nbsp;data&nbsp;to&nbsp;(whether&nbsp;it's&nbsp;the&nbsp;<BR>
one&nbsp;returned&nbsp;by&nbsp;socket()&nbsp;or&nbsp;the&nbsp;one&nbsp;you&nbsp;got&nbsp;with&nbsp;accept().)&nbsp;msg&nbsp;is&nbsp;a&nbsp;pointer&nbsp;<BR>
&nbsp;<BR>
to&nbsp;the&nbsp;data&nbsp;you&nbsp;want&nbsp;to&nbsp;send,&nbsp;and&nbsp;len&nbsp;is&nbsp;the&nbsp;length&nbsp;of&nbsp;that&nbsp;data&nbsp;in&nbsp;bytes.&nbsp;<BR>
Just&nbsp;set&nbsp;flags&nbsp;to&nbsp;0.&nbsp;(See&nbsp;the&nbsp;send()&nbsp;man&nbsp;page&nbsp;for&nbsp;more&nbsp;information&nbsp;<BR>
concerning&nbsp;flags.)&nbsp;<BR>
Some&nbsp;sample&nbsp;code&nbsp;might&nbsp;be:&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;char&nbsp;*msg&nbsp;=&nbsp;&quot;Beej&nbsp;was&nbsp;here!&quot;;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;len,&nbsp;bytes_sent;&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;.&nbsp;<BR>
&nbsp;&nbsp;&n