到处都是Unix的胎记
一说起Unix编程,不必多说,最著名的系统调用就是fork,pipe,exec,kill或是socket了(fork(2)
,execve(2)
, pipe(2)
, socketpair(2)
, select(2)
, kill(2)
, sigaction(2)
)这些系统调用都像是Unix编程的胎记或签名一样,表明着它来自于Unix。
下面这篇文章,将向大家展示Unix下最经典的socket的编程例子——使用fork + socket来创建一个TCP/IP的服务程序。这个编程模式很简单,首先是创建Socket,然后把其绑定在某个IP和Port上上侦听连接,接下来的一般做法是使用一个fork创建一个client服务进程再加上一个死循环用于处理和client的交互。这个模式是Unix下最经典的Socket编程例子。
下面,让我们看看用C,Ruby,Python,Perl,PHP和Haskell来实现这一例子,你会发现这些例子中的Unix的胎记。如果你想知道这些例子中的技术细节,那么,向你推荐两本经典书——《Unix高级环境编程》和《Unix网络编程》。
C语言
我们先来看一下经典的C是怎么实现的。
/** * A simple preforking echo server in C. * * Building: * * $ gcc -Wall -o echo echo.c * * Usage: * * $ ./echo * * ~ then in another terminal ... ~ * * $ echo 'Hello, world!' | nc localhost 4242 * */ #include <unistd.h> /* fork, close */ #include <stdlib.h> /* exit */ #include <string.h> /* strlen */ #include <stdio.h> /* perror, fdopen, fgets */ #include <sys/socket.h> #include <sys/wait.h> /* waitpid */ #include <netdb.h> /* getaddrinfo */ #define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0) #define PORT "4242" #define NUM_CHILDREN 3 #define MAXLEN 1024 int readline(int fd, char *buf, int maxlen); // forward declaration int main(int argc, char** argv) { int i, n, sockfd, clientfd; int yes = 1; // used in setsockopt(2) struct addrinfo *ai; struct sockaddr_in *client; socklen_t client_t; pid_t cpid; // child pid char line[MAXLEN]; char cpid_s[32]; char welcome[32]; /* Create a socket and get its file descriptor -- socket(2) */ sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd == -1) { die("Couldn't create a socket"); } /* Prevents those dreaded "Address already in use" errors */ if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&yes, sizeof(int)) == -1) { die("Couldn't setsockopt"); } /* Fill the address info struct (host + port) -- getaddrinfo(3) */ if (getaddrinfo(NULL, PORT, NULL, &ai) != 0) { die("Couldn't get address"); } /* Assign address to this socket's fd */ if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) != 0) { die("Couldn't bind socket to address"); } /* Free the memory used by our address info struct */ freeaddrinfo(ai); /* Mark this socket as able to accept incoming connections */ if (listen(sockfd, 10) == -1) { die("Couldn't make socket listen"); } /* Fork you some child processes. */ for (i = 0; i < NUM_CHILDREN; i++) { cpid = fork(); if (cpid == -1) { die("Couldn't fork"); } if (cpid == 0) { // We're in the child ... for (;;) { // Run forever ... /* Necessary initialization for accept(2) */ client_t = sizeof client; /* Blocks! */ clientfd = accept(sockfd, (struct sockaddr *)&client, &client_t); if (clientfd == -1) { die("Couldn't accept a connection"); } /* Send a welcome message/prompt */ bzero(cpid_s, 32); bzero(welcome, 32); sprintf(cpid_s, "%d", getpid()); sprintf(welcome, "Child %s echo> ", cpid_s); send(clientfd, welcome, strlen(welcome), 0); /* Read a line from the client socket ... */ n = readline(clientfd, line, MAXLEN); if (n == -1) { die("Couldn't read line from connection"); } /* ... and echo it back */ send(clientfd, line, n, 0); /* Clean up the client socket */ close(clientfd); } } } /* Sit back and wait for all child processes to exit */ while (waitpid(-1, NULL, 0) > 0); /* Close up our socket */ close(sockfd); return 0; } /** * Simple utility function that reads a line from a file descriptor fd, * up to maxlen bytes -- ripped from Unix Network Programming, Stevens. */ int readline(int fd, char *buf, int maxlen) { int n, rc; char c; for (n = 1; n < maxlen; n++) { if ((rc = read(fd, &c, 1)) == 1) { *buf++ = c; if (c == '\n') break; } else if (rc == 0) { if (n == 1) return 0; // EOF, no data read else break; // EOF, read some data } else return -1; // error } *buf = ''; // null-terminate return n; }
Ruby
下面是Ruby,你可以看到其中的fork
# simple preforking echo server in Ruby require 'socket' # Create a socket, bind it to localhost:4242, and start listening. # Runs once in the parent; all forked children inherit the socket's # file descriptor. acceptor = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0) address = Socket.pack_sockaddr_in(4242, 'localhost') acceptor.bind(address) acceptor.listen(10) # Close the socket when we exit the parent or any child process. This # only closes the file descriptor in the calling process, it does not # take the socket out of the listening state (until the last fd is # closed). # # The trap is guaranteed to happen, and guaranteed to happen only # once, right before the process exits for any reason (unless # it's terminated with a SIGKILL). trap('EXIT') { acceptor.close } # Fork you some child processes. In the parent, the call to fork # returns immediately with the pid of the child process; fork never # returns in the child because we exit at the end of the block. 3.times do fork do # now we're in the child process; trap (Ctrl-C) interrupts and # exit immediately instead of dumping stack to stderr. trap('INT') { exit } puts "child #$$ accepting on shared socket (localhost:4242)" loop { # This is where the magic happens. accept(2) blocks until a # new connection is ready to be dequeued. socket, addr = acceptor.accept socket.write "child #$$ echo> " socket.flush message = socket.gets socket.write message socket.close puts "child #$$ echo'd: '#{message.strip}'" } exit end end # Trap (Ctrl-C) interrupts, write a note, and exit immediately # in parent. This trap is not inherited by the forks because it # runs after forking has commenced. trap('INT') { puts "\nbailing" ; exit } # Sit back and wait for all child processes to exit. Process.waitall
Python
""" Simple preforking echo server in Python. """ import os import sys import socket # Create a socket, bind it to localhost:4242, and start # listening. Runs once in the parent; all forked children # inherit the socket's file descriptor. acceptor = socket.socket() acceptor.bind(('localhost', 4242)) acceptor.listen(10) # Ryan's Ruby code here traps EXIT and closes the socket. This # isn't required in Python; the socket will be closed when the # socket object gets garbage collected. # Fork you some child processes. In the parent, the call to # fork returns immediately with the pid of the child process; # fork never returns in the child because we exit at the end # of the block. for i in range(3): pid = os.fork() # os.fork() returns 0 in the child process and the child's # process id in the parent. So if pid == 0 then we're in # the child process. if pid == 0: # now we're in the child process; trap (Ctrl-C) # interrupts by catching KeyboardInterrupt) and exit # immediately instead of dumping stack to stderr. childpid = os.getpid() print "Child %s listening on localhost:4242" % childpid try: while 1: # This is where the magic happens. accept(2) # blocks until a new connection is ready to be # dequeued. conn, addr = acceptor.accept() # For easier use, turn the socket connection # into a file-like object. flo = conn.makefile() flo.write('Child %s echo> ' % childpid) flo.flush() message = flo.readline() flo.write(message) flo.close() conn.close() print "Child %s echo'd: %r" % \ (childpid, message.strip()) except KeyboardInterrupt: sys.exit() # Sit back and wait for all child processes to exit. # # Trap interrupts, write a note, and exit immediately in # parent. This trap is not inherited by the forks because it # runs after forking has commenced. try: os.waitpid(-1, 0) except KeyboardInterrupt: print "\nbailing" sys.exit()
Perl
END { $acceptor->close } # Fork you some child processes. The code after the run_fork block runs # in all process, but because the child block ends in an exit call, only # the parent executes the rest of the program. If a parent block were # specified here, it would be invoked in the parent only, and passed the # PID of the child process. for ( 1 .. 3 ) { run_fork { child { while (1) { my $socket = $acceptor->accept; $socket->printflush( "child $$ echo> " ); my $message = $socket->getline; $socket->print( $message ); $socket->close; say "child $$ echo'd: '${\strip $message}'"; } exit; } } } # Trap (Ctrl-C) interrupts, write a note, and exit immediately # in parent. This trap is not inherited by the forks because it # runs after forking has commenced. $SIG{ 'INT' } = sub { print "bailing\n"; exit }; # Sit back and wait for all child processes to exit. 1 while 0 < waitpid -1, 0;
PHP
<? /* Simple preforking echo server in PHP. Russell Beattie (russellbeattie.com) */ /* Allow the script to hang around waiting for connections. */ set_time_limit(0); # Create a socket, bind it to localhost:4242, and start # listening. Runs once in the parent; all forked children # inherit the socket's file descriptor. $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP); socket_bind($socket,'localhost', 4242); socket_listen($socket, 10); pcntl_signal(SIGTERM, 'shutdown'); pcntl_signal(SIGINT, 'shutdown'); function shutdown($signal){ global $socket; socket_close($socket); exit(); } # Fork you some child processes. In the parent, the call to # fork returns immediately with the pid of the child process; # fork never returns in the child because we exit at the end # of the block. for($x = 1; $x <= 3; $x++){ $pid = pcntl_fork(); # pcntl_fork() returns 0 in the child process and the child's # process id in the parent. So if $pid == 0 then we're in # the child process. if($pid == 0){ $childpid = posix_getpid(); echo "Child $childpid listening on localhost:4242 \n"; while(true){ # This is where the magic happens. accept(2) # blocks until a new connection is ready to be # dequeued. $conn = socket_accept($socket); $message = socket_read($conn,1000,PHP_NORMAL_READ); socket_write($conn, "Child $childpid echo> $message"); socket_close($conn); echo "Child $childpid echo'd: $message \n"; } } } # # Trap interrupts, write a note, and exit immediately in # parent. This trap is not inherited by the forks because it # runs after forking has commenced. try{ pcntl_waitpid(-1, $status); } catch (Exception $e) { echo "bailing \n"; exit(); }
Haskell
import Network import Prelude hiding ((-)) import Control.Monad import System.IO import Control.Applicative import System.Posix import System.Exit import System.Posix.Signals main :: IO () main = with =<< (listenOn - PortNumber 4242) where with socket = do replicateM 3 - forkProcess work wait where work = do installHandler sigINT (Catch trap_int) Nothing pid <- show <$> getProcessID puts - "child " ++ pid ++ " accepting on shared socket (localhost:4242)" forever - do (h, _, _) <- accept socket let write = hPutStr h flush = hFlush h getline = hGetLine h close = hClose h write - "child " ++ pid ++ " echo> " flush message <- getline write - message ++ "\n" puts - "child " ++ pid ++ " echo'd: '" ++ message ++ "'" close wait = forever - do ( const () <$> getAnyProcessStatus True True ) `catch` const trap_exit trap_int = exitImmediately ExitSuccess trap_exit = do puts "\nbailing" sClose socket exitSuccess puts = putStrLn (-) = ($) infixr 0 -
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