到处都是Unix的胎记

[netkiller]

到处都是Unix的胎记
2009年10月11日陈皓发表评论阅读评论 6,216 人阅读
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。

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/**
* 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 = '\0'; // null-terminate
return n;
}
Ruby

下面是Ruby，你可以看到其中的fork

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# 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

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"""
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

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#!/usr/bin/perl
use 5.010;
use strict;

# simple preforking echo server in Perl
use Proc::Fork;
use IO::Socket::INET;

sub strip { s/\A\s+//, s/\s+\z// for my @r = @_; @r }

# 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.
my $acceptor = IO::Socket::INET->new(
LocalPort => 4242,
Reuse => 1,
Listen => 10,
) or die "Couln't start server: $!\n";

# 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).
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

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<?
/*
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

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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 -