unix 域套接字 socketpari()

一、UNIX Domain Socket IPC 

socket API原本是为网络通讯设计的，但后来在socket的框架上发展出一种IPC机制，就是UNIX Domain Socket。虽然网络socket也可用于同一台主机的进程间通讯（通过loopback地址127.0.0.1），但是UNIX Domain Socket用于IPC更有效率：不需要经过网络协议栈，不需要打包拆包、计算校验和、维护序号和应答等，只是将应用层数据从一个进程拷贝到另一个进程。UNIX域套接字与TCP套接字相比较，在同一台主机的传输速度前者是后者的两倍。这是因为，IPC机制本质上是可靠的通讯，而网络协议是为不可靠的通讯设计的。UNIX Domain Socket也提供面向流和面向数据包两种API接口，类似于TCP和UDP，但是面向消息的UNIXDomain Socket也是可靠的，消息既不会丢失也不会顺序错乱。

使用UNIX Domain Socket的过程和网络socket十分相似，也要先调用socket()创建一个socket文件描述符，address family指定为AF_UNIX，type可以选择SOCK_DGRAM或SOCK_STREAM，protocol参数仍然指定为0即可。 

UNIX Domain Socket与网络socket编程最明显的不同在于地址格式不同，用结构体sockaddr_un表示，网络编程的socket地址是IP地址加端口号，而UNIX Domain Socket的地址是一个socket类型的文件在 文件系统中的路径 ，这个socket文件由bind()调用创建，如果调用bind()时该文件已存在，则bind()错误返回。

unix-socket-c.py

#!/usr/bin/env python

import socket
import os
import time

SERVER_PATH = "/tmp/python_unix_socket_server"
 
def run_unix_domain_socket_server():
    if os.path.exists(SERVER_PATH):
        os.remove( SERVER_PATH )
     
    print "starting unix domain socket server."
    server = socket.socket( socket.AF_UNIX, socket.SOCK_DGRAM )
    server.bind(SERVER_PATH)
     
    print "Listening on path: %s" %SERVER_PATH
    while True:
        datagram = server.recv( 1024 )
        if not datagram:
            break
        else:
            print "-" * 20
            print datagram
        if "DONE" == datagram:
            break
    print "-" * 20
    print "Server is shutting down now..."
    server.close()
    os.remove(SERVER_PATH)
    print "Server shutdown and path removed."

if __name__ == '__main__':
    run_unix_domain_socket_server()

unix-socket-s.py

#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter - 3
# This program is optimized for Python 2.7.
# It may run on any other version with/without modifications.

import socket
import sys

SERVER_PATH = "/tmp/python_unix_socket_server"

def run_unix_domain_socket_client():
    """ Run "a Unix domain socket client """
    sock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
    
    # Connect the socket to the path where the server is listening
    server_address = SERVER_PATH 
    print "connecting to %s" % server_address
    try:
        sock.connect(server_address)
    except socket.error, msg:
        print >>sys.stderr, msg
        sys.exit(1)
    
    try:
        message = "This is the message.  This will be echoed back!"
        print  "Sending [%s]" %message
        sock.sendall(message)
        amount_received = 0
        amount_expected = len(message)
        
        while amount_received < amount_expected:
            data = sock.recv(16)
            amount_received += len(data)
            print >>sys.stderr, "Received [%s]" % data
    
    finally:
        print "Closing client"
        sock.close()

if __name__ == '__main__':
    run_unix_domain_socket_client()

socket.socketpair()

#!/usr/bin/env python
#--coding:utf8--

import socket
import os
BUFSIZE = 1024
def test_socketpair():
    """ Test Unix socketpair"""
    parent, child = socket.socketpair()
    print("os.getpgid:%d"%os.getpid())
    print('socketpair:parent:')
    print parent
    print('socketpair:child:')
    print child
    pid = os.fork()
    print "pid:%d"%pid
    try:
        if pid:
            print "[if pid]pid:%d"%pid
            print "@Parent, sending message..."
            child.close()
            parent.sendall("Hello from parent!")
            response = parent.recv(BUFSIZE)
            print "Response from child:", response
            parent.close()
        else:
            print "[else]pid:%d"%pid
            print "@Child, waiting for message from parent"
            parent.close()
            message = child.recv(BUFSIZE)
            print "Message from parent:", message
            child.sendall("Hello from child!!")
            child.close()
    except Exception, err:
        print "Error: %s" %err
if __name__ == '__main__':
    test_socketpair()