unix domain socket

unix domain socket 是在socket架構(gòu)上發(fā)展起來(lái)的用于同一臺(tái)主機(jī)的進(jìn)程間通訊（IPC: Inter-Process Communication），它不需要經(jīng)過(guò)網(wǎng)絡(luò)協(xié)議棧，不需要打包拆包、計(jì)算校驗(yàn)和、維護(hù)序號(hào)和應(yīng)答等，只是將應(yīng)用層數(shù)據(jù)從一個(gè)進(jìn)程拷貝到另一個(gè)進(jìn)程。UNIX Domain Socket有SOCK_DGRAM或SOCK_STREAM兩種工作模式，類似于UDP和TCP，但是面向消息的UNIX Domain Socket也是可靠的，消息既不會(huì)丟失也不會(huì)順序錯(cuò)亂。

UNIX Domain Socket可用于兩個(gè)沒(méi)有親緣關(guān)系的進(jìn)程，是全雙工的，是目前使用最廣泛的IPC機(jī)制，比如X Window服務(wù)器和GUI程序之間就是通過(guò)UNIX Domain Socket通訊的。

UNIX Domain socket與網(wǎng)絡(luò)socket類似，可以與網(wǎng)絡(luò)socket對(duì)比應(yīng)用。

上述二者編程的不同如下：

• address family為AF_UNIX
• 因?yàn)閼?yīng)用于IPC，所以UNIXDomain socket不需要IP和端口，取而代之的是文件路徑來(lái)表示“網(wǎng)絡(luò)地址”。這點(diǎn)體現(xiàn)在下面兩個(gè)方面。
• 地址格式不同，UNIXDomain socket用結(jié)構(gòu)體sockaddr_un表示，是一個(gè)socket類型的文件在文件系統(tǒng)中的路徑，這個(gè)socket文件由bind()調(diào)用創(chuàng)建，如果調(diào)用bind()時(shí)該文件已存在，則bind()錯(cuò)誤返回。
• UNIX Domain Socket客戶端一般要顯式調(diào)用bind函數(shù)，而不象網(wǎng)絡(luò)socket一樣依賴系統(tǒng)自動(dòng)分配的地址?？蛻舳薭ind的socket文件名可以包含客戶端的pid，這樣服務(wù)器就可以區(qū)分不同的客戶端。

下面用python代碼演示uds的使用

Python代碼演示

服務(wù)端

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Created on 12/11/17 11:55 AM
@author: Chen Liang
@function: socket_echo_server_uds
"""

import sys

reload(sys)
sys.setdefaultencoding('utf-8')
import socket
import os

server_address = './uds_socket'

# Make sure the socket does not already exist
try:
    os.unlink(server_address)
except OSError:
    if os.path.exists(server_address):
        raise

# Create a UDS socket
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)

# Bind the socket to the address
print('starting up on {}'.format(server_address))
sock.bind(server_address)

# Listen for incoming connections
sock.listen(1)

while True:
    # Wait for a connection
    print('waiting for a connection')
    connection, client_address = sock.accept()
    try:
        print('connection from', client_address)

        # Receive the data in small chunks and retransmit it
        while True:
            data = connection.recv(16)
            print('received {!r}'.format(data))
            if data:
                print('sending data back to the client')
                connection.sendall(data)
            else:
                print('no data from', client_address)
                break

    finally:
        # Clean up the connection
        connection.close()

客戶端

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Created on 12/11/17 11:55 AM
@author: Chen Liang
@function: socket_echo_client_uds
"""

import sys

reload(sys)
sys.setdefaultencoding('utf-8')


import socket
import sys

# Create a UDS socket
sock = socket.socket(family=socket.AF_UNIX, type=socket.SOCK_STREAM)

# Connect the socket to the port where the server is listening
server_address = './uds_socket'
print('connecting to {}'.format(server_address))
try:
    sock.connect(server_address)
except socket.error as msg:
    print(msg)
    sys.exit(1)

try:

    # Send data
    message = b'This is the message.  It will be repeated.'
    print('sending {!r}'.format(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('received {!r}'.format(data))

finally:
    print('closing socket')
    sock.close()

客戶端一次發(fā)送，服務(wù)端分批返回。

服務(wù)端輸出結(jié)果如下

root@ubuntu:~/PycharmProjects/python_scripts# python socket_echo_server_uds.py 
starting up on ./uds_socket
waiting for a connection
('connection from', '')
received 'This is the mess'
sending data back to the client
received 'age.  It will be'
sending data back to the client
received ' repeated.'
sending data back to the client
received ''
('no data from', '')
waiting for a connection

客戶端輸出結(jié)果如下

root@ubuntu:~/PycharmProjects/python_scripts# python socket_echo_client_uds.py 
connecting to ./uds_socket
sending 'This is the message.  It will be repeated.'
received 'This is the mess'
received 'age.  It will be'
received ' repeated.'
closing socket

查看套接字文件的類型如下

root@ubuntu:~/PycharmProjects/python_scripts# ls -l ./uds_socket
srwxr-xr-x 1 root root 0 Dec 11 13:45 ./uds_socket

可見(jiàn)uds文件是socket類型。具體的linux文件類型有以下幾種：

Linux的文件類型有以下幾種:

參考：

• Python實(shí)例淺談之九使用本地socket文件
• Linux下的IPC－UNIX Domain Socket
• pymotw3 unix domain socket

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