什麼是twisted？
twisted是一個用python語言寫的事件驅動的網絡框架，他支持很多種協議，包括UDP,TCP,TLS和其他應用層協議，比如HTTP，SMTP，NNTM，IRC，XMPP/Jabber。 非常好的一點是twisted實現和很多應用層的協議，開發人員可以直接只用這些協議的實現。其實要修改Twisted的SSH服務器端實現非常簡單。很多時候，開發人員需要實現protocol類。
一個Twisted程序由reactor發起的主循環和一些回調函數組成。當事件發生了，比如一個client連接到了server，這時候服務器端的事件會被觸發執行。
用Twisted寫一個簡單的TCP服務器
下面的代碼是一個TCPServer，這個server記錄客戶端發來的數據信息。
==== code1.py ====import sys from twisted.internet.protocol import ServerFactory from twisted.protocols.basic import LineReceiver from twisted.python import log from twisted.internet import reactor class CmdProtocol(LineReceiver): delimiter = '\n' def connectionMade(self): self.client_ip = self.transport.getPeer()[1] log.msg("Client connection from %s" % self.client_ip) if len(self.factory.clients) >= self.factory.clients_max: log.msg("Too many connections. bye !") self.client_ip = None self.transport.loseConnection() else: self.factory.clients.append(self.client_ip) def connectionLost(self, reason): log.msg('Lost client connection. Reason: %s' % reason) if self.client_ip: self.factory.clients.remove(self.client_ip) def lineReceived(self, line): log.msg('Cmd received from %s : %s' % (self.client_ip, line)) class MyFactory(ServerFactory): protocol = CmdProtocol def __init__(self, clients_max=10): self.clients_max = clients_max self.clients = [] log.startLogging(sys.stdout) reactor.listenTCP(9999, MyFactory(2)) reactor.run()
下面的代碼至關重要：
from twisted.internet import reactor reactor.run()
這兩行代碼會啓動reator的主循環。
在上面的代碼中我們創建了"ServerFactory"類，這個工廠類負責返回“CmdProtocol”的實例。 每一個連接都由實例化的“CmdProtocol”實例來做處理。 Twisted的reactor會在TCP連接上後自動創建CmdProtocol的實例。如你所見，protocol類的方法都對應着一種事件處理。
當client連上server之後會觸發“connectionMade"方法，在這個方法中你可以做一些鑑權之類的操作，也可以限制客戶端的連接總數。每一個protocol的實例都有一個工廠的引用，使用self.factory可以訪問所在的工廠實例。
上面實現的”CmdProtocol“是twisted.protocols.basic.LineReceiver的子類，LineReceiver類會將客戶端發送的數據按照換行符分隔，每到一個換行符都會觸發lineReceived方法。稍後我們可以增強LineReceived來解析命令。
Twisted實現了自己的日誌系統，這裏我們配置將日誌輸出到stdout
當執行reactor.listenTCP時我們將工廠綁定到了9999端口開始監聽。
user@lab:~/TMP$ python code1.py 2011-08-29 13:32:32+0200 [-] Log opened. 2011-08-29 13:32:32+0200 [-] __main__.MyFactory starting on 99992011-08-29 13:32:32+0200 [-] Starting factory <__main__.MyFactory instance at 0x227e3202011-08-29 13:32:35+0200 [__main__.MyFactory] Client connection from 127.0.0.12011-08-29 13:32:38+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : hello server
使用Twisted來調用外部進程
下面我們給前面的server添加一個命令，通過這個命令可以讀取/var/log/syslog的內容
import sys import os from twisted.internet.protocol import ServerFactory, ProcessProtocol from twisted.protocols.basic import LineReceiver from twisted.python import log from twisted.internet import reactor class TailProtocol(ProcessProtocol): def __init__(self, write_callback): self.write = write_callback def outReceived(self, data): self.write("Begin lastlog\n") data = [line for line in data.split('\n') if not line.startswith('==')] for d in data: self.write(d + '\n') self.write("End lastlog\n") def processEnded(self, reason): if reason.value.exitCode != 0: log.msg(reason) class CmdProtocol(LineReceiver): delimiter = '\n' def processCmd(self, line): if line.startswith('lastlog'): tailProtocol = TailProtocol(self.transport.write) reactor.spawnProcess(tailProtocol, '/usr/bin/tail', args=['/usr/bin/tail', '-10', '/var/log/syslog']) elif line.startswith('exit'): self.transport.loseConnection() else: self.transport.write('Command not found.\n') def connectionMade(self): self.client_ip = self.transport.getPeer()[1] log.msg("Client connection from %s" % self.client_ip) if len(self.factory.clients) >= self.factory.clients_max: log.msg("Too many connections. bye !") self.client_ip = None self.transport.loseConnection() else: self.factory.clients.append(self.client_ip) def connectionLost(self, reason): log.msg('Lost client connection. Reason: %s' % reason) if self.client_ip: self.factory.clients.remove(self.client_ip) def lineReceived(self, line): log.msg('Cmd received from %s : %s' % (self.client_ip, line)) self.processCmd(line) class MyFactory(ServerFactory): protocol = CmdProtocol def __init__(self, clients_max=10): self.clients_max = clients_max self.clients = [] log.startLogging(sys.stdout) reactor.listenTCP(9999, MyFactory(2)) reactor.run()
在上面的代碼中，沒從客戶端接收到一行內容後會執行processCmd方法，如果收到的一行內容是exit命令，那麼服務器端會斷開連接，如果收到的是lastlog，我們要吐出一個子進程來執行tail命令，並將tail命令的輸出重定向到客戶端。這裏我們需要實現ProcessProtocol類，需要重寫該類的processEnded方法和outReceived方法。在tail命令有輸出時會執行outReceived方法，當進程退出時會執行processEnded方法。
如下是執行結果樣例：
user@lab:~/TMP$ python code2.py 2011-08-29 15:13:38+0200 [-] Log opened. 2011-08-29 15:13:38+0200 [-] __main__.MyFactory starting on 99992011-08-29 15:13:38+0200 [-] Starting factory <__main__.MyFactory instance at 0x1a5a3f8> 2011-08-29 15:13:47+0200 [__main__.MyFactory] Client connection from 127.0.0.12011-08-29 15:13:58+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : test 2011-08-29 15:14:02+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : lastlog 2011-08-29 15:14:05+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : exit 2011-08-29 15:14:05+0200 [CmdProtocol,0,127.0.0.1] Lost client connection. Reason: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.
可以使用下面的命令作爲客戶端發起命令：
user@lab:~$ netcat 127.0.0.1 9999test Command not found. lastlog Begin lastlog Aug 29 15:02:03 lab sSMTP[5919]: Unable to locate mail Aug 29 15:02:03 lab sSMTP[5919]: Cannot open mail:25Aug 29 15:02:03 lab CRON[4945]: (CRON) error (grandchild #4947 failed with exit status 1) Aug 29 15:02:03 lab sSMTP[5922]: Unable to locate mail Aug 29 15:02:03 lab sSMTP[5922]: Cannot open mail:25Aug 29 15:02:03 lab CRON[4945]: (logcheck) MAIL (mailed 1 byte of output; but got status 0x0001, #012) Aug 29 15:05:01 lab CRON[5925]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1) Aug 29 15:10:01 lab CRON[5930]: (root) CMD (test -x /usr/lib/atsar/atsa1 && /usr/lib/atsar/atsa1) Aug 29 15:10:01 lab CRON[5928]: (CRON) error (grandchild #5930 failed with exit status 1) Aug 29 15:13:21 lab pulseaudio[3361]: ratelimit.c: 387 events suppressed End lastlog exit
使用Deferred對象
reactor是一個循環，這個循環在等待事件的發生。 這裏的事件可以是數據庫操作，也可以是長時間的計算操作。 只要這些操作可以返回一個Deferred對象。Deferred對象可以自動得在事件發生時觸發回調函數。reactor會block當前代碼的執行。
現在我們要使用Defferred對象來計算SHA1哈希。
import sys import os import hashlib from twisted.internet.protocol import ServerFactory, ProcessProtocol from twisted.protocols.basic import LineReceiver from twisted.python import log from twisted.internet import reactor, threads class TailProtocol(ProcessProtocol): def __init__(self, write_callback): self.write = write_callback def outReceived(self, data): self.write("Begin lastlog\n") data = [line for line in data.split('\n') if not line.startswith('==')] for d in data: self.write(d + '\n') self.write("End lastlog\n") def processEnded(self, reason): if reason.value.exitCode != 0: log.msg(reason) class HashCompute(object): def __init__(self, path, write_callback): self.path = path self.write = write_callback def blockingMethod(self): os.path.isfile(self.path) data = file(self.path).read() # uncomment to add more delay # import time # time.sleep(10) return hashlib.sha1(data).hexdigest() def compute(self): d = threads.deferToThread(self.blockingMethod) d.addCallback(self.ret) d.addErrback(self.err) def ret(self, hdata): self.write("File hash is : %s\n" % hdata) def err(self, failure): self.write("An error occured : %s\n" % failure.getErrorMessage()) class CmdProtocol(LineReceiver): delimiter = '\n' def processCmd(self, line): if line.startswith('lastlog'): tailProtocol = TailProtocol(self.transport.write) reactor.spawnProcess(tailProtocol, '/usr/bin/tail', args=['/usr/bin/tail', '-10', '/var/log/syslog']) elif line.startswith('comphash'): try: useless, path = line.split(' ') except: self.transport.write('Please provide a path.\n') return hc = HashCompute(path, self.transport.write) hc.compute() elif line.startswith('exit'): self.transport.loseConnection() else: self.transport.write('Command not found.\n') def connectionMade(self): self.client_ip = self.transport.getPeer()[1] log.msg("Client connection from %s" % self.client_ip) if len(self.factory.clients) >= self.factory.clients_max: log.msg("Too many connections. bye !") self.client_ip = None self.transport.loseConnection() else: self.factory.clients.append(self.client_ip) def connectionLost(self, reason): log.msg('Lost client connection. Reason: %s' % reason) if self.client_ip: self.factory.clients.remove(self.client_ip) def lineReceived(self, line): log.msg('Cmd received from %s : %s' % (self.client_ip, line)) self.processCmd(line) class MyFactory(ServerFactory): protocol = CmdProtocol def __init__(self, clients_max=10): self.clients_max = clients_max self.clients = [] log.startLogging(sys.stdout) reactor.listenTCP(9999, MyFactory(2)) reactor.run()
blockingMethod從文件系統讀取一個文件計算SHA1，這裏我們使用twisted的deferToThread方法，這個方法返回一個Deferred對象。這裏的Deferred對象是調用後馬上就返回了，這樣主進程就可以繼續執行處理其他的事件。當傳給deferToThread的方法執行完畢後會馬上觸發其回調函數。如果執行中出錯，blockingMethod方法會拋出異常。如果成功執行會通過hdata的ret返回計算的結果。
codego.net代碼節選