<?xml version="1.0"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en"><head><title>Twisted Documentation: Writing a client with Twisted.Conch</title><link href="../howto/stylesheet.css" type="text/css" rel="stylesheet" /></head><body bgcolor="white"><h1 class="title">Writing a client with Twisted.Conch</h1><div class="toc"><ol><li><a href="#auto0">Introduction</a></li><li><a href="#auto1">Writing a client</a></li><li><a href="#auto2">The Transport</a></li><li><a href="#auto3">The Authorization Client</a></li><li><a href="#auto4">The Connection</a></li><li><a href="#auto5">The Channel</a></li><li><a href="#auto6">The main() function</a></li></ol></div><div class="content"><span></span><h2>Introduction<a name="auto0"></a></h2><p>In the original days of computing, rsh/rlogin were used to connect to remote computers and execute commands. These commands had the problem that the passwords and commands were sent in the clear. To solve this problem, the SSH protocol was created. Twisted.Conch implements the second version of this protocol.</p><h2>Writing a client<a name="auto1"></a></h2><p>Writing a client with Conch involves sub-classing 4 classes: <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.conch.ssh.transport.SSHClientTransport.html" title="twisted.conch.ssh.transport.SSHClientTransport">twisted.conch.ssh.transport.SSHClientTransport</a></code>, <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.conch.ssh.userauth.SSHUserAuthClient.html" title="twisted.conch.ssh.userauth.SSHUserAuthClient">twisted.conch.ssh.userauth.SSHUserAuthClient</a></code>, <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.conch.ssh.connection.SSHConnection.html" title="twisted.conch.ssh.connection.SSHConnection">twisted.conch.ssh.connection.SSHConnection</a></code>, and <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.conch.ssh.channel.SSHChannel.html" title="twisted.conch.ssh.channel.SSHChannel">twisted.conch.ssh.channel.SSHChannel</a></code>. We'll start out with <code class="python">SSHClientTransport</code> because it's the base of the client.</p><h2>The Transport<a name="auto2"></a></h2><pre class="python"> <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">conch</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">error</span><span class="py-src-newline"> </span><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">conch</span><span class="py-src-op">.</span><span class="py-src-variable">ssh</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">transport</span><span class="py-src-newline"> </span><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">defer</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-keyword">class</span> <span class="py-src-identifier">ClientTransport</span><span class="py-src-op">(</span><span class="py-src-parameter">transport</span><span class="py-src-op">.</span><span class="py-src-parameter">SSHClientTransport</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">def</span> <span class="py-src-identifier">verifyHostKey</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">,</span> <span class="py-src-parameter">pubKey</span><span class="py-src-op">,</span> <span class="py-src-parameter">fingerprint</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">if</span> <span class="py-src-variable">fingerprint</span> <span class="py-src-op">!=</span> <span class="py-src-string">'b1:94:6a:c9:24:92:d2:34:7c:62:35:b4:d2:61:11:84'</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">return</span> <span class="py-src-variable">defer</span><span class="py-src-op">.</span><span class="py-src-variable">fail</span><span class="py-src-op">(</span><span class="py-src-variable">error</span><span class="py-src-op">.</span><span class="py-src-variable">ConchError</span><span class="py-src-op">(</span><span class="py-src-string">'bad key'</span><span class="py-src-op">)</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">else</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">return</span> <span class="py-src-variable">defer</span><span class="py-src-op">.</span><span class="py-src-variable">succeed</span><span class="py-src-op">(</span><span class="py-src-number">1</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">connectionSecure</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">requestService</span><span class="py-src-op">(</span><span class="py-src-variable">ClientUserAuth</span><span class="py-src-op">(</span><span class="py-src-string">'user'</span><span class="py-src-op">,</span> <span class="py-src-variable">ClientConnection</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-op">)</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-dedent"></span><span class="py-src-dedent"></span><span class="py-src-endmarker"></span></pre><p>See how easy it is? <code class="python">SSHClientTransport</code> handles the negotiation of encryption and the verification of keys for you. The one security element that you as a client writer need to implement is <code class="python">verifyHostKey()</code>. This method is called with two strings: the public key sent by the server and its fingerprint. You should verify the host key the server sends, either by checking against a hard-coded value as in the example, or by asking the user. <code class="python">verifyHostKey</code> returns a <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.internet.defer.Deferred.html" title="twisted.internet.defer.Deferred">twisted.internet.defer.Deferred</a></code> which gets a callback if the host key is valid, or an errback if it is not. Note that in the above, replace 'user' with the username you're attempting to ssh with, for instance a call to <code class="python">os.getlogin()</code> for the current user.</p><p>The second method you need to implement is <code class="python">connectionSecure()</code>. It is called when the encryption is set up and other services can be run. The example requests that the <code class="python">ClientUserAuth</code> service be started. This service will be discussed next.</p><h2>The Authorization Client<a name="auto3"></a></h2><pre class="python"> <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">conch</span><span class="py-src-op">.</span><span class="py-src-variable">ssh</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">keys</span><span class="py-src-op">,</span> <span class="py-src-variable">userauth</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-comment"># these are the public/private keys from test_conch </span><span class="py-src-nl"> </span><span class="py-src-variable">publicKey</span> <span class="py-src-op">=</span> <span class="py-src-string">'ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAGEArzJx8OYOnJmzf4tfBEvLi8DVPrJ3\ /c9k2I/Az64fxjHf9imyRJbixtQhlH9lfNjUIx+4LmrJH5QNRsFporcHDKOTwTTYLh5KmRpslkYHR\ ivcJSkbh/C+BR3utDS555mV'</span> <span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-variable">privateKey</span> <span class="py-src-op">=</span> <span class="py-src-string">"""-----BEGIN RSA PRIVATE KEY----- MIIByAIBAAJhAK8ycfDmDpyZs3+LXwRLy4vA1T6yd/3PZNiPwM+uH8Yx3/YpskSW 4sbUIZR/ZXzY1CMfuC5qyR+UDUbBaaK3Bwyjk8E02C4eSpkabJZGB0Yr3CUpG4fw vgUd7rQ0ueeZlQIBIwJgbh+1VZfr7WftK5lu7MHtqE1S1vPWZQYE3+VUn8yJADyb Z4fsZaCrzW9lkIqXkE3GIY+ojdhZhkO1gbG0118sIgphwSWKRxK0mvh6ERxKqIt1 xJEJO74EykXZV4oNJ8sjAjEA3J9r2ZghVhGN6V8DnQrTk24Td0E8hU8AcP0FVP+8 PQm/g/aXf2QQkQT+omdHVEJrAjEAy0pL0EBH6EVS98evDCBtQw22OZT52qXlAwZ2 gyTriKFVoqjeEjt3SZKKqXHSApP/AjBLpF99zcJJZRq2abgYlf9lv1chkrWqDHUu DZttmYJeEfiFBBavVYIF1dOlZT0G8jMCMBc7sOSZodFnAiryP+Qg9otSBjJ3bQML pSTqy7c3a2AScC/YyOwkDaICHnnD3XyjMwIxALRzl0tQEKMXs6hH8ToUdlLROCrP EhQ0wahUTCk1gKA4uPD6TMTChavbh4K63OvbKg== -----END RSA PRIVATE KEY-----"""</span> <span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-keyword">class</span> <span class="py-src-identifier">ClientUserAuth</span><span class="py-src-op">(</span><span class="py-src-parameter">userauth</span><span class="py-src-op">.</span><span class="py-src-parameter">SSHUserAuthClient</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">def</span> <span class="py-src-identifier">getPassword</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">,</span> <span class="py-src-parameter">prompt</span> <span class="py-src-op">=</span> <span class="py-src-parameter">None</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">return</span> <span class="py-src-newline"> </span> <span class="py-src-comment"># this says we won't do password authentication </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">getPublicKey</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">return</span> <span class="py-src-variable">keys</span><span class="py-src-op">.</span><span class="py-src-variable">getPublicKeyString</span><span class="py-src-op">(</span><span class="py-src-variable">data</span> <span class="py-src-op">=</span> <span class="py-src-variable">publicKey</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">getPrivateKey</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">return</span> <span class="py-src-variable">defer</span><span class="py-src-op">.</span><span class="py-src-variable">succeed</span><span class="py-src-op">(</span><span class="py-src-variable">keys</span><span class="py-src-op">.</span><span class="py-src-variable">getPrivateKeyObject</span><span class="py-src-op">(</span><span class="py-src-variable">data</span> <span class="py-src-op">=</span> <span class="py-src-variable">privateKey</span><span class="py-src-op">)</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-dedent"></span><span class="py-src-dedent"></span><span class="py-src-endmarker"></span></pre><p>Again, fairly simple. The <code class="python">SSHUserAuthClient</code> takes care of most of the work, but the actual authentication data needs to be supplied. <code class="python">getPassword()</code> asks for a password, <code class="python">getPublicKey()</code> and <code class="python">getPrivateKey()</code> get public and private keys, respectively. <code class="python">getPassword()</code> returns a <code class="python">Deferred</code> that is called back with the password to use. <code class="python">getPublicKey()</code> returns the SSH key data for the public key to use. <code class="python">keys.getPublicKeyString()</code> will take keys in OpenSSH and LSH format, and convert them to the required format. <code class="python">getPrivateKey()</code> returns a <code class="python">Deferred</code> which is called back with the key object (as used in PyCrypto) for the private key. <code class="python">getPassword()</code> and <code class="python">getPrivateKey()</code> return <code class="python">Deferreds</code> because they may need to ask the user for input.</p><p>Once the authentication is complete, <code class="python">SSHUserAuthClient</code> takes care of starting the code <code class="python">SSHConnection</code> object given to it. Next, we'll look at how to use the <code class="python">SSHConnection</code></p><h2>The Connection<a name="auto4"></a></h2><pre class="python"> <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">conch</span><span class="py-src-op">.</span><span class="py-src-variable">ssh</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">connection</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-keyword">class</span> <span class="py-src-identifier">ClientConnection</span><span class="py-src-op">(</span><span class="py-src-parameter">connection</span><span class="py-src-op">.</span><span class="py-src-parameter">SSHConnection</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">def</span> <span class="py-src-identifier">serviceStarted</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">openChannel</span><span class="py-src-op">(</span><span class="py-src-variable">CatChannel</span><span class="py-src-op">(</span><span class="py-src-variable">conn</span> <span class="py-src-op">=</span> <span class="py-src-variable">self</span><span class="py-src-op">)</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-dedent"></span><span class="py-src-dedent"></span><span class="py-src-endmarker"></span></pre><p><code class="python">SSHConnection</code> is the easiest, as it's only responsible for starting the channels. It has other methods, those will be examined when we look at <code class="python">SSHChannel</code>.</p><h2>The Channel<a name="auto5"></a></h2><pre class="python"> <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">conch</span><span class="py-src-op">.</span><span class="py-src-variable">ssh</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">channel</span><span class="py-src-op">,</span> <span class="py-src-variable">common</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-keyword">class</span> <span class="py-src-identifier">CatChannel</span><span class="py-src-op">(</span><span class="py-src-parameter">channel</span><span class="py-src-op">.</span><span class="py-src-parameter">SSHChannel</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-indent"> </span><span class="py-src-variable">name</span> <span class="py-src-op">=</span> <span class="py-src-string">'session'</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-keyword">def</span> <span class="py-src-identifier">channelOpen</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">,</span> <span class="py-src-parameter">data</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">d</span> <span class="py-src-op">=</span> <span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">conn</span><span class="py-src-op">.</span><span class="py-src-variable">sendRequest</span><span class="py-src-op">(</span><span class="py-src-variable">self</span><span class="py-src-op">,</span> <span class="py-src-string">'exec'</span><span class="py-src-op">,</span> <span class="py-src-variable">common</span><span class="py-src-op">.</span><span class="py-src-variable">NS</span><span class="py-src-op">(</span><span class="py-src-string">'cat'</span><span class="py-src-op">)</span><span class="py-src-op">,</span><span class="py-src-nl"> </span> <span class="py-src-variable">wantReply</span> <span class="py-src-op">=</span> <span class="py-src-number">1</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">d</span><span class="py-src-op">.</span><span class="py-src-variable">addCallback</span><span class="py-src-op">(</span><span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">_cbSendRequest</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">catData</span> <span class="py-src-op">=</span> <span class="py-src-string">''</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">_cbSendRequest</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">,</span> <span class="py-src-parameter">ignored</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">write</span><span class="py-src-op">(</span><span class="py-src-string">'This data will be echoed back to us by "cat."\r\n'</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">conn</span><span class="py-src-op">.</span><span class="py-src-variable">sendEOF</span><span class="py-src-op">(</span><span class="py-src-variable">self</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">loseConnection</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">dataReceived</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">,</span> <span class="py-src-parameter">data</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">catData</span> <span class="py-src-op">+=</span> <span class="py-src-variable">data</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span> <span class="py-src-dedent"></span><span class="py-src-keyword">def</span> <span class="py-src-identifier">closed</span><span class="py-src-op">(</span><span class="py-src-parameter">self</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-keyword">print</span> <span class="py-src-string">'We got this from "cat":'</span><span class="py-src-op">,</span> <span class="py-src-variable">self</span><span class="py-src-op">.</span><span class="py-src-variable">catData</span><span class="py-src-newline"> </span><span class="py-src-dedent"></span><span class="py-src-dedent"></span><span class="py-src-endmarker"></span></pre><p>Now that we've spent all this time getting the server and client connected, here is where that work pays off. <code class="python">SSHChannel</code> is the interface between you and the other side. This particular channel opens a session and plays with the 'cat' program, but your channel can implement anything, so long as the server supports it.</p><p>The <code class="python">channelOpen()</code> method is where everything gets started. It gets passed a chunk of data; however, this chunk is usually nothing and can be ignored. Our <code class="python">channelOpen()</code> initializes our channel, and sends a request to the other side, using the <code class="python">sendRequest()</code> method of the <code class="python">SSHConnection</code> object. Requests are used to send events to the other side. We pass the method self so that it knows to send the request for this channel. The 2nd argument of 'exec' tells the server that we want to execute a command. The third argument is the data that accompanies the request. <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/common.NS.html" title="common.NS">common.NS</a></code> encodes the data as a length-prefixed string, which is how the server expects the data. We also say that we want a reply saying that the process has a been started. <code class="python">sendRequest()</code> then returns a <code class="python">Deferred</code> which we add a callback for.</p><p>Once the callback fires, we send the data. <code class="python">SSHChannel</code> supports the <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/ twisted.internet.interface.Transport.html" title=" twisted.internet.interface.Transport"> twisted.internet.interface.Transport</a></code> interface, so it can be given to Protocols to run them over the secure connection. In our case, we just write the data directly. <code class="python">sendEOF()</code> does not follow the interface, but Conch uses it to tell the other side that we will write no more data. <code class="python">loseConnection()</code> shuts down our side of the connection, but we will still receive data through <code class="python">dataReceived()</code>. The <code class="python">closed()</code> method is called when both sides of the connection are closed, and we use it to display the data we received (which should be the same as the data we sent.)</p><p>Finally, let's actually invoke the code we've set up.</p><h2>The main() function<a name="auto6"></a></h2><pre class="python"> <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span><span class="py-src-op">.</span><span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">protocol</span><span class="py-src-op">,</span> <span class="py-src-variable">reactor</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-keyword">def</span> <span class="py-src-identifier">main</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">factory</span> <span class="py-src-op">=</span> <span class="py-src-variable">protocol</span><span class="py-src-op">.</span><span class="py-src-variable">ClientFactory</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">factory</span><span class="py-src-op">.</span><span class="py-src-variable">protocol</span> <span class="py-src-op">=</span> <span class="py-src-variable">ClientTransport</span><span class="py-src-newline"> </span> <span class="py-src-variable">reactor</span><span class="py-src-op">.</span><span class="py-src-variable">connectTCP</span><span class="py-src-op">(</span><span class="py-src-string">'localhost'</span><span class="py-src-op">,</span> <span class="py-src-number">22</span><span class="py-src-op">,</span> <span class="py-src-variable">factory</span><span class="py-src-op">)</span><span class="py-src-newline"> </span> <span class="py-src-variable">reactor</span><span class="py-src-op">.</span><span class="py-src-variable">run</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-nl"> </span><span class="py-src-dedent"></span><span class="py-src-keyword">if</span> <span class="py-src-variable">__name__</span> <span class="py-src-op">==</span> <span class="py-src-string">"__main__"</span><span class="py-src-op">:</span><span class="py-src-newline"> </span><span class="py-src-indent"> </span><span class="py-src-variable">main</span><span class="py-src-op">(</span><span class="py-src-op">)</span><span class="py-src-newline"> </span><span class="py-src-dedent"></span><span class="py-src-endmarker"></span></pre><p>We call <code class="python">connectTCP()</code> to connect to localhost, port 22 (the standard port for ssh), and pass it an instance of <code class="API"><a href="http://twistedmatrix.com/documents/TwistedDocs/TwistedDocs-1.3.0/api/twisted.internet.protocol.ClientFactory.html" title="twisted.internet.protocol.ClientFactory">twisted.internet.protocol.ClientFactory</a></code>. This instance has the attribute <code class="python">protocol</code> set to our earlier <code class="python">ClientTransport</code> class. Note that the protocol is set to the class <code class="python">ClientFactory</code>, not an instance of <code class="python">ClientFactory</code>! When the <code class="python">connectTCP</code> call completes, the protocol will be called to create a <code class="python">ClientTransport()</code> object - this then invokes all our previous work.</p><p>It's worth noting that in the example <code class="python">main()</code> routine, the <code class="python">reactor.run()</code> call never returns. If you want to make the program exit, call <code class="python">reactor.stop()</code> in the earlier <code class="python">closed()</code> method.</p><p>If you wish to observe the interactions in more detail, adding a call to <code class="python">log.startLogging(sys.stdout, setStdout=0)</code> before the <code class="python">reactor.run()</code> call will send all logging to stdout.</p></div><p><a href="../howto/index.html">Index</a></p><span class="version">Version: 1.3.0</span></body></html>