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CHAPTER 14 DEVELOPING A TRANSPORT CHANNEL
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Encapsulating the Protocols
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Now that you ve got some of the protocol basics down, you re ready for the source code for this channel. Okay, here goes. First you have to encapsulate the SMTP and POP3 protocols that are later used in the client-side and server-side transport channel sinks. The first part of this is shown in Listing 14-1. This source file encapsulates the lower-level SMTP protocol. It provides a public constructor that needs the hostname of your SMTP-server as a parameter. Its SendMessage() method takes the sender s and recipient s e-mail address and the full e-mail s text (including the headers) as parameters. It then connects to the SMTP server and sends the specified mail. Listing 14-1. Encapsulating the Lower-Level SMTP Protocol using using using using using System; System.Net.Sockets; System.Net; System.IO; System.Text;
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namespace SmtpChannel { public class SmtpConnection { private String _hostname; private TcpClient _SmtpConnection; private NetworkStream _smtpStream; private StreamReader _smtpResponse; public SmtpConnection(String hostname) { _hostname = hostname; } private void Connect() { _SmtpConnection = new TcpClient(_hostname,25); _smtpStream = _SmtpConnection.GetStream(); _smtpResponse = new StreamReader(_smtpStream); } private void Disconnect() { _smtpStream.Close(); _smtpResponse.Close(); _SmtpConnection.Close(); } private void SendCommand(String command, int expectedResponseClass) { // command: the SMTP command to send // expectedResponseClass: first digit of the expected smtp response
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CHAPTER 14 DEVELOPING A TRANSPORT CHANNEL
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// throws an exception if the server's responsecode's first // digit (resonse class) is > the expectedResponseClass. // if expectedResponseClass == 0, it will be ignored command = command + "\r\n"; byte[] cmd = Encoding.ASCII.GetBytes(command); _smtpStream.Write(cmd,0,cmd.Length); String response = _smtpResponse.ReadLine(); if (expectedResponseClass != 0) { int resp = Convert.ToInt32(response.Substring(0,1)); if (resp > expectedResponseClass) { throw new Exception("SMTP Server returned unexpected " + "response:\n'" + response + "'"); } } } public void SendMessage(String from, String to, String text) { try { Connect(); SendCommand("HELO localhost",2); SendCommand("MAIL FROM: <" + from + ">",2); SendCommand("RCPT TO: <" + to + ">",2); SendCommand("DATA",3); byte[] bodybytes = Encoding.ASCII.GetBytes(text + "\r\n"); _smtpStream.Write(bodybytes,0,bodybytes.Length); SendCommand(".",3); SendCommand("QUIT",0); } finally { try { Disconnect(); } catch (Exception e) {/*ignore*/}; } } } } To encapsulate the POP3 protocol, you first have to add a class that will hold the parsed message and its headers. This is shown in Listing 14-2. Listing 14-2. A Retrieved and Parsed Message using System; using System.Collections;
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CHAPTER 14 DEVELOPING A TRANSPORT CHANNEL
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namespace SmtpChannel { public class POP3Msg { public String From; public String To; public String Body; public String Headers; public String MessageId; public String InReplyTo; } } The helper class POP3Connection encapsulates the lower-level details of the POP3 protocol. After construction, it connects to the server, authenticates the user, and issues a LIST command to retrieve the list of messages waiting. using using using using using using System; System.Net.Sockets; System.Net; System.IO; System.Collections; System.Text;
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namespace SmtpChannel { public class POP3Connection { private class MessageIndex { // will be used to store the result of the LIST command internal int Number; internal int Bytes; internal MessageIndex(int num, int msgbytes) { Number = num; Bytes = msgbytes; } } private String _hostname; private String _username; private String _password; private private private private TcpClient _pop3Connection; NetworkStream _pop3Stream; StreamReader _pop3Response; IDictionary _msgs;
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CHAPTER 14 DEVELOPING A TRANSPORT CHANNEL
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public POP3Connection(String hostname, String username, String password) { // try to connect to the server with the supplied username // and password. _hostname = hostname; _username = username; _password = password; try { Connect(); } catch (Exception e) { try { Disconnect(); } catch (Exception ex) {/* ignore */} throw e; } } private void Connect() { // initialize the list of messages _msgs = new Hashtable(); // open the connection _pop3Connection = new TcpClient(_hostname,110); _pop3Stream = _pop3Connection.GetStream(); _pop3Response = new StreamReader(_pop3Stream); // ignore first line (server's greeting) String response = _pop3Response.ReadLine(); // authenticate SendCommand("USER " + _username,true); SendCommand("PASS " + _password,true); // retrieve the list of messages SendCommand("LIST",true); response = _pop3Response.ReadLine(); while (response != ".") { // add entries to _msgs dictionary int pos = response.IndexOf(" ");
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