INTERNET PROTOCOLS (lập TRÌNH MẠNG cơ bản SLIDE)

INTERNET PROTOCOLS


Objective
 URL class in Java
 SMTP
 POP3
 FTP

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Uniform Resource Locator: URL

 Hierarchy of Classes
 Methods of the Class
 Examples of Using the Class

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Hierarchy of Classes

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URL Class

 Class URL is a description of a resource location on the Internet.
 Complete URL: :1547/~john/pub/index.html
-- protocol : http://
-- host : www.cs.joensuu.f
-- port : 1547
-- path : ~smith/pub/index.html

 Java provides a class—java.net.URL—to manipulate
URLs.

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Methods of URL Class
• URL(String

url): create an object using the string parameter (exception

MalformedURLException).

• URL(String, String, String): protocol, host, path of the resource.
• String toString(): return the URL as a strings.
• String getHost(): return the name of the host linked to this URL.
• String getProtocol(): return le protocol of this URL.
• String getPort(): return the number of the associate port.

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Methods of URL Class

• InputStream openStream(): realize the connection to the URL previously
instantiated.
• An InputStream object is returned and permits to retrieve information specifed

into the URL.
• If the connection fails, the exception IOException is raised.

String getContentType();
String getContentLength();
long getLastModified();

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Creating a URL Instance
 The following statement creates a Java URL object:

String str = "”;
try
{

URL location = new URL(str);
}
catch(MalformedURLException ex){ }

 You can also build a URL by setting each part individually:
URL u = new URL(“http”, www.cs.rpi.edu,80,”/~hollingd/”);

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Retrieving Remote Files
Rather than reading the fle from the local system, this example reads the fle
from a Web server.
private void showFile() {
URL url = null;
try

{

url = new URL(urlString);
InputStream is = url.openStream();
infile = new BufferedReader(
new InputStreamReader(is));
}
catch (FileNotFoundException e) {
catch (IOException e) {

...

...

}

}

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Retrieving a Resource with the URL Class
import java.net.*;
import java.io.*;
public class FtpUrls {
public static void main(String[] args) throws IOException {
// URL url = new URL("ftp://pvtinh:/t.txt");
URL url = new URL("http://192.168.1.2/cackhoa.html");
InputStream uin = url.openStream();
BufferedReader in = new BufferedReader(new
InputStreamReader(uin));
String line;
while ((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
}
}
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SMTP

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Format of an email

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Commands and response

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Command

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Response

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Response (con)

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Status code
 The Server responds with a 3 digit code that may be followed by text info
 2## - Success
 3## - Command can be accepted with

more information

 4## - Command was rejected, but error

condition is temporary

 5## - Command rejected, Bad User!

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Connection establishment

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F

Message transfer

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F

Connection termination

20

TCP/IP Protocol Suite

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Example
Let us see how we can directly use SMTP to send an email and simulate the commands and responses we described in this section. We
use TELNET to log into port 25 (the well-known port for SMTP). We then use the commands directly to send an email. In this
example, is sending an email to himself. The first few lines show TELNET trying to connect to the adelphia
mail server.

$ telnet mail.adelphia.net 25
Trying 68.168.78.100...
Connected to mail.adelphia.net (68.168.78.100).

After connection, we can type the SMTP commands and then receive the responses as shown below. We have shown the commands in
black and the responses in color. Note that we have added for clarification some comment lines, designated by the “=” sign. These
lines are not part of the email procedure.

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Example
================== Connection Establishment ================
220 mta13.adelphia.net SMTP server ready Fri, 6 Aug 2004 . . .
HELO mail.adelphia.net
250 mta13.adelphia.net
===================== Envelope ===================
MAIL FROM:
250 Sender <> Ok

RCPT TO:
250 Recipient <> Ok
=================== Header and Body ==================
DATA
354 Ok Send data ending with <CRLF>.<CRLF>
From: Forouzan
TO: Forouzan

This is a test message
to show SMTP in action.
.
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Example

============= Connection Termination===============
250 Message received:
QUIT
221 mta13.adelphia.net SMTP server closing connection
Connection closed by foreign host.

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SMTP & Sending E-Mail

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Simple Mail Transfer Protocol - RFC 821
 To send e-mail, you make a socket connection to port 25, the SMTP port. SMTP is the Simple Mail
Transport Protocol that describes the format for e-mail messages.

 Open a socket to your host.
Socket s = new Socket("mail.yourserver.com", 25);
PrintWriter out = new PrintWriter(s.getOutputStream());

 Send the following information to the print stream:
HELO sending host # Domain name
MAIL FROM:<sender email address>
RCPT TO:<recipient email address>
DATA
mail message
(any number of lines)

.
QUIT

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