SDSU Client-Server Programming
Spring Semester, 2005
HTTP & POP
Previous     Lecture Notes Index     Next     
© 2005 All Rights Reserved, SDSU & Roger Whitney
San Diego State University -- This page last updated March 22, 2005

CS 580 Client-Server Programming

Spring Semester, 2005

Doc 14 HTTP & POP

Contents

 

HTTP    

HTTP Message Format    

Client Request    

Full-Request    

Server Response    

Request Methods    

POP3 Protocol    

Command Format    

States    

Commands    

Optional POP3 Commands    

 

 

Copyright ©, All rights reserved. 2005 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent ( http://www.opencontent.org/opl.shtml ) license defines the copyright on this document.

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 2

 

References

 

Hypertext Transfer Protocol - HTTP/1.0, Berners-Lee, Fielding, Nielson, rfc1945, http://www.w3.org/Protocols/rfc1945/rfc1945

 

Hypertext Transfer Protocol -- HTTP/1.1, Fielding, Gettys, Mogul, Masinter, Leach, Berners-Lee, rfc2616, http://www.w3.org/Protocols/rfc2616/rfc2616.html

 

Uniform Resource Identifiers (URI): Generic Syntax, Berners-Lee, Fielding, Masinter, rfc2396 http://www.ietf.org/rfc/rfc2396.txt

 

RFC 1939, http://www.ietf.org/rfc/rfc1939.txt

 

 

Reading

 

HTTP/1.0 rfc1945, http://ftp.ics.uci.edu/pub/ietf/http/rfc1945.html

 

Post Office Protocol RFC 1939, http://www.ietf.org/rfc/rfc1939.txt

CS580 Spring 2005Doc 14, HTTP & POP Slide # 3

 

HTTP

 

  1. Stateless (http 1.0)

  1. Object-oriented protocol

 

The typing and negotiation of data representation, allows systems to be built independently of the data being transferred

 

Assigned port 80

 

 

Basic Server-Client Interaction (http 1.0)

 

Client:    Open connection

 

Server:     Accept/Reject connection

 

Client:    Send request

 

Server:    Send response to request

 

Connection closed

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 4

 

HTTP Message Format

 

HTTP-message   =    Simple-Request         (HTTP/0.9 messages)

    | Simple-Response

    | Full-Request                    (HTTP/1.0 messages)

    | Full-Response

    

    

Full-Request   =    Request-Line

    *( General-Header   | Request-Header  | Entity-Header )

    CRLF

    [ Entity-Body ]

    

    

Full-Response  =     Status-Line      

    *( General-Header   | Request-Header   | Entity-Header )

    CRLF

    [ Entity-Body ]

    

    

HTTP-header    = field-name ":" [ field-value ] CRLF

    

Entity-Body    = *OCTET

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 5

 

Client Request

 

Request    = Simple-Request | Full-Request

Simple-Request = "GET" SP Request-URI CRLF

 

Simple-Request Example

 

rohan 11-> telnet www.eli.sdsu.edu 80

Trying 130.191.226.80...

Connected to www.eli.sdsu.edu.

Escape character is '^]'.

GET /courses/fall00/cs580/index.html

<HTML>

<HEAD>

        <TITLE>CS 580: Course Web Site</TITLE>

</HEAD>

<BODY BGCOLOR="#FFFFFF">

 

<TABLE BORDER=0 WIDTH="100%">

 

…stuff removed…

 

</sub>Visitors since 21-Aug-00

</center>

</BODY>

</HTML>

Connection closed by foreign host.

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 6

 

Full-Request

Full-Request   =    Request-Line

    *( General-Header   | Request-Header   | Entity-Header )

    CRLF

    [ Entity-Body ]

 

Request-Line   = Method SP URI SP HTTP-Version CRLF

 

rohan 13-> telnet www.eli.sdsu.edu 80

Trying 130.191.226.80...

Connected to www.eli.sdsu.edu.

Escape character is '^]'.

GET /courses/fall00/cs580/index.html HTTP/1.0

 

HTTP/1.1 200 OK

Date: Tue, 05 Sep 2000 19:31:14 GMT

Server: Apache/1.3.9 (Unix) PHP/3.0.12

Last-Modified: Mon, 04 Sep 2000 21:03:56 GMT

ETag: "14c199-7e8-39b40e3c"

Accept-Ranges: bytes

Content-Length: 2024

Connection: close

Content-Type: text/html

X-Pad: avoid browser bug

 

<HTML>

<HEAD>

        <TITLE>CS 580: Course Web Site</TITLE>

</HTML>

… stuff removed here…

Connection closed by foreign host.

Note 2 CRLF are needed to end the full request

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 7

 

HTTP 1.1 Example

 

rohan 14-> telnet www.eli.sdsu.edu 80

Trying 130.191.226.80...

Connected to www.eli.sdsu.edu.

Escape character is '^]'.

GET /courses/fall00/cs580/index.html HTTP/1.1

Connection: close

Host: www.eli.sdsu.edu

 

HTTP/1.1 200 OK

Date: Tue, 05 Sep 2000 22:41:26 GMT

Server: Apache/1.3.9 (Unix) PHP/3.0.12

Last-Modified: Mon, 04 Sep 2000 21:03:56 GMT

ETag: "14c199-7e8-39b40e3c"

Accept-Ranges: bytes

Content-Length: 2024

Connection: close

Content-Type: text/html

X-Pad: avoid browser bug

 

<HTML>

<HEAD>

        <TITLE>CS 580: Course Web Site</TITLE>

</HEAD>

…stuff removed here…

</BODY>

</HTML>

Connection closed by foreign host.

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 8

 

Server Response

 

Example Full-response

 

HTTP/1.0 200 Document follows

MIME-Version: 1.0

Server: CERN/3.0

Date: Thursday, 21-Mar-96 17:00:45 GMT

Content-Type: text/html

Content-Length: 2686

Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

 

 

field-name

field-value

MIME-Version:

1.0

Server:

CERN/3.0

Date:

Thursday, 21-Mar-96 17:00:45 GMT

Content-Type:

text/html

Content-Length:

2686

Last-Modified:

Tuesday, 27-Feb-96 05:34:12 GMT

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 9

 

What is the big Deal?

 

image-0.pict

 

 

What are the data fields in this?

 

1.0; CERN/3.0; Thursday, 21-Mar-96 17:00:45 GMT; text/html; 2686; Tuesday, 27-Feb-96 05:34:12 GMT

 

 

What are the data fields in this?

 

MIME-Version: 1.0

Server: CERN/3.0

Date: Thursday, 21-Mar-96 17:00:45 GMT

Content-Type: text/html

Content-Length: 2686

Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

 

Which is Safer?

 

Which is Easier to Parse?

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 10

 

Name -Value Pairs are Good

 

Does Order Matter?

 

MIME-Version: 1.0

Server: CERN/3.0

Date: Thursday, 21-Mar-96 17:00:45 GMT

Content-Type: text/html

Content-Length: 2686

Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

 

Server: CERN/3.0

Content-Type: text/html

MIME-Version: 1.0

Content-Length: 2686

Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

Date: Thursday, 21-Mar-96 17:00:45 GMT

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 11

 

Extending Protocols

 

MIME-Version: 1.0

Server: CERN/3.0

Date: Thursday, 21-Mar-96 17:00:45 GMT

Content-Type: text/html

Forwarded: by http://rohan.sdsu.edu/ for cs.sdsu.edu

Content-Length: 2686

WhitneyInfo : Hi Mom

Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

 

 

Cookies were added to HTTP by adding a new name-value pair

 

Clients/servers that were not programmed for cookies ignored the new name-value pair

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 12

 

Name -Value Pairs are Everywhere

 

Data Files

Which is easier for a program to parse?

Which is safer

 

Allen, Sally

87

92

85

55

74

10

Battista, Joe

92

98

98

55

78

10

Biag, Sam

83

91

78

51

72

8

Chen, Pete

89

92

89

57

79

10

Chen, Roger

74

68

59

61

55

10

 

 

 

name

course

hwork

exam1

exam2

final

as1

Allen, Sally

87

92

85

55

74

10

Battista, Joe

92

98

98

55

78

10

Biag, Sam

83

91

78

51

72

8

Chen, Pete

89

92

89

57

79

10

Chen, Roger

74

68

59

61

55

10

 

 

lastName:Allen, lastName:Sally, course:87, hwork:92, exam1:85, exam2:55, final:74, as1:10

lastName:Battista, lastName:Joe, course:92, hwork:98, exam1:98, exam2:55, final:78, as1:10

lastName:Baig, lastName:Sam, course:83, hwork:91, exam1:78, exam2:51, final:72, as1:8

lastName:Chen, lastName:Pete, course:89, hwork:92, exam1:89, exam2:57, final:79, as1:10

lastName:Chen, lastName:Roger, course:74, hwork:68, exam1:59, exam2:61, final:55, as1:10

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 13

 

Name-Value Pairs and Parameters

 

Most languages use positional matching for parameters

 

“The cat in the hat came back”.substring( 2, 6);

 

 

Smallktalk uses name-value pairs

 

 ‘The cat in the hat came back’ copyFrom: 2 to: 6

 

copyFrom:to: is on method

 

Keyword (name)

Parameter (value)

copyFrom:

2

to:

6

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 14

 

Name -Value Pairs are Your Friends

 

Don't program without them

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 15

 

Big Issue: In-line data

 

If we send binary data or data of unknown format how does receiver know when the data ends?

 

 

POP solution

 

Use termination sequence

 

Insure that termination sequence does not occur in data

 

 

HTTP Solution

 

Full-Response  = Status-Line

    *General-Header        

    *Response-Header      

    *Entity-Header      

    CRLF

    [ Entity-Body ]        

 

 

Send length of data to be sent in header

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 16

 

Request Methods

 

Method         = "GET" | "HEAD" | "PUT" | "POST"

    | "DELETE" | "LINK" | "UNLINK"

    | extension-method

 

 

All HTTP/1.0 servers must support GET and HEAD

 

 

Servers should return the Status-Code

 

"501 Not Implemented"

 

if the method is unknown.

 

GET

 

Retrieves whatever item is identified by the URI.

 

The URI can refer to a data-producing process, or a script

 

The produced data which shall be returned as the Entity-Body

 

 

 

HEAD

 

Identical to GET except that the server must not return any Entity-Body in the response

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 17

 

POST

 

 

Request that the origin server accept the item enclosed in the request as a new subordinate of the resource identified by the URI

 

Allows a uniform function to:

 

  1. Annotation of existing documents;

 

  1. Posting a message to a bulletin board topic, newsgroup, mailing list, or similar group of articles;

 

  1. Providing a block of data (usually a form) to a data-handling process, or a script, which can be run by such a process;

 

  1. Extending a document during authorship

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 18

 

These are not always supported

 

Why?

 

PUT

 

The enclosed item in the request is to be stored under the supplied URI

 

DELETE

 

Requests that the server delete the resource identified by the given URI

 

 

 

LINK

 

Establishes one or more Link relationships between the existing resource identified by the URI and other existing resources

 

 

 

UNLINK

 

UNLINK method removes one or more Link relationships from the existing resource identified by the URI

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 19

 

POP3 Protocol

Purpose:  Allow PC's, Macs, etc. to download mail from server

 

Port number 110

 

Protocol uses ASCII only

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 20

 

Command Format

 

Format of commands to server

 

keyword  blank  argument 1  [ blank argument k ]  CRLF

 

| keyword  | = 3, 4 characters

 

| argument |  <= 40 characters

 

keyword  and arguments are separated by single space character

 

Server Response

 

Status  keyword  additionalInfo

 

Status is either "+OK" or "-ERR0.3."

 

A single line response ends in CRLF

 

If response requires more than one line:

 

  1. Each line ends in a CRLF

  1.  

  1. The response ends in CRLF.CRLF  

  1.  

  1. If a line starts with a "." prepend a "." to it

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 21

 

Timeouts

 

A POP3 server may have an autologout timer

 

A server must wait at least 10 minutes before timing out a client

 

The POP3 server on cs.sdsu.edu times out in 2 minutes

 

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 22

 

States

 

AUTHORIZATION

 

Must log in with password before entering transaction state

 

 

TRANSACTION

 

Client can request actions of server, get mail for example

 

 

UPDATE

 

Updates mail box to reflect actions taken in transaction state

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 23

 

Commands

AUTHORIZATION

 

Server acknowledges connection from client with

 

    +OK  "message"

 

    +OK UCB Pop server (version 2.1.2-R3) at sciences.sdsu.edu starting.

 

 

Commands:  USER,  PASS,  APOP,  QUIT

 

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 24

 

USER PASS

 

Combination is used to progress to transaction state

 

USER must come first

PASS or QUIT must come after USER

 

Example

Ti 38-> telnet cs.sdsu.edu 110

Trying 130.191.226.116...

Connected to cs.sdsu.edu.

Escape character is '^]'.

+OK QPOP (version 3.1.2) at sciences.sdsu.edu starting.  

USER whitney

+OK Password required for whitney.

PASS typeYourPasswordHere

+OK whitney has 116 visible messages (0 hidden) in 640516 octets.

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 25

 

TRANSACTION

 

Commands: STAT, LIST, RETR, RSET, QUIT

 

STAT

 

Arguments: none

 

Returns "+OK" numberOfMessages SizeOfMail

 

Example

 

STAT

+OK 22 45595

 

 

LIST

 

Arguments: a message-number ( optional )

 

Returns: size of message in octets

 

Examples:

 

LIST 2

+OK 2 3064

 

LIST

+OK 116 visible messages (640516 octets)

1 2980

2 3064    ( message 3 - 116 deleted to save space )

116 1290

.

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 26

 

RETR

 

Arguments: a message-number

 

Returns: the message

 

Example:

 

RETR 21

+OK 825 octets

Received: from [130.191.9.18] (ebb2p9.sdsu.edu [130.191.9.18]) by sciences.sdsu.edu

 (4.1/8.6.10) with SMTP id UAA29486 for < whitney@saturn.sdsu.edu >; Mon, 11 Mar

1996 20:16:07 -0800 (PST)

X-Sender: whitney@cs.sdsu.edu (Unverified)

Message-Id: <v02110100ad6aaaf097b6@[130.191.9.70]>

Mime-Version: 1.0

Content-Type: text/plain; charset="us-ascii"

Date: Mon, 11 Mar 1996 20:16:50 -0800

To: whitney@saturn.sdsu.edu

From: whitney@saturn.sdsu.edu (Roger Whitney)

Subject: Sample Mail

X-UIDL: 826604201.000

 

this is a test

..

the end

---

Roger Whitney               Math & Computer Science Dept.

whitney@cs.sdsu.edu                    San Diego State University

http://www.eli.sdsu.edu       San Diego, CA 92182-7720

(619) 594-3535

(619) 594-6746 (fax)

 

.

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 27

 

DELE

 

Arguments: a message-number to delete

 

Returns: a confirmation of deletion

 

Marks a message to be deleted

 

 

NOOP

 

Arguments: none

 

Returns: a positive response

 

Does nothing

 

 

QUIT

 

Arguments: none

 

Returns: a positive response

 

Send POP3 server to UPDATE state

 

 

UPDATE State

 

Updates mail box to reflect transactions taken during the transaction state, then logs user out

 

If session ends by any method except the QUIT command during the transaction state, the update state is not entered

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 28

 

Optional POP3 Commands

TOP

 

Arguments: a message-number and number of lines to return

 

Returns: Requested lines of indicated message

 

State allowed in:  transaction

 

UIDL

 

Arguments: a message-number ( optional )

 

Returns: a unique-id listing for message

 

State allowed in:  transaction

 

Examples:

UIDL 1

+OK 1 826312760.001

 

UIDL

+OK uidl command accepted.

1 826312760.001

2 826312760.006

3 826493796.004

etc.

.

 

 

CS580 Spring 2005Doc 14, HTTP & POP Slide # 29

 

APOP

 

Arguments: a mailbox and a MD5 digest string

 

 

State allowed in:  authorization

 

Action: If MD5 string is correct move to transaction state

 

 

Copyright ©, All rights reserved.

2005 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.

OpenContent license defines the copyright on this document.

Previous     visitors since March 22, 2005     Next