CS 596 Client-Server Programming
Protocol
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San Diego State University -- This page last updated March 12, 1996
Contents of Protocol Lecture
- Client/Server Protocol
- POP3 Protocol
- AUTHORIZATION
- TRANSACTION
- UPDATE State
- Optional POP3 Commands
Protocol
- Set of rules and conventions used by communicating participants
Client/Server Protocol
- Protocol used by client and server
- Sit above TCP/IP
- Levels 5 - 7
Protocol Requirements
- * Well defined ( Protocol can not be vague )
- * Complete ( All situation must be addressed )
- * Computer program must be able to parse protocol
- * Extendible
Purpose: Allow PC's, Macs, etc. to download mail from server
Port number 110
Protocol uses ASCII only
Command to server
- keyword blank argument1 [ blank argumentk ] 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 "-ERR"
-
- A single line response ends in CRLF
-
- If response requires more than one line:
-
- Each line ends in a CRLF
-
- The response ends in CRLF.CRLF
-
- If a line starts with a "." prepend a "." to it
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 saturn times out in 2 minutes
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
Server acknowledges connection from client with
- +OK "message"
-
- +OK UCB Pop server (version 2.1.2-R3) at saturn starting.
Commands: USER, PASS, APOP, QUIT
USER PASS
combination is used to progress to transaction state
USER must come first
PASS or QUIT must come after USER
Example
- rohan 14-> telnet saturn 110
- Trying 130.191.229.1...
- Connected to saturn.sdsu.edu.
- Escape character is '^]'.
- +OK UCB Pop server (version 2.1.2-R3) at saturn starting.
- USER whitney
- +OK Password required for whitney.
- PASS don'tyouwish
- +OK whitney has 21 message(s) (44285 octets).
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 22 messages (45595 octets)
- 1 2980
- 2 3064
- ( message 3 - 21 deleted to save space )
- 22 1290
- .
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
saturn.sdsu.ed
- u (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 Mathematical Science Department
- whitney@cs.sdsu.edu San Diego State University
- http://cs.sdsu.edu:8080/~whitney San Diego, CA 92182-7720
- (619) 594-3535
- (619) 594-6746 (fax)
-
- .
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
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
TOP
Arguments: a message-number
Returns: Top 10 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
- 4 826510843.001
- 5 826510843.002
- 6 826576073.000
- 7 826594928.004
- 8 826603475.000
- 9 826648617.001
- 10 826648617.002
- .
APOP
Arguments: a mailbox and a MD5 digest string
State allowed in: authorization
Action: If MD5 string is correct move to transaction state
