Socket Programming

Present: KS Wu

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Outline

UDP client/server communication Introduction of socket functions How MSN Messenger works

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Outline

UDP client/server communication Introduction of socket functions How MSN Messenger works

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sendto()

recvfrom()

socket()

socket()

bind()

recvfrom()

sendto()

UDP Client

UDP Server

Wait for a request from

client

Process request

Socket functions for UDP client-server

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Outline

UDP client/server communication Introduction of socket functions How MSN Messenger works

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Socket functions

WSAStartup( )

socket( )bind( )sendto( )recvfrom( )closesocket( )

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WSAStartup Function

WSADATA wsadata;

WSAStartup(0x101, (LPWSADATA) &wsadata)

version: 1.1

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socket Function

int socket( int af, int type, int protocol );

Returns: nonnegative descriptor if OK, negative number on error

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Parameters

family DescriptionAF_INET IPv4 protocolsAF_INET6 IPv6 protocols

type DescriptionSOCK_STREAM stream socket (TCP)SOCK_DGRAM datagram socket (UDP)

protocol Description0 Normally set to 0

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bind Function

int bind( SOCKET sockfd, const struct sockaddr* name, int namelen );

Returns: 0 if OK, negative number on error

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Parameters

sockfd Descriptor identifying an unbound socket. (retur

ned by the socket function.)name

A pointer to a protocol-specific addressnamelen

Length of the value in the name parameter, in bytes.

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sendto Function

int sendto( SOCKET sockfd, const char* buf, int len, int flags, const struct sockaddr* to, int tolen );

Returns: # of bytes sent (< len) if OK, negative number on error

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Parameters

sockfd Descriptor identifying a bound socket.

buf Buffer containing the data to be transmitted.

len Length of the data in buf, in bytes.

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Parameters (cont.)

flags Indicator specifying the way in which the call is

made. (usually set to 0)to

Optional pointer to a sockaddr structure that contains the address of the target socket.

tolen Size of the address in to, in bytes.

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recvfrom Function

int recvfrom( SOCKET sockfd, char* buf, int len, int flags, struct sockaddr* from, int* fromlen );

Returns: # of bytes received (< len) if OK, 0 if connection has been gracefully closed, negative number on error

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Parameters

sockfd Descriptor identifying a bound socket.

buf Buffer for the incoming data.

len Length of the data in buf, in bytes.

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Parameters (cont.)

flags Indicator specifying the way in which the call is

made. (usually set to 0)from

Optional pointer to a buffer in a sockaddr structure that will hold the source address upon return.

fromlen Optional pointer to the size, in bytes, of the from

buffer.

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closesocket Function

int closesocket( SOCKET sockfd );

Returns: 0 if OK, negative number on error

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Parameters

sockfd Descriptor identifying the socket to close.

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Outline

UDP client/server communication Introduction of socket functions How MSN Messenger works

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How MSN Messenger works

2 phases Authentication Phase Instant Messaging Phase

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How MSN Messenger works (cont.)

Authentication Phase logging into the MSN messenger server Retrieve the friend list

Instant Messaging Phase Session-based sending/accepting requests for an Instant

Messaging session sending/receiving messages

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Authentication Phase

Protocol versioning Server policy information Authentication Referral Client user property synchronization List retrieval and property management Client states List modifications Notification messages Connection closed

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Instant Messaging Phase

Referral to switchboardSwitchboard connections and

authenticationInviting users to a switchboard sessionSession participant changesLeaving a switchboard sessionInstant messagesReceiving an instant message

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Server Components

Dispatch serverNotification serverSwitchboard server

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Dispatch server

protocol version negotiationdetermination of which NS is associated

with the client making a connectionreferring the client to the proper NS

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Notification server

authenticate, synchronize user propertiesexchange asynchronous event

notifications

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Switchboard server

provide instant messaging sessions

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Scenario

DS

Client

1.Protocol Versioning

TCP (port 1863)version

2.Server policy information

Policy?SP (MD5)

3.Authentication

Initiate infoChallenge info Passwd + challengeuserID + nickname

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Scenario

DS

Client

4.Referral

NS addr:port

NS

Log in

5.Client User Property Synchronization

Latest properties? (cache)Yes

No, update!

6.List Retrieval And Property Management

List?List

aa@aaa.com nickname

b@bbb.com nickname

…

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Scenario

Client

NS

7.Client States

State

Online

Offline

InvisibleOK!

8.List Modifications

OK! (new SN)

ADD/REM xx@xxx.com nickname

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Scenario

Client

NS

SS?

Referral to Switchboard

SS addr

SP (CHI)

cookie

Switchboard Connections and Authentication

SS

userID cookieOK!

Inviting Users to a Switchboard Session

called userID

Session ID

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Scenario

Client

NS SS

Getting Invited to a Switchboard Session

SessionID

SS addr

SP

Cookie

callerID nickname

userID cookie sessionID

index

# of participants

Session Participant Changes

New userID nickname

JOIN!Left!

Left userIDBye!

Leaving a Switchboard Session

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Scenario

Client

NS SS

Sending a instant message

Msg

Receiving an Instant Message

Msg

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Reference

“Unix Network Programming”“WinSock 網路程式設計之鑰”http://msdn.microsoft.comhttp://www.hypothetic.org/docs/msn/ietf_dr

aft.php

Thanks for attention!