Tcp-ip Socket Programming

Tcp-ip Socket Programming - Transcript

CS4514 B06 HELP Session 1

Presented by Mingzhe Li lmz cs wpi edu

CS4514 TCP IP Socket Programming

Outline
Project 1 Overview Unix Network Programming
TCP Client TCP Server

Processing commands How to find help and other tips
2 CS4514 B05 TCP IP Socket Programming

CS4514 Project1
Your programs should compile and work on ccc wpi edu computers which are running Linux Programs should be written in C or C If your program is developed on another platform or machine you should test the software on ccc before turning in the assignment Make sure you have the correct include in your program
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Project 1 missions in handout
The Client
1 Reading a command from a script file or from console 2 Sending the command to the server 3 Receiving and displaying the information from the server 4 Writing the results to the log file LClient log
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Project 1 missions in handout
Server
1 Processing the command from the client and return the result to the client 2 Maintaining the records to keep the location information 3 Writing the complete database to the file LDatabase txt when the server received the quit EOF command
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Outline
Project 1 Overview Unix Network Programming
TCP Client TCP Server

Processing commands How to find help and other tips
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Server connection oriented protocol socket bind listen accept blocks until connection from client read process request write data reply data request Client

Socket system calls for Socket connection oriented connection oriented protocol TCP

socket

connection establishment connect

write

read

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CS4514 B05 TCP IP Socket Programming

What Do We Need
Data communication between two hosts on the Internet require the five components protocol local addr local process foreignaddr foreign process The different system calls for sockets provides values for one or more of these components
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What Do We Need
The socket system call just fills in one element of the five tuple we ve looked at the protocol The remaining are filled in by the other calls as shown in the figure
protocol
Connection Oriented Server TCP Connection oriented Client TCP Connectionless Server UDP Connectionless Client UDP

local addr local process

foreign addr foreign process

socket bind socket socket socket bind bind

accept connect recvfrom sendto
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CS4514 B05 TCP IP Socket Programming

TCP Connection Client
Connection Oriented
Specify transport address once at connection
socket connect read write recv send close

Use File Operations
read write

or
recv send

Reliable Protocol
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Example TCP Client
int sd struct hostent hp usr include netdb h struct sockaddr in server usr include netinet in h prepare a socket if sd socket AF INET SOCK STREAM 0 0 perror strerror errno exit 1
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Example TCP Client Continued
prepare server address bzero char server sizeof server server sin family AF INET server sin port htons SERVER PORT if hp gethostbyname SERVER NAME NULL perror strerror errno exit 1 bcopy hp h addr char server sin addr hp h length
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Example TCP Client Continued
connect to the server if connect sd struct sockaddr server sizeof server 0 perror strerror errno exit 1 send receive data while 1 read write close socket 13 close sd
CS4514 B05 TCP IP Socket Programming

TCP Connection Server
Bind transport address to socket Listen to the socket Accept connection on a new socket
socket bind listen accept read write close
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Example TCP Server
int sd nsd struct sockaddr in server usr include netinet in h sd socket AF INET SOCK STREAM 0 bzero char server sizeof server server sin family AF INET server sin port htons YOUR SERVER PORT server sin addr s addr htonl INADDR ANY
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Example TCP Server Continued
bind sd struct sockaddr server sizeof server listen sd backlog while 1 nsd accept sd struct sockaddr client sizeof client read write close nsd close sd
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Outline
Project 1 Overview Unix Network Programming
TCP Client TCP Server

Processing commands How to find help and other tips
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Processing commands
Each command triggers a communication conversion between client and server Then we have
login add remove quit list attn this one is different from above commands most complex one
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Commands
In the login add remove and quit commands
The server only returns one message to the client

In the list command The server could return multiple messages to the client
Each entry which meets the search condition is sent as a separate TCP message back to the Client
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Login Command
Login Command Format
login

Login Command Handling
For The Client When the Client reads a login command the client establishes a TCP connection to the Server For The Server When the Server receives a login it replies Hello to the client 20
CS4514 B05 TCP IP Socket Programming

Add Command
Add Command Format
add first name last name id number location
Notes first name last name and location are nonblank ascii string For example Tony Smith 12 Institute rd worcester id number is 9 digital number similar to SSN number example 321654987

For the Client
reads and sends the add command to the server and displays the result returned from server
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Add Command cont d
For the Server
When the server gets the Add command it will
add the four items as an entry into the location database in the proper location and return a successful message to client If a duplicate id number is received the server simply overwrites information associated with this id number and returns a successful message to the server If the command s parameter is not valid the server returns an Error message to the client For example Add Tony Smith 12033 000 worcester MA returns an invalid add commands 22
CS4514 B05 TCP IP Socket Programming

Remove Command
Remove command format remove id number
example remove 123456789 is a valid command



For the Client
sends the remove command to the server and displays the result returned from server
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Remove command cont d
For the Server
When the server receives remove command the server searches the database for a match on id number
If the id number entry exists in the database for a person that entry is removed from the location database and a success message that contains the first and last name of the person removed is sent back If there is not a match in the database the server does not modify the database and sends an appropriate error message back to the Client
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Quit Command
Quit Command format
quit EOF
For example quit and quit EOF are valid commands

For the Client
sends the quit command to the server and when the client received the response message from server the client know the connection will be closed If EOF is specified the client will close the log file and terminate 25
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Quit Command Cont d
For the Server
When server received quit command it sends a response back to the Client indicating that the connection will be closed The server returns to wait for a new connection triggered by a subsequent login request If quit EOF is received the Server additionally writes out the complete database to the file LDatabase txt and then terminates
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List Command
List Command format
list start finish Notes start finish are two single letter of the alphabet Examples list A N Find the entries whose last names with A as the first letter up to and including all last names with N as the first letter such Anderson Lincoln etc list C C Find the entries whose last names begin with C list W A Invalid Command 27
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List Command cont d
For the Client
Sends the command to the server and displays the response message from the server

For the Server
When received the list command sends All location entries satisfying the list limits sends no such records if there are no entries satisfying the list request sends invalid command if the list command is in illegal format for example list Z A or list A
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Outline
Project 1 Overview Unix Network Programming
TCP Client TCP Server

Processing a command How to find help and other tips
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Some Useful System Calls
Gethostbyname map hostname to IP addr
struct hostent gethostbyname char name

Getservbyname look up service name given
struct servent getservbyname const char servname const char protocol

Gethostname get own hostname
int gethostname char name size t len
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Others Tips
Include files
include sys types h include netinet in h include netdb h include signal h include fcntl h include sys time h include memory h include sys socket h include arpa inet h include unistd h include stdio h include errno h include stdlib h include string h

Programming tips

always check the return value for each function call consult the UNIX on line manual pages man for a complete description Internet Beej s Guide to Network Programming http www ecst csuchico edu beej guide net 31

CS4514 B05 TCP IP Socket Programming

Server Database
There are many possible data structure choices for implementing the server data base Two of them are
Linked list Easy to add remove an entry Array The simplest data structure
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Sorting in Database
The server s database is maintained alphabetically by last name
There is no secondary key in the database If the people have the same last name you don t need to sort them based on their first name For example based on a linked list Andy Smith and Tony Smith in the database
Smith Andy Smith Tony Smith Tony Smith Andy

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Case insensitive string comparison
The case insensitive string compare functions in Linux
int strcasecmp const char s1 const char s2 int strncasecmp const char s1 const char s2 size t n Their usage is similar to strcmp function

An Alternative method Storing the information in upper case letters in
server s database Smith SMITH
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HELP
Bring printouts to office hours Email questions to Prof TA SA cs4514 staff cs wpi edu You CAN email a specific TA SA but do not expect immediate results better to use the staff mailing list We do have a class mailing list that could be used as a last resort
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Questions

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More Tips File and Stdio
In Linux a device could be treated as a file For example the standard input device could be handled as a file
fgets will read a line from the keyboard fp stdin fgets buffer buffer len fp next fgets will read a line from the file named script txt fp fopen script txt r 37 fgets buffer buffer len fp
CS4514 B05 TCP IP Socket Programming