Project 1A Chat Client Due Oct 22 3 50 pm EE122 Introduction to Communication Networks Fall 2008 Department of Electrical Engineering and Computer Sciences College of Engineering University of California Berkeley Project Goal Create a Chat application consisting of a chat client and a chat server The client and server must be written in C or C and must use sockets Project Timeline Project 1 consists of two parts 1 The first part part A is to implement the chat client It is due on Oct 6 We will provide you a server that can be reached at IP 128 32 48 187 port 10000 You can use this server to test your client In addition we will provide you the binary for the server that you can execute on instructional UNIX machines Your overarching goal for this part is to make your client work with our server 2 The entire project is due on Oct 20 It includes both the client and server code The specification for the server will be provided soon Section I Introduction The chat application allows multiple chat clients to connect to a chat server Connected clients can list the members already logged in log in with a username exchange messages with other logged in users and log out The server has to accept and maintain connections to all the clients and relay chat messages between them Section II Chat Client Overview The chat client application has to do the following tasks 1 Connect to a chat server The client obtains the server IP address and the port it is listening on from command line arguments For example client 128 32 48 187 10000 Then the client immediately attempts to connect to the server socket using TCP If it fails the client application prints an error message to the console and returns To print the error message the client must call function perror defined in stdio h with the name of the socket function that failed in lowercase For example perror socket If on the other hand the connection succeeds the client continues to step 2 2 Accept console text commands from the user The client must be able to handle the following commands Parameters are enclosed in a login username b list c sendto username message d logout e exit Each line must begin with a command The parameters if any are separated by a space The commands and parameters are described in more detail below In order to implement these commands correctly the client will have to send and receive the following messages to from the server a Send messages to the server The client must be able to send the following messages to the server These messages are described in detail in section 4 of the document i Login Message ii List Message iii Sendto Message iv Logout Message b Accept incoming messages from the server The client must be able to properly react to the following messages These messages are shown in section 5 of the document i List Message ii Response Message iii Sendto Message Section III Console Commands We now present the console commands that a client must handle Note whenever a client prints an error message it should not perform any other action login sends a login message to register with the server using the provided username o Parameter s a string to be used as the username o Rules The string may not contain any white space Screen names are treated as case sensitive Any extra parameters after the username must cause the client to print an error The error must also be printed if the username is more than 20 characters in length or if the username is not present The following is the error Bad username o Examples The following is an example of a valid command login John The following is an example of an invalid command login John Doe list sends a list message requesting the list of users already logged in o Parameter s none o Rules Any extra parameters must cause the client to print the following error Invalid command o Examples The following is an example of a valid command list The following is an example of an invalid command list bob sendto sends a sendto message to the server to communicate with another client o Parameters The user name of the destination client and the text to send o Rules If either or both of the parameters are missing or if the username contains more than 20 characters the following error message should be printed to the console Bad username If there are more than 65535 characters of text the following error message should be printed to the console Bad message o Examples The following is an example of a valid command sendto John Hello how are you The following is an example of an invalid command sendto JohnHello logout sends a logout message to the server o Parameters none o Rules Any extra parameters must cause the client to print the error Invalid command The client should not close the connection with the server when executing this command After executing this command the client should still be able to execute the list and login commands o Examples The following is an example of a valid command logout The following is an example of an invalid command logout Joe exit closes the client socket and exits the program o o o Parameters Takes no parameters Rules Any extra parameters must cause the client to print the error Invalid command Examples The following is an example of a valid command exit The following is an example of an invalid command exit client Protocol Overview For each message that the client sends to the server the server will send a message back For a successful List Message the server will return a List Message back see the messages specification for details For all other messages or an unsuccessful List Message the server will respond with a Response Message The client never sends messages back in response to messages received from the server Section IV Messages Sent from Client to Server The following is the structure for messages the client sends to the server In all of these diagrams B is a shortcut for Byte and XB refers to a variable length field Also the client must expect a response from the server whenever it sends a message and must block user input until it receives that message Login message Field values MSG TYPE Set to 0x01 UNAME Login username o Rules UNAME must be padded to twenty bytes i e if Bob is the user name it must be followed by 17 null bytes UNAME does not have to be null terminated i e can contain a user name with 20 characters UNAME cannot contain any white space List message Field values MSG TYPE Set to 0x02 Sendto message o o Field values MSG TYPE Set to
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