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COMP445COMP445Fall 2006Fall 2006

Lab assignment 1

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STEP1: Get the name of the second party

STEP2: Get phone number from white pages

CALLER RECEIVER

STEP1: Plug the phone, and listen for incoming calls on a certain line

STEP3: Copy the number for your records

STEP4: Call the other party

ConnectionEstablished.

Chat…

STEP2: Get a call and accept it. “Caller ID” will give you the caller’s phone number.

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Program architectureProgram architecture

ClientServerport 7070

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Socket Programming

• Berkeley added a new interface to the operating system to support network communication. This interface is generally known as the Berkeley Sockets Interface and is the basis for almost all existing TCP/IP network protocol interfaces, including Windows Sockets

(commonly referred to as WinSock). • A socket is very much like a telephone - it's the endpoint

of a two-way communications channel. By connecting two sockets together you can pass data between

processes running on different computers.

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Main steps – client sideMain steps – client sideCreating a socket

SOCKET socket(int domain, int type, int protocol);

s = socket(AF_INET,SOCK_STREAM,0)

The structure we fill in is defined below.

struct sockaddr_in { short sin_family; // address family u_short

sin_port;// service port struct in_addr 16 bit TCP or UDP port number, network byte order

sin_addr; // internet address char 32 bits IPv4 address, Network Bytes Order

sin_zero[8]; // filler

}sa_in

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Main steps – client sideMain steps – client sideClient needs the address of the server.User inputs the server’s hostname.rp=gethostbyname(remotehost)

Fill in the server address memset(&sa_in,0,sizeof(sa_in)); memcpy(&sa_in.sin_addr,rp->h_addr,rp->h_length); sa_in.sin_family = rp->h_addrtype; sa_in.sin_port = htons(port); //port = 7070 host to network 16 bits

Connectingif (connect(s,(LPSOCKADDR)&sa_in,sizeof(sa_in)) == SOCKET_ERROR)

throw "connect failed\n"; Sending frames

ibytessent = send(s, (char*)&message_frame, sizeof(message_frame), 0);

Receiving frames

ibytesrecv = recv(s, (char*)& data_frame, sizeof(data_frame),0)

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Main steps – server sideMain steps – server side

Creating a socket

s = socket(AF_INET,SOCK_STREAM,0)

Fill in the server port and address info

sa.sin_family = AF_INET;

sa.sin_port = htons(port);

sa.sin_addr.s_addr = htonl(INADDR_ANY);

Bind the server port if (bind(s,(LPSOCKADDR)&sa,sizeof(sa)) == SOCKET_ERROR)

Listen for client requests if(listen(s,10) == SOCKET_ERROR)

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Main steps – server sideMain steps – server sideWatching for new messages

FD_SET(s,&readfds); //always check the listener if(!(outfds=select(infds,&readfds,NULL,NULL,tp))) {} else if (outfds == SOCKET_ERROR)

throw "failure in Select";

else if (FD_ISSET(s,&readfds))

cout << "got a connection request" << endl;

Accept the request

if((s1=accept(s,&ca.generic,&calen))==INVALID_SOCKET) throw "Couldn't accept connection\n";

Read a message

if((ibytesrecv = recv(s1,szbuffer,128,0)) == SOCKET_ERROR)

Send a message

if((ibytessent = send(s1,szbuffer,ibufferlen,0))== SOCKET_ERROR)

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Socket Functions

• int socket(int family, int type, int protocol);

returns: nonnegative descriptor if OK, -1 on error

• int connect(int sockfd, const struct sockaddr * servaddr, int addrlen);

return:0 if OK -1 on error

• int bind(int sockfd, const struct sockaddr * myaddr, int addrlen);

return: 0 if OK, -1 on error

• int listen(int sockfd, int backlog);

return: 0 of OK, -1 on error

• int accept(int sockfd, struct sockaddr * cliaddr, int * addrlen);

returns: nonnegative descriptor if OK,-1 on error

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CLIENT SERVERPURPOSE: File Transfer-Get a file-Send a file

•Should inform the server if the required action is to get a file from the server to upload a file to the server.•Should specify the name of theFile.•Respond to possible error messages.

•If a file is asked for, then it shouldsend an error message if file doesn’t exist.•If file exists, send it.•If file is being sent to you, save it.

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Transferring the data in and Transferring the data in and from the packet structurefrom the packet structure

Struct CONTROL_FRAME {unsigned char direction; //GET or PUTchar fname[MAX]; //filename

}

struct MESSAGE_FRAME {unsigned char header; //ERROR,DATA,LASTPACKET, etc.char data[MAX_SIZE]; //data or error message

} message_frame;

YOU ARE FREE TO DESIGN YOUR OWN STRUCTURES

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Reading from a fileReading from a filevoid main( void ) {

FILE *stream;

int numread, numwritten;

if( (stream = fopen( "fread.out", "r+b" )) != NULL ) {

…

numread = fread(message_frame.data,sizeof(char), MAX_SIZE, stream);

…}

else

printf( "File could not be opened\n" );

…}

fclose( stream );

}

Be careful if you use strcpy when reading from a binary file use memcpy.

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Writing in a fileWriting in a filevoid main( void ) {

FILE *stream;

int numread, numwritten;

if( (stream = fopen( "fread.out", "w" )) != NULL ) {

…

numwritten = fwrite(szbuffer, sizeof(char), MAX_SIZE, stream );

…}

else{

printf( "Problem opening the file\n" );

…}

fclose( stream );

}

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Decrypting the headerDecrypting the headerUse a switch to treat each of the cases:

switch (message_frame.header){   

case 1 : …;        break;   

case 2 : …;        break;   

case 3 : …;        break;

…………………………………………………………………………

default: …

}

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HintsHints• Use a log file in each side in order to

monitor all the actions:– receiving a packet– sending a packet, etc.

• Open and close the log file after each read/write operation if your program freezes and you cannot read the log file.

• Do not use any string library function! You will be able to send only text files but not binary ones (jpeg or exe for example).

• Instead use memcpy for transferring data.• Do not care about the order of the receiving

packets in this assignment (TCP will do it for you).

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Assignment 1

• No GUI

• Use Visual C++ 6

• Groups of NOT more than 2• wsock32.lib or you add the following

command to your code:#pragma comment(lib,"wsock32.lib")

• Implement only whatever you’re asked to do.

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Multi-thread in Windows

uintptr_t _beginthread( void( __cdecl *start_address )( void * ), unsigned stack_size, void *arglist );

Parameters:

start_address

Start address of routine that begins execution of new thread.

stack_size

Stack size for new thread or 0.

arglist

Argument list to be passed to new thread or NULL.

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The C++ Thread Class provided to you#define STKSIZE 16536class Thread{ public:Thread(){}

virtual ~Thread() {}static void * pthread_callback (void * ptrThis);virtual void run () =0 ;void start();

};

void * Thread::pthread_callback (void * ptrThis) { if ( ptrThis == NULL ) return NULL ; Thread * ptr_this =(Thread *)(ptrThis) ; ptr_this->run(); return NULL;} void Thread::start () { int result; if(( result = _beginthread((void (*)(void *))Thread::pthread_callback,STKSIZE,this ))<0)

{printf("_beginthread error\n");exit(-1);

} }

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How to make _beginthread work in VC6.00++

Right click the project and go to the Setting->C/C++->Category. Change the Category to “Code Generation” and change Use run-time library to “Multithreaded”.Note:You will encounter such a error “error C2065: '_beginthread' : undeclared identifier” at the compile time if you don’t do the above setting.