Chapter 04. TCP Server/Client

Chapter 04.

TCP Server/Client

IT COOKBOOKIT COOKBOOK

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Goal

• Basic structure and principle of TCP server/client

• Socket system call for TCP application• Understanding application protocol


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TCP server/client operation (1/6)

• TCP server/client example

Web client Web client

Web serverGET / HTTP/1.1Accept: image/gif, ...

<HTML><HEAD>...</HEAD>...


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• TCP server/client operation

TCP server TCP client

listen

accept

recv

send

connect

send

recv

network


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• TCP server/client socket calls (cont’d)- bind : to assign a name to an unnamed socket. - listen: to indicate that it is willing to receive connections.- connect: to establish a connection with a server - send: to send data to peer side- accept: to accept the connection request from client- recv: to receive the data that client sent


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TCP server/client operation(4/6)

• TCP server/client operation principle

TCP server

waiting

TCP server

TCP clients #1

Client connecting


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• TCP server/client operation principle (cont’d)

TCP server

TCP client #1

TCP client #2

Comm. Comm.waiting

TCP server

TCP client #1

Comm.

waiting


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• TCP server/client operation principle (cont’d)

TCP server

TCP client #1

waiting

TCP client #n

. . .

. . . . . .

. . .


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TCP server/client example

• Code Example(TCPServer.cpp, TCPClient.cpp)

TCP client TCP server

fgets() send()

printf()

recv() printf()

send()recv()


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TCP server/client analysis (1/2)

• Socket requires three components① protocol

• Defined by Socket() system call

② local IP address and port number• Server or client side

③ remote IP address and port number


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TCP server/client analysis (2/2)

• Socket data structure

server

local IP addr.

Local port num.

Remote IP addr.

Remote port num.

client

local IP addr.

Local port num.

Remote IP addr.

Remote port num.

application

OS

network

• • • • • •


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Socket call for TCP server (1/8)

• TCP server side

socket()

bind()

recv()

send()

closesocket()

socket()

send()

recv()

closesocket()


connect()

listen()

accept()

network


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• bind() – Assign a name to an unnamed socket – Define IP address and port number of server side

int bind ( SOCKET s, const struct sockaddr* name, int namelen) ; success: 0, fail: SOCKET_ERROR


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• bind() example

050 SOCKADDR_IN serveraddr;051 ZeroMemory(&serveraddr, sizeof(serveraddr));052 serveraddr.sin_family = AF_INET;053 serveraddr.sin_port = htons(9000);054 serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);055 retval = bind(listen_sock, (SOCKADDR *)&serveraddr, sizeof(serveraddr));056 if(retval == SOCKET_ERROR) err_quit("bind()");


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• listen()– transit TCP port state to LISTENING state- ready to receive connections.

int listen ( SOCKET s, int backlog) ; success: 0, fail: SOCKET_ERROR


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• listen() example

059 retval = listen(listen_sock, SOMAXCONN);060 if(retval == SOCKET_ERROR) err_quit("listen()");


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• accept()– accept the connection request from client– tell the IP address and port number of client

SOCKET accept ( SOCKET s, struct sockaddr* addr, int* addrlen) ; success: new socket, fail: INVALID_SOCKET


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• accept() example

062 // variables for data communiction063 SOCKET client_sock;064 SOCKADDR_IN clientaddr;065 int addrlen;...068 while(1){069 // accept()070 addrlen = sizeof(clientaddr);071 client_sock = accept(listen_sock, (SOCKADDR *)&clientaddr, &addrlen);072 if(client_sock == INVALID_SOCKET){073 err_display("accept()");074 continue;075 }


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• accept() example (cont’d)

076 printf("\n[TCP server] client connection: IP addr=%s, port num=%d\n", 077 inet_ntoa(clientaddr.sin_addr), ntohs(clientaddr.sin_port));078 079 // data comm with client080 while(1){...101 }102 103 // closesocket()104 closesocket(client_sock);105 printf("[TCP server] client exit: IP addr=%s, port num=%d\n", 106 inet_ntoa(clientaddr.sin_addr), ntohs(clientaddr.sin_port));107 }


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Socket call for TCP client (1/3)

• TCP client side

socket()

bind()

recv()

send()

closesocket()

socket()

send()

recv()

closesocket()


connect()

listen()

accept()

network


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• connect()– to establish a connection with a server

int connect ( SOCKET s, const struct sockaddr* name, int namelen) ; success: 0, fail: SOCKET_ERROR


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• connect() example

070 SOCKADDR_IN serveraddr;071 serveraddr.sin_family = AF_INET;072 serveraddr.sin_port = htons(9000);073 serveraddr.sin_addr.s_addr = inet_addr("127.0.0.1");074 retval = connect(sock, (SOCKADDR *)&serveraddr, sizeof(serveraddr));075 if(retval == SOCKET_ERROR) err_quit("connect()");


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Data transfer socket call (1/10)

• Socket data structure

server

Local IP addrLocal port num

Remote IP addrRemote port num

client

Local IP addrLocal port num

Remote IP addrRemote port num

application

OS

network

• • • • • •

Recv bufferSend buffer


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• send() 함수– Data transfer to peer side

int send ( SOCKET s, const char* buf, int len, int flags); success: num of sent bytes, fail: SOCKET_ERROR


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• recv()– Data receving from peer side

int recv ( SOCKET s, char* buf, int len, int flags); success: num of received bytes or 0(the remote side has closed

the connection ), fail: SOCKET_ERROR


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• recvn() function037 int recvn(SOCKET s, char *buf, int len, int flags)038 {039 int received;040 char *ptr = buf;041 int left = len;042 043 while(left > 0){044 received = recv(s, ptr, left, flags);045 if(received == SOCKET_ERROR) 046 return SOCKET_ERROR;047 else if(received == 0) 048 break;049 left -= received;050 ptr += received;051 }052 053 return (len - left);054 }


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• recvn() function principle

buf

ptrleft

buflen

ptr left

len

읽은 데이터


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• Data send/recv example – TCP client078 char buf[BUFSIZE+1];079 int len;...082 while(1){083 // data input084 ZeroMemory(buf, sizeof(buf));085 printf("\n[sending data] ");086 if(fgets(buf, BUFSIZE+1, stdin) == NULL)087 break;088 089 // '\n' char delete090 len = strlen(buf);091 if(buf[len-1] == '\n')092 buf[len-1] = '\0';093 if(strlen(buf) == 0)094 break;


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• Data send/recv example – TCP client (cont’d)

096 // data sending097 retval = send(sock, buf, strlen(buf), 0);098 if(retval == SOCKET_ERROR){099 err_display("send()");100 break;101 }102 printf("[TCP client] %d bytes sent...\n", retval);103 104 // data receiving105 retval = recvn(sock, buf, retval, 0);106 if(retval == SOCKET_ERROR){107 err_display("recv()");108 break;109 }110 else if(retval == 0)111 break;


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• Data send/recv example – TCP client(cont’d)

113 // print received data114 buf[retval] = '\0';115 printf("[TCP client] %d bytes received...\n", retval);116 printf("[received data] %s\n", buf);117 }


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• Data send/recv example– TCP server066 char buf[BUFSIZE+1];...080 while(1){081 // data receiving082 retval = recv(client_sock, buf, BUFSIZE, 0);083 if(retval == SOCKET_ERROR){084 err_display("recv()");085 break;086 }087 else if(retval == 0)088 break;089 090 // print received data091 buf[retval] = '\0';092 printf("[TCP/%s:%d] %s\n", inet_ntoa(clientaddr.sin_addr),093 ntohs(clientaddr.sin_port), buf);


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• Data send/recv example– TCP server(cont’d)095 // data sending096 retval = send(client_sock, buf, retval, 0);097 if(retval == SOCKET_ERROR){098 err_display("send()");099 break;100 }101 }


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Application protocol and message design (1/3)

• Application protocol– Define data format and semantic which is

exchanged in application level

• Application protocol example

network


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• Message definition ①

• Message definition ②

struct DrawMessage1{ int x1, y1; // line starting point int x2, y2; // line ending point int width; // line width int color; // line color};

struct DrawMessage2{ int x1, y1; // circle center int r; // circle radius int fillcolor; // internal color int width; // line width int color; // line color};


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• Message definition ③struct DrawMessage1{ int type; // = LINE int x1, y1; // line starting point int x2, y2; // line starting point int width; // line width int color; // line color};

struct DrawMessage2{ int type; // = CIRCLE int x1, y1; // circle center int r; // circle radius int fillcolor; // internal color int width; // line width int color; // line color};


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• FileSender.cpp, FileReceiver.cpp

Chapter 04. TCP Server/Client

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