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Chapter 04. TCP Server/Client

Chapter 04. TCP Server/Client. Goal. Basic structure and principle of TCP server/client Socket system call for TCP application Understanding application protocol. TCP server/client operation (1/6). TCP server/client example. GET / HTTP/1.1 Accept: image/gif,. <HTML>

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Chapter 04. TCP Server/Client

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  1. Chapter 04. TCP Server/Client

  2. Goal • Basic structure and principle of TCP server/client • Socket system call for TCP application • Understanding application protocol

  3. TCP server/client operation (1/6) • TCP server/client example GET / HTTP/1.1 Accept: image/gif, ... <HTML> <HEAD>...</HEAD>... Web server Web client Web client

  4. TCP server TCP client listen network accept connect recv send send recv TCP server/client operation (2/6) • TCP server/client operation

  5. TCP server/client operation (3/6) • 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

  6. TCP server waiting TCP server Client connecting TCP clients #1 TCP server/client operation(4/6) • TCP server/client operation principle

  7. TCP server waiting Comm. Comm. TCP server TCP client #1 TCP client #2 waiting Comm. TCP client #1 TCP server/client operation(5/6) • TCP server/client operation principle (cont’d)

  8. TCP server . . . . . . waiting TCP client #1 . . . . . . TCP client #n TCP server/client operation(6/6) • TCP server/client operation principle (cont’d)

  9. fgets() send() recv() printf() TCP client TCP server printf() recv() send() TCP server/client example • Code Example(TCPServer.cpp, TCPClient.cpp)

  10. TCP server/client analysis (1/2) • Socket requires three components ① protocol • Defined by Socket() system call ② local IP address and port number • Server or client side ③ remote IP address and port number

  11. network server client application local IP addr. local IP addr. Local port num. Local port num. Remote IP addr. Remote IP addr. OS Remote port num. Remote port num. ••• ••• TCP server/client analysis (2/2) • Socket data structure

  12. TCP server TCP client socket() socket() bind() listen() network accept() connect() recv() send() send() recv() closesocket() closesocket() Socket call for TCP server (1/8) • TCP server side

  13. Socket call for TCP server (2/8) • 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

  14. Socket call for TCP server (3/8) • 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()");

  15. Socket call for TCP server (4/8) • listen() • transit TCP port state to LISTENING state - ready to receive connections. int listen ( SOCKET s, int backlog ) ; success: 0, fail: SOCKET_ERROR

  16. Socket call for TCP server (5/8) • listen() example 059 retval = listen(listen_sock, SOMAXCONN); 060 if(retval == SOCKET_ERROR) err_quit("listen()");

  17. Socket call for TCP server (6/8) • 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

  18. Socket call for TCP server (7/8) • accept() example 062 // variables for data communiction 063 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 }

  19. Socket call for TCP server (8/8) • 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 client 080 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 }

  20. Socket call for TCP client (1/3) • TCP client side TCP server TCP client socket() socket() bind() listen() network accept() connect() recv() send() send() recv() closesocket() closesocket()

  21. Socket call for TCP client (2/3) • connect() • to establish a connection with a server int connect ( SOCKET s, const struct sockaddr* name, int namelen ) ; success: 0, fail: SOCKET_ERROR

  22. Socket call for TCP client (3/3) • 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()");

  23. network server client application Local IP addr Local IP addr Local port num Local port num Remote IP addr Remote IP addr OS Remote port num Remote port num Recv buffer Send buffer ••• ••• Data transfer socket call (1/10) • Socket data structure

  24. Data transfer socket call (2/10) • 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

  25. Data transfer socket call (3/10) • 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

  26. Data transfer socket call (4/10) • recvn() function 037 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 }

  27. buf len left ptr buf len left ptr 읽은 데이터 Data transfer socket call (5/10) • recvn() function principle

  28. Data transfer socket call (6/10) • Data send/recv example – TCP client 078 char buf[BUFSIZE+1]; 079 int len; ... 082 while(1){ 083 // data input 084 ZeroMemory(buf, sizeof(buf)); 085 printf("\n[sending data] "); 086 if(fgets(buf, BUFSIZE+1, stdin) == NULL) 087 break; 088 089 // '\n' char delete 090 len = strlen(buf); 091 if(buf[len-1] == '\n') 092 buf[len-1] = '\0'; 093 if(strlen(buf) == 0) 094 break;

  29. Data transfer socket call (7/10) • Data send/recv example – TCP client (cont’d) 096 // data sending 097 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 receiving 105 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;

  30. Data transfer socket call (8/10) • Data send/recv example – TCP client(cont’d) 113 // print received data 114 buf[retval] = '\0'; 115 printf("[TCP client] %d bytes received...\n", retval); 116 printf("[received data] %s\n", buf); 117 }

  31. Data transfer socket call (9/10) • Data send/recv example– TCP server 066 char buf[BUFSIZE+1]; ... 080 while(1){ 081 // data receiving 082 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 data 091 buf[retval] = '\0'; 092 printf("[TCP/%s:%d] %s\n", inet_ntoa(clientaddr.sin_addr), 093 ntohs(clientaddr.sin_port), buf);

  32. Data transfer socket call (10/10) • Data send/recv example– TCP server(cont’d) 095 // data sending 096 retval = send(client_sock, buf, retval, 0); 097 if(retval == SOCKET_ERROR){ 098 err_display("send()"); 099 break; 100 } 101 }

  33. network Application protocol and message design (1/3) • Application protocol • Define data format and semantic which is exchanged in application level • Application protocol example

  34. Application protocol and message design (2/3) • 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 };

  35. Application protocol and message design (3/3) • Message definition ③ struct 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 };

  36. Application protocol and message design (3/3) • FileSender.cpp, FileReceiver.cpp

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