TCP Network Programming in C

Transcription

1 CPSC 360 Network Programming TCP Network Programming in C Michele Weigle Department of Computer Science Clemson University mweigle@cs.clemson.edu 1 Sockets Identified by protocol and local/remote address/port Applications may refer to many sockets Sockets accessed by many applications 2

2 Socket Programming in C Include Files #include <stdio.h> /* printf() and fprintf() */ #include <sys/types.h /* Socket data types */ #include <sys/socket.h> /* socket(), connect(), send(), recv() */ #include <netinet/in.h> /* IP Socket data types */ #include <arpa/inet.h> /* sockaddr_in, inet_addr() */ #include <stdlib.h> /* atoi() */ #include <string.h> /* memset() */ #include <unistd.h> /* close() */ #include diewitherror.h /* DieWithError() */ 3 TCP/IP Sockets mysock = socket(family, type, protocol); TCP/IP-specific sockets Family Type Protocol TCP UDP PF_INET SOCK_STREAM SOCK_DGRAM IPPROTO_TCP IPPROTO_UDP Socket reference» File (socket) descriptor in UNIX 4

3 Generic struct sockaddr { unsigned short sa_family; /* Address family (e.g., AF_INET) */ char sa_data[14]; /* Protocol-specific address information */ }; IP Specific struct sockaddr_in { unsigned short sin_family; /* Internet protocol (AF_INET) */ unsigned short sin_port; /* Port (16-bits) */ struct in_addr sin_addr; /* Internet address (32-bits) */ char sin_zero[8]; /* Not used */ }; struct in_addr { unsigned long s_addr; /* Internet address (32-bits) */ }; sockaddr Family Blob 2 bytes 2 bytes 4 bytes 8 bytes sockaddr_in Family Port Internet address Not used s and s : Initiates the connection : Bob : Jane Hi. I m Bob. Hi, Bob. I m Jane Nice to meet you, Jane. : Passively waits to respond 6

4 starts by getting ready to receive client connections 7 /* Create socket for incoming connections */ if ((servsock = socket(pf_inet, SOCK_STREAM, IPPROTO_TCP)) < 0) DieWithError("socket() failed"); 8

5 echoservaddr.sin_family = AF_INET; /* Internet address family */ echoservaddr.sin_addr.s_addr = htonl(inaddr_any); /* Any incoming interface */ echoservaddr.sin_port = htons(echoservport); /* Local port */ if (bind(servsock, (struct sockaddr *)&echoservaddr, sizeof(echoservaddr)) < 0) DieWithError("bind() failed"); 9 /* Mark the socket so it will listen for incoming connections */ if (listen(servsock, MAXPENDING) < 0) DieWithError("listen() failed"); 10

6 for (;;) /* Run forever */ { clntlen = sizeof(echoclntaddr); if ((clntsock=accept(servsock,(struct sockaddr *) &echoclntaddr, &clntlen)) < 0) DieWithError("accept() failed"); 11 is now blocked waiting for connection from a client Later, a client decides to talk to the server 12

7 /* Create a reliable, stream socket using TCP */ if ((sock = socket(pf_inet, SOCK_STREAM, IPPROTO_TCP)) < 0) DieWithError("socket() failed"); 13 echoservaddr.sin_family = AF_INET; /* Internet address family */ echoservaddr.sin_addr.s_addr = inet_addr(servip); /* IP address */ echoservaddr.sin_port = htons(echoservport); /* port */ if (connect(sock, (struct sockaddr *) &echoservaddr, sizeof(echoservaddr)) < 0) DieWithError("connect() failed"); 14

8 if ((clntsock=accept(servsock,(struct sockaddr *) &echoclntaddr, &clntlen)) < 0) DieWithError("accept() failed"); 15 echostringlen = strlen(echostring); /* Determine input length */ /* Send the string to the server */ if (send(sock, echostring, echostringlen, 0)!= echostringlen) DieWithError("send() sent a different number of bytes than expected"); 16

9 /* Receive message from client */ if ((recvmsgsize = recv(clntsocket, echobuffer, RCVBUFSIZE, 0)) < 0) DieWithError("recv() failed"); 17 close(sock); close(clntsocket); 18

10 TCP Tidbits must know the server s address and port only needs to know its own port No correlation between send() and recv() send( Hello Bob ) recv() -> Hello recv() -> Bob send( Hi ) send( Jane ) recv() -> Hi Jane 19 Closing a Connection close() used to delimit communication Analogous to EOF Echo Echo send(string) recv(buffer) while (not received entire string) recv(buffer) print(buffer) close(socket) while(client has not closed connection) send(buffer) recv(buffer) close(client socket) 20

11 Compiling % gcc -o TCPEcho TCPEcho.c -lsocket -lnsl -o executable - name of the executable (instead of a.out) -lsocket -lnsl - includes libraries necessary for socket communication Running %./TCPEcho Echo this! Full Example Differences from Textbook In both client and server» include extra #include statements» remove void DieWithError(char *errormessage); In server only» Add HandleTCP() code to TCPEcho.c instead of using a different file 22