Berkeley Socket API – Creating a TCP/IP client in C

Programming Languages

C

API

Berkeley Socket API

Data Structure used to store socked details

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struct sockaddr_in6 {     u_char      sin6_len;   // length of this structure     u_char      sin6_family;    // AF_INET6     u_int16m_t  sin6_port;  // Transport layer port #     u_int32m_t  sin6_flowinfo;  // IPv6 flow information     struct in6_addr sin6_addr;  // IPv6 address };

Filling the socket local address

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// Declare the vars to use struct sockaddr_in6 localaddress, remoteaddress; // Fill the structures with zero's memset(&localaddress,0,sizeof(localaddress)); memset(&remoteaddress,0,sizeof(remoteaddress)); // Client socket details // Listen on any ipv6 address localaddress.sin6_addr = in6addr_any; // Address Family AF_INET6 is required localaddress.sin6_family = AF_INET6; // A client usually runs on a random port, the server has a static port localaddress.sin6_port = 0; // Server socket details // Fill remote.sin6_addr with the network address inet_pton(AF_INET6,"2001:41d0:1:f574::1111", &remote.sin6_addr); // Address Family AF_INET6 is required remote.sin6_family = AF_INET6; // Server port remote.sin6_port = htons(8000);

Creating the socket

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

domain

AF_UNIX – UNIX internal protocols
AF_INET – ARPA Internet protocols
AF_ISO – ISO protocols
AF_NS – Xerox Network Systems protocols
AF_IMPLINK – IMP host at IMP link layer

Type

SOCK_STREAM – provides sequenced, reliable, two-way connection based byte streams
SOCK_DGRAM – connectionless, unreliable messages of a fixed (typically small) maximum length
SOCK_RAW – sockets provide access to internal network protocols and interfaces
SOCK_SEQPACKET – provide a sequenced, reliable, two-way connection-based data transmission path for datagrams of fixed maximum length
SOCK_RDM – Not implemented

Returns

0 – Error
1+ – Socket descriptor

Bind the socket

1	int bind(int socket, const struct sockaddr *address, socklen_t address_len);

socket – Socket descriptor
address – Socket address (address, port, family…)
address_len – Structure address size

Connect to remote socket

1	int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen);

socket – Socket descriptor
address – Socket address (address, port, family…)
address_len – Structure address size

Returns

0 – OK
-1 – Error

Read and write from a socket

It works exactly like when we’re reading from a file, pipe, etc.

Read from socket

1	read(sockd, &buffer, 100);

Write to socket

1	write(sockd, &buffer, strlen(buffer));

Client code revealed

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#include <stdio.h> #include <sys/types.h> #include <fcntl.h> #include <sys/socket.h> #include <sys/param.h> #include <sys/stat.h> #include <unistd.h> #include <netinet/in.h> #include <string.h> #include <stdlib.h>   void newConnectionHandler(int sockd){     char buffer[100] = {'t', 'e', 's', 't', '\0'};       if(write(sockd, &buffer, strlen(buffer)) < 1)         perror("Unable to write on socket");     if(read(sockd, &buffer, 100) < 0)         perror("Unable to read from socket");       printf("Received: %s\n", buffer); }   int main(int argc, char *argv[]) {     int sockd,newsockd,tmpint;     struct sockaddr_in6 localaddress,remoteaddress;     fd_set descriptorslist;     struct timeval timeout;       // Client address     memset(&localaddress,0,sizeof(localaddress));     localaddress.sin6_addr = in6addr_any;     localaddress.sin6_family = AF_INET6;     localaddress.sin6_port = 0;       // Server address     memset(&remoteaddress,0,sizeof(remoteaddress));     inet_pton(AF_INET6, "2001:41d0:1:f574::1111", &remoteaddress.sin6_addr);     remoteaddress.sin6_family = AF_INET6;     remoteaddress.sin6_port = htons(8000);       // Create the socket     if((sockd = socket(AF_INET6, SOCK_STREAM,0))<1){         perror("Unable to create socket");         return 1;     }       // Bind socket sockfd on localaddress     if(bind(sockd, (struct sockaddr *)&localaddress, sizeof(localaddress)) != 0){         perror("Unable to bind socket");         return 1;     }       tmpint = sizeof(remoteaddress);     if(connect(sockd,(struct sockaddr *)&remoteaddress, tmpint) == -1){         perror("Unable to connect");         return 1;     }       newConnectionHandler(sockd); }

 

http://www.silviosilva.com/2009/07/15/berkeley-socket-api-creating-a-tcpip-server-in-c/