15.6 Unix Domain Datagram ClientServer

15.6 Unix Domain Datagram Client/Server

We now recode our UDP client/server from Sections 8.3 and 8.5 to use Unix domain datagram sockets. Figure 15.5 shows the server, which is a modification of Figure 8.3.

Figure 15.4 Unix domain stream protocol echo client.

unixdomain/unixstrcli01.c

 1 #include    "unp.h"  2 int  3 main(int argc, char **argv)  4 {  5     int     sockfd;  6     struct sockaddr_un servaddr;  7     sockfd = Socket(AF_LOCAL, SOCK_STREAM, 0);  8     bzero(&servaddr, sizeof(servaddr));  9     servaddr.sun_family = AF_LOCAL; 10     strcpy(servaddr.sun_path, UNIXSTR_PATH); 11     Connect(sockfd, (SA *) &servaddr, sizeof(servaddr)); 12     str_cli(stdin, sockfd);     /* do it all */ 13     exit(0); 14 } 

Figure 15.5 Unix domain datagram protocol echo server.

unixdomain/unixdgserv01.c

 1 #include    "unp.h"  2 int  3 main(int argc, char **argv)  4 {  5     int     sockfd;  6     struct sockaddr_un servaddr, cliaddr;  7     sockfd = Socket(AF_LOCAL, SOCK_DGRAM, 0);  8     unlink(UNIXDG_PATH);  9     bzero(&servaddr, sizeof(servaddr)); 10     servaddr.sun_family = AF_LOCAL; 11     strcpy(servaddr.sun_path, UNIXDG_PATH); 12     Bind(sockfd, (SA *) &servaddr, sizeof(servaddr)); 13     dg_echo(sockfd, (SA *) &cliaddr, sizeof(cliaddr)); 14 } 

6 The datatype of the two socket address structures is now sockaddr_un .

7 The first argument to socket is AF_LOCAL , to create a Unix domain datagram socket.

8 “12 The constant UNIXDG_PATH is defined in unp.h to be /tmp/unix.dg . We first unlink the pathname, in case it exists from an earlier run of the server, and then initialize the socket address structure before calling bind . An error from unlink is acceptable.

13 The same dg_echo function is used (Figure 8.4).

Figure 15.6 is the Unix domain datagram protocol echo client. It is a modification of Figure 8.7.

Figure 15.6 Unix domain datagram protocol echo client.

unixdomain/unixdgcli01.c

 1 #include    "unp.h"  2 int  3 main(int argc, char **argv)  4 {  5     int     sockfd;  6     struct sockaddr_un cliaddr, servaddr;  7     sockfd = Socket(AF_LOCAL, SOCK_DGRAM, 0);  8     bzero(&cliaddr, sizeof(cliaddr));   /* bind an address for us */  9     cliaddr.sun_family = AF_LOCAL; 10     strcpy(cliaddr.sun_path, tmpnam(NULL)); 11     Bind(sockfd, (SA *) &cliaddr, sizeof(cliaddr)); 12     bzero(&servaddr, sizeof(servaddr)); /* fill in server's address */ 13     servaddr.sun_family = AF_LOCAL; 14     strcpy(servaddr.sun_path, UNIXDG_PATH); 15     dg_cli(stdin, sockfd, (SA *) &servaddr, sizeof(servaddr)); 16     exit(0); 17 } 

6 The socket address structure to contain the server's address is now a sockaddr_un structure. We also allocate one of these structures to contain the client's address, which we will talk about shortly.

7 The first argument to socket is AF_LOCAL .

8 “11 Unlike our UDP client, when using the Unix domain datagram protocol, we must explicitly bind a pathname to our socket so that the server has a pathname to which it can send its reply. We call tmpnam to assign a unique pathname that we then bind to our socket. Recall from Section 15.4 that sending a datagram on an unbound Unix domain datagram socket does not implicitly bind a pathname to the socket. Therefore, if we omit this step, the server's call to recvfrom in the dg_echo function returns a null pathname, which then causes an error when the server calls sendto .

12 “14 The code to fill in the socket address structure with the server's well-known pathname is identical to the code shown earlier for the server.

15 The function dg_cli is the same as that shown in Figure 8.8.