mirror of https://github.com/mkerrisk/man-pages
unix.7: Add example
A complete example demonstrating the usage of sockets for local interprocess communication is added. Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Heinrich Schuchardt
Michael Kerrisk
parent
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15545eb6d7
280
man7/unix.7
280
man7/unix.7
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@ -1,5 +1,6 @@
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.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
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.\" and Copyright (C) 2008-2014, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>,
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.\" Copyright (C) 2008-2014, Michael Kerrisk <mtk.manpages@gmail.com>,
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.\" and Copyright (C) 2016, Heinrich Schuchardt <xypron.glpk@gmx.de>
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.\"
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.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
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.\" and Copyright (C) 2008, 2012 Michael Kerrisk <mtk.manpages@gmail.com>
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@ -619,9 +620,280 @@ that the applications that
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pathname sockets follow the rules outlined above under
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.IR "Pathname sockets" .
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.SH EXAMPLE
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See
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.BR bind (2).
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The following code demonstrates the usage of sockets for local interprocess
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communication.
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It comprises two programs.
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The server program waits for a connection from the client program.
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The client sends all of its command line arguments.
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The server treats them as integers and adds them up.
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The client sends the command string END.
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The server returns the result.
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The client prints the sum of the received integers and exits.
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The server waits for the next client to connect.
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To stop the server the client is called with the command line argument
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DOWN.
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.PP
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The following output was recorded while running the server in the background
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and repeatedly calling the client.
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Execution of the server program ended when receiving the DOWN command.
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.SS Example output
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.in +4n
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.nf
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$ ./server &
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[1] 25887
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$ ./client 3 4
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Result = 7
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$ ./client 11 \-5
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Result = 6
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$ ./client DOWN
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Result = 0
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[1]+ Done ./server
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$
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.fi
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.in
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.SS Program source
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.nf
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/*
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* File connection.h
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*/
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#define SOCKET_NAME "/tmp/9Lq7BNBnBycd6nxy.socket"
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#define BUFFER_SIZE 12
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/*
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* File server.c
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <unistd.h>
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#include "connection.h"
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int
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main(int argc, char *argv[])
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{
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struct sockaddr_un name;
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int down_flag = 0;
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int ret;
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int connection_socket;
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int data_socket;
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int result;
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char buffer[BUFFER_SIZE];
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/*
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* In case the program exited inadvertently on the last run
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* remove the socket.
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*/
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unlink(SOCKET_NAME);
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/* Create local socket. */
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connection_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0);
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if (connection_socket == \-1) {
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perror("socket");
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exit(EXIT_FAILURE);
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}
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/*
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* For portability clear the whole structure, since some implementations
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* have additional (nonstandard) fields in the structure.
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*/
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memset(&name, 0, sizeof(struct sockaddr_un));
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/* Bind socket to socket name. */
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name.sun_family = AF_UNIX;
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strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) \- 1);
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ret = bind(connection_socket, (const struct sockaddr *) &name,
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sizeof(struct sockaddr_un));
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if (ret == \-1) {
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perror("bind");
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exit(EXIT_FAILURE);
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}
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/*
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* Prepare for accepting connections. The backlog size is set to 20. So
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* while one request is being processed other requests can be waiting.
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*/
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ret = listen(connection_socket, 20);
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if (ret == \-1) {
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perror("listen");
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exit(EXIT_FAILURE);
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}
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/* This is the main loop for handling connections. */
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for (;;) {
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/* Wait for incoming connection. */
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data_socket = accept(connection_socket, NULL, NULL);
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if (ret == \-1) {
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perror("accept");
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exit(EXIT_FAILURE);
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}
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result = 0;
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for(;;) {
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/* Wait for next data packet. */
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ret = read(data_socket, buffer, BUFFER_SIZE);
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if (ret == \-1) {
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perror("recv");
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exit(EXIT_FAILURE);
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}
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/* Ensure buffer is 0\-terminated. */
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buffer[BUFFER_SIZE \- 1] = 0;
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/* Handle commands. */
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if (!strncmp(buffer, "DOWN", BUFFER_SIZE)) {
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down_flag = 1;
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break;
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}
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if (!strncmp(buffer, "END", BUFFER_SIZE)) {
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break;
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}
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/* Add received summand. */
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result += atoi(buffer);
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}
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/* Send result. */
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sprintf(buffer, "%d", result);
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ret = write(data_socket, buffer, BUFFER_SIZE);
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if (ret == \-1) {
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perror("send");
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exit(EXIT_FAILURE);
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}
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/* Close socket. */
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close(data_socket);
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/* Quit on DOWN command. */
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if (down_flag) {
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break;
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}
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}
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close(connection_socket);
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/* Unlink the socket. */
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unlink(SOCKET_NAME);
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exit(EXIT_SUCCESS);
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}
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/*
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* File client.c
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*/
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <unistd.h>
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#include "connection.h"
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int
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main(int argc, char *argv[])
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{
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struct sockaddr_un name;
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int i;
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int ret;
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int data_socket;
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char buffer[BUFFER_SIZE];
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/* Create local socket. */
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data_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0);
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if (data_socket == \-1) {
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perror("socket");
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exit(EXIT_FAILURE);
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}
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/*
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* For portability clear the whole structure, since some implementations
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* have additional (nonstandard) fields in the structure.
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*/
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memset(&name, 0, sizeof(struct sockaddr_un));
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/* Connect socket to socket name. */
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name.sun_family = AF_UNIX;
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strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) \- 1);
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ret = connect (data_socket, (const struct sockaddr *) &name,
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sizeof(struct sockaddr_un));
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if (ret == \-1) {
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fprintf(stderr, "The server is down.\\n");
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exit(EXIT_FAILURE);
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}
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/* Send arguments. */
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for (i = 1; i < argc; ++i) {
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ret = write(data_socket, argv[i], strlen(argv[i]) + 1);
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if (ret == \-1) {
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perror("send");
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break;
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}
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}
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/* Request result. */
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strcpy (buffer, "END");
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ret = write(data_socket, buffer, strlen(buffer) + 1);
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if (ret == \-1) {
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perror("send");
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exit(EXIT_FAILURE);
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}
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/* Receive result. */
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ret = read(data_socket, buffer, BUFFER_SIZE);
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if (ret == \-1) {
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perror("recv");
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exit(EXIT_FAILURE);
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}
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/* Ensure buffer is 0\-terminated. */
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buffer[BUFFER_SIZE \- 1] = 0;
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printf("Result = %s\\n", buffer);
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/* Close socket. */
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close(data_socket);
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exit(EXIT_SUCCESS);
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}
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.fi
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.PP
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For an example of the use of
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.BR SCM_RIGHTS
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see
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