A complete example demonstrating the usage of sockets for local interprocess
communication is added.
v2:
Add missing [] for argv.
Use meaningful variable names.
Use AF_UNIX instead of PF_LOCAL.
memset name structure to 0.
Use read, write instead of recv, send.
Thx to Michael for reviewing.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
---
man7/unix.7 | 280 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 276 insertions(+), 4 deletions(-)
diff --git a/man7/unix.7 b/man7/unix.7
index e6e311f..5a4ad63 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -1,5 +1,6 @@
-.\" This man page is Copyright (C) 1999 Andi Kleen <ak@xxxxxx>.
-.\" and Copyright (C) 2008-2014, Michael Kerrisk <mtk.manpages@xxxxxxxxx>
+.\" This man page is Copyright (C) 1999 Andi Kleen <ak@xxxxxx>,
+.\" Copyright (C) 2008-2014, Michael Kerrisk <mtk.manpages@xxxxxxxxx>,
+.\" and Copyright (C) 2016, Heinrich Schuchardt <xypron.glpk@xxxxxx>
.\"
.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
.\" and Copyright (C) 2008, 2012 Michael Kerrisk <mtk.manpages@xxxxxxxxx>
@@ -618,9 +619,280 @@ that the applications that
pathname sockets follow the rules outlined above under
.IR "Pathname sockets" .
.SH EXAMPLE
-See
-.BR bind (2).
+The following code demonstrates the usage of sockets for local interprocess
+communication.
+It comprises two programs.
+The server program waits for a connection from the client program.
+The client sends all of its command line arguments.
+The server treats them as integers and adds them up.
+The client sends the command string END.
+The server returns the result.
+The client prints the sum of the received integers and exits.
+The server waits for the next client to connect.
+To stop the server the client is called with the command line argument
+DOWN.
+.PP
+The following output was recorded while running the server in the background
+and repeatedly calling the client.
+Execution of the server program ended when receiving the DOWN command.
+.SS Example output
+.in +4n
+.nf
+$ ./server &
+[1] 25887
+$ ./client 3 4
+Result = 7
+$ ./client 11 \-5
+Result = 6
+$ ./client DOWN
+Result = 0
+[1]+ Done ./server
+$
+.fi
+.in
+.SS Program source
+.nf
+/*
+ * File connection.h
+ */
+
+#define SOCKET_NAME "/tmp/9Lq7BNBnBycd6nxy.socket"
+#define BUFFER_SIZE 12
+
+/*
+ * File server.c
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+#include "connection.h"
+
+int
+main(int argc, char *argv[])
+{
+ struct sockaddr_un name;
+ int down_flag = 0;
+ int ret;
+ int connection_socket;
+ int data_socket;
+ int result;
+ char buffer[BUFFER_SIZE];
+
+ /*
+ * In case the program exited inadvertently on the last run
+ * remove the socket.
+ */
+
+ unlink(SOCKET_NAME);
+
+ /* Create local socket. */
+
+ connection_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0);
+ if (connection_socket == \-1) {
+ perror("socket");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * For portability clear the whole structure, since some implementations
+ * have additional (nonstandard) fields in the structure.
+ */
+
+ memset(&name, 0, sizeof(struct sockaddr_un));
+
+ /* Bind socket to socket name. */
+
+ name.sun_family = AF_UNIX;
+ strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) \- 1);
+
+ ret = bind(connection_socket, (const struct sockaddr *) &name,
+ sizeof(struct sockaddr_un));
+ if (ret == \-1) {
+ perror("bind");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * Prepare for accepting connections. The backlog size is set to 20. So
+ * while one request is being processed other requests can be waiting.
+ */
+
+ ret = listen(connection_socket, 20);
+ if (ret == \-1) {
+ perror("listen");
+ exit(EXIT_FAILURE);
+ }
+
+ /* This is the main loop for handling connections. */
+
+ for (;;) {
+
+
+ /* Wait for incoming connection. */
+
+ data_socket = accept(connection_socket, NULL, NULL);
+ if (ret == \-1) {
+ perror("accept");
+ exit(EXIT_FAILURE);
+ }
+
+ result = 0;
+ for(;;) {
+
+ /* Wait for next data packet. */
+
+ ret = read(data_socket, buffer, BUFFER_SIZE);
+ if (ret == \-1) {
+ perror("recv");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Ensure buffer is 0\-terminated. */
+
+ buffer[BUFFER_SIZE \- 1] = 0;
+
+ /* Handle commands. */
+
+ if (!strncmp(buffer, "DOWN", BUFFER_SIZE)) {
+ down_flag = 1;
+ break;
+ }
+
+ if (!strncmp(buffer, "END", BUFFER_SIZE)) {
+ break;
+ }
+
+ /* Add received summand. */
+
+ result += atoi(buffer);
+ }
+ /* Send result. */
+
+ sprintf(buffer, "%d", result);
+ ret = write(data_socket, buffer, BUFFER_SIZE);
+
+ if (ret == \-1) {
+ perror("send");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Close socket. */
+
+ close(data_socket);
+
+ /* Quit on DOWN command. */
+
+ if (down_flag) {
+ break;
+ }
+ }
+
+ close(connection_socket);
+
+ /* Unlink the socket. */
+
+ unlink(SOCKET_NAME);
+
+ exit(EXIT_SUCCESS);
+}
+
+/*
+ * File client.c
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+#include "connection.h"
+
+int
+main(int argc, char *argv[])
+{
+ struct sockaddr_un name;
+ int i;
+ int ret;
+ int data_socket;
+ char buffer[BUFFER_SIZE];
+
+ /* Create local socket. */
+
+ data_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0);
+ if (data_socket == \-1) {
+ perror("socket");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * For portability clear the whole structure, since some implementations
+ * have additional (nonstandard) fields in the structure.
+ */
+
+ memset(&name, 0, sizeof(struct sockaddr_un));
+
+ /* Connect socket to socket name. */
+
+ name.sun_family = AF_UNIX;
+ strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) \- 1);
+
+ ret = connect (data_socket, (const struct sockaddr *) &name,
+ sizeof(struct sockaddr_un));
+ if (ret == \-1) {
+ fprintf(stderr, "The server is down.\\n");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Send arguments. */
+
+ for (i = 1; i < argc; ++i) {
+ ret = write(data_socket, argv[i], strlen(argv[i]) + 1);
+ if (ret == \-1) {
+ perror("send");
+ break;
+ }
+ }
+
+ /* Request result. */
+
+ strcpy (buffer, "END");
+ ret = write(data_socket, buffer, strlen(buffer) + 1);
+ if (ret == \-1) {
+ perror("send");
+ exit(EXIT_FAILURE);
+ }
+
+
+ /* Receive result. */
+
+ ret = read(data_socket, buffer, BUFFER_SIZE);
+ if (ret == \-1) {
+ perror("recv");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Ensure buffer is 0\-terminated. */
+
+ buffer[BUFFER_SIZE \- 1] = 0;
+
+ printf("Result = %s\\n", buffer);
+
+ /* Close socket. */
+
+ close(data_socket);
+
+ exit(EXIT_SUCCESS);
+}
+
+.fi
+.PP
For an example of the use of
.BR SCM_RIGHTS
see
--
2.1.4
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
