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samples: sockets: socketpair: sample application and docs
Support for the socketpair(2) system call was recently added for 2.3.0 . This change adds a sample application that demonstrates how it can be used. Fixes #25527 Signed-off-by: Christopher Friedt <[email protected]>
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‎samples/net/sockets/socketpair/CMakeLists.txt‎

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.13.1)
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find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
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project(sockets_socketpair)
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FILE(GLOB app_sources src/*.c)
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target_sources(app PRIVATE ${app_sources})
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include(${ZEPHYR_BASE}/samples/net/common/common.cmake)

‎samples/net/sockets/socketpair/Makefile.posix‎

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#
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# Copyright (c) 2020 Friedt Professional Engineering Services, Inc
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#
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# SPDX-License-Identifier: Apache-2.0
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#
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socketpair_example: src/socketpair_example.c
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$(CXX) $^ -o $@ -lpthread

‎samples/net/sockets/socketpair/README.rst‎

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.. _sockets-socketpair-sample:
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Socketpair Example
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##################
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Overview
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********
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The sockets/socketpair sample application for Zephyr demonstrates a
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multi-threaded application communicating over pairs of unnamed,
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connected UNIX-domain sockets. The pairs of sockets are created with
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socketpair(2), as you might have guessed. Such sockets are compatible
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with the BSD Sockets API, and therefore the purpose of this sample
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is also to reinforce that it is possible to develop a sockets
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application portable to both POSIX and Zephyr.
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The source code for this sample application can be found at:
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:zephyr_file:`samples/net/sockets/socketpair`.
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Requirements
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************
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None
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Building and Running
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********************
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Build the Zephyr version of the sockets/echo application like this:
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.. zephyr-app-commands::
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:zephyr-app: samples/net/sockets/socketpair
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:board: <board_to_use>
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:goals: build
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:compact:
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After the sample starts, several clients thread are spawned and each client
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thread sends a fixed number of messages to the server (main). Each client
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sends a message (it's name) to the server.
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.. code-block:: console
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*** Booting Zephyr OS build v2.3.0-rc1-215-g0e36f9686836 ***
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Alpha: socketpair: 3 <=> 4
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Bravo: socketpair: 5 <=> 7
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Charlie: socketpair: 8 <=> 9
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Charlie closed fd 9
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fd: 8: read 21 bytes
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fd: 8: hung up
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main: closed fd 8
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joined Charlie
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Alpha closed fd 4
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fd: 3: read 15 bytes
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fd: 3: hung up
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main: closed fd 3
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joined Alpha
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Bravo closed fd 7
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fd: 5: read 15 bytes
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fd: 5: hung up
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main: closed fd 5
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joined Bravo
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finished!
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Running application on POSIX Host
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=================================
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The same application source code can be built for a POSIX system, e.g.
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Linux.
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To build for a host POSIX OS:
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.. code-block:: console
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$ make -f Makefile.posix
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To run:
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.. code-block:: console
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$ ./socketpair_example
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Alpha: socketpair: 3 <=> 4
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Bravo: socketpair: 5 <=> 6
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Charlie: socketpair: 7 <=> 8
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Alpha closed fd 4
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fd: 3: read 15 bytes
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fd: 3: hung up
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main: closed fd 3
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joined Alpha
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fd: 5: read 15 bytes
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fd: 5: hung up
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Bravo closed fd 6
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main: closed fd 5
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joined Bravo
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Charlie closed fd 8
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fd: 7: read 21 bytes
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fd: 7: hung up
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main: closed fd 7
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joined Charlie
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finished!
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As can be seen, the behavior of the application is approximately the same as
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the Zephyr version.

‎samples/net/sockets/socketpair/prj.conf‎

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# Provide some heap space
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CONFIG_HEAP_MEM_POOL_SIZE=2048
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# Networking config
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CONFIG_NETWORKING=y
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CONFIG_NET_SOCKETS=y
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CONFIG_NET_SOCKETS_POSIX_NAMES=y
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CONFIG_NET_SOCKETPAIR=y
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# Network driver config
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CONFIG_TEST_RANDOM_GENERATOR=y
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# Use Portable threads
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CONFIG_PTHREAD_IPC=y
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CONFIG_NET_SOCKETS_POSIX_NAMES=y

‎samples/net/sockets/socketpair/sample.yaml‎

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sample:
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description: BSD Sockets API TCP socketpair sample
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name: socket_socketpair
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tests:
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sample.net.sockets.socketpair:
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harness: net
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tags: net socket

‎samples/net/sockets/socketpair/src/socketpair_example.c‎

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/*
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* Copyright (c) 2020 Friedt Professional Engineering Services, Inc
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#if defined(__ZEPHYR__) && !(defined(CONFIG_BOARD_NATIVE_POSIX_32BIT) \
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|| defined(CONFIG_BOARD_NATIVE_POSIX_64BIT) \
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|| defined(CONFIG_SOC_SERIES_BSIM_NRFXX))
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#include <net/socket.h>
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#include <posix/pthread.h>
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#include <sys/util.h>
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#include <posix/unistd.h>
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#else
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#include <poll.h>
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#include <pthread.h>
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#include <sys/socket.h>
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#include <sys/types.h>
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#include <unistd.h>
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#define ARRAY_SIZE(x) (sizeof(x)/sizeof((x)[0]))
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#endif
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#include <errno.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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#define NUM_SOCKETPAIRS 3
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#define NUM_REPITITIONS 3
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struct ctx {
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int spair[2];
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pthread_t thread;
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char *name;
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};
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static const char *const names[] = {
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"Alpha",
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"Bravo",
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"Charlie",
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};
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static void hello(int fd, const char *name)
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{
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/* write(2) should be used after #25443 */
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send(fd, name, strlen(name), 0);
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}
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static void *fun(void *arg)
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{
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struct ctx *const ctx = (struct ctx *)arg;
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int fd = ctx->spair[1];
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const char *name = ctx->name;
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for (size_t i = 0; i < NUM_REPITITIONS; ++i) {
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hello(fd, name);
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}
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close(fd);
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printf("%s closed fd %d\n", name, fd);
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ctx->spair[1] = -1;
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return NULL;
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}
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static int fd_to_idx(int fd, struct ctx *ctx, size_t n)
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{
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int r = -1;
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size_t i;
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for (i = 0; i < n; ++i) {
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if (ctx[i].spair[0] == fd) {
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r = i;
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break;
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}
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}
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return r;
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}
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#ifdef __ZEPHYR__
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void zephyr_app_main(void)
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{
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#else
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int main(int argc, char *argv[])
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{
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(void) argc;
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(void) argv;
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#endif
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int r;
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int fd;
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int idx;
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int poll_r;
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size_t i;
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size_t num_active;
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char buf[32];
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struct ctx ctx[NUM_SOCKETPAIRS] = {};
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struct pollfd fds[NUM_SOCKETPAIRS] = {};
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void *unused;
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for (i = 0; i < ARRAY_SIZE(ctx); ++i) {
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ctx[i].name = (char *)names[i];
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socketpair(AF_UNIX, SOCK_STREAM, 0, ctx[i].spair);
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pthread_create(&ctx[i].thread, NULL, fun, &ctx[i]);
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printf("%s: socketpair: %d <=> %d\n",
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ctx[i].name, ctx[i].spair[0], ctx[i].spair[1]);
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}
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/* loop until all threads are done */
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for (;;) {
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/* count threads that are still running and fill in pollfds */
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for (i = 0, num_active = 0; i < ARRAY_SIZE(ctx); ++i) {
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if (ctx[i].spair[0] == -1) {
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continue;
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}
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fds[num_active].fd = ctx[i].spair[0];
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fds[num_active].events = POLLIN;
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fds[num_active].revents = 0;
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num_active++;
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}
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if (num_active == 0) {
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/* all threads are done */
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break;
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}
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poll_r = poll(fds, num_active, -1);
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for (size_t i = 0; i < num_active; ++i) {
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fd = fds[i].fd;
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idx = fd_to_idx(fd, ctx, ARRAY_SIZE(ctx));
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if ((fds[i].revents & POLLIN) != 0) {
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memset(buf, '\0', sizeof(buf));
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/* read(2) should be used after #25443 */
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r = recv(fd, buf, sizeof(buf), 0);
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printf("fd: %d: read %d bytes\n", fd, r);
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}
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if ((fds[i].revents & POLLERR) != 0) {
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printf("fd: %d: error\n", fd);
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}
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if ((fds[i].revents & POLLHUP) != 0) {
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printf("fd: %d: hung up\n", fd);
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close(ctx[idx].spair[0]);
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printf("main: closed fd %d\n",
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ctx[idx].spair[0]);
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pthread_join(ctx[idx].thread, &unused);
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printf("joined %s\n", ctx[idx].name);
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ctx[idx].spair[0] = -1;
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}
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}
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}
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printf("finished!\n");
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#ifndef __ZEPHYR__
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return 0;
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#endif
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}

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