examples: add posix_select example

examples/posix_select/Makefile

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+# name of your application
+APPLICATION = posix_sockets_example
+
+# If no BOARD is found in the environment, use this default:
+BOARD ?= native
+
+# This has to be the absolute path to the RIOT base directory:
+RIOTBASE ?= $(CURDIR)/../..
+
+# Include packages that pull up and auto-init the link layer.
+# NOTE: 6LoWPAN will be included if IEEE802.15.4 devices are present
+USEMODULE += gnrc_netdev_default
+USEMODULE += auto_init_gnrc_netif
+# Specify the mandatory networking modules for socket communication via UDP
+USEMODULE += gnrc_ipv6_default
+# Add stack-specific implementations of sock modules
+USEMODULE += gnrc_sock_async
+USEMODULE += gnrc_sock_udp
+# Add POSIX modules
+USEMODULE += posix_select
+USEMODULE += posix_sockets
+USEMODULE += posix_inet
+
+# Comment this out to disable code in RIOT that does safety checking
+# which is not needed in a production environment but helps in the
+# development process:
+DEVELHELP ?= 1
+
+# Change this to 0 show compiler invocation lines by default:
+QUIET ?= 1
+
+include $(RIOTBASE)/Makefile.include

examples/posix_select/Makefile.ci

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+BOARD_INSUFFICIENT_MEMORY := \
+    arduino-duemilanove \
+    arduino-leonardo \
+    arduino-mega2560 \
+    arduino-nano \
+    arduino-uno \
+    atmega328p \
+    chronos \
+    i-nucleo-lrwan1 \
+    msb-430 \
+    msb-430h \
+    nucleo-f030r8 \
+    nucleo-f031k6 \
+    nucleo-f042k6 \
+    nucleo-f303k8 \
+    nucleo-f334r8 \
+    nucleo-l031k6 \
+    nucleo-l053r8 \
+    stm32f030f4-demo \
+    stm32f0discovery \
+    stm32l0538-disco \
+    telosb \
+    waspmote-pro \
+    wsn430-v1_3b \
+    wsn430-v1_4 \
+    z1 \
+    #

examples/posix_select/README.md

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+examples/posix_sockets
+======================
+This application is a showcase for RIOT's POSIX select support. To
+keep things simple this application has only one-hop support and
+no routing capabilities.
+
+Usage
+=====
+
+Build, flash and start the application:
+```sh
+export BOARD=your_board
+make
+make flash
+make term
+```
+
+The `term` make target starts a terminal emulator for your board. It
+connects to a default port so you can interact with the shell, usually
+that is `/dev/ttyUSB0`. If your port is named differently, the
+`PORT=/dev/yourport` (not to be confused with the UDP port) variable can
+be used to override this.
+
+
+Example output
+==============
+
+The application starts 4 UDP servers on a selection of different ports that wait
+for input simultaneously:
+```
+2019-12-17 16:36:45,559 # RIOT select example application
+2019-12-17 16:36:45,561 # Started UDP server at [fe80::14ac:fb65:106b:1115]:1350
+2019-12-17 16:36:45,562 # Started UDP server at [fe80::14ac:fb65:106b:1115]:4973
+2019-12-17 16:36:45,562 # Started UDP server at [fe80::14ac:fb65:106b:1115]:6717
+2019-12-17 16:36:45,562 # Started UDP server at [fe80::14ac:fb65:106b:1115]:9673
+```
+
+If you do not see any output you might need to reset the node. Either, by
+pressing the hardware reset button on the board or by running
+```sh
+make reset
+```
+
+There is no shell in this application. You can use the [`posix_sockets` example]
+from another board to send a packet to the node:
+
+```
+> udp send fe80::14ac:fb65:106b:1115 6717 "Hello World!"
+2019-12-17 16:47:01,789 # udp send fe80::14ac:fb65:106b:1115 6717 "Hello World!"
+2019-12-17 16:47:01,795 # Success: send 12 byte to fe80::14ac:fb65:106b:1115:6717
+```
+
+On the board with the `posix_select` example you will see then something like
+this:
+
+```
+2019-12-17 16:47:01,796 # Received data from [fe80::589d:9386:2208:6579]:192:
+2019-12-17 16:47:01,796 # Hello World!
+```
+
+Alternatively, with `native` or if your host also can connect to the board, you
+can also use [`netcat`][netcat] to send multiple packets simultaneously. E.g.
+when the node is connected to the host via the interface `tapbr0`:
+
+```sh
+echo -ne "Hello World!" | nc -6u "fe80::78b9:ecff:fe96:8279%tapbr0" 4973 & \
+    echo -ne "Hello Space!" | nc -6u "fe80::78b9:ecff:fe96:8279%tapbr0" 1350
+killall nc
+```
+
+This is what the `native` node will then show:
+
+```
+Received data from [fe80::3ccc:8dff:fe9f:9991]:14279:
+Hello World!
+
+Received data from [fe80::3ccc:8dff:fe9f:9991]:58817:
+Hello Space!
+
+```
+
+[`posix_sockets` example]: ../posix_sockets
+[netcat]: https://www.unix.com/man-page/Linux/1/netcat/

examples/posix_select/main.c

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+/*
+ * Copyright (C) 2019 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     examples
+ * @{
+ *
+ * @file
+ * @brief       Example application for demonstrating the RIOT's POSIX select()
+ *              implementation
+ *
+ * @author      Martine Lenders <[email protected]>
+ *
+ * @}
+ */
+
+#include <stdbool.h>
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include "od.h"
+#include "net/gnrc/netif.h"
+#include "thread.h"
+
+#define SERVER_BUFFER_SIZE      (128U)
+#define SERVER_PORTS            { 1350U, 4973U, 6717U, 9673U }
+#define SERVER_SOCKETS_NUM      (4U)
+
+static char server_buffer[SERVER_BUFFER_SIZE];
+static char addr_str[IPV6_ADDR_MAX_STR_LEN];
+
+static int _run_server(void *local_addr)
+{
+    struct sockaddr_in6 server_addr = { .sin6_family = AF_INET6,
+                                        .sin6_addr = IN6ADDR_ANY_INIT };
+    static const uint16_t ports[SERVER_SOCKETS_NUM] = SERVER_PORTS;
+    int server_sockets[SERVER_SOCKETS_NUM] = { 0 };
+    int max_fd = -1;
+    int ret = 0;
+
+    /* open SERVER_SOCKETS_NUM sockets with respective port */
+    for (unsigned i = 0; i < SERVER_SOCKETS_NUM; i++) {
+        server_sockets[i] = socket(AF_INET6, SOCK_DGRAM, 0);
+        if (server_sockets[i] < 0) {
+            puts("error initializing socket");
+            ret = 1;
+            goto end;
+        }
+        server_addr.sin6_port = htons(ports[i]);
+        if (bind(server_sockets[i],
+                 (struct sockaddr *)&server_addr,
+                 sizeof(server_addr)) < 0) {
+            puts("error binding socket");
+            ret = 1;
+            goto end;
+        }
+        printf("Started UDP server at [%s]:%u\n",
+               inet_ntop(AF_INET6, local_addr, addr_str, sizeof(addr_str)),
+               ports[i]);
+        if (max_fd < server_sockets[i]) {
+            max_fd = server_sockets[i];
+        }
+    }
+
+    while (true) {
+        fd_set readfds;
+
+        /* add bound sockets to set of file descriptors to read */
+        FD_ZERO(&readfds);
+        for (unsigned i = 0; i < SERVER_SOCKETS_NUM; i++) {
+            FD_SET(server_sockets[i], &readfds);
+        }
+        /* wait for bound sockets to be notified for reading*/
+        if (select(max_fd + 1, &readfds, NULL, NULL, NULL) < 0) {
+            puts("error on select");
+            continue;
+        }
+        for (unsigned i = 0; i < SERVER_SOCKETS_NUM; i++) {
+            /* if socket is in set of file descriptors to check for reading */
+            if (FD_ISSET(server_sockets[i], &readfds)) {
+                int res;
+                struct sockaddr_in6 src;
+                socklen_t src_len = sizeof(struct sockaddr_in6);
+
+                /* receive data from socket */
+                if ((res = recvfrom(server_sockets[i], server_buffer,
+                                    sizeof(server_buffer), 0,
+                                    (struct sockaddr *)&src, &src_len)) < 0) {
+                    puts("Error on receive");
+                }
+                else if (res == 0) {
+                    puts("Peer did shut down");
+                }
+                else {
+                    printf("Received data from [%s]:%u:\n",
+                           inet_ntop(AF_INET6, &src.sin6_addr,
+                                     addr_str, sizeof(addr_str)),
+                           src.sin6_port);
+                    res = ((unsigned)res < SERVER_BUFFER_SIZE) ? res : (res - 1);
+                    /* terminate string */
+                    server_buffer[res] = '\0';
+                    printf("%s\n", server_buffer);
+                }
+            }
+        }
+    }
+
+end:
+    /* close all open sockets */
+    for (unsigned i = 0; i < SERVER_SOCKETS_NUM; i++) {
+        if (server_sockets[i] > 0) {
+            close(server_sockets[i]);
+        }
+    }
+    return ret;
+}
+
+int main(void)
+{
+    /* TODO: use TBD POSIX API to get link-local address */
+    gnrc_netif_t *netif = gnrc_netif_iter(NULL);
+    ipv6_addr_t addr;
+
+    puts("RIOT select example application");
+
+    /* get first address on the interface */
+    if (gnrc_netif_ipv6_addrs_get(netif, &addr, sizeof(addr)) < 0) {
+        puts("Unable to get first address of the interface");
+        return 1;
+    }
+    return _run_server(&addr);
+}