examples/telnet_server: add telnet server example

examples/telnet_server/Makefile

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+# name of your application
+APPLICATION = telnet_server
+
+# 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 += netdev_default
+USEMODULE += auto_init_gnrc_netif
+# Activate ICMPv6 error messages
+USEMODULE += gnrc_icmpv6_error
+# Specify the mandatory networking modules for IPv6
+USEMODULE += gnrc_ipv6_default
+# Additional networking modules that can be dropped if not needed
+USEMODULE += gnrc_icmpv6_echo
+USEMODULE += netutils
+# Add also the shell, some shell commands
+USEMODULE += shell
+USEMODULE += shell_commands
+USEMODULE += ps
+# Include the telnet server
+USEMODULE += stdio_telnet
+
+# Enable faster re-connects
+CFLAGS += -DCONFIG_GNRC_TCP_EXPERIMENTAL_DYN_MSL_EN=1
+
+# Acknowledge that telnet is bad
+I_UNDERSTAND_THAT_TELNET_IS_INSECURE = 1
+
+# enable debug output via UART
+FEATURES_OPTIONAL += periph_uart
+
+# Optionally include DNS support. This includes resolution of names at an
+# upstream DNS server and the handling of RDNSS options in Router Advertisements
+# to auto-configure that upstream DNS server.
+# USEMODULE += sock_dns              # include DNS client
+# USEMODULE += gnrc_ipv6_nib_dns     # include RDNSS option handling
+
+# 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
+
+include $(RIOTBASE)/Makefile.include
+
+# Set a custom channel if needed
+include $(RIOTMAKE)/default-radio-settings.inc.mk

examples/telnet_server/Makefile.ci

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+BOARD_INSUFFICIENT_MEMORY := \
+    arduino-duemilanove \
+    arduino-leonardo \
+    arduino-mega2560 \
+    arduino-nano \
+    arduino-uno \
+    atmega1284p \
+    atmega328p \
+    atmega328p-xplained-mini \
+    atxmega-a3bu-xplained \
+    bluepill-stm32f030c8 \
+    derfmega128 \
+    i-nucleo-lrwan1 \
+    mega-xplained \
+    microduino-corerf \
+    msb-430 \
+    msb-430h \
+    nucleo-f030r8 \
+    nucleo-f031k6 \
+    nucleo-f042k6 \
+    nucleo-f303k8 \
+    nucleo-f334r8 \
+    nucleo-l011k4 \
+    nucleo-l031k6 \
+    nucleo-l053r8 \
+    samd10-xmini \
+    stk3200 \
+    slstk3400a \
+    stm32f030f4-demo \
+    stm32f0discovery \
+    stm32g0316-disco \
+    stm32l0538-disco \
+    telosb \
+    waspmote-pro \
+    z1 \
+    zigduino \
+    #

examples/telnet_server/main.c

@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2021 ML!PA Consulting GmbH
+ *
+ * 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 telnet server
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "net/ipv6/addr.h"
+#include "net/gnrc.h"
+#include "net/gnrc/netif.h"
+#include "net/telnet.h"
+#include "shell.h"
+#include "msg.h"
+
+#define MAIN_QUEUE_SIZE     (8)
+static msg_t _main_msg_queue[MAIN_QUEUE_SIZE];
+
+static void _print_addr(void)
+{
+    gnrc_netif_t *netif = NULL;
+    while ((netif = gnrc_netif_iter(netif))) {
+        ipv6_addr_t ipv6_addrs[CONFIG_GNRC_NETIF_IPV6_ADDRS_NUMOF];
+        int res = gnrc_netapi_get(netif->pid, NETOPT_IPV6_ADDR, 0, ipv6_addrs,
+                                  sizeof(ipv6_addrs));
+
+        if (res < 0) {
+            continue;
+        }
+        for (unsigned i = 0; i < (unsigned)(res / sizeof(ipv6_addr_t)); i++) {
+            char ipv6_addr[IPV6_ADDR_MAX_STR_LEN];
+
+            ipv6_addr_to_str(ipv6_addr, &ipv6_addrs[i], IPV6_ADDR_MAX_STR_LEN);
+            printf("My address is %s\n", ipv6_addr);
+        }
+    }
+}
+
+static void _print_motd(void)
+{
+    puts("RIOT telnet example application");
+
+    puts("╔═══════════════════════════════════════════════════╗");
+    puts("║telnet is entirely unencrypted and unauthenticated.║");
+    puts("║Do not use this on public networks.                ║");
+    puts("╚═══════════════════════════════════════════════════╝");
+}
+
+void telnet_cb_pre_connected(sock_tcp_t *sock)
+{
+    sock_tcp_ep_t ep;
+    char addr_str[IPV6_ADDR_MAX_STR_LEN];
+
+    sock_tcp_get_local(sock, &ep);
+    ipv6_addr_to_str(addr_str, (ipv6_addr_t *)ep.addr.ipv6, sizeof(addr_str));
+
+    printf("%s connected\n", addr_str);
+}
+
+void telnet_cb_disconneced(void)
+{
+    puts("disconnected");
+}
+
+void telnet_cb_connected(sock_tcp_t *sock)
+{
+    (void)sock;
+    _print_motd();
+}
+
+int main(void)
+{
+    /* we need a message queue for the thread running the shell in order to
+     * receive potentially fast incoming networking packets */
+    msg_init_queue(_main_msg_queue, MAIN_QUEUE_SIZE);
+
+    _print_motd();
+
+    /* print address so we can connect to it */
+    _print_addr();
+
+    /* start shell */
+    printf("All up, awaiting connection on port %u\n", CONFIG_TELNET_PORT);
+    printf("Local shell disabled");
+    char line_buf[SHELL_DEFAULT_BUFSIZE];
+    shell_run(NULL, line_buf, SHELL_DEFAULT_BUFSIZE);
+
+    /* should be never reached */
+    return 0;
+}