File: tcpecho.c
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 2020-2025 pacman64
   5 
   6 Permission is hereby granted, free of charge, to any person obtaining a copy of
   7 this software and associated documentation files (the “Software”), to deal
   8 in the Software without restriction, including without limitation the rights to
   9 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  10 of the Software, and to permit persons to whom the Software is furnished to do
  11 so, subject to the following conditions:
  12 
  13 The above copyright notice and this permission notice shall be included in all
  14 copies or substantial portions of the Software.
  15 
  16 THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22 SOFTWARE.
  23 */
  24 
  25 /*
  26 You can build this command-line app by running
  27 
  28 cc -Wall -s -O3 -flto -o ./tcpecho ./tcpecho.c
  29 */
  30 
  31 #include <arpa/inet.h>
  32 #include <fcntl.h>
  33 #include <netinet/in.h>
  34 #include <stdbool.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <sys/socket.h>
  39 #include <sys/types.h>
  40 #include <unistd.h>
  41 
  42 #ifdef _WIN32
  43 #include <windows.h>
  44 #endif
  45 
  46 #ifdef RED_ERRORS
  47 #define ERROR_STYLE "\x1b[38;2;204;0;0m"
  48 #ifdef __APPLE__
  49 #define ERROR_STYLE "\x1b[31m"
  50 #endif
  51 #define RESET_STYLE "\x1b[0m"
  52 #else
  53 #define ERROR_STYLE
  54 #define RESET_STYLE
  55 #endif
  56 
  57 #define ERROR_LINE(MSG) (ERROR_STYLE MSG RESET_STYLE "\n")
  58 
  59 #define BAD_ALLOC 2
  60 
  61 const char* info = ""
  62 "tcpecho [port] [words...]\n"
  63 "\n"
  64 "\n"
  65 "Start a TCP server which always replies with a plain-text line made from\n"
  66 "the arguments given after the port number, joined by single spaces.\n"
  67 "\n"
  68 "\n"
  69 "Options, all of which can start with either 1 or 2 dashes:\n"
  70 "\n"
  71 "\n"
  72 "  -h          show this help message\n"
  73 "  -help       show this help message\n"
  74 "";
  75 
  76 // is_help_option simplifies control-flow for func main
  77 bool is_help_option(const char* s) {
  78     return (s[0] == '-') && (
  79         strcmp(s, "-h") == 0 ||
  80         strcmp(s, "-help") == 0 ||
  81         strcmp(s, "--h") == 0 ||
  82         strcmp(s, "--help") == 0
  83     );
  84 }
  85 
  86 int main(int argc, char** argv) {
  87 #ifdef _WIN32
  88     setmode(fileno(stdin), O_BINARY);
  89     // ensure output lines end in LF instead of CRLF on windows
  90     setmode(fileno(stdout), O_BINARY);
  91     setmode(fileno(stderr), O_BINARY);
  92 #endif
  93 
  94     // handle any of the help options, if given
  95     if (argc > 1 && is_help_option(argv[1])) {
  96         printf("%s", info);
  97         return 0;
  98     }
  99 
 100     if (argc < 2) {
 101         const char* m = "you forgot the port number as the leading argument";
 102         fprintf(stderr, ERROR_LINE("%s"), m);
 103         return 1;
 104     }
 105 
 106     char* end;
 107     int port = strtol(argv[1], &end, 10);
 108     if (*end != 0 || port < 1 || port > 65535) {
 109         const char* msg;
 110         msg = "isn't a valid port number";
 111         fprintf(stderr, ERROR_LINE("%s %s"), argv[1], msg);
 112         msg = "maybe you forgot the port number as the leading argument";
 113         fprintf(stderr, ERROR_LINE("%s"), msg);
 114         return 1;
 115     }
 116 
 117     // count spaces between words
 118     size_t msglen = argc - 2;
 119     // count word lengths
 120     for (size_t i = 2; i < argc; i++) {
 121         msglen += strlen(argv[i]);
 122     }
 123     // remember the final line-feed
 124     msglen++;
 125 
 126     // also remember that strings are ended with an extra null byte
 127     char* msg = malloc(msglen + 1);
 128     if (msg == NULL) {
 129         fprintf(stderr, ERROR_LINE("out of memory"));
 130         exit(BAD_ALLOC);
 131     }
 132 
 133     for (size_t i = 2, pos = 0; i < argc; i++) {
 134         if (i > 2) {
 135             msg[pos] = ' ';
 136             pos++;
 137         }
 138 
 139         for (size_t j = 0; argv[i][j] != 0; j++) {
 140             msg[pos] = argv[i][j];
 141             pos++;
 142         }
 143     }
 144 
 145     msg[msglen - 1] = '\n';
 146     msg[msglen] = 0;
 147 
 148     int fd = socket(AF_INET, SOCK_STREAM, 0);
 149     if (fd < 0 || fcntl(fd, F_GETFD) == -1) {
 150         free(msg);
 151         fprintf(stderr, ERROR_LINE("can't open socket connection"));
 152         return 1;
 153     }
 154 
 155     struct sockaddr_in srv;
 156     memset(&srv, 0, sizeof(srv));
 157     srv.sin_family = AF_INET;
 158     srv.sin_addr.s_addr = htonl(INADDR_ANY);
 159     srv.sin_port = htons(port);
 160 
 161     if (bind(fd, (struct sockaddr*)&srv, sizeof(srv)) != 0) {
 162         free(msg);
 163         fprintf(stderr, ERROR_LINE("can't open socket connection"));
 164         return 1;
 165     }
 166 
 167     if (listen(fd, 1) != 0) {
 168         free(msg);
 169         fprintf(stderr, ERROR_LINE("can't listen on open connection"));
 170         return 1;
 171     }
 172 
 173     while (true) {
 174         int conn = accept(fd, NULL, NULL);
 175         send(conn, msg, msglen, 0);
 176         close(conn);
 177     }
 178 
 179     free(msg);
 180     return 0;
 181 }