1 | #include <stdio.h> |
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2 | #include <stdlib.h> |
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3 | #include <string.h> |
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4 | #include <sys/socket.h> |
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5 | #include <arpa/inet.h> |
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6 | #include <netdb.h> |
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7 | #include <unistd.h> |
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8 | #include <signal.h> |
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9 | #include <errno.h> |
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10 | #include <sys/wait.h> |
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11 | #include <sys/stat.h> |
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12 | #include <stdarg.h> |
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13 | #include <syslog.h> |
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14 | |
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15 | /* Buffer size, in bytes, used for copying in the Cat() function. */ |
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16 | const size_t BUF_SIZE = 10240; |
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17 | |
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18 | /* Typedef for a signal handler function. */ |
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19 | typedef void (*signal_handler_t) (int); |
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20 | |
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21 | /* Prototypes for functions in this file. */ |
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22 | void ParseArgs (int argc, char *argv[], struct in_addr *ra, |
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23 | unsigned short *rp, struct in_addr *la, unsigned short *lp); |
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24 | void Initialise (void); |
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25 | void sig_child (int signo); |
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26 | int CreateServerSocket (struct in_addr addr, unsigned short port); |
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27 | void Daemonise (void); |
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28 | void MainLoop (int listen_fd, struct in_addr rem_addr, |
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29 | unsigned short rem_port); |
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30 | void Proxy (int server_fd, int client_fd); |
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31 | int AcceptClientConnection (int listen_fd); |
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32 | int ConnectToServer (struct in_addr addr, unsigned short port); |
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33 | void Cat (int in_fd, int out_fd); |
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34 | int NameToAddr (const char *name, struct in_addr *p_inaddr); |
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35 | int NameToPort (const char *name, unsigned short *port, const char *proto); |
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36 | #ifdef __GNUC__ |
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37 | void quit (const char *fmt, ...) __attribute__ ((format (printf, 1, 2))); |
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38 | void pbomb (const char *fmt, ...) __attribute__ ((format (printf, 1, 2))); |
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39 | void hbomb (const char *fmt, ...) __attribute__ ((format (printf, 1, 2))); |
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40 | #else |
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41 | void quit (const char *fmt, ...); |
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42 | void pbomb (const char *fmt, ...); |
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43 | void hbomb (const char *fmt, ...); |
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44 | #endif |
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45 | void set_signal_handler (int signum, signal_handler_t sig_handler_func); |
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46 | |
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47 | /* Global variables */ |
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48 | char g_program_name[100]; /* Initialised from argv[0] in ParseArgs() */ |
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49 | |
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50 | int |
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51 | main (int argc, char *argv[]) |
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52 | { |
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53 | struct in_addr remote_addr, local_addr; |
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54 | unsigned short remote_port, local_port; |
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55 | int listen_fd; |
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56 | |
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57 | ParseArgs (argc, argv, &remote_addr, &remote_port, &local_addr, |
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58 | &local_port); |
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59 | |
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60 | Initialise (); |
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61 | |
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62 | /* Create server socket before becoming a daemon so there is still a |
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63 | * chance to print an error message. */ |
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64 | listen_fd = CreateServerSocket (local_addr, local_port); |
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65 | if (listen_fd < 0) |
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66 | pbomb ("Unable to create server socket"); |
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67 | |
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68 | Daemonise (); |
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69 | |
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70 | MainLoop (listen_fd, remote_addr, remote_port); /* never returns */ |
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71 | |
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72 | exit (EXIT_SUCCESS); |
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73 | } |
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74 | |
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75 | /* ParseArgs(): Parse the command line arguments to extract the remote and |
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76 | * * local adresses and port numbers, ra, rp, la & lp. Exit the program |
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77 | * * gracefully upon error. |
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78 | * */ |
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79 | void |
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80 | ParseArgs (int argc, char *argv[], struct in_addr *ra, unsigned short *rp, |
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81 | struct in_addr *la, unsigned short *lp) |
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82 | { |
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83 | /* |
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84 | * * argv[0] = program name |
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85 | * * argv[1] = remote_addr |
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86 | * * argv[2] = remote_port |
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87 | * * argv[3] = local_addr (optional) |
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88 | * * argv[4] = local_port (optional) |
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89 | * */ |
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90 | |
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91 | char *p = strrchr (argv[0], '/'); |
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92 | |
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93 | strncpy (g_program_name, (p == NULL) ? argv[0] : p + 1, |
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94 | sizeof (g_program_name) - 1); |
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95 | |
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96 | if ((argc < 3) || (argc > 5)) |
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97 | { |
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98 | fprintf (stderr, |
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99 | "usage: %s remote_addr remote_port [local_addr] [local_port]\n", |
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100 | argv[0]); |
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101 | exit (EXIT_FAILURE); |
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102 | } |
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103 | |
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104 | if (NameToAddr (argv[1], ra)) |
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105 | hbomb ("Unable to resolve \"%s\" to an ip address", argv[1]); |
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106 | |
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107 | if (NameToPort (argv[2], rp, "tcp")) |
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108 | quit ("Unable to resolve \"%s\" to a port number", argv[2]); |
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109 | |
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110 | if (argc < 4) |
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111 | la->s_addr = htonl (INADDR_ANY); |
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112 | else if (NameToAddr (argv[3], la)) |
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113 | hbomb ("Unable to resolve \"%s\" to an ip address", argv[3]); |
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114 | |
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115 | if (argc < 5) |
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116 | memcpy (lp, rp, sizeof (*lp)); |
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117 | else if (NameToPort (argv[4], lp, "tcp")) |
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118 | quit ("Unable to resolve \"%s\" to a port number", argv[4]); |
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119 | } |
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120 | |
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121 | /* Initialise(): Setup syslog, signal handlers, and other intialisation. |
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122 | * */ |
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123 | void |
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124 | Initialise (void) |
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125 | { |
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126 | openlog (g_program_name, LOG_PID, LOG_USER); |
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127 | syslog (LOG_INFO, "%s started", g_program_name); |
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128 | |
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129 | chdir ("/"); /* Change working directory to the root. */ |
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130 | |
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131 | umask (0); /* Clear our file mode creation mask */ |
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132 | |
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133 | set_signal_handler (SIGCHLD, sig_child); |
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134 | |
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135 | signal (SIGPIPE, SIG_IGN); |
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136 | } |
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137 | |
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138 | /* sig_child(): Handles SIGCHLD from exiting child processes. |
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139 | * */ |
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140 | void |
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141 | sig_child (int signo) |
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142 | { |
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143 | pid_t pid; |
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144 | |
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145 | (void) signo; /* suppress compiler warning */ |
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146 | |
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147 | for (;;) |
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148 | { |
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149 | pid = waitpid (WAIT_ANY, NULL, WNOHANG); |
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150 | |
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151 | if (pid > 0) |
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152 | syslog (LOG_INFO, "Caught SIGCHLD from pid %d", pid); |
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153 | else |
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154 | break; |
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155 | } |
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156 | |
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157 | if ((pid < 0) && (errno != ECHILD)) |
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158 | syslog (LOG_ERR, "waitpid(): %m"), exit (EXIT_FAILURE); |
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159 | |
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160 | return; |
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161 | } |
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162 | |
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163 | /* CreateServerSocket(): Create a socket, bind it to the specified address |
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164 | * * and port, and set it to listen for client connections. Returns <0 on |
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165 | * * failure to bind, bombs on error otherwise, returns the fd of the new |
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166 | * * socket on success. |
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167 | * */ |
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168 | int |
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169 | CreateServerSocket (struct in_addr addr, unsigned short port) |
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170 | { |
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171 | int err, fd; |
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172 | const int on = 1; |
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173 | struct sockaddr_in sa; |
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174 | |
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175 | /* Create a socket and get its descriptor. */ |
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176 | fd = socket (AF_INET, SOCK_STREAM, 0); |
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177 | if (fd < 0) |
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178 | syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE); |
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179 | |
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180 | /* Set SO_REUSEADDR socket option */ |
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181 | if (setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof (on)) < 0) |
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182 | syslog (LOG_ERR, "setsockopt(fd%d, SO_REUSEADDR): %m", fd); |
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183 | |
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184 | /* Load a sa structure with the specified address and port */ |
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185 | sa.sin_family = AF_INET; |
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186 | sa.sin_port = htons (port); |
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187 | sa.sin_addr = addr; |
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188 | memset (sa.sin_zero, 0, sizeof (sa.sin_zero)); |
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189 | |
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190 | /* Bind our socket to the address and port specified */ |
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191 | err = bind (fd, (struct sockaddr *) &sa, sizeof (sa)); |
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192 | if (err < 0) |
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193 | { |
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194 | syslog (LOG_ERR, "bind(): %m"); |
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195 | return err; |
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196 | } |
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197 | |
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198 | /* Tell socket to listen and queue up to 5 incoming connections. */ |
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199 | if (listen (fd, 5) < 0) |
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200 | syslog (LOG_ERR, "listen(): %m"), exit (EXIT_FAILURE); |
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201 | |
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202 | return fd; |
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203 | } |
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204 | |
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205 | /* Daemonise(): Put the program in the background, set PPID=1, create a new |
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206 | * * session and process group, without a controlling tty. |
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207 | * */ |
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208 | void |
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209 | Daemonise (void) |
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210 | { |
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211 | pid_t pid; |
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212 | |
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213 | /* Close stdin, stdout & stderr */ |
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214 | /* TODO: open /dev/null and dup the fd to stdin, stdout & stderr |
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215 | * close(STDIN_FILENO); |
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216 | * close(STDOUT_FILENO); |
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217 | * close(STDERR_FILENO); |
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218 | * */ |
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219 | |
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220 | syslog (LOG_INFO, "%s daemonising", g_program_name); |
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221 | |
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222 | /* Fork the process to put it in the background. */ |
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223 | |
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224 | pid = fork (); |
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225 | if (pid == -1) |
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226 | syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE); |
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227 | |
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228 | /* parent terminates here, so shell thinks the command is done. */ |
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229 | if (pid) |
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230 | exit (0); |
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231 | |
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232 | syslog (LOG_INFO, "%s in background", g_program_name); |
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233 | |
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234 | /* 1st child continues to run in the background with PPID=1 */ |
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235 | |
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236 | /* Become leader of a new session and a new process group, |
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237 | * with no controlling tty. */ |
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238 | setsid (); |
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239 | |
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240 | /* Fork again to guarantee the process will not be able to aquire a |
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241 | * controlling tty. */ |
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242 | |
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243 | /*signal (SIGHUP, SIG_IGN); *//* required according to Stevens' UNP2 p333 */ |
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244 | |
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245 | pid = fork (); |
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246 | if (pid == -1) |
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247 | syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE); |
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248 | |
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249 | if (pid) /* 1st child terminates */ |
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250 | exit (0); |
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251 | |
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252 | /* 2nd child continues, no longer a session or group leader */ |
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253 | |
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254 | syslog (LOG_INFO, "%s daemonised", g_program_name); |
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255 | } |
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256 | |
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257 | /* MainLoop(): Classic concurrent server model. Wait for a client to connect, |
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258 | * * fork a child process to do the business with the client, parent process |
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259 | * * continues to wait for the next connection. This function does not return. |
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260 | * */ |
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261 | void |
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262 | MainLoop (int listen_fd, struct in_addr rem_addr, unsigned short rem_port) |
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263 | { |
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264 | int server_fd, client_fd; |
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265 | pid_t child_pid; |
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266 | |
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267 | for (;;) |
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268 | { |
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269 | client_fd = AcceptClientConnection (listen_fd); |
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270 | |
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271 | child_pid = fork (); |
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272 | if (child_pid == -1) |
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273 | syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE); |
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274 | |
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275 | if (child_pid) /* parent */ |
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276 | { |
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277 | close (client_fd); |
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278 | |
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279 | syslog (LOG_INFO, "Forked child pid %d to deal with client", |
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280 | child_pid); |
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281 | |
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282 | continue; |
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283 | } |
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284 | else /* child */ |
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285 | { |
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286 | close (listen_fd); |
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287 | |
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288 | server_fd = ConnectToServer (rem_addr, rem_port); |
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289 | |
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290 | Proxy (server_fd, client_fd); |
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291 | |
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292 | syslog (LOG_INFO, "exiting"); |
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293 | _exit (0); |
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294 | } |
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295 | } |
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296 | } |
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297 | |
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298 | /* Proxy(): Copies data between server_fd and client_fd in both directions |
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299 | * * until one or other peer closes their connection. |
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300 | * */ |
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301 | void |
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302 | Proxy (int server_fd, int client_fd) |
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303 | { |
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304 | pid_t helper_pid; |
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305 | |
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306 | syslog (LOG_INFO, "Proxy(fd%d, fd%d)", server_fd, client_fd); |
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307 | |
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308 | signal (SIGCHLD, SIG_IGN); |
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309 | |
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310 | helper_pid = fork (); |
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311 | if (helper_pid == -1) |
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312 | syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE); |
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313 | |
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314 | if (helper_pid) /* parent */ |
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315 | { |
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316 | syslog (LOG_INFO, "Forked child pid %d to help with proxying", |
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317 | helper_pid); |
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318 | |
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319 | Cat (server_fd, client_fd); |
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320 | |
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321 | shutdown (client_fd, 1); |
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322 | close (server_fd); |
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323 | close (client_fd); |
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324 | |
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325 | wait (0); /* wait for helper to exit */ |
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326 | } |
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327 | else /* child (helper) */ |
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328 | { |
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329 | Cat (client_fd, server_fd); |
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330 | |
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331 | shutdown (server_fd, 1); |
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332 | |
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333 | syslog (LOG_INFO, "exiting"); |
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334 | exit (0); /* helper exits here */ |
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335 | } |
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336 | } |
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337 | |
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338 | /* AcceptClientConnection(): waits for a tcp connect to the socket listen_fd, |
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339 | * * which must already be bound and set to listen on a local port. Bombs on |
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340 | * * error, returns the fd of the new socket on success. |
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341 | * */ |
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342 | int |
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343 | AcceptClientConnection (int listen_fd) |
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344 | { |
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345 | int newfd; |
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346 | struct sockaddr_in sa; |
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347 | socklen_t socklen; |
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348 | |
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349 | syslog (LOG_INFO, "AcceptClientConnection(fd%d)", listen_fd); |
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350 | |
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351 | /* Accept the connection and create a new socket for it. */ |
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352 | socklen = sizeof (sa); |
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353 | memset (&sa, 0, socklen); |
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354 | do |
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355 | { |
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356 | newfd = accept (listen_fd, (struct sockaddr *) &sa, &socklen); |
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357 | } |
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358 | while ((newfd < 0) && (errno == EINTR)); |
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359 | |
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360 | syslog (LOG_INFO, "Accepted client connection on new socket fd%d", newfd); |
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361 | |
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362 | if (newfd < 0) |
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363 | syslog (LOG_ERR, "accept(): %m"), exit (EXIT_FAILURE); |
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364 | |
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365 | if (socklen != sizeof (sa)) |
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366 | syslog (LOG_ERR, "accept() screwed up!"), exit (EXIT_FAILURE); |
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367 | |
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368 | return (newfd); |
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369 | } |
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370 | |
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371 | /* ConnectToServer(): attempts a tcp connect to the server specified by addr |
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372 | * * and port. Bombs on failure to connect, returns the fd of the new socket |
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373 | * * on success. |
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374 | * */ |
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375 | int |
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376 | ConnectToServer (struct in_addr addr, unsigned short port) |
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377 | { |
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378 | /* TODO: have a timeout for connect() - see Unix socket FAQ 6.2 */ |
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379 | |
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380 | int fd, err; |
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381 | struct sockaddr_in sa; |
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382 | |
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383 | /* Create a socket and get its descriptor. */ |
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384 | fd = socket (AF_INET, SOCK_STREAM, 0); |
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385 | if (fd < 0) |
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386 | syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE); |
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387 | |
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388 | sa.sin_family = AF_INET; |
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389 | sa.sin_port = htons (port); |
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390 | sa.sin_addr = addr; |
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391 | memset (sa.sin_zero, 0, sizeof (sa.sin_zero)); |
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392 | |
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393 | err = connect (fd, (struct sockaddr *) &sa, sizeof (sa)); |
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394 | if (err < 0) |
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395 | { |
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396 | syslog (LOG_ERR, "Unable to connect socket fd%d to server: %m", fd); |
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397 | exit (EXIT_FAILURE); |
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398 | } |
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399 | |
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400 | syslog (LOG_INFO, "Connected socket fd%d to server", fd); |
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401 | |
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402 | return fd; |
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403 | } |
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404 | |
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405 | /* Cat(): read data from in_fd and write it to out_fd until the connection is |
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406 | * * closed by one of the peers. Data is copied using a dynamically allocated |
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407 | * * buffer. |
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408 | * */ |
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409 | void |
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410 | Cat (int in_fd, int out_fd) |
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411 | { |
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412 | unsigned char *const buf = malloc (BUF_SIZE); |
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413 | int bytes_rcvd, bytes_sent = 0, i; |
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414 | |
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415 | syslog (LOG_INFO, "Cat(fd%d, fd%d)", in_fd, out_fd); |
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416 | |
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417 | if (buf == NULL) |
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418 | syslog (LOG_ERR, "malloc(): %m"), exit (EXIT_FAILURE); |
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419 | |
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420 | do |
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421 | { |
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422 | bytes_rcvd = recv (in_fd, buf, BUF_SIZE, 0); |
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423 | |
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424 | for (i = 0; i < bytes_rcvd; i += bytes_sent) |
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425 | { |
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426 | bytes_sent = send (out_fd, buf + i, bytes_rcvd - i, 0); |
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427 | |
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428 | if (bytes_sent < 0) |
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429 | break; |
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430 | } |
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431 | |
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432 | } |
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433 | while ((bytes_rcvd > 0) && (bytes_sent > 0)); |
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434 | |
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435 | if ((bytes_rcvd < 0) && (errno != ECONNRESET)) |
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436 | syslog (LOG_ERR, "recv(): %m"), exit (EXIT_FAILURE); |
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437 | |
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438 | if ((bytes_sent < 0) && (errno != EPIPE)) |
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439 | syslog (LOG_ERR, "send(): %m"), exit (EXIT_FAILURE); |
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440 | |
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441 | free (buf); |
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442 | } |
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443 | |
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444 | /* NameToAddress(): Convert name to an ip address. Returns 0 on success, |
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445 | * * -1 on failure. |
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446 | * */ |
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447 | int |
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448 | NameToAddr (const char *name, struct in_addr *p_inaddr) |
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449 | { |
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450 | struct hostent *he; |
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451 | |
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452 | /* First, attempt to convert from string ip format */ |
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453 | /* TODO: use inet_aton() instead */ |
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454 | p_inaddr->s_addr = inet_addr (name); |
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455 | if (p_inaddr->s_addr != -1U) /* Success */ |
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456 | return 0; |
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457 | |
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458 | /* Next, attempt to read from /etc/hosts or do a DNS lookup */ |
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459 | he = gethostbyname (name); |
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460 | if (he != NULL) /* Success */ |
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461 | { |
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462 | memcpy (p_inaddr, he->h_addr, sizeof (struct in_addr)); |
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463 | return 0; |
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464 | } |
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465 | |
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466 | return -1; /* Failed to resolve name to an ip address */ |
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467 | } |
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468 | |
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469 | /* NameToPort(): Convert name to a port number. Name can either be a port |
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470 | * * name (in which case proto must also be set to either "tcp" or "udp") or |
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471 | * * name can be the ascii representation of the port number. Returns 0 on |
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472 | * * success, -1 on failure. |
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473 | * */ |
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474 | int |
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475 | NameToPort (const char *name, unsigned short *port, const char *proto) |
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476 | { |
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477 | unsigned long lport; |
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478 | char *errpos; |
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479 | struct servent *se; |
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480 | |
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481 | /* First, attempt to convert string to integer */ |
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482 | lport = strtoul (name, &errpos, 0); |
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483 | if ((*errpos == 0) && (lport <= 65535)) /* Success */ |
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484 | { |
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485 | *port = lport; |
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486 | return 0; |
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487 | } |
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488 | |
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489 | /* Next, attempt to read the string from /etc/services */ |
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490 | se = getservbyname (name, proto); |
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491 | if (se != NULL) /* Success */ |
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492 | { |
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493 | *port = ntohs (se->s_port); |
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494 | return 0; |
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495 | } |
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496 | |
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497 | return -1; /* Failed to resolve port name to a number */ |
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498 | } |
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499 | |
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500 | /* quit(), pbomb(), hbomb(): Print an error message to stderr and syslog, then |
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501 | * * exit the program. pbomb() and hbomb() additionally include the string |
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502 | * * representation of errno and h_errno respectively. |
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503 | * */ |
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504 | void |
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505 | quit (const char *fmt, ...) /* quit with msg */ |
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506 | { |
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507 | va_list ap; |
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508 | |
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509 | fflush (stdout); |
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510 | |
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511 | fprintf (stderr, "%s: ", g_program_name); |
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512 | |
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513 | va_start (ap, fmt); |
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514 | vfprintf (stderr, fmt, ap); |
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515 | va_end (ap); |
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516 | |
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517 | fputc ('\n', stderr); |
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518 | |
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519 | syslog (LOG_ERR, "I quit!"); |
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520 | |
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521 | exit (EXIT_FAILURE); |
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522 | } |
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523 | |
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524 | void |
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525 | pbomb (const char *fmt, ...) /* bomb with perror */ |
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526 | { |
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527 | va_list ap; |
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528 | int errno_save = errno; |
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529 | char buf[100]; |
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530 | |
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531 | fflush (stdout); |
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532 | |
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533 | fprintf (stderr, "%s: ", g_program_name); |
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534 | |
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535 | va_start (ap, fmt); |
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536 | vsnprintf (buf, sizeof (buf), fmt, ap); |
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537 | va_end (ap); |
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538 | |
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539 | errno = errno_save; |
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540 | perror (buf); |
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541 | |
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542 | syslog (LOG_ERR, "Bang!: %s: %m", buf); |
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543 | |
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544 | exit (EXIT_FAILURE); |
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545 | } |
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546 | |
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547 | void |
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548 | hbomb (const char *fmt, ...) /* bomb with herror */ |
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549 | { |
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550 | va_list ap; |
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551 | int h_errno_save = h_errno; |
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552 | char buf[100]; |
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553 | |
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554 | fflush (stdout); |
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555 | |
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556 | fprintf (stderr, "%s: ", g_program_name); |
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557 | |
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558 | va_start (ap, fmt); |
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559 | vsnprintf (buf, sizeof (buf), fmt, ap); |
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560 | va_end (ap); |
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561 | |
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562 | h_errno = h_errno_save; |
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563 | herror (buf); |
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564 | |
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565 | syslog (LOG_ERR, "Bang!: %s: %s", buf, hstrerror (h_errno)); |
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566 | |
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567 | exit (EXIT_FAILURE); |
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568 | } |
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569 | |
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570 | /* set_signal_handler(): Sets a signal handler function. Similar to signal() |
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571 | * * but this method is more portable between platforms. |
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572 | * */ |
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573 | void |
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574 | set_signal_handler (int signum, signal_handler_t sa_handler_func) |
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575 | { |
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576 | struct sigaction act; |
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577 | |
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578 | act.sa_handler = sa_handler_func; |
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579 | sigemptyset (&(act.sa_mask)); |
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580 | act.sa_flags = 0; |
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581 | |
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582 | if (sigaction (signum, &act, NULL) < 0) |
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583 | { |
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584 | syslog (LOG_ERR, "Error setting handler for signal %d: %m", signum); |
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585 | exit (EXIT_FAILURE); |
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586 | } |
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587 | } |
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