/* DESC: This script implements a lightweight SMTP server which is able to receive mail and forward them as SMS to a phone number.
* Copyright (C) 2012 NetModule AG, Switzerland
*/
MAX_CONECTIONS = 1; /* maximum of concurrent connections */
TIMEOUT = 10; /* receive timeout in seconds */
MAX_ERRORS = 5; /* max. number of error per session */
MAX_MESSAGES = 32; /* max. number of messages per session */
MAX_HEADER_LEN = 1024; /* max. header length */
MAX_BODY_LEN = 160; /* max. body length */
DOMAIN = "domain.net"; /* recipient domain */
AUTHENTICATE = 1; /* force authentication */
ALLOWED_SENDERS = mkarray("sender1@domain.local",
"sender2@domain.local");
ALLOWED_NUMBERS = mkarray("+123456789",
"+987654321");
string extract_addr (string str)
{
addr = trim(str);
/* check for @ */
pos = strchr(addr, "@");
if (is_void(pos) || pos == 0) {
nb_syslog("malformed address");
return "";
}
pos = strchr(addr, "<");
if (!is_void(pos)) {
addr = substr(addr, pos + 1);
pos = strchr(addr, ">");
if (is_void(pos) || pos < 1) {
nb_syslog("malformed address");
return "";
}
addr = left(addr, pos);
}
return addr;
}
string validate_sender (string from)
{
/* extract mail addr */
sender = extract_addr(from);
if (strlen(sender) == 0) return "";
/* check if sender is allowed */
for (i = 0; i < length(ALLOWED_SENDERS); i++) {
s = ALLOWED_SENDERS[i];
if (left(sender, strlen(s)) == s) {
nb_syslog("sender %s can pass", sender);
return sender;
}
}
nb_syslog("sender %s is now allowed to send something", sender);
return "";
}
string validate_number (string rcpt)
{
/* extract mail addr */
addr = extract_addr(rcpt);
if (strlen(addr) == 0) return "";
pos = strchr(addr, "@");
if (is_void(pos) || pos == 0) {
nb_syslog("malformed address");
return "";
}
number = left(addr, pos);
domain = substr(addr, pos + 1);
if (domain != DOMAIN) {
nb_syslog("invalid domain");
return "";
}
for (i = 0; i < length(ALLOWED_NUMBERS); i++) {
n = ALLOWED_NUMBERS[i];
if (left(number, strlen(n)) == n) {
nb_syslog("number %s is allowed", number);
return number;
}
}
nb_syslog("number %s is not allowed", number);
return number;
}
string add_to_header (string header, string msg)
{
if ((strlen(header) + strlen(msg) + 1) > MAX_HEADER_LEN) {
nb_syslog("header length exceeded");
return header;
}
return strcat(header, msg, "\n");
}
string add_to_body (string body, string msg)
{
len = strlen(body) + strlen(msg) + 1;
if (len > MAX_BODY_LEN) {
nb_syslog("body length exceeded (%d bytes, max %d)", len, MAX_BODY_LEN);
return body;
}
return strcat(body, msg, "\n");
}
void usage()
{
nb_syslog("usage: email-to-sms.are <port>");
exit(1);
}
/* main */
if (argc < 2) {
usage();
}
PORT = (int) argv[1];
HOSTNAME = nb_config_get("network.hostname");
if (strlen(hostname) == 0) {
HOSTNAME = "host";
}
if (AUTHENTICATE) {
PASSWORD = nb_config_get("admin.password");
if (strlen(PASSWORD) == 0) {
PASSWORD = "admin01";
}
}
st = nb_config_get("smsd.status");
if (st != "1") {
nb_syslog("SMS daemon is not enabled");
exit(1);
}
if (PORT < 1024 || PORT >= 65536) {
nb_syslog("invalid port %d specified (must be 1024..65535)", PORT);
exit(1);
}
/* raise socket */
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0) {
nb_syslog("unable to open socket");
exit(1);
}
ret = bind(sock, PORT, "");
if (ret == -1) {
nb_syslog("unable to bind port %d", PORT);
close(sock);
exit(1);
}
ret = listen(sock, MAX_CONECTIONS);
if (ret == -1) {
nb_syslog("unable to listen");
close(sock);
exit(1);
}
/* listen for clients */
nb_syslog("listening for connections on port %d", PORT);
state = "disconnected";
while (1) {
client = accept(sock);
if (client < 0) {
printf("accept failed\n");
sleep(1);
continue;
}
nb_syslog("new client has connected");
user = pass = number = rcpt = sender = header = body = subject = "";
errors = messages = 0;
state = "connected";
send(client, "220 %s.%s ESTMP arena\r\n", HOSTNAME, DOMAIN);
while (1) {
/* wait for socket data */
rv = select(client, TIMEOUT);
if (rv == -1) {
nb_syslog("select failed, client endpoint stalled");
break;
} else if (rv == 0) {
nb_syslog("select timed out");
break;
} else {
/* data available */
msg = recv(client);
if (strlen(msg) == 0) {
nb_syslog("empty message received, stopping transaction");
break;
}
messages++;
if (errors > MAX_ERRORS || messages > MAX_MESSAGES) {
nb_syslog("discarding client because of too many errors");
send(client,"554 Transaction failed\r\n");
break;
}
pos1 = strchr(msg, "\r");
pos2 = strchr(msg, "\n");
if (pos1 >= 0 && pos1 < pos2) {
pos = pos1;
} else {
pos = pos2;
}
if (!is_void(pos)) {
line = substr(msg, 0, pos);
cmd = tolower(line);
} else {
/* not a valid command */
line = cmd = "";
}
/*
dump(msg);
nb_syslog("state is '%s', got cmd '%s'", state, cmd);
*/
if (left(cmd, 4) == "quit" || left(cmd, 3) == "bye") {
send(client,"221 Bye\r\n");
state = "disconnected";
break;
}
if (state == "connected") {
/* expect hello */
if (left(cmd, 4) == "helo") {
state = "heloSent";
send(client, "250 %s.%s Hello\r\n", HOSTNAME, DOMAIN);
} else if (left(cmd, 4) == "ehlo") {
if (AUTHENTICATE) {
state = "heloSent";
send(client,
"250-%s.%s at your service\r\n250-8BITMIME\r\n250-AUTH LOGIN PLAIN\r\n250 ENHANCEDSTATUSCODES\r\n",
HOSTNAME, DOMAIN);
} else {
state = "heloSent";
send(client, "220 %s.%s Hello\r\n", HOSTNAME, DOMAIN);
}
} else {
send(client, "500 polite people say hello first\r\n");
errors++;
}
} else if (state == "heloSent" || state == "authenticated") {
if (AUTHENTICATE && state != "authenticated") {
if (left(cmd, 10) == "auth login") {
/* prompt for username */
send(client, "334 %s\r\n", base64_encode("Username:"));
state = "userPrompted";
} else {
send(client, "500 not authenticated yet\r\n");
errors++;
}
} else {
/* expect mail from */
if (left(cmd, 10) == "mail from:") {
/* rewind mail settings */
user = pass = number = rcpt = sender = header = body = subject = "";
sender = validate_sender(substr(cmd, 10, 64));
if (strlen(sender) > 0) {
state = "fromReceived";
send(client, "250 sender ok\r\n");
} else {
send(client, "500 invalid sender\r\n");
errors++;
}
} else {
send(client, "500 need mail from\r\n");
errors++;
}
}
} else if (state == "userPrompted") {
/* read username */
user = base64_decode(trim(line));
if (user != "admin") {
nb_syslog("invalid user specified for authentication");
send(client, "500 invalid user specified\r\n");
errors++;
} else {
send(client, "334 %s\r\n", base64_encode("Password:"));
state = "passwordPrompted";
}
} else if (state == "passwordPrompted") {
/* read username */
pass = base64_decode(trim(line));
if (pass != PASSWORD) {
nb_syslog("authentication for '%s' failed", user);
send(client, "500 authentication failed\r\n");
errors++;
} else {
nb_syslog("authentication succeeded for user %s", user);
send(client, "235 OK\r\n");
state = "authenticated";
}
} else if (state == "fromReceived") {
/* expect rcpt to */
if (left(cmd, 8) == "rcpt to:") {
number = validate_number(substr(cmd, 8, 64));
if (strlen(number) > 0) {
state = "rcptReceived";
send(client, "250 rcpt ok\r\n");
} else {
send(client, "500 invalid rcpt\r\n");
errors++;
}
} else {
send(client, "500 need rcpt to\r\n");
errors++;
}
} else if (state == "rcptReceived") {
/* expect DATA */
if (left(cmd, 4) == "data") {
state = "dataReady";
send(client, "354 End data with <CR><LF>.<CR><LF>\r\n");
} else {
send(client, "500 need data\r\n");
errors++;
}
} else if (state == "dataReady" || state == "headerReceived") {
gotEOF = 0;
pos = strstr(msg, "\r\n.\r\n");
if (!is_void(pos)) {
gotEOF = 1;
msg = left(msg, pos);
}
if (state != "headerReceived") {
pos = strstr(msg, "\n\n");
if (is_void(pos)) pos = strstr(msg, "\r\n\r\n");
if (is_void(pos)) {
header = add_to_header(header, msg);
} else {
state = "headerReceived";
header = add_to_header(header, substr(msg, 0, pos));
body = add_to_body(body, ltrim(substr(msg, pos+1)));
}
} else {
body = add_to_body(body, msg, "\n");
}
if (gotEOF) {
if (state != "headerReceived") {
nb_syslog("no body message data has been received");
send(client,"554 Transaction failed (no body data)\r\n");
errors++;
} else {
body = trim(body);
if (strlen(body) > 0 && strlen(number) > 0) {
/* dump(body); */
nb_syslog("sending message to %s (%d bytes)", number, strlen(body));
id = nb_sms_send(number, body);
if (id) {
nb_syslog("spooled message to %s (ID %s)", number, id);
send(client,"250 OK message queued as %s\r\n", id);
errors = 0;
} else {
nb_syslog("unable to send message to %s", number);
send(client,"554 Transaction failed\r\n");
errors++;
}
} else {
nb_syslog("no message data");
send(client,"554 Transaction failed (no message data)\r\n");
errors++;
}
}
state = "heloSent";
}
} else {
nb_syslog("rejecting client due to invalid state");
break;
}
}
}
nb_syslog("disconnecting client");
close(client);
}
nb_syslog("terminating");
close(sock);
exit(0);
