help text

README

@@ -0,0 +1,47 @@
+bitcoin-seeder
+==============
+
+Bitcoin-seeder is a crawler for the Bitcoin network, which exposes a list
+of reliable nodes via a built-in DNS server.
+
+Features:
+* regularly revisits known nodes to check their availability
+* bans nodes after enough failures, or bad behaviour
+* accepts nodes down to v0.3.19 to request new IP addresses from,
+  but only reports good post-v0.3.24 nodes.
+* keeps statistics over (exponential) windows of 2 hours, 8 hours,
+  1 day and 1 week, to base decisions on.
+* very low memory (a few tens of megabytes) and cpu requirements.
+* crawlers run in parallel (by default 24 threads simultaneously).
+
+USAGE
+-----
+
+Assuming you want to run a dns seed on dnsseed.example.com, you will
+need an authorative NS record in example.com's domain record, pointing
+to for example vps.example.com:
+
+$ dig -t NS dnsseed.example.com
+
+;; ANSWER SECTION
+dnsseed.example.com.   86400    IN      NS     vps.example.com.
+
+On the system vps.example.com, you can now run dnsseed:
+
+./dnsseed -h dnsseed.example.com -n vps.example.com
+
+If you want the DNS server to report SOA records, please provide an
+e-mailadres (with the @ part replaced by .) using -m.
+
+RUNNING AS NON-ROOT
+-------------------
+
+Typically, you'll need root privileges to listen to port 53 (name service).
+
+One solution is using an iptables rule (Linux only) to redirect it to
+a non-privileged port:
+
+$ iptables -t nat -A PREROUTING -p udp --dport 53 -j REDIRECT --to-port 5353
+
+If properly configured, this will allow you to run dnsseed in userspace, using
+the -p 5353 option.

main.cpp

@@ -21,13 +21,27 @@ class CDnsSeedOpts {
   CDnsSeedOpts() : nThreads(24), nPort(53), mbox(NULL), ns(NULL), host(NULL) {}
 
   void ParseCommandLine(int argc, char **argv) {
+    static const char *help = "Bitcoin-seeder\n"
+                              "Usage: %s -h <host> -n <ns> [-m <mbox>] [-t <threads>] [-p <port>]\n"
+                              "\n"
+                              "Options:\n"
+                              "-h <host>       Hostname of the DNS seed\n"
+                              "-n <ns>         Hostname of the nameserver\n"
+                              "-m <mbox>       E-Mail address reported in SOA records\n"
+                              "-t <threads>    Number of crawlers to run in parallel (default 24)\n"
+                              "-p <port>       UDP port to listen on (default 53)\n"
+                              "-?, --help      Show this text\n"
+                              "\n";
+    bool showHelp = false;
+
     while(1) {
       static struct option long_options[] = {
         {"host", required_argument, 0, 'h'},
         {"ns",   required_argument, 0, 'n'},
         {"mbox", required_argument, 0, 'm'},
         {"threads", required_argument, 0, 't'},
         {"port", required_argument, 0, 'p'},
+        {"help", no_argument, 0, 'h'},
         {0, 0, 0, 0}
       };
       int option_index = 0;
@@ -52,14 +66,23 @@ class CDnsSeedOpts {
         case 't': {
           int n = strtol(optarg, NULL, 10);
           if (n > 0 && n < 1000) nThreads = n;
+          break;
         }
 
         case 'p': {
           int p = strtol(optarg, NULL, 10);
           if (p > 0 && p < 65536) nPort = p;
+          break;
+        }
+
+        case '?': {
+          showHelp = true;
+          break;
         }
       }
     }
+    if (host == NULL || ns == NULL) showHelp = true;
+    if (showHelp) fprintf(stderr, help, argv[0]);
   }
 };
 
@@ -175,6 +198,7 @@ int main(int argc, char **argv) {
   }
   if (!opts.host) {
     fprintf(stderr, "No hostname set. Please use -h.\n");
+    exit(1);
   }
   FILE *f = fopen("dnsseed.dat","r");
   if (f) {