Merge #84: Add --address, bind to specific address

bf40486 Add --address, bind to specific address (uhliksk)

Pull request description:

  - Fix #83 (will reply from same address as provided)
  - Fix #59 (will work if you bind to specific IPv4 address)
  - Fix #51 (will work with systemd-resolved service if you bind to specific address)

ACKs for top commit:
  sipa:
    ACK bf40486

Tree-SHA512: 1924533a31f4e1b1149e1863454c28b5860eea6bd90e4d54fea761b608ad47ad8e15e6e2a745c91717658466cdd6c2cdc221f2587968f94c798d09774e4ddca0

dns.cpp

@@ -425,7 +425,7 @@ int dnsserver(dns_opt_t *opt) {
     memset((char *) &si_me, 0, sizeof(si_me));
     si_me.sin6_family = AF_INET6;
     si_me.sin6_port = htons(opt->port);
-    si_me.sin6_addr = in6addr_any;
+    inet_pton(AF_INET6, opt->addr, &si_me.sin6_addr);
     if (bind(listenSocket, (struct sockaddr*)&si_me, sizeof(si_me))==-1)
       return -2;
   }

dns.h

@@ -16,6 +16,7 @@ struct dns_opt_t {
   int datattl;
   int nsttl;
   const char *host;
+  const char *addr;
   const char *ns;
   const char *mbox;
   int (*cb)(void *opt, char *requested_hostname, addr_t *addr, int max, int ipv4, int ipv6);

main.cpp

@@ -28,11 +28,12 @@ class CDnsSeedOpts {
   const char *ns;
   const char *host;
   const char *tor;
+  const char *ip_addr;
   const char *ipv4_proxy;
   const char *ipv6_proxy;
   std::set<uint64_t> filter_whitelist;
 
-  CDnsSeedOpts() : nThreads(96), nDnsThreads(4), nPort(53), mbox(NULL), ns(NULL), host(NULL), tor(NULL), fUseTestNet(false), fWipeBan(false), fWipeIgnore(false), ipv4_proxy(NULL), ipv6_proxy(NULL) {}
+  CDnsSeedOpts() : nThreads(96), nDnsThreads(4), ip_addr("::"), nPort(53), mbox(NULL), ns(NULL), host(NULL), tor(NULL), fUseTestNet(false), fWipeBan(false), fWipeIgnore(false), ipv4_proxy(NULL), ipv6_proxy(NULL) {}
 
   void ParseCommandLine(int argc, char **argv) {
     static const char *help = "Bitcoin-seeder\n"
@@ -44,6 +45,7 @@ class CDnsSeedOpts {
                               "-m <mbox>       E-Mail address reported in SOA records\n"
                               "-t <threads>    Number of crawlers to run in parallel (default 96)\n"
                               "-d <threads>    Number of DNS server threads (default 4)\n"
+                              "-a <address>    Address to listen on (default ::)\n"
                               "-p <port>       UDP port to listen on (default 53)\n"
                               "-o <ip:port>    Tor proxy IP/Port\n"
                               "-i <ip:port>    IPV4 SOCKS5 proxy IP/Port\n"
@@ -63,6 +65,7 @@ class CDnsSeedOpts {
         {"mbox", required_argument, 0, 'm'},
         {"threads", required_argument, 0, 't'},
         {"dnsthreads", required_argument, 0, 'd'},
+        {"address", required_argument, 0, 'a'},
         {"port", required_argument, 0, 'p'},
         {"onion", required_argument, 0, 'o'},
         {"proxyipv4", required_argument, 0, 'i'},
@@ -75,7 +78,7 @@ class CDnsSeedOpts {
         {0, 0, 0, 0}
       };
       int option_index = 0;
-      int c = getopt_long(argc, argv, "h:n:m:t:p:d:o:i:k:w:", long_options, &option_index);
+      int c = getopt_long(argc, argv, "h:n:m:t:a:p:d:o:i:k:w:", long_options, &option_index);
       if (c == -1) break;
       switch (c) {
         case 'h': {
@@ -105,6 +108,18 @@ class CDnsSeedOpts {
           break;
         }
 
+        case 'a': {
+          if (strchr(optarg, ':')==NULL) {
+            char* ip4_addr = (char*) malloc(strlen(optarg)+8);
+            strcpy(ip4_addr, "::FFFF:");
+            strcat(ip4_addr, optarg);
+            ip_addr = ip4_addr;
+          } else {
+            ip_addr = optarg;
+          }
+          break;
+        }
+
         case 'p': {
           int p = strtol(optarg, NULL, 10);
           if (p > 0 && p < 65536) nPort = p;
@@ -261,6 +276,7 @@ class CDnsThread {
     dns_opt.datattl = 3600;
     dns_opt.nsttl = 40000;
     dns_opt.cb = GetIPList;
+    dns_opt.addr = opts->ip_addr;
     dns_opt.port = opts->nPort;
     dns_opt.nRequests = 0;
     dbQueries = 0;