Limit ipv6 udp replies to an amount that does not create too large UDP packets. Credits to anonymous donor

ot_udp.c

@@ -141,9 +141,9 @@ int handle_udp6( int64 serversocket, struct ot_workstruct *ws ) {
       /* We do only want to know, if it is zero */
       left  = inpacket[64/4] | inpacket[68/4];
 
-      /* Limit amount of peers to 200 */
+      /* Limit amount of peers to OT_MAX_PEERS_UDP */
       numwant = ntohl( inpacket[92/4] );
-      if (numwant > 200) numwant = 200;
+      if (numwant > OT_MAX_PEERS_UDP) numwant = OT_MAX_PEERS_UDP;
 
       event    = ntohl( inpacket[80/4] );
       port     = *(uint16_t*)( ((char*)inpacket) + 96 );

trackerlogic.c

@@ -259,8 +259,12 @@ static size_t return_peers_selection( struct ot_workstruct *ws, ot_peerlist *pee
 }
 
 /* Compiles a list of random peers for a torrent
-   * reply must have enough space to hold 92+6*amount bytes
-   * does not yet check not to return self
+   * Reply must have enough space to hold:
+   * 92 + 6 * amount bytes for TCP/IPv4
+   * 92 + 18 * amount bytes for TCP/IPv6
+   * 12 + 6 * amount bytes for UDP/IPv4
+   * 12 + 18 * amount bytes for UDP/IPv6
+   * Does not yet check not to return self
 */
 size_t return_peers_for_torrent( struct ot_workstruct * ws, ot_torrent *torrent, size_t amount, char *reply, PROTO_FLAG proto ) {
   ot_peerlist *peer_list = torrent->peer_list;

trackerlogic.h

@@ -44,6 +44,13 @@ typedef struct { ot_ip6 address; int bits; }
 
 #define OT_CLIENT_REQUEST_INTERVAL_RANDOM ( OT_CLIENT_REQUEST_INTERVAL - OT_CLIENT_REQUEST_VARIATION/2 + (int)( nrand48(ws->rand48_state) % OT_CLIENT_REQUEST_VARIATION ) )
 
+/* List of peers should fit in a single UDP packet (around 1200 bytes) */
+#ifdef WANT_V6
+#define OT_MAX_PEERS_UDP 66
+#else
+#define OT_MAX_PEERS_UDP 200
+#endif
+
 /* If WANT_MODEST_FULLSCRAPES is on, ip addresses may not
    fullscrape more frequently than this amount in seconds */
 #define OT_MODEST_PEER_TIMEOUT (60*5)