Do not use third party services for IP detection.

This is a simplified re-do of closed pull #3088.

This patch eliminates the privacy and reliability problematic use
of centralized web services for discovering the node's addresses
for advertisement.

The Bitcoin protocol already allows your peers to tell you what
IP they think you have, but this data isn't trustworthy since
they could lie. So the challenge is using it without creating a
DOS vector.

To accomplish this we adopt an approach similar to the one used
by P2Pool: If we're announcing and don't have a better address
discovered (e.g. via UPNP) or configured we just announce to
each peer the address that peer told us. Since peers could
already replace, forge, or drop our address messages this cannot
create a new vulnerability... but if even one of our peers is
giving us a good address we'll eventually make a useful
advertisement.

We also may randomly use the peer-provided address for the
daily rebroadcast even if we otherwise have a seemingly routable
address, just in case we've been misconfigured (e.g. by UPNP).

To avoid privacy problems, we only do these things if discovery
is enabled.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/net.h b/src/net.h
index 340158512d..e48acf5644 100644
--- a/src/net.h
+++ b/src/net.h
@@ -60,7 +60,6 @@ unsigned int SendBufferSize();
 
 void AddOneShot(std::string strDest);
 bool RecvLine(SOCKET hSocket, std::string& strLine);
-bool GetMyExternalIP(CNetAddr& ipRet);
 void AddressCurrentlyConnected(const CService& addr);
 CNode* FindNode(const CNetAddr& ip);
 CNode* FindNode(const std::string& addrName);
@@ -96,12 +95,13 @@ enum
     LOCAL_IF,     // address a local interface listens on
     LOCAL_BIND,   // address explicit bound to
     LOCAL_UPNP,   // address reported by UPnP
-    LOCAL_HTTP,   // address reported by whatismyip.com and similar
     LOCAL_MANUAL, // address explicitly specified (-externalip=)
 
     LOCAL_MAX
 };
 
+bool IsPeerAddrLocalGood(CNode *pnode);
+void AdvertizeLocal(CNode *pnode);
 void SetLimited(enum Network net, bool fLimited = true);
 bool IsLimited(enum Network net);
 bool IsLimited(const CNetAddr& addr);