net: add an internal subnet for representing unresolved hostnames

We currently do two resolves for dns seeds: one for the results, and one to
serve in addrman as the source for those addresses.

There's no requirement that the source hostname resolves to the stored
identifier, only that the mapping is unique. So rather than incurring the
second lookup, combine a private subnet with a hash of the hostname.

The resulting v6 ip is guaranteed not to be publicy routable, and has only a
negligible chance of colliding with a user's internal network (which would be
of no consequence anyway).

src/net.cpp

@@ -240,7 +240,7 @@ bool RemoveLocal(const CService& addr)
 /** Make a particular network entirely off-limits (no automatic connects to it) */
 void SetLimited(enum Network net, bool fLimited)
 {
-    if (net == NET_UNROUTABLE)
+    if (net == NET_UNROUTABLE || net == NET_INTERNAL)
         return;
     LOCK(cs_mapLocalHost);
     vfLimited[net] = fLimited;

src/netaddress.cpp

@@ -15,6 +15,9 @@
 static const unsigned char pchIPv4[12] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff };
 static const unsigned char pchOnionCat[] = {0xFD,0x87,0xD8,0x7E,0xEB,0x43};
 
+// 0xFD + sha256("bitcoin")[0:5]
+static const unsigned char g_internal_prefix[] = { 0xFD, 0x6B, 0x88, 0xC0, 0x87, 0x24 };
+
 void CNetAddr::Init()
 {
     memset(ip, 0, sizeof(ip));
@@ -42,6 +45,18 @@ void CNetAddr::SetRaw(Network network, const uint8_t *ip_in)
     }
 }
 
+bool CNetAddr::SetInternal(const std::string &name)
+{
+    if (name.empty()) {
+        return false;
+    }
+    unsigned char hash[32] = {};
+    CSHA256().Write((const unsigned char*)name.data(), name.size()).Finalize(hash);
+    memcpy(ip, g_internal_prefix, sizeof(g_internal_prefix));
+    memcpy(ip + sizeof(g_internal_prefix), hash, sizeof(ip) - sizeof(g_internal_prefix));
+    return true;
+}
+
 bool CNetAddr::SetSpecial(const std::string &strName)
 {
     if (strName.size()>6 && strName.substr(strName.size() - 6, 6) == ".onion") {
@@ -84,7 +99,7 @@ bool CNetAddr::IsIPv4() const
 
 bool CNetAddr::IsIPv6() const
 {
-    return (!IsIPv4() && !IsTor());
+    return (!IsIPv4() && !IsTor() && !IsInternal());
 }
 
 bool CNetAddr::IsRFC1918() const
@@ -199,6 +214,9 @@ bool CNetAddr::IsValid() const
     if (IsRFC3849())
         return false;
 
+    if (IsInternal())
+        return false;
+
     if (IsIPv4())
     {
         // INADDR_NONE
@@ -217,11 +235,19 @@ bool CNetAddr::IsValid() const
 
 bool CNetAddr::IsRoutable() const
 {
-    return IsValid() && !(IsRFC1918() || IsRFC2544() || IsRFC3927() || IsRFC4862() || IsRFC6598() || IsRFC5737() || (IsRFC4193() && !IsTor()) || IsRFC4843() || IsLocal());
+    return IsValid() && !(IsRFC1918() || IsRFC2544() || IsRFC3927() || IsRFC4862() || IsRFC6598() || IsRFC5737() || (IsRFC4193() && !IsTor()) || IsRFC4843() || IsLocal() || IsInternal());
+}
+
+bool CNetAddr::IsInternal() const
+{
+   return memcmp(ip, g_internal_prefix, sizeof(g_internal_prefix)) == 0;
 }
 
 enum Network CNetAddr::GetNetwork() const
 {
+    if (IsInternal())
+        return NET_INTERNAL;
+
     if (!IsRoutable())
         return NET_UNROUTABLE;
 
@@ -238,6 +264,8 @@ std::string CNetAddr::ToStringIP() const
 {
     if (IsTor())
         return EncodeBase32(&ip[6], 10) + ".onion";
+    if (IsInternal())
+        return EncodeBase32(ip + sizeof(g_internal_prefix), sizeof(ip) - sizeof(g_internal_prefix)) + ".internal";
     CService serv(*this, 0);
     struct sockaddr_storage sockaddr;
     socklen_t socklen = sizeof(sockaddr);
@@ -305,9 +333,15 @@ std::vector<unsigned char> CNetAddr::GetGroup() const
         nClass = 255;
         nBits = 0;
     }
-
-    // all unroutable addresses belong to the same group
-    if (!IsRoutable())
+    // all internal-usage addresses get their own group
+    if (IsInternal())
+    {
+        nClass = NET_INTERNAL;
+        nStartByte = sizeof(g_internal_prefix);
+        nBits = (sizeof(ip) - sizeof(g_internal_prefix)) * 8;
+    }
+    // all other unroutable addresses belong to the same group
+    else if (!IsRoutable())
     {
         nClass = NET_UNROUTABLE;
         nBits = 0;
@@ -393,7 +427,7 @@ int CNetAddr::GetReachabilityFrom(const CNetAddr *paddrPartner) const
         REACH_PRIVATE
     };
 
-    if (!IsRoutable())
+    if (!IsRoutable() || IsInternal())
         return REACH_UNREACHABLE;
 
     int ourNet = GetExtNetwork(this);
@@ -552,7 +586,7 @@ std::string CService::ToStringPort() const
 
 std::string CService::ToStringIPPort() const
 {
-    if (IsIPv4() || IsTor()) {
+    if (IsIPv4() || IsTor() || IsInternal()) {
         return ToStringIP() + ":" + ToStringPort();
     } else {
         return "[" + ToStringIP() + "]:" + ToStringPort();

src/netaddress.h

@@ -22,6 +22,7 @@ enum Network
     NET_IPV4,
     NET_IPV6,
     NET_TOR,
+    NET_INTERNAL,
 
     NET_MAX,
 };
@@ -45,6 +46,12 @@ class CNetAddr
          */
         void SetRaw(Network network, const uint8_t *data);
 
+        /**
+          * Transform an arbitrary string into a non-routable ipv6 address.
+          * Useful for mapping resolved addresses back to their source.
+         */
+        bool SetInternal(const std::string& name);
+
         bool SetSpecial(const std::string &strName); // for Tor addresses
         bool IsIPv4() const;    // IPv4 mapped address (::FFFF:0:0/96, 0.0.0.0/0)
         bool IsIPv6() const;    // IPv6 address (not mapped IPv4, not Tor)
@@ -64,6 +71,7 @@ class CNetAddr
         bool IsTor() const;
         bool IsLocal() const;
         bool IsRoutable() const;
+        bool IsInternal() const;
         bool IsValid() const;
         enum Network GetNetwork() const;
         std::string ToString() const;

src/rpc/net.cpp

@@ -397,7 +397,7 @@ static UniValue GetNetworksInfo()
     for(int n=0; n<NET_MAX; ++n)
     {
         enum Network network = static_cast<enum Network>(n);
-        if(network == NET_UNROUTABLE)
+        if(network == NET_UNROUTABLE || network == NET_INTERNAL)
             continue;
         proxyType proxy;
         UniValue obj(UniValue::VOBJ);

src/test/netbase_tests.cpp

@@ -25,6 +25,13 @@ static CSubNet ResolveSubNet(const char* subnet)
     return ret;
 }
 
+static CNetAddr CreateInternal(const char* host)
+{
+    CNetAddr addr;
+    addr.SetInternal(host);
+    return addr;
+}
+
 BOOST_AUTO_TEST_CASE(netbase_networks)
 {
     BOOST_CHECK(ResolveIP("127.0.0.1").GetNetwork()                              == NET_UNROUTABLE);
@@ -32,6 +39,7 @@ BOOST_AUTO_TEST_CASE(netbase_networks)
     BOOST_CHECK(ResolveIP("8.8.8.8").GetNetwork()                                == NET_IPV4);
     BOOST_CHECK(ResolveIP("2001::8888").GetNetwork()                             == NET_IPV6);
     BOOST_CHECK(ResolveIP("FD87:D87E:EB43:edb1:8e4:3588:e546:35ca").GetNetwork() == NET_TOR);
+    BOOST_CHECK(CreateInternal("foo.com").GetNetwork()                           == NET_INTERNAL);
 
 }
 
@@ -58,6 +66,8 @@ BOOST_AUTO_TEST_CASE(netbase_properties)
     BOOST_CHECK(ResolveIP("8.8.8.8").IsRoutable());
     BOOST_CHECK(ResolveIP("2001::1").IsRoutable());
     BOOST_CHECK(ResolveIP("127.0.0.1").IsValid());
+    BOOST_CHECK(CreateInternal("FD6B:88C0:8724:edb1:8e4:3588:e546:35ca").IsInternal());
+    BOOST_CHECK(CreateInternal("bar.com").IsInternal());
 
 }
 
@@ -281,6 +291,9 @@ BOOST_AUTO_TEST_CASE(netbase_getgroup)
     BOOST_CHECK(ResolveIP("2001:470:abcd:9999:9999:9999:9999:9999").GetGroup() == std::vector<unsigned char>({(unsigned char)NET_IPV6, 32, 1, 4, 112, 175})); //he.net
     BOOST_CHECK(ResolveIP("2001:2001:9999:9999:9999:9999:9999:9999").GetGroup() == std::vector<unsigned char>({(unsigned char)NET_IPV6, 32, 1, 32, 1})); //IPv6
 
+    // baz.net sha256 hash: 12929400eb4607c4ac075f087167e75286b179c693eb059a01774b864e8fe505
+    std::vector<unsigned char> internal_group = {NET_INTERNAL, 0x12, 0x92, 0x94, 0x00, 0xeb, 0x46, 0x07, 0xc4, 0xac, 0x07};
+    BOOST_CHECK(CreateInternal("baz.net").GetGroup() == internal_group);
 }
 
 BOOST_AUTO_TEST_SUITE_END()