Merge #10446: net: avoid extra dns query per seed

c1be285 chainparams: make supported service bits option explicit (Cory Fields)
d5c7c1c net: use an internal address for fixed seeds (Cory Fields)
6cdc488 net: switch to dummy internal ip for dns seed source (Cory Fields)
6d0bd5b net: do not allow resolving to an internal address (Cory Fields)
7f31762 net: add an internal subnet for representing unresolved hostnames (Cory Fields)

Tree-SHA512: 9bf1042bef546ac3ef0e0d3a9a5555eb21628ff2674a0cf8c6367194b22bfdab477adf452c0e7c56f44e0fb37debc5e14bdb623452e076fb9c492c7702601d7a

8 files changed, 96 insertions, 37 deletions

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 3b42c5fb23..dc4d2621ee 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -124,12 +124,12 @@ public:
         assert(genesis.hashMerkleRoot == uint256S("0x4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"));
 
         // Note that of those with the service bits flag, most only support a subset of possible options
-        vSeeds.push_back(CDNSSeedData("bitcoin.sipa.be", "seed.bitcoin.sipa.be", true)); // Pieter Wuille, only supports x1, x5, x9, and xd
-        vSeeds.push_back(CDNSSeedData("bluematt.me", "dnsseed.bluematt.me", true)); // Matt Corallo, only supports x9
-        vSeeds.push_back(CDNSSeedData("dashjr.org", "dnsseed.bitcoin.dashjr.org")); // Luke Dashjr
-        vSeeds.push_back(CDNSSeedData("bitcoinstats.com", "seed.bitcoinstats.com", true)); // Christian Decker, supports x1 - xf
-        vSeeds.push_back(CDNSSeedData("bitcoin.jonasschnelli.ch", "seed.bitcoin.jonasschnelli.ch", true)); // Jonas Schnelli, only supports x1, x5, x9, and xd
-        vSeeds.push_back(CDNSSeedData("petertodd.org", "seed.btc.petertodd.org", true)); // Peter Todd, only supports x1, x5, x9, and xd
+        vSeeds.emplace_back("seed.bitcoin.sipa.be", true); // Pieter Wuille, only supports x1, x5, x9, and xd
+        vSeeds.emplace_back("dnsseed.bluematt.me", true); // Matt Corallo, only supports x9
+        vSeeds.emplace_back("dnsseed.bitcoin.dashjr.org", false); // Luke Dashjr
+        vSeeds.emplace_back("seed.bitcoinstats.com", true); // Christian Decker, supports x1 - xf
+        vSeeds.emplace_back("seed.bitcoin.jonasschnelli.ch", true); // Jonas Schnelli, only supports x1, x5, x9, and xd
+        vSeeds.emplace_back("seed.btc.petertodd.org", true); // Peter Todd, only supports x1, x5, x9, and xd
 
         base58Prefixes[PUBKEY_ADDRESS] = std::vector<unsigned char>(1,0);
         base58Prefixes[SCRIPT_ADDRESS] = std::vector<unsigned char>(1,5);
@@ -225,10 +225,10 @@ public:
         vFixedSeeds.clear();
         vSeeds.clear();
         // nodes with support for servicebits filtering should be at the top
-        vSeeds.push_back(CDNSSeedData("testnetbitcoin.jonasschnelli.ch", "testnet-seed.bitcoin.jonasschnelli.ch", true));
-        vSeeds.push_back(CDNSSeedData("petertodd.org", "seed.tbtc.petertodd.org", true));
-        vSeeds.push_back(CDNSSeedData("bluematt.me", "testnet-seed.bluematt.me"));
-        vSeeds.push_back(CDNSSeedData("bitcoin.schildbach.de", "testnet-seed.bitcoin.schildbach.de"));
+        vSeeds.emplace_back("testnet-seed.bitcoin.jonasschnelli.ch", true);
+        vSeeds.emplace_back("seed.tbtc.petertodd.org", true);
+        vSeeds.emplace_back("testnet-seed.bluematt.me", false);
+        vSeeds.emplace_back("testnet-seed.bitcoin.schildbach.de", false);
 
         base58Prefixes[PUBKEY_ADDRESS] = std::vector<unsigned char>(1,111);
         base58Prefixes[SCRIPT_ADDRESS] = std::vector<unsigned char>(1,196);
diff --git a/src/chainparams.h b/src/chainparams.h
index a2f136171b..f55ae4cf7f 100644
--- a/src/chainparams.h
+++ b/src/chainparams.h
@@ -15,9 +15,9 @@
 #include <vector>
 
 struct CDNSSeedData {
-    std::string name, host;
+    std::string host;
     bool supportsServiceBitsFiltering;
-    CDNSSeedData(const std::string &strName, const std::string &strHost, bool supportsServiceBitsFilteringIn = false) : name(strName), host(strHost), supportsServiceBitsFiltering(supportsServiceBitsFilteringIn) {}
+    CDNSSeedData(const std::string &strHost, bool supportsServiceBitsFilteringIn) : host(strHost), supportsServiceBitsFiltering(supportsServiceBitsFilteringIn) {}
 };
 
 struct SeedSpec6 {
diff --git a/src/net.cpp b/src/net.cpp
index 73f020273b..43bd0eb0d5 100644
--- a/src/net.cpp
+++ b/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;
@@ -1604,7 +1604,12 @@ void CConnman::ThreadDNSAddressSeed()
             std::vector<CNetAddr> vIPs;
             std::vector<CAddress> vAdd;
             ServiceFlags requiredServiceBits = nRelevantServices;
-            if (LookupHost(GetDNSHost(seed, &requiredServiceBits).c_str(), vIPs, 0, true))
+            std::string host = GetDNSHost(seed, &requiredServiceBits);
+            CNetAddr resolveSource;
+            if (!resolveSource.SetInternal(host)) {
+                continue;
+            }
+            if (LookupHost(host.c_str(), vIPs, 0, true))
             {
                 for (const CNetAddr& ip : vIPs)
                 {
@@ -1614,18 +1619,7 @@ void CConnman::ThreadDNSAddressSeed()
                     vAdd.push_back(addr);
                     found++;
                 }
-            }
-            if (interruptNet) {
-                return;
-            }
-            // TODO: The seed name resolve may fail, yielding an IP of [::], which results in
-            // addrman assigning the same source to results from different seeds.
-            // This should switch to a hard-coded stable dummy IP for each seed name, so that the
-            // resolve is not required at all.
-            if (!vIPs.empty()) {
-                CService seedSource;
-                Lookup(seed.name.c_str(), seedSource, 0, true);
-                addrman.Add(vAdd, seedSource);
+                addrman.Add(vAdd, resolveSource);
             }
         }
     }
@@ -1724,7 +1718,7 @@ void CConnman::ThreadOpenConnections()
             if (!done) {
                 LogPrintf("Adding fixed seed nodes as DNS doesn't seem to be available.\n");
                 CNetAddr local;
-                LookupHost("127.0.0.1", local, false);
+                local.SetInternal("fixedseeds");
                 addrman.Add(convertSeed6(Params().FixedSeeds()), local);
                 done = true;
             }
diff --git a/src/netaddress.cpp b/src/netaddress.cpp
index 34a7029862..89f257c642 100644
--- a/src/netaddress.cpp
+++ b/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();
diff --git a/src/netaddress.h b/src/netaddress.h
index fbc4d1a65f..80716600d1 100644
--- a/src/netaddress.h
+++ b/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;
diff --git a/src/netbase.cpp b/src/netbase.cpp
index 32557dd179..a23f92e1ed 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -108,17 +108,22 @@ bool static LookupIntern(const char *pszName, std::vector<CNetAddr>& vIP, unsign
     struct addrinfo *aiTrav = aiRes;
     while (aiTrav != NULL && (nMaxSolutions == 0 || vIP.size() < nMaxSolutions))
     {
+        CNetAddr resolved;
         if (aiTrav->ai_family == AF_INET)
         {
             assert(aiTrav->ai_addrlen >= sizeof(sockaddr_in));
-            vIP.push_back(CNetAddr(((struct sockaddr_in*)(aiTrav->ai_addr))->sin_addr));
+            resolved = CNetAddr(((struct sockaddr_in*)(aiTrav->ai_addr))->sin_addr);
         }
 
         if (aiTrav->ai_family == AF_INET6)
         {
             assert(aiTrav->ai_addrlen >= sizeof(sockaddr_in6));
             struct sockaddr_in6* s6 = (struct sockaddr_in6*) aiTrav->ai_addr;
-            vIP.push_back(CNetAddr(s6->sin6_addr, s6->sin6_scope_id));
+            resolved = CNetAddr(s6->sin6_addr, s6->sin6_scope_id);
+        }
+        /* Never allow resolving to an internal address. Consider any such result invalid */
+        if (!resolved.IsInternal()) {
+            vIP.push_back(resolved);
         }
 
         aiTrav = aiTrav->ai_next;
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index aecedb48b2..5cab0ad5bd 100644
--- a/src/rpc/net.cpp
+++ b/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);
diff --git a/src/test/netbase_tests.cpp b/src/test/netbase_tests.cpp
index e4b4b85720..b45a7fcc57 100644
--- a/src/test/netbase_tests.cpp
+++ b/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());
 
 }
 
@@ -103,6 +113,11 @@ BOOST_AUTO_TEST_CASE(netbase_lookupnumeric)
     BOOST_CHECK(TestParse("[::]:8333", "[::]:8333"));
     BOOST_CHECK(TestParse("[127.0.0.1]", "127.0.0.1:65535"));
     BOOST_CHECK(TestParse(":::", "[::]:0"));
+
+    // verify that an internal address fails to resolve
+    BOOST_CHECK(TestParse("[fd6b:88c0:8724:1:2:3:4:5]", "[::]:0"));
+    // and that a one-off resolves correctly
+    BOOST_CHECK(TestParse("[fd6c:88c0:8724:1:2:3:4:5]", "[fd6c:88c0:8724:1:2:3:4:5]:65535"));
 }
 
 BOOST_AUTO_TEST_CASE(onioncat_test)
@@ -281,6 +296,9 @@ 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()