Bug 1810362 - Sort the addresses in a DNS lookup result so the IPv6 ones come first. r=valentin,necko-reviewers,kershaw

Introduce network.dns.preferIPv6 pref to place IPv6 addresses first in a DNS lookup result.

Differential Revision: https://phabricator.services.mozilla.com/D206843

modules/libpref/init/StaticPrefList.yaml

@@ -13156,6 +13156,12 @@
   value: false
   mirror: always
 
+# Whether to prefer IPv6 name lookups.
+- name: network.dns.preferIPv6
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 # Whether to add additional record IPs to the cache
 - name: network.trr.add_additional_records
   type: RelaxedAtomicBool

netwerk/dns/DNS.h

@@ -216,6 +216,11 @@ class AddrInfo {
       mInfo->mAddresses = std::move(addresses);
     }
 
+    template <class Comparator>
+    void SortAddresses(const Comparator& aComp) {
+      mInfo->mAddresses.Sort(aComp);
+    }
+
     void SetCanonicalHostname(const nsACString& aCname) {
       mInfo->mCanonicalName = aCname;
     }

netwerk/dns/nsHostResolver.cpp

@@ -1490,6 +1490,18 @@ nsHostResolver::LookupStatus nsHostResolver::CompleteLookup(
                               aReason, aTRRRequest, lock);
 }
 
+namespace {
+class NetAddrIPv6FirstComparator {
+ public:
+  static bool Equals(const NetAddr& aLhs, const NetAddr& aRhs) {
+    return aLhs.raw.family == aRhs.raw.family;
+  }
+  static bool LessThan(const NetAddr& aLhs, const NetAddr& aRhs) {
+    return aLhs.raw.family > aRhs.raw.family;
+  }
+};
+}  // namespace
+
 nsHostResolver::LookupStatus nsHostResolver::CompleteLookupLocked(
     nsHostRecord* rec, nsresult status, AddrInfo* aNewRRSet, bool pb,
     const nsACString& aOriginsuffix, TRRSkippedReason aReason,
@@ -1601,6 +1613,16 @@ nsHostResolver::LookupStatus nsHostResolver::CompleteLookupLocked(
       old_addr_info = std::move(newRRSet);
     }
     addrRec->negative = !addrRec->addr_info;
+
+    if (addrRec->addr_info && StaticPrefs::network_dns_preferIPv6() &&
+        addrRec->addr_info->Addresses().Length() > 1 &&
+        addrRec->addr_info->Addresses()[0].IsIPAddrV4()) {
+      // Sort IPv6 addresses first.
+      auto builder = addrRec->addr_info->Build();
+      builder.SortAddresses(NetAddrIPv6FirstComparator());
+      addrRec->addr_info = builder.Finish();
+    }
+
     PrepareRecordExpirationAddrRecord(addrRec);
   }
 

netwerk/test/unit/test_dns_service.js

@@ -121,3 +121,36 @@ add_task(
     }
   }
 );
+
+add_task(
+  {
+    skip_if: () =>
+      Services.appinfo.processType != Ci.nsIXULRuntime.PROCESS_TYPE_DEFAULT,
+  },
+  async function test_sort_family() {
+    Services.prefs.setBoolPref("network.dns.preferIPv6", true);
+    overrideService.clearOverrides();
+    overrideService.addIPOverride("example.com", "1.2.3.4");
+    overrideService.addIPOverride("example.com", "3.4.5.6");
+    overrideService.addIPOverride("example.com", "::1");
+    overrideService.addIPOverride("example.com", "::2");
+
+    let listener = new Listener();
+    Services.dns.asyncResolve(
+      "example.com",
+      Ci.nsIDNSService.RESOLVE_TYPE_DEFAULT,
+      Ci.nsIDNSService.RESOLVE_CANONICAL_NAME,
+      null, // resolverInfo
+      listener,
+      mainThread,
+      defaultOriginAttributes
+    );
+
+    let [, inRecord] = await listener;
+    inRecord.QueryInterface(Ci.nsIDNSAddrRecord);
+    Assert.equal(inRecord.getNextAddrAsString(), "::1");
+    Assert.equal(inRecord.getNextAddrAsString(), "::2");
+    Assert.equal(inRecord.getNextAddrAsString(), "1.2.3.4");
+    Assert.equal(inRecord.getNextAddrAsString(), "3.4.5.6");
+  }
+);