Bug 1518730 - Only send AAAA TRR requests when the system has IPv6 connectivity r=dragana

This is an optimization. If we detect that the system can't use the IPv6
address, there's no point in making a request for it.

Depends on D33475

Differential Revision: https://phabricator.services.mozilla.com/D33476

--HG--
extra : moz-landing-system : lando

modules/libpref/init/all.js

@@ -5534,6 +5534,8 @@ pref("network.trr.blacklist-duration", 60);
 pref("network.trr.request-timeout", 1500);
 // Allow AAAA entries to be used "early", before the A results are in
 pref("network.trr.early-AAAA", false);
+// When true, it only sends AAAA when the system has IPv6 connectivity
+pref("network.trr.skip-AAAA-when-not-supported", true);
 // Explicitly disable ECS (EDNS Client Subnet, RFC 7871)
 pref("network.trr.disable-ECS", true);
 // After this many failed TRR requests in a row, consider TRR borked

netwerk/base/nsINetworkConnectivityService.idl

@@ -21,11 +21,15 @@ interface nsINetworkConnectivityService : nsISupports
   };
 
   /* If DNS v4/v6 queries actually work on the current network */
+  [infallible]
   readonly attribute nsINetworkConnectivityService_ConnectivityState DNSv4;
+  [infallible]
   readonly attribute nsINetworkConnectivityService_ConnectivityState DNSv6;
 
   /* If connecting to IPv4/v6 works on the current network */
+  [infallible]
   readonly attribute nsINetworkConnectivityService_ConnectivityState IPv4;
+  [infallible]
   readonly attribute nsINetworkConnectivityService_ConnectivityState IPv6;
 
   /* Starts the DNS request to check for DNS v4/v6 availability */

netwerk/dns/TRRService.cpp

@@ -252,6 +252,14 @@ nsresult TRRService::ReadPrefs(const char* name) {
       mEarlyAAAA = tmp;
     }
   }
+
+  if (!name || !strcmp(name, TRR_PREF("skip-AAAA-when-not-supported"))) {
+    bool tmp;
+    if (NS_SUCCEEDED(Preferences::GetBool(
+            TRR_PREF("skip-AAAA-when-not-supported"), &tmp))) {
+      mCheckIPv6Connectivity = tmp;
+    }
+  }
   if (!name || !strcmp(name, kDisableIpv6Pref)) {
     bool tmp;
     if (NS_SUCCEEDED(Preferences::GetBool(kDisableIpv6Pref, &tmp))) {

netwerk/dns/TRRService.h

@@ -35,6 +35,7 @@ class TRRService : public nsIObserver,
   bool AllowRFC1918() { return mRfc1918; }
   bool UseGET() { return mUseGET; }
   bool EarlyAAAA() { return mEarlyAAAA; }
+  bool CheckIPv6Connectivity() { return mCheckIPv6Connectivity; }
   bool DisableIPv6() { return mDisableIPv6; }
   bool DisableECS() { return mDisableECS; }
   nsresult GetURI(nsCString& result);
@@ -85,8 +86,9 @@ class TRRService : public nsIObserver,
       mCaptiveIsPassed;           // set when captive portal check is passed
   Atomic<bool, Relaxed> mUseGET;  // do DOH using GET requests (instead of POST)
   Atomic<bool, Relaxed> mEarlyAAAA;  // allow use of AAAA results before A is in
-  Atomic<bool, Relaxed> mDisableIPv6;  // don't even try
-  Atomic<bool, Relaxed> mDisableECS;   // disable EDNS Client Subnet in requests
+  Atomic<bool, Relaxed> mCheckIPv6Connectivity;  // check IPv6 connectivity
+  Atomic<bool, Relaxed> mDisableIPv6;            // don't even try
+  Atomic<bool, Relaxed> mDisableECS;  // disable EDNS Client Subnet in requests
   Atomic<uint32_t, Relaxed>
       mDisableAfterFails;  // this many fails in a row means failed TRR service
 

netwerk/dns/nsHostResolver.cpp

@@ -45,6 +45,7 @@
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/StaticPrefs.h"
+#include "mozilla/net/NetworkConnectivityService.h"
 
 using namespace mozilla;
 using namespace mozilla::net;
@@ -1240,10 +1241,15 @@ nsresult nsHostResolver::TrrLookup(nsHostRecord* aRec, TRR* pushedTRR) {
     }
     bool sendAgain;
 
+    RefPtr<NetworkConnectivityService> ncs =
+        NetworkConnectivityService::GetSingleton();
+
     do {
       sendAgain = false;
       if ((TRRTYPE_AAAA == rectype) && gTRRService &&
-          gTRRService->DisableIPv6()) {
+          (gTRRService->DisableIPv6() ||
+           (gTRRService->CheckIPv6Connectivity() &&
+            ncs->GetIPv6() == nsINetworkConnectivityService::NOT_AVAILABLE))) {
         break;
       }
       LOG(("TRR Resolve %s type %d\n", addrRec->host.get(), (int)rectype));