dns: switch to callback exception wrapping.

source/common/network/dns_impl.cc

@@ -120,8 +120,18 @@ void DnsResolverImpl::PendingResolution::onAresHostCallback(int status, int time
 
   if (completed_) {
     if (!cancelled_) {
-      dispatcher_.post(
-          [callback = callback_, al = std::move(address_list)] { callback(std::move(al)); });
+      try {
+        callback_(std::move(address_list));
+      } catch (const EnvoyException& e) {
+        ENVOY_LOG(critical, "EnvoyException in c-ares callback");
+        dispatcher_.post([e] { throw e; });
+      } catch (const std::exception& e) {
+        ENVOY_LOG(critical, "std::exception in c-ares callback");
+        dispatcher_.post([s = std::string(e.what())] { throw EnvoyException(s); });
+      } catch (...) {
+        ENVOY_LOG(critical, "Unknown exception in c-ares callback");
+        dispatcher_.post([] { throw EnvoyException("unknown"); });
+      }
     }
     if (owned_) {
       delete this;

source/common/network/dns_impl.h

@@ -64,7 +64,7 @@ class DnsResolverImpl : public DnsResolver, protected Logger::Loggable<Logger::I
 
     // Caller supplied callback to invoke on query completion or error.
     const ResolveCb callback_;
-    // Dispatcher to post callback_ to.
+    // Dispatcher to post any callback_ exceptions to.
     Event::Dispatcher& dispatcher_;
     // Does the object own itself? Resource reclamation occurs via self-deleting
     // on query completion or error.

test/common/network/dns_impl_test.cc

@@ -492,7 +492,6 @@ TEST_P(DnsImplTest, LocalLookup) {
                            [&](const std::list<Address::InstanceConstSharedPtr>&& results) -> void {
                              address_list = results;
                            }));
-    dispatcher_.run(Event::Dispatcher::RunType::NonBlock);
     EXPECT_TRUE(hasAddress(address_list, "127.0.0.1"));
     EXPECT_FALSE(hasAddress(address_list, "::1"));
   }
@@ -507,7 +506,6 @@ TEST_P(DnsImplTest, LocalLookup) {
                              address_list = results;
                            }))
         << error_msg;
-    dispatcher_.run(Event::Dispatcher::RunType::NonBlock);
     EXPECT_TRUE(hasAddress(address_list, "::1")) << error_msg;
     EXPECT_FALSE(hasAddress(address_list, "127.0.0.1"));
 
@@ -517,7 +515,6 @@ TEST_P(DnsImplTest, LocalLookup) {
                              address_list = results;
                            }))
         << error_msg;
-    dispatcher_.run(Event::Dispatcher::RunType::NonBlock);
     EXPECT_FALSE(hasAddress(address_list, "127.0.0.1"));
     EXPECT_TRUE(hasAddress(address_list, "::1")) << error_msg;
   }
@@ -557,6 +554,29 @@ TEST_P(DnsImplTest, DnsIpAddressVersionV6) {
   EXPECT_TRUE(hasAddress(address_list, "1::2"));
 }
 
+// Validate exception behavior during c-ares callbacks.
+TEST_P(DnsImplTest, CallbackException) {
+  // Force immediate resolution, which will trigger a c-ares exception unsafe
+  // state providing regression coverage for #4307.
+  EXPECT_EQ(nullptr, resolver_->resolve(
+                         "1.2.3.4", DnsLookupFamily::V4Only,
+                         [&](const std::list<Address::InstanceConstSharedPtr> &&
+                             /*results*/) -> void { throw EnvoyException("Envoy exception"); }));
+  EXPECT_THROW_WITH_MESSAGE(dispatcher_.run(Event::Dispatcher::RunType::Block), EnvoyException,
+                            "Envoy exception");
+  EXPECT_EQ(nullptr, resolver_->resolve(
+                         "1.2.3.4", DnsLookupFamily::V4Only,
+                         [&](const std::list<Address::InstanceConstSharedPtr> &&
+                             /*results*/) -> void { throw std::runtime_error("runtime error"); }));
+  EXPECT_THROW_WITH_MESSAGE(dispatcher_.run(Event::Dispatcher::RunType::Block), EnvoyException,
+                            "runtime error");
+  EXPECT_EQ(nullptr, resolver_->resolve("1.2.3.4", DnsLookupFamily::V4Only,
+                                        [&](const std::list<Address::InstanceConstSharedPtr> &&
+                                            /*results*/) -> void { throw std::string(); }));
+  EXPECT_THROW_WITH_MESSAGE(dispatcher_.run(Event::Dispatcher::RunType::Block), EnvoyException,
+                            "unknown");
+}
+
 TEST_P(DnsImplTest, DnsIpAddressVersion) {
   std::list<Address::InstanceConstSharedPtr> address_list;
   server_->addHosts("some.good.domain", {"1.2.3.4"}, A);