Android: <= 7 might require sys/system_properties.h

The autotools rewrite in c-ares 1.25 might have broken detection
of __system_property_get() which is needed on Android versions
prior to v8 in order to read DNS server settings.

This might fix #907
Authored-By: Brad House (@bradh352)

CMakeLists.txt

@@ -262,7 +262,7 @@ ENDIF ()
 # Set system-specific compiler flags
 IF (CMAKE_SYSTEM_NAME STREQUAL "Darwin")
 	LIST (APPEND SYSFLAGS -D_DARWIN_C_SOURCE)
-ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "Linux")
+ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "Linux" OR CMAKE_SYSTEM_NAME STREQUAL "Android")
 	LIST (APPEND SYSFLAGS -D_GNU_SOURCE -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700)
 ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "SunOS")
 	LIST (APPEND SYSFLAGS -D__EXTENSIONS__ -D_REENTRANT -D_XOPEN_SOURCE=700)

configure.ac

@@ -397,7 +397,7 @@ AS_HELP_STRING([--enable-libgcc],[use libgcc when linking]),
 dnl check for a few basic system headers we need.  It would be nice if we could
 dnl split these on separate lines, but for some reason autotools on Windows doesn't
 dnl allow this, even tried ending lines with a backslash.
-AC_CHECK_HEADERS([malloc.h memory.h AvailabilityMacros.h sys/types.h sys/time.h sys/select.h sys/socket.h sys/filio.h sys/ioctl.h sys/param.h sys/uio.h sys/random.h sys/event.h sys/epoll.h assert.h iphlpapi.h netioapi.h netdb.h netinet/in.h netinet6/in6.h netinet/tcp.h net/if.h ifaddrs.h fcntl.h errno.h socket.h strings.h stdbool.h time.h poll.h limits.h arpa/nameser.h arpa/nameser_compat.h arpa/inet.h ],
+AC_CHECK_HEADERS([malloc.h memory.h AvailabilityMacros.h sys/types.h sys/time.h sys/select.h sys/socket.h sys/filio.h sys/ioctl.h sys/param.h sys/uio.h sys/random.h sys/event.h sys/epoll.h assert.h iphlpapi.h netioapi.h netdb.h netinet/in.h netinet6/in6.h netinet/tcp.h net/if.h ifaddrs.h fcntl.h errno.h socket.h strings.h stdbool.h time.h poll.h limits.h arpa/nameser.h arpa/nameser_compat.h arpa/inet.h sys/system_properties.h ],
 dnl to do if not found
 [],
 dnl to do if found
@@ -512,6 +512,9 @@ cares_all_includes="
 #ifdef HAVE_RESOLV_H
 #  include <resolv.h>
 #endif
+#ifdef HAVE_SYS_SYSTEM_PROPERTIES_H
+#  include <sys/system_properties.h>
+#endif
 #ifdef HAVE_IPHLPAPI_H
 #  include <iphlpapi.h>
 #endif

src/lib/ares_event_thread.c

@@ -328,13 +328,15 @@ static void *ares_event_thread(void *arg)
 
     e->ev_sys->wait(e, timeout_ms);
 
+    /* Relock before we loop again */
+    ares__thread_mutex_lock(e->mutex);
+
     /* Each iteration should do timeout processing */
     if (e->isup) {
+      ares__thread_mutex_unlock(e->mutex);
       ares_process_fd(e->channel, ARES_SOCKET_BAD, ARES_SOCKET_BAD);
+      ares__thread_mutex_lock(e->mutex);
     }
-
-    /* Relock before we loop again */
-    ares__thread_mutex_lock(e->mutex);
   }
 
   /* Lets cleanup while we're in the thread itself */

src/lib/ares_getaddrinfo.c

@@ -487,6 +487,18 @@ static void terminate_retries(const struct host_query *hquery,
   query->no_retries = ARES_TRUE;
 }
 
+static ares_bool_t ai_has_ipv4(struct ares_addrinfo *ai)
+{
+  struct ares_addrinfo_node *node;
+
+  for (node = ai->nodes; node != NULL; node = node->ai_next) {
+    if (node->ai_family == AF_INET) {
+      return ARES_TRUE;
+    }
+  }
+  return ARES_FALSE;
+}
+
 static void host_callback(void *arg, ares_status_t status, size_t timeouts,
                           const ares_dns_record_t *dnsrec)
 {
@@ -502,7 +514,27 @@ static void host_callback(void *arg, ares_status_t status, size_t timeouts,
       addinfostatus =
         ares__parse_into_addrinfo(dnsrec, ARES_TRUE, hquery->port, hquery->ai);
     }
-    if (addinfostatus == ARES_SUCCESS) {
+
+    /* We sent out ipv4 and ipv6 requests simultaneously.  If we got a
+     * successful ipv4 response, we want to go ahead and tell the ipv6 request
+     * that if it fails or times out to not try again since we have the data
+     * we need.
+     *
+     * Our initial implementation of this would terminate retries if we got any
+     * successful response (ipv4 _or_ ipv6).  But we did get some user-reported
+     * issues with this that had bad system configs and odd behavior:
+     *  https://github.com/alpinelinux/docker-alpine/issues/366
+     *
+     * Essentially the ipv6 query succeeded but the ipv4 query failed or timed
+     * out, and so we only returned the ipv6 address, but the host couldn't
+     * use ipv6.  If we continued to allow ipv4 retries it would have found a
+     * server that worked and returned both address classes (this is clearly
+     * unexpected behavior).
+     *
+     * At some point down the road if ipv6 actually becomes required and
+     * reliable we can drop this ipv4 check.
+     */
+    if (addinfostatus == ARES_SUCCESS && ai_has_ipv4(hquery->ai)) {
       terminate_retries(hquery, ares_dns_record_get_id(dnsrec));
     }
   }

src/lib/ares_send.c

@@ -86,6 +86,11 @@ ares_status_t ares_send_nolock(ares_channel_t          *channel,
 
   status = ares_dns_write(dnsrec, &query->qbuf, &query->qlen);
   if (status != ARES_SUCCESS) {
+    /* Sometimes we might get a EBADRESP response from duplicate due to
+     * the way it works (write and parse), rewrite it to EBADQUERY. */
+    if (status == ARES_EBADRESP) {
+      status = ARES_EBADQUERY;
+    }
     ares_free(query);
     callback(arg, status, 0, NULL);
     return status;

test/ares-test-mock-ai.cc

@@ -721,6 +721,72 @@ class NoRotateMultiMockTestAI : public MockMultiServerChannelTestAI {
   NoRotateMultiMockTestAI() : MockMultiServerChannelTestAI(nullptr, ARES_OPT_NOROTATE) {}
 };
 
+/* We want to terminate retries of other address classes on getaddrinfo if one
+ * address class is returned already to return replies faster.
+ * UPDATE: actually we want to do this only if the address class we received
+ *         was ipv4.  We've seen issues if ipv6 was returned but the host was
+ *         really only capable of ipv4.
+ */
+TEST_P(NoRotateMultiMockTestAI, v4Worksv6Timesout) {
+  std::vector<byte> nothing;
+
+  DNSPacket rsp4;
+  rsp4.set_response().set_aa()
+    .add_question(new DNSQuestion("www.example.com", T_A))
+    .add_answer(new DNSARR("www.example.com", 0x0100, {0x01, 0x02, 0x03, 0x04}));
+
+  EXPECT_CALL(*servers_[0], OnRequest("www.example.com", T_A))
+    .WillOnce(SetReply(servers_[0].get(), &rsp4));
+  EXPECT_CALL(*servers_[0], OnRequest("www.example.com", T_AAAA))
+    .WillOnce(SetReplyData(servers_[0].get(), nothing));
+
+  AddrInfoResult result;
+  struct ares_addrinfo_hints hints = {0, 0, 0, 0};
+  hints.ai_family = AF_UNSPEC;
+  hints.ai_flags = ARES_AI_NOSORT;
+  ares_getaddrinfo(channel_, "www.example.com.", NULL, &hints, AddrInfoCallback, &result);
+  Process();
+  EXPECT_TRUE(result.done_);
+  EXPECT_EQ(result.status_, ARES_SUCCESS);
+  EXPECT_THAT(result.ai_, IncludesNumAddresses(1));
+  EXPECT_THAT(result.ai_, IncludesV4Address("1.2.3.4"));
+}
+
+TEST_P(NoRotateMultiMockTestAI, v6Worksv4TimesoutFirst) {
+  std::vector<byte> nothing;
+
+  DNSPacket rsp4;
+  rsp4.set_response().set_aa()
+    .add_question(new DNSQuestion("www.example.com", T_A))
+    .add_answer(new DNSARR("www.example.com", 0x0100, {0x01, 0x02, 0x03, 0x04}));
+
+  DNSPacket rsp6;
+  rsp6.set_response().set_aa()
+    .add_question(new DNSQuestion("www.example.com", T_AAAA))
+    .add_answer(new DNSAaaaRR("www.example.com", 100,
+                              {0x21, 0x21, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+                               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x03}));
+
+  EXPECT_CALL(*servers_[0], OnRequest("www.example.com", T_A))
+    .WillOnce(SetReplyData(servers_[0].get(), nothing));
+  EXPECT_CALL(*servers_[0], OnRequest("www.example.com", T_AAAA))
+    .WillOnce(SetReply(servers_[0].get(), &rsp6));
+  EXPECT_CALL(*servers_[1], OnRequest("www.example.com", T_A))
+    .WillOnce(SetReply(servers_[1].get(), &rsp4));
+
+  AddrInfoResult result;
+  struct ares_addrinfo_hints hints = {0, 0, 0, 0};
+  hints.ai_family = AF_UNSPEC;
+  hints.ai_flags = ARES_AI_NOSORT;
+  ares_getaddrinfo(channel_, "www.example.com.", NULL, &hints, AddrInfoCallback, &result);
+  Process();
+  EXPECT_TRUE(result.done_);
+  EXPECT_EQ(result.status_, ARES_SUCCESS);
+  EXPECT_THAT(result.ai_, IncludesNumAddresses(2));
+  EXPECT_THAT(result.ai_, IncludesV4Address("1.2.3.4"));
+  EXPECT_THAT(result.ai_, IncludesV6Address("2121:0000:0000:0000:0000:0000:0000:0303"));
+
+}
 
 TEST_P(NoRotateMultiMockTestAI, ThirdServer) {
   struct ares_options opts;