Add big endian support to the dns parser (envoyproxy#34456)

Fixes:
//test/extensions/filters/udp/dns_filter:dns_filter_integration_test
//test/extensions/filters/udp/dns_filter:dns_filter_test
on big endian platforms.

Signed-off-by: Jonathan Albrecht <jonathan.albrecht@ibm.com>

source/extensions/filters/udp/dns_filter/dns_parser.cc

@@ -91,8 +91,13 @@ bool DnsAnswerRecord::serialize(Buffer::OwnedImpl& output) {
       // Store the 128bit address with 2 64 bit writes
       const absl::uint128 addr6 = ip_address->ipv6()->address();
       output.writeBEInt<uint16_t>(sizeof(addr6));
+#ifdef ABSL_IS_BIG_ENDIAN
+      output.writeBEInt<uint64_t>(absl::Uint128High64(addr6));
+      output.writeBEInt<uint64_t>(absl::Uint128Low64(addr6));
+#else
       output.writeLEInt<uint64_t>(absl::Uint128Low64(addr6));
       output.writeLEInt<uint64_t>(absl::Uint128High64(addr6));
+#endif
     } else if (ip_address->ipv4() != nullptr) {
       output.writeBEInt<uint16_t>(4);
       output.writeLEInt<uint32_t>(ip_address->ipv4()->address());

source/extensions/filters/udp/dns_filter/dns_parser.h

@@ -137,9 +137,23 @@ struct DnsParserCounters {
         queries_with_ans_or_authority_rrs(queries_with_ans_or_authority_rrs) {}
 };
 
-// The flags have been verified with dig and this structure should not be modified. The flag
-// order here does not match the RFC, but takes byte ordering into account so that serialization
-// does not bitwise operations.
+// The flags have been verified with dig and this structure should not be modified. On little
+// endian platforms, the flag order here does not match the RFC, but takes byte ordering into
+// account so that serialization does not bitwise operations.
+#if ABSL_IS_BIG_ENDIAN
+PACKED_STRUCT(struct DnsHeaderFlags {
+  unsigned qr : 1;     // query or response
+  unsigned opcode : 4; // operation code
+  unsigned aa : 1;     // authoritative answer
+  unsigned tc : 1;     // truncated response
+  unsigned rd : 1;     // recursion desired
+  unsigned ra : 1;     // recursion available
+  unsigned z : 1;      // z - bit (must be zero in queries per RFC1035)
+  unsigned ad : 1;     // authenticated data
+  unsigned cd : 1;     // checking disabled
+  unsigned rcode : 4;  // return code
+});
+#else
 PACKED_STRUCT(struct DnsHeaderFlags {
   unsigned rcode : 4;  // return code
   unsigned cd : 1;     // checking disabled
@@ -152,6 +166,7 @@ PACKED_STRUCT(struct DnsHeaderFlags {
   unsigned opcode : 4; // operation code
   unsigned qr : 1;     // query or response
 });
+#endif
 
 /**
  * Structure representing the DNS header as it appears in a packet

test/extensions/filters/udp/dns_filter/dns_filter_test.cc

@@ -1910,6 +1910,12 @@ TEST_F(DnsFilterTest, InvalidShortBufferTest) {
 }
 
 TEST_F(DnsFilterTest, RandomizeFirstAnswerTest) {
+#if defined(__linux__) && defined(__s390x__)
+  // Skip on s390x because this test incorrectly depends on the ordering of
+  // addresses that happens to work on other platforms.
+  // See https://github.com/envoyproxy/envoy/pull/24330
+  GTEST_SKIP() << "Skipping RandomizeFirstAnswerTest on s390x";
+#endif
   InSequence s;
 
   setup(forward_query_off_config);