Improve HTTPS RDATA fuzzer

Parse from two separate portions of the input and attempt IsEqual()
between the two resulting parsed rdatas.  Improves our ability to
discover issues in the comparison logic.

Bug: 1146873
Change-Id: Ib561dfce0a704a876cc731ef9037759d304f71ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2525772
Commit-Queue: Eric Orth <ericorth@chromium.org>
Reviewed-by: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825908}

net/dns/https_record_rdata_fuzzer.cc

@@ -4,10 +4,13 @@
 
 #include "net/dns/https_record_rdata.h"
 
+#include <fuzzer/FuzzedDataProvider.h>
+
 #include <stdint.h>
 
 #include <memory>
 #include <set>
+#include <string>
 #include <vector>
 
 #include "base/check.h"
@@ -18,17 +21,29 @@
 namespace net {
 namespace {
 
-void ParseAndExercise(base::StringPiece data) {
-  std::unique_ptr<HttpsRecordRdata> parsed = HttpsRecordRdata::Parse(data);
-  std::unique_ptr<HttpsRecordRdata> parsed2 = HttpsRecordRdata::Parse(data);
+void ParseAndExercise(FuzzedDataProvider& data_provider) {
+  std::string data1 = data_provider.ConsumeRandomLengthString();
+  std::unique_ptr<HttpsRecordRdata> parsed = HttpsRecordRdata::Parse(data1);
+  std::unique_ptr<HttpsRecordRdata> parsed2 = HttpsRecordRdata::Parse(data1);
+  std::unique_ptr<HttpsRecordRdata> parsed3 =
+      HttpsRecordRdata::Parse(data_provider.ConsumeRemainingBytesAsString());
 
   CHECK_EQ(!!parsed, !!parsed2);
 
   if (!parsed)
     return;
 
+  // `parsed` and `parsed2` parsed from the same data, so they should always be
+  // equal.
   CHECK(parsed->IsEqual(parsed.get()));
   CHECK(parsed->IsEqual(parsed2.get()));
+  CHECK(parsed2->IsEqual(parsed.get()));
+
+  // Attempt comparison with an rdata parsed from separate data. IsEqual() will
+  // probably return false most of the time, but easily could be true if the
+  // input data is similar enough.
+  if (parsed3)
+    CHECK_EQ(parsed->IsEqual(parsed3.get()), parsed3->IsEqual(parsed.get()));
 
   CHECK_EQ(parsed->Type(), dns_protocol::kTypeHttps);
   if (parsed->IsAlias()) {
@@ -65,8 +80,8 @@ void ParseAndExercise(base::StringPiece data) {
 }  // namespace
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-  ParseAndExercise(
-      base::StringPiece(reinterpret_cast<const char*>(data), size));
+  FuzzedDataProvider data_provider(data, size);
+  ParseAndExercise(data_provider);
   return 0;
 }