[libfuzzer] Add expat_xml_parse_fuzzer for third_party/expat.

third_party/expat/fuzz/expat_xml_parse_fuzzer.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "third_party/expat/files/lib/expat.h"
+
+#include <array>
+
+static void XMLCALL
+startElement(void* userData, const char* name, const char** atts) {
+  int* depthPtr = static_cast<int*>(userData);
+  (void)atts;
+
+  for (int i = 0; i < *depthPtr; i++)
+    (void)name;
+
+  *depthPtr += 1;
+}
+
+
+static void XMLCALL
+endElement(void* userData, const char* name) {
+  int* depthPtr = static_cast<int*>(userData);
+  (void)name;
+
+  *depthPtr -= 1;
+}
+
+
+std::array<const char*, 7> kEncodings = {{ "UTF-16", "UTF-8", "ISO_8859_1",
+                                           "US_ASCII", "UTF_16BE", "UTF_16LE",
+                                            nullptr }};
+
+
+// Entry point for LibFuzzer.
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  for (auto enc : kEncodings) {
+    XML_Parser parser = XML_ParserCreate(enc);
+    if (!parser)
+      return 0;
+
+    int depth = 0;
+    XML_SetUserData(parser, &depth);
+    XML_SetElementHandler(parser, startElement, endElement);
+
+    const char* dataPtr = reinterpret_cast<const char*>(data);
+
+    // Feed the data with two different values of |isFinal| for better coverage.
+    for (int isFinal = 0; isFinal <= 1; ++isFinal) {
+      if (XML_Parse(parser, dataPtr, size, isFinal) == XML_STATUS_ERROR) {
+        XML_ErrorString(XML_GetErrorCode(parser));
+        XML_GetCurrentLineNumber(parser);
+      }
+    }
+
+    XML_ParserFree(parser);
+  }
+
+  return 0;
+}