Ignore bom at the beginning of the UTF-8 text

Add a testcase about bom.

Author: dota17

src/lib_json/json_reader.cpp

@@ -18,6 +18,7 @@
 #include <memory>
 #include <set>
 #include <sstream>
+#include <string.h>
 #include <utility>
 
 #include <cstdio>
@@ -939,6 +940,7 @@ class OurReader {
 
   bool readToken(Token& token);
   void skipSpaces();
+  void skipBom();
   bool match(const Char* pattern, int patternLength);
   bool readComment();
   bool readCStyleComment(bool* containsNewLineResult);
@@ -1009,7 +1011,6 @@ bool OurReader::parse(const char* beginDoc, const char* endDoc, Value& root,
   if (!features_.allowComments_) {
     collectComments = false;
   }
-
   begin_ = beginDoc;
   end_ = endDoc;
   collectComments_ = collectComments;
@@ -1022,6 +1023,8 @@ bool OurReader::parse(const char* beginDoc, const char* endDoc, Value& root,
     nodes_.pop();
   nodes_.push(&root);
 
+  // skip byte order mark if it exists at the beginning of the UTF-8 text.
+  skipBom();
   bool successful = readValue();
   nodes_.pop();
   Token token;
@@ -1268,6 +1271,13 @@ void OurReader::skipSpaces() {
   }
 }
 
+void OurReader::skipBom() {
+  if (strncmp(begin_, "\xEF\xBB\xBF", 3) == 0) {
+    begin_ += 3;
+    current_ = begin_;
+  }
+}
+
 bool OurReader::match(const Char* pattern, int patternLength) {
   if (end_ - current_ < patternLength)
     return false;

src/test_lib_json/main.cpp

@@ -3578,6 +3578,19 @@ JSONTEST_FIXTURE_LOCAL(BuilderTest, settings) {
   }
 }
 
+struct BomTest : JsonTest::TestCase {};
+
+JSONTEST_FIXTURE_LOCAL(BomTest, withBom) {
+  const std::string with_bom = u8"\xEF\xBB\xBF{\"key\" : \"value\"}";
+  Json::Value root;
+  JSONCPP_STRING errs;
+  std::istringstream iss(with_bom);
+  bool ok = parseFromStream(Json::CharReaderBuilder(), iss, &root, &errs);
+  JSONTEST_ASSERT(ok);
+  JSONTEST_ASSERT(errs.empty());
+  JSONTEST_ASSERT_STRING_EQUAL(root["key"].asString(), "value");
+}
+
 struct IteratorTest : JsonTest::TestCase {};
 
 JSONTEST_FIXTURE_LOCAL(IteratorTest, convert) {