Expose getLocationLineAndColumn() as a public API

include/json/reader.h

@@ -395,6 +395,14 @@ bool JSON_API parseFromStream(CharReader::Factory const&, IStream&, Value* root,
  */
 JSON_API IStream& operator>>(IStream&, Value&);
 
+/** Line and column within a document (1-based). */
+struct DocumentLocation {
+  int line;
+  int column;
+};
+
+/** Return the location of a character within a string. */
+DocumentLocation JSON_API locateInDocument(char const* beginDoc, size_t offset);
 } // namespace Json
 
 #pragma pack(pop)

src/lib_json/json_reader.cpp

@@ -608,7 +608,7 @@ bool Reader::decodeDouble(Token& token, Value& decoded) {
       value = -std::numeric_limits<double>::infinity();
     else if (!std::isinf(value))
       return addError(
-        "'" + String(token.start_, token.end_) + "' is not a number.", token);
+          "'" + String(token.start_, token.end_) + "' is not a number.", token);
   }
   decoded = value;
   return true;
@@ -767,24 +767,9 @@ Reader::Char Reader::getNextChar() {
 
 void Reader::getLocationLineAndColumn(Location location, int& line,
                                       int& column) const {
-  Location current = begin_;
-  Location lastLineStart = current;
-  line = 0;
-  while (current < location && current != end_) {
-    Char c = *current++;
-    if (c == '\r') {
-      if (*current == '\n')
-        ++current;
-      lastLineStart = current;
-      ++line;
-    } else if (c == '\n') {
-      lastLineStart = current;
-      ++line;
-    }
-  }
-  // column & line start at 1
-  column = int(location - lastLineStart) + 1;
-  ++line;
+  auto loc = locateInDocument(document_.data(), location - document_.data());
+  line = loc.line;
+  column = loc.column;
 }
 
 String Reader::getLocationLineAndColumn(Location location) const {
@@ -1660,7 +1645,7 @@ bool OurReader::decodeDouble(Token& token, Value& decoded) {
       value = -std::numeric_limits<double>::infinity();
     else if (!std::isinf(value))
       return addError(
-        "'" + String(token.start_, token.end_) + "' is not a number.", token);
+          "'" + String(token.start_, token.end_) + "' is not a number.", token);
   }
   decoded = value;
   return true;
@@ -1991,6 +1976,28 @@ bool parseFromStream(CharReader::Factory const& fact, IStream& sin, Value* root,
   return reader->parse(begin, end, root, errs);
 }
 
+DocumentLocation locateInDocument(char const* beginDoc, size_t offset) {
+  int line = 1;
+  int col = 1;
+  const char* last = beginDoc + offset;
+  for (; beginDoc != last; ++beginDoc) {
+    switch (*beginDoc) {
+    case '\r':
+      if (beginDoc + 1 != last && beginDoc[1] == '\n')
+        continue;      // consume CRLF as a single token.
+      [[fallthrough]]; // CR without a following LF is same as LF
+    case '\n':
+      col = 1;
+      ++line;
+      break;
+    default:
+      ++col;
+      break;
+    }
+  }
+  return {line, col};
+}
+
 IStream& operator>>(IStream& sin, Value& root) {
   CharReaderBuilder b;
   String errs;

src/test_lib_json/main.cpp

@@ -3903,6 +3903,36 @@ JSONTEST_FIXTURE_LOCAL(FuzzTest, fuzzDoesntCrash) {
                              example.size()));
 }
 
+struct LocateInDocumentTest : JsonTest::TestCase {
+  void testLocateInDocument(const char* doc, size_t location, int row,
+                            int column) {
+    Json::DocumentLocation actualLocation =
+        Json::locateInDocument(doc, location);
+    JSONTEST_ASSERT_EQUAL(row, actualLocation.line);
+    JSONTEST_ASSERT_EQUAL(column, actualLocation.column);
+  }
+};
+
+JSONTEST_FIXTURE_LOCAL(LocateInDocumentTest, locateInDocTest) {
+  const std::string example1 = "line 1\nline 2\r\nline 3\rline 4";
+  const char* example2 = "\nline 2\r\r\n\nline 5\0 \n\rline 7\r\n";
+  struct TestSpec {
+    const char* doc;
+    size_t offset;
+    int line;
+    int column;
+  };
+  const TestSpec specs[] = {
+      {example1.data(), example1.find("line 1"), 1, 1},
+      {example1.data(), example1.find("e 4"), 4, 4},
+      // string terminates at \0, can't use find()
+      {example2, 21, 7, 1},
+  };
+  for (const auto& spec : specs) {
+    testLocateInDocument(spec.doc, spec.offset, spec.line, spec.column);
+  }
+}
+
 int main(int argc, const char* argv[]) {
   JsonTest::Runner runner;