Index out of range panic in DiffCharsToLines on large JSON diff

diffmatchpatch/diff.go

@@ -392,13 +392,13 @@ func (dmp *DiffMatchPatch) diffBisectSplit(runes1, runes2 []rune, x, y int,
 // DiffLinesToChars splits two texts into a list of strings, and educes the texts to a string of hashes where each Unicode character represents one line.
 // It's slightly faster to call DiffLinesToRunes first, followed by DiffMainRunes.
 func (dmp *DiffMatchPatch) DiffLinesToChars(text1, text2 string) (string, string, []string) {
- chars1, chars2, lineArray := dmp.DiffLinesToRunes(text1, text2)
- return string(chars1), string(chars2), lineArray
+ chars1, chars2, lineArray := dmp.diffLinesToStrings(text1, text2)
+ return chars1, chars2, lineArray
 }
 
-// DiffLinesToRunes splits two texts into a list of runes. Each rune represents one line.
+// DiffLinesToRunes splits two texts into a list of runes.
 func (dmp *DiffMatchPatch) DiffLinesToRunes(text1, text2 string) ([]rune, []rune, []string) {
- chars1, chars2, lineArray := dmp.DiffLinesToStrings(text1, text2)
+ chars1, chars2, lineArray := dmp.diffLinesToStrings(text1, text2)
  return []rune(chars1), []rune(chars2), lineArray
 }
 
@@ -1308,8 +1308,8 @@ func (dmp *DiffMatchPatch) DiffFromDelta(text1 string, delta string) (diffs []Di
  return diffs, nil
 }
 
-// DiffLinesToStrings splits two texts into a list of strings. Each string represents one line.
-func (dmp *DiffMatchPatch) DiffLinesToStrings(text1, text2 string) (string, string, []string) {
+// diffLinesToStrings splits two texts into a list of strings. Each string represents one line.
+func (dmp *DiffMatchPatch) diffLinesToStrings(text1, text2 string) (string, string, []string) {
  // '\x00' is a valid character, but various debuggers don't like it. So we'll insert a junk entry to avoid generating a null character.
  lineArray := []string{""} // e.g. lineArray[4] == 'Hello\n'
 
@@ -1324,14 +1324,13 @@ func (dmp *DiffMatchPatch) DiffLinesToStrings(text1, text2 string) (string, stri
  return str1, str2, lineArray
 }
 
-// diffLinesToStringsMunge splits a text into an array of strings, and reduces the texts to a []rune where each Unicode character represents one line.
-// We use strings instead of []runes as input mainly because you can't use []rune as a map key.
+// diffLinesToStringsMunge splits a text into an array of strings, and reduces the texts to a []string.
 func (dmp *DiffMatchPatch) diffLinesToStringsMunge(text string, lineArray *[]string) []string {
  // Walk the text, pulling out a substring for each line. text.split('\n') would would temporarily double our memory footprint. Modifying text would create many large strings to garbage collect.
  lineHash := map[string]int{} // e.g. lineHash['Hello\n'] == 4
  lineStart := 0
  lineEnd := -1
- strings := []string{}
+ strs := []string{}
 
  for lineEnd < len(text)-1 {
  lineEnd = indexOf(text, "\n", lineStart)
@@ -1345,13 +1344,13 @@ func (dmp *DiffMatchPatch) diffLinesToStringsMunge(text string, lineArray *[]str
  lineValue, ok := lineHash[line]
 
  if ok {
- strings = append(strings, strconv.Itoa(lineValue))
+ strs = append(strs, strconv.Itoa(lineValue))
  } else {
  *lineArray = append(*lineArray, line)
  lineHash[line] = len(*lineArray) - 1
- strings = append(strings, strconv.Itoa(len(*lineArray)-1))
+ strs = append(strs, strconv.Itoa(len(*lineArray)-1))
  }
  }
 
- return strings
+ return strs
 }

diffmatchpatch/diff_test.go

@@ -1500,21 +1500,6 @@ func BenchmarkDiffMainRunesLargeLines(b *testing.B) {
  }
 }
 
-func BenchmarkDiffMainStringsLargeLines(b *testing.B) {
- s1, s2 := speedtestTexts()
-
- dmp := New()
-
- b.ResetTimer()
-
- for i := 0; i < b.N; i++ {
- text1, text2, linearray := dmp.DiffLinesToStrings(s1, s2)
-
- diffs := dmp.DiffMain(text1, text2, false)
- diffs = dmp.DiffCharsToLines(diffs, linearray)
- }
-}
-
 func BenchmarkDiffMainRunesLargeDiffLines(b *testing.B) {
  fp, _ := os.Open("../testdata/diff10klinestest.txt")
  defer fp.Close()