Go | Golang | Regex replace all byte submatches | regexp.ReplaceAllSubmatchFunc |

regex.go

// replaceAllSubmatchFunc is the missing regexp.ReplaceAllSubmatchFunc; to use it:
//
// 	pattern := regexp.MustCompile(...)
// 	data = replaceAllSubmatchFunc(pattern, data, func(groups [][]byte) [][]byte {
// 		// mutate groups here
// 		return groups
// 	})
//
// This snippet is MIT licensed. Please cite by leaving this comment in place. Find
// the latest version at:
//
//  https://gist.github.com/slimsag/14c66b88633bd52b7fa710349e4c6749
//
func replaceAllSubmatchFunc(re *regexp.Regexp, src []byte, repl func([][]byte) [][]byte, n int) []byte {
	var (
		result  = make([]byte, 0, len(src))
		matches = re.FindAllSubmatchIndex(src, n)
		last    = 0
	)
	for _, match := range matches {
		// Append bytes between our last match and this one (i.e. non-matched bytes).
		matchStart := match[0]
		matchEnd := match[1]
		result = append(result, src[last:matchStart]...)
		last = matchEnd

		// Determine the groups / submatch bytes and indices.
		groups := [][]byte{}
		groupIndices := [][2]int{}
		for i := 2; i < len(match); i += 2 {
			start := match[i]
			end := match[i+1]
			groups = append(groups, src[start:end])
			groupIndices = append(groupIndices, [2]int{start, end})
		}

		// Replace the groups as desired.
		groups = repl(groups)

		// Append match data.
		lastGroup := matchStart
		for i, newValue := range groups {
			// Append bytes between our last group match and this one (i.e. non-group-matched bytes)
			groupStart := groupIndices[i][0]
			groupEnd := groupIndices[i][1]
			result = append(result, src[lastGroup:groupStart]...)
			lastGroup = groupEnd

			// Append the new group value.
			result = append(result, newValue...)
		}
		result = append(result, src[lastGroup:matchEnd]...) // remaining
	}
	result = append(result, src[last:]...) // remaining
	return result
}