*: Fix issue 393

See: https://github.com/pingcap/tidb/issues/393

util/stringutil/string_util.go

@@ -0,0 +1,57 @@
+// Copyright 2014 The ql Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSES/QL-LICENSE file.
+
+// Copyright 2015 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package stringutil
+
+import (
+	"bytes"
+	"strings"
+)
+
+// See: https://dev.mysql.com/doc/refman/5.7/en/string-literals.html#character-escape-sequences
+const validEscapeChars = `0'"bntrz\\%_`
+
+// RemoveUselessBackslash removes backslashs which could be ignored in the string literal.
+// See: https://dev.mysql.com/doc/refman/5.7/en/string-literals.html
+// " Each of these sequences begins with a backslash (“\”), known as the escape character.
+// MySQL recognizes the escape sequences shown in Table 9.1, “Special Character Escape Sequences”.
+// For all other escape sequences, backslash is ignored. That is, the escaped character is
+// interpreted as if it was not escaped. For example, “\x” is just “x”. These sequences are case sensitive.
+// For example, “\b” is interpreted as a backspace, but “\B” is interpreted as “B”."
+func RemoveUselessBackslash(s string) string {
+	var (
+		buf bytes.Buffer
+		i   = 0
+	)
+	for i < len(s)-1 {
+		if s[i] != '\\' {
+			buf.WriteByte(s[i])
+			i++
+			continue
+		}
+		next := s[i+1]
+		if strings.IndexByte(validEscapeChars, next) != -1 {
+			buf.WriteByte(s[i])
+		}
+		buf.WriteByte(next)
+		i += 2
+	}
+	if i == len(s)-1 {
+		buf.WriteByte(s[i])
+	}
+	return buf.String()
+}