prometheus/util/strutil/quote.go

224 lines
5.1 KiB
Go

// Copyright 2015 The Prometheus Authors
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package strutil
import (
"errors"
"unicode/utf8"
)
// ErrSyntax indicates that a value does not have the right syntax for the target type.
var ErrSyntax = errors.New("invalid syntax")
// Unquote interprets s as a single-quoted, double-quoted, or backquoted
// Prometheus query language string literal, returning the string value that s
// quotes.
//
// NOTE: This function as well as the necessary helper functions below
// (unquoteChar, contains, unhex) and associated tests have been adapted from
// the corresponding functions in the "strconv" package of the Go standard
// library to work for Prometheus-style strings. Go's special-casing for single
// quotes was removed and single quoted strings are now treated the same as
// double quoted ones.
func Unquote(s string) (t string, err error) {
n := len(s)
if n < 2 {
return "", ErrSyntax
}
quote := s[0]
if quote != s[n-1] {
return "", ErrSyntax
}
s = s[1 : n-1]
if quote == '`' {
if contains(s, '`') {
return "", ErrSyntax
}
return s, nil
}
if quote != '"' && quote != '\'' {
return "", ErrSyntax
}
if contains(s, '\n') {
return "", ErrSyntax
}
// Is it trivial? Avoid allocation.
if !contains(s, '\\') && !contains(s, quote) {
return s, nil
}
var runeTmp [utf8.UTFMax]byte
buf := make([]byte, 0, 3*len(s)/2) // Try to avoid more allocations.
for len(s) > 0 {
c, multibyte, ss, err := unquoteChar(s, quote)
if err != nil {
return "", err
}
s = ss
if c < utf8.RuneSelf || !multibyte {
buf = append(buf, byte(c))
} else {
n := utf8.EncodeRune(runeTmp[:], c)
buf = append(buf, runeTmp[:n]...)
}
}
return string(buf), nil
}
// unquoteChar decodes the first character or byte in the escaped string
// or character literal represented by the string s.
// It returns four values:
//
// 1) value, the decoded Unicode code point or byte value;
// 2) multibyte, a boolean indicating whether the decoded character requires a multibyte UTF-8 representation;
// 3) tail, the remainder of the string after the character; and
// 4) an error that will be nil if the character is syntactically valid.
//
// The second argument, quote, specifies the type of literal being parsed
// and therefore which escaped quote character is permitted.
// If set to a single quote, it permits the sequence \' and disallows unescaped '.
// If set to a double quote, it permits \" and disallows unescaped ".
// If set to zero, it does not permit either escape and allows both quote characters to appear unescaped.
func unquoteChar(s string, quote byte) (value rune, multibyte bool, tail string, err error) {
// easy cases
switch c := s[0]; {
case c == quote && (quote == '\'' || quote == '"'):
err = ErrSyntax
return
case c >= utf8.RuneSelf:
r, size := utf8.DecodeRuneInString(s)
return r, true, s[size:], nil
case c != '\\':
return rune(s[0]), false, s[1:], nil
}
// Hard case: c is backslash.
if len(s) <= 1 {
err = ErrSyntax
return
}
c := s[1]
s = s[2:]
switch c {
case 'a':
value = '\a'
case 'b':
value = '\b'
case 'f':
value = '\f'
case 'n':
value = '\n'
case 'r':
value = '\r'
case 't':
value = '\t'
case 'v':
value = '\v'
case 'x', 'u', 'U':
n := 0
switch c {
case 'x':
n = 2
case 'u':
n = 4
case 'U':
n = 8
}
var v rune
if len(s) < n {
err = ErrSyntax
return
}
for j := 0; j < n; j++ {
x, ok := unhex(s[j])
if !ok {
err = ErrSyntax
return
}
v = v<<4 | x
}
s = s[n:]
if c == 'x' {
// Single-byte string, possibly not UTF-8.
value = v
break
}
if v > utf8.MaxRune {
err = ErrSyntax
return
}
value = v
multibyte = true
case '0', '1', '2', '3', '4', '5', '6', '7':
v := rune(c) - '0'
if len(s) < 2 {
err = ErrSyntax
return
}
for j := 0; j < 2; j++ { // One digit already; two more.
x := rune(s[j]) - '0'
if x < 0 || x > 7 {
err = ErrSyntax
return
}
v = (v << 3) | x
}
s = s[2:]
if v > 255 {
err = ErrSyntax
return
}
value = v
case '\\':
value = '\\'
case '\'', '"':
if c != quote {
err = ErrSyntax
return
}
value = rune(c)
default:
err = ErrSyntax
return
}
tail = s
return
}
// contains reports whether the string contains the byte c.
func contains(s string, c byte) bool {
for i := 0; i < len(s); i++ {
if s[i] == c {
return true
}
}
return false
}
func unhex(b byte) (v rune, ok bool) {
c := rune(b)
switch {
case '0' <= c && c <= '9':
return c - '0', true
case 'a' <= c && c <= 'f':
return c - 'a' + 10, true
case 'A' <= c && c <= 'F':
return c - 'A' + 10, true
}
return
}