Add Unquote() strutil function.

util/strutil/quote.go

@@ -0,0 +1,221 @@
+// 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.
+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
+}

util/strutil/quote_test.go

@@ -0,0 +1,125 @@
+// 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 (
+	"testing"
+)
+
+type quoteTest struct {
+	in    string
+	out   string
+	ascii string
+}
+
+var quotetests = []quoteTest{
+	{"\a\b\f\r\n\t\v", `"\a\b\f\r\n\t\v"`, `"\a\b\f\r\n\t\v"`},
+	{"\\", `"\\"`, `"\\"`},
+	{"abc\xffdef", `"abc\xffdef"`, `"abc\xffdef"`},
+	{"\u263a", `"☺"`, `"\u263a"`},
+	{"\U0010ffff", `"\U0010ffff"`, `"\U0010ffff"`},
+	{"\x04", `"\x04"`, `"\x04"`},
+}
+
+type unQuoteTest struct {
+	in  string
+	out string
+}
+
+var unquotetests = []unQuoteTest{
+	{`""`, ""},
+	{`"a"`, "a"},
+	{`"abc"`, "abc"},
+	{`"☺"`, "☺"},
+	{`"hello world"`, "hello world"},
+	{`"\xFF"`, "\xFF"},
+	{`"\377"`, "\377"},
+	{`"\u1234"`, "\u1234"},
+	{`"\U00010111"`, "\U00010111"},
+	{`"\U0001011111"`, "\U0001011111"},
+	{`"\a\b\f\n\r\t\v\\\""`, "\a\b\f\n\r\t\v\\\""},
+	{`"'"`, "'"},
+
+	{`''`, ""},
+	{`'a'`, "a"},
+	{`'abc'`, "abc"},
+	{`'☺'`, "☺"},
+	{`'hello world'`, "hello world"},
+	{`'\xFF'`, "\xFF"},
+	{`'\377'`, "\377"},
+	{`'\u1234'`, "\u1234"},
+	{`'\U00010111'`, "\U00010111"},
+	{`'\U0001011111'`, "\U0001011111"},
+	{`'\a\b\f\n\r\t\v\\\''`, "\a\b\f\n\r\t\v\\'"},
+	{`'"'`, "\""},
+
+	{"``", ``},
+	{"`a`", `a`},
+	{"`abc`", `abc`},
+	{"`☺`", `☺`},
+	{"`hello world`", `hello world`},
+	{"`\\xFF`", `\xFF`},
+	{"`\\377`", `\377`},
+	{"`\\`", `\`},
+	{"`\n`", "\n"},
+	{"`	`", `	`},
+}
+
+var misquoted = []string{
+	``,
+	`"`,
+	`"a`,
+	`"'`,
+	`b"`,
+	`"\"`,
+	`"\9"`,
+	`"\19"`,
+	`"\129"`,
+	`'\'`,
+	`'\9'`,
+	`'\19'`,
+	`'\129'`,
+	`"\x1!"`,
+	`"\U12345678"`,
+	`"\z"`,
+	"`",
+	"`xxx",
+	"`\"",
+	`"\'"`,
+	`'\"'`,
+	"\"\n\"",
+	"\"\\n\n\"",
+	"'\n'",
+}
+
+func TestUnquote(t *testing.T) {
+	for _, tt := range unquotetests {
+		if out, err := Unquote(tt.in); err != nil && out != tt.out {
+			t.Errorf("Unquote(%#q) = %q, %v want %q, nil", tt.in, out, err, tt.out)
+		}
+	}
+
+	// run the quote tests too, backward
+	for _, tt := range quotetests {
+		if in, err := Unquote(tt.out); in != tt.in {
+			t.Errorf("Unquote(%#q) = %q, %v, want %q, nil", tt.out, in, err, tt.in)
+		}
+	}
+
+	for _, s := range misquoted {
+		if out, err := Unquote(s); out != "" || err != ErrSyntax {
+			t.Errorf("Unquote(%#q) = %q, %v want %q, %v", s, out, err, "", ErrSyntax)
+		}
+	}
+}