unvis: implement partial unvis(3) implementation
Also add some unit tests -- one of which currently fails due to ongoing design discussion about how certain escape codes should be handled. Signed-off-by: Aleksa Sarai <asarai@suse.de>
This commit is contained in:
Aleksa Sarai
parent
1e8de82690
commit
cd1de45ba5
3 changed files with 385 additions and 0 deletions
255
unvis.go
Normal file
255
unvis.go
Normal file
|
|
@ -0,0 +1,255 @@
|
|||
/*
|
||||
* govis: unicode aware vis(3) encoding implementation
|
||||
* Copyright (C) 2017 SUSE LLC.
|
||||
*
|
||||
* 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 govis
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
"strconv"
|
||||
"unicode/utf8"
|
||||
)
|
||||
|
||||
// unvisParser stores the current state of the token parser.
|
||||
type unvisParser struct {
|
||||
tokens []rune
|
||||
idx int
|
||||
flag VisFlag
|
||||
}
|
||||
|
||||
// Next moves the index to the next character.
|
||||
func (p *unvisParser) Next() {
|
||||
p.idx++
|
||||
}
|
||||
|
||||
// Peek gets the current token.
|
||||
func (p *unvisParser) Peek() (rune, error) {
|
||||
if p.idx >= len(p.tokens) {
|
||||
return utf8.RuneError, fmt.Errorf("tried to read past end of token list")
|
||||
}
|
||||
return p.tokens[p.idx], nil
|
||||
}
|
||||
|
||||
// End returns whether all of the tokens have been consumed.
|
||||
func (p *unvisParser) End() bool {
|
||||
return p.idx >= len(p.tokens)
|
||||
}
|
||||
|
||||
func newParser(input string, flag VisFlag) *unvisParser {
|
||||
return &unvisParser{
|
||||
tokens: []rune(input),
|
||||
idx: 0,
|
||||
flag: flag,
|
||||
}
|
||||
}
|
||||
|
||||
// While a recursive descent parser is overkill for parsing simple escape
|
||||
// codes, this is IMO much easier to read than the ugly 80s coroutine code used
|
||||
// by the original unvis(3) parser. Here's the EBNF for an unvis sequence:
|
||||
//
|
||||
// <input> ::= (<rune>)*
|
||||
// <rune> ::= ("\" <escape-sequence>) | ("%" <escape-hex>) | <plain-rune>
|
||||
// <plain-rune> ::= any rune
|
||||
// <escape-sequence> ::= ("x" <escape-hex>) | ("M") | <escape-cstyle> | <escape-octal>
|
||||
// <escape-hex> ::= [0-9a-f] [0-9a-f]
|
||||
// <escape-cstyle> ::= "\" | "n" | "r" | "b" | "a" | "v" | "t" | "f"
|
||||
// <escape-octal> ::= [0-7] ([0-7] ([0-7])?)?
|
||||
|
||||
func unvisPlainRune(p *unvisParser) (string, error) {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("plain rune: %s", ch)
|
||||
}
|
||||
p.Next()
|
||||
return string(ch), nil
|
||||
}
|
||||
|
||||
func unvisEscapeCStyle(p *unvisParser) (string, error) {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("escape hex: %s", err)
|
||||
}
|
||||
|
||||
output := ""
|
||||
switch ch {
|
||||
case 'n':
|
||||
output = "\n"
|
||||
case 'r':
|
||||
output = "\r"
|
||||
case 'b':
|
||||
output = "\b"
|
||||
case 'a':
|
||||
output = "\x07"
|
||||
case 'v':
|
||||
output = "\v"
|
||||
case 't':
|
||||
output = "\t"
|
||||
case 'f':
|
||||
output = "\f"
|
||||
case 's':
|
||||
output = " "
|
||||
case 'E':
|
||||
output = "\x1b"
|
||||
case '\n':
|
||||
// Hidden newline.
|
||||
case '$':
|
||||
// Hidden marker.
|
||||
default:
|
||||
// XXX: We should probably allow falling through and return "\" here...
|
||||
return "", fmt.Errorf("escape cstyle: unknown escape character: %q", ch)
|
||||
}
|
||||
|
||||
p.Next()
|
||||
return output, nil
|
||||
}
|
||||
|
||||
func unvisEscapeHex(p *unvisParser) (string, error) {
|
||||
var output rune
|
||||
|
||||
for i := 0; i < 2; i++ {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("escape hex: %s", err)
|
||||
}
|
||||
|
||||
digit, err := strconv.ParseInt(string(ch), 16, 32)
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("escape hex: parse int: %s", err)
|
||||
}
|
||||
|
||||
output = (output << 4) | rune(digit)
|
||||
p.Next()
|
||||
}
|
||||
|
||||
// TODO: We need to handle runes properly to output byte strings again. In
|
||||
// particular, if rune has 0xf0 set then we know that we're currently
|
||||
// decoding a messed up string.
|
||||
return string(output), nil
|
||||
}
|
||||
|
||||
func unvisEscapeOctal(p *unvisParser) (string, error) {
|
||||
var output rune
|
||||
var err error
|
||||
|
||||
for i := 0; i < 3; i++ {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
if i == 0 {
|
||||
err = fmt.Errorf("escape octal[first]: %s", err)
|
||||
}
|
||||
break
|
||||
}
|
||||
|
||||
digit, err := strconv.ParseInt(string(ch), 8, 32)
|
||||
if err != nil {
|
||||
if i == 0 {
|
||||
err = fmt.Errorf("escape octal[first]: parse int: %s", err)
|
||||
}
|
||||
break
|
||||
}
|
||||
|
||||
output = (output << 3) | rune(digit)
|
||||
p.Next()
|
||||
}
|
||||
|
||||
// TODO: We need to handle runes properly to output byte strings again. In
|
||||
// particular, if rune has 0xf0 set then we know that we're currently
|
||||
// decoding a messed up string.
|
||||
return string(output), err
|
||||
}
|
||||
|
||||
func unvisEscapeSequence(p *unvisParser) (string, error) {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("escape sequence: %s", err)
|
||||
}
|
||||
|
||||
switch ch {
|
||||
case '\\':
|
||||
p.Next()
|
||||
return "\\", nil
|
||||
|
||||
case '0', '1', '2', '3', '4', '5', '6', '7':
|
||||
return unvisEscapeOctal(p)
|
||||
|
||||
case 'x':
|
||||
p.Next()
|
||||
return unvisEscapeHex(p)
|
||||
|
||||
case 'M':
|
||||
// TODO
|
||||
case '^':
|
||||
// TODO
|
||||
|
||||
default:
|
||||
return unvisEscapeCStyle(p)
|
||||
}
|
||||
|
||||
return "", fmt.Errorf("escape sequence: unsupported sequence: %q", ch)
|
||||
}
|
||||
|
||||
func unvisRune(p *unvisParser) (string, error) {
|
||||
ch, err := p.Peek()
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("rune: %s", err)
|
||||
}
|
||||
|
||||
switch ch {
|
||||
case '\\':
|
||||
p.Next()
|
||||
return unvisEscapeSequence(p)
|
||||
|
||||
case '%':
|
||||
// % HEX HEX only applies to HTTPStyle encodings.
|
||||
if p.flag&VisHTTPStyle == VisHTTPStyle {
|
||||
p.Next()
|
||||
return unvisEscapeHex(p)
|
||||
}
|
||||
fallthrough
|
||||
|
||||
default:
|
||||
return unvisPlainRune(p)
|
||||
}
|
||||
}
|
||||
|
||||
func unvis(p *unvisParser) (string, error) {
|
||||
output := ""
|
||||
for !p.End() {
|
||||
ch, err := unvisRune(p)
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("input: %s", err)
|
||||
}
|
||||
output += ch
|
||||
}
|
||||
return output, nil
|
||||
}
|
||||
|
||||
// Unvis takes a string formatted with the given Vis flags (though only the
|
||||
// VisHTTPStyle flag is checked) and output the un-encoded version of the
|
||||
// encoded string. An error is returned if any escape sequences in the input
|
||||
// string were invalid.
|
||||
func Unvis(input string, flag VisFlag) (string, error) {
|
||||
// TODO: Check all of the VisFlag bits.
|
||||
p := newParser(input, flag)
|
||||
output, err := unvis(p)
|
||||
if err != nil {
|
||||
return "", fmt.Errorf("unvis: %s", err)
|
||||
}
|
||||
if !p.End() {
|
||||
return "", fmt.Errorf("unvis: trailing characters at end of input")
|
||||
}
|
||||
return output, nil
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue