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https://github.com/vbatts/go-mtree.git
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subtree merge: cyphar/govis
govis is a reimplementation of vis(3) and unvis(3) specifically made to be unicode aware. It was specifically rewritten to replace cvis and the other go vis reimplementation we have in go-mtree. Signed-off-by: Aleksa Sarai <asarai@suse.de>
This commit is contained in:
Aleksa Sarai
commit
91d7ec8c89
9 changed files with 1254 additions and 0 deletions
294
pkg/govis/unvis.go
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294
pkg/govis/unvis.go
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/*
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* govis: unicode aware vis(3) encoding implementation
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* Copyright (C) 2017 SUSE LLC.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package govis
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import (
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"fmt"
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"strconv"
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"unicode"
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)
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// unvisParser stores the current state of the token parser.
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type unvisParser struct {
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tokens []rune
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idx int
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flag VisFlag
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}
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// Next moves the index to the next character.
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func (p *unvisParser) Next() {
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p.idx++
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}
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// Peek gets the current token.
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func (p *unvisParser) Peek() (rune, error) {
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if p.idx >= len(p.tokens) {
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return unicode.ReplacementChar, fmt.Errorf("tried to read past end of token list")
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}
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return p.tokens[p.idx], nil
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}
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// End returns whether all of the tokens have been consumed.
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func (p *unvisParser) End() bool {
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return p.idx >= len(p.tokens)
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}
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func newParser(input string, flag VisFlag) *unvisParser {
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return &unvisParser{
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tokens: []rune(input),
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idx: 0,
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flag: flag,
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}
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}
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// While a recursive descent parser is overkill for parsing simple escape
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// codes, this is IMO much easier to read than the ugly 80s coroutine code used
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// by the original unvis(3) parser. Here's the EBNF for an unvis sequence:
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//
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// <input> ::= (<rune>)*
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// <rune> ::= ("\" <escape-sequence>) | ("%" <escape-hex>) | <plain-rune>
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// <plain-rune> ::= any rune
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// <escape-sequence> ::= ("x" <escape-hex>) | ("M" <escape-meta>) | ("^" <escape-ctrl) | <escape-cstyle> | <escape-octal>
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// <escape-meta> ::= ("-" <escape-meta1>) | ("^" <escape-ctrl>)
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// <escape-meta1> ::= any rune
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// <escape-ctrl> ::= "?" | any rune
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// <escape-cstyle> ::= "\" | "n" | "r" | "b" | "a" | "v" | "t" | "f"
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// <escape-hex> ::= [0-9a-f] [0-9a-f]
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// <escape-octal> ::= [0-7] ([0-7] ([0-7])?)?
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func unvisPlainRune(p *unvisParser) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("plain rune: %c", ch)
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}
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p.Next()
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// XXX: Maybe we should not be converting to runes and then back to strings
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// here. Are we sure that the byte-for-byte representation is the
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// same? If the bytes change, then using these strings for paths will
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// break...
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str := string(ch)
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return []byte(str), nil
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}
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func unvisEscapeCStyle(p *unvisParser) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("escape hex: %s", err)
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}
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output := ""
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switch ch {
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case 'n':
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output = "\n"
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case 'r':
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output = "\r"
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case 'b':
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output = "\b"
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case 'a':
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output = "\x07"
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case 'v':
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output = "\v"
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case 't':
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output = "\t"
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case 'f':
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output = "\f"
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case 's':
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output = " "
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case 'E':
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output = "\x1b"
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case '\n':
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// Hidden newline.
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case '$':
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// Hidden marker.
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default:
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// XXX: We should probably allow falling through and return "\" here...
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return nil, fmt.Errorf("escape cstyle: unknown escape character: %q", ch)
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}
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p.Next()
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return []byte(output), nil
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}
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func unvisEscapeDigits(p *unvisParser, base int, force bool) ([]byte, error) {
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var code int
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for i := int(0xFF); i > 0; i /= base {
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ch, err := p.Peek()
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if err != nil {
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if !force && i != 0xFF {
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break
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}
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return nil, fmt.Errorf("escape base %d: %s", base, err)
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}
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digit, err := strconv.ParseInt(string(ch), base, 8)
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if err != nil {
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if !force && i != 0xFF {
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break
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}
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return nil, fmt.Errorf("escape base %d: could not parse digit: %s", base, err)
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}
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code = (code * base) + int(digit)
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p.Next()
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}
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if code > unicode.MaxLatin1 {
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return nil, fmt.Errorf("escape base %d: code %q outside latin-1 encoding", base, code)
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}
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char := byte(code & 0xFF)
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return []byte{char}, nil
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}
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func unvisEscapeCtrl(p *unvisParser, mask byte) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("escape ctrl: %s", err)
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}
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if ch > unicode.MaxLatin1 {
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return nil, fmt.Errorf("escape ctrl: code %q outside latin-1 encoding", ch)
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}
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char := byte(ch) & 0x1f
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if ch == '?' {
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char = 0x7f
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}
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p.Next()
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return []byte{mask | char}, nil
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}
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func unvisEscapeMeta(p *unvisParser) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("escape meta: %s", err)
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}
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mask := byte(0x80)
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switch ch {
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case '^':
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// The same as "\^..." except we apply a mask.
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p.Next()
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return unvisEscapeCtrl(p, mask)
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case '-':
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p.Next()
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("escape meta1: %s", err)
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}
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if ch > unicode.MaxLatin1 {
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return nil, fmt.Errorf("escape meta1: code %q outside latin-1 encoding", ch)
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}
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// Add mask to character.
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p.Next()
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return []byte{mask | byte(ch)}, nil
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}
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return nil, fmt.Errorf("escape meta: unknown escape char: %s", err)
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}
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func unvisEscapeSequence(p *unvisParser) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("escape sequence: %s", err)
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}
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switch ch {
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case '\\':
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p.Next()
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return []byte("\\"), nil
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case '0', '1', '2', '3', '4', '5', '6', '7':
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return unvisEscapeDigits(p, 8, false)
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case 'x':
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p.Next()
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return unvisEscapeDigits(p, 16, true)
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case '^':
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p.Next()
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return unvisEscapeCtrl(p, 0x00)
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case 'M':
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p.Next()
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return unvisEscapeMeta(p)
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default:
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return unvisEscapeCStyle(p)
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}
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}
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func unvisRune(p *unvisParser) ([]byte, error) {
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ch, err := p.Peek()
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if err != nil {
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return nil, fmt.Errorf("rune: %s", err)
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}
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switch ch {
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case '\\':
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p.Next()
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return unvisEscapeSequence(p)
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case '%':
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// % HEX HEX only applies to HTTPStyle encodings.
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if p.flag&VisHTTPStyle == VisHTTPStyle {
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p.Next()
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return unvisEscapeDigits(p, 16, true)
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}
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fallthrough
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default:
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return unvisPlainRune(p)
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}
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}
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func unvis(p *unvisParser) (string, error) {
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var output []byte
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for !p.End() {
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ch, err := unvisRune(p)
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if err != nil {
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return "", fmt.Errorf("input: %s", err)
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}
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output = append(output, ch...)
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}
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return string(output), nil
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}
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// Unvis takes a string formatted with the given Vis flags (though only the
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// VisHTTPStyle flag is checked) and output the un-encoded version of the
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// encoded string. An error is returned if any escape sequences in the input
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// string were invalid.
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func Unvis(input string, flag VisFlag) (string, error) {
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// TODO: Check all of the VisFlag bits.
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p := newParser(input, flag)
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output, err := unvis(p)
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if err != nil {
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return "", fmt.Errorf("unvis: %s", err)
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}
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if !p.End() {
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return "", fmt.Errorf("unvis: trailing characters at end of input")
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}
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return output, nil
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}
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