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/*
* 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"
"unicode"
)
func isunsafe(ch rune) bool {
return ch == '\b' || ch == '\007' || ch == '\r'
}
func isglob(ch rune) bool {
return ch == '*' || ch == '?' || ch == '[' || ch == '#'
}
// ishttp is defined by RFC 1808.
func ishttp(ch rune) bool {
// RFC1808 does not really consider characters outside of ASCII, so just to
// be safe always treat characters outside the ASCII character set as "not
// HTTP".
if ch > unicode.MaxASCII {
return false
}
return unicode.IsDigit(ch) || unicode.IsLetter(ch) ||
// Safe characters.
ch == '$' || ch == '-' || ch == '_' || ch == '.' || ch == '+' ||
// Extra characters.
ch == '!' || ch == '*' || ch == '\'' || ch == '(' ||
ch == ')' || ch == ','
}
func isgraph(ch rune) bool {
return unicode.IsGraphic(ch) && !unicode.IsSpace(ch) && ch <= unicode.MaxASCII
}
// vis converts a single *byte* into its encoding. While Go supports the
// concept of runes (and thus native utf-8 parsing), in order to make sure that
// the bit-stream will be completely maintained through an Unvis(Vis(...))
// round-trip. The downside is that Vis() will never output unicode -- but on
// the plus side this is actually a benefit on the encoding side (it will
// always work with the simple unvis(3) implementation). It also means that we
// don't have to worry about different multi-byte encodings.
func vis(b byte, flag VisFlag) (string, error) {
// Treat the single-byte character as a rune.
ch := rune(b)
// XXX: This is quite a horrible thing to support.
if flag&VisHTTPStyle == VisHTTPStyle {
if !ishttp(ch) {
return "%" + fmt.Sprintf("%.2X", ch), nil
}
}
// Figure out if the character doesn't need to be encoded. Effectively, we
// encode most "normal" (graphical) characters as themselves unless we have
// been specifically asked not to. Note though that we *ALWAYS* encode
// everything outside ASCII.
// TODO: Switch this to much more logical code.
if ch > unicode.MaxASCII {
/* ... */
} else if flag&VisGlob == VisGlob && isglob(ch) {
/* ... */
} else if isgraph(ch) ||
(flag&VisSpace != VisSpace && ch == ' ') ||
(flag&VisTab != VisTab && ch == '\t') ||
(flag&VisNewline != VisNewline && ch == '\n') ||
(flag&VisSafe != 0 && isunsafe(ch)) {
encoded := string(ch)
if ch == '\\' && flag&VisNoSlash == 0 {
encoded += "\\"
}
return encoded, nil
}
// Try to use C-style escapes first.
if flag&VisCStyle == VisCStyle {
switch ch {
case ' ':
return "\\s", nil
case '\n':
return "\\n", nil
case '\r':
return "\\r", nil
case '\b':
return "\\b", nil
case '\a':
return "\\a", nil
case '\v':
return "\\v", nil
case '\t':
return "\\t", nil
case '\f':
return "\\f", nil
case '\x00':
// Output octal just to be safe.
return "\\000", nil
}
}
// For graphical characters we generate octal output (and also if it's
// being forced by the caller's flags). Also spaces should always be
// encoded as octal.
if flag&VisOctal == VisOctal || isgraph(ch) || ch&0x7f == ' ' {
// Always output three-character octal just to be safe.
return fmt.Sprintf("\\%.3o", ch), nil
}
// Now we have to output meta or ctrl escapes. As far as I can tell, this
// is not actually defined by any standard -- so this logic is basically
// copied from the original vis(3) implementation. Hopefully nobody
// actually relies on this (octal and hex are better).
encoded := ""
if flag&VisNoSlash == 0 {
encoded += "\\"
}
// Meta characters have 0x80 set, but are otherwise identical to control
// characters.
if b&0x80 != 0 {
b &= 0x7f
encoded += "M"
}
if unicode.IsControl(rune(b)) {
encoded += "^"
if b == 0x7f {
encoded += "?"
} else {
encoded += fmt.Sprintf("%c", b+'@')
}
} else {
encoded += fmt.Sprintf("-%c", b)
}
return encoded, nil
}
// Vis encodes the provided string to a BSD-compatible encoding using BSD's
// vis() flags. However, it will correctly handle multi-byte encoding (which is
// not done properly by BSD's vis implementation).
func Vis(src string, flag VisFlag) (string, error) {
if flag&visMask != flag {
return "", fmt.Errorf("vis: flag %q contains unknown or unsupported flags", flag)
}
output := ""
for _, ch := range []byte(src) {
encodedCh, err := vis(ch, flag)
if err != nil {
return "", err
}
output += encodedCh
}
return output, nil
}
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