matterbridge/vendor/github.com/mattermost/mattermost-server/v5/shared/markdown/autolink.go

256 lines
6.8 KiB
Go

// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.
package markdown
import (
"regexp"
"strings"
"unicode"
"unicode/utf8"
)
// Based off of extensions/autolink.c from https://github.com/github/cmark
var (
DefaultURLSchemes = []string{"http", "https", "ftp", "mailto", "tel"}
wwwAutoLinkRegex = regexp.MustCompile(`^www\d{0,3}\.`)
)
// Given a string with a w at the given position, tries to parse and return a range containing a www link.
// if one exists. If the text at the given position isn't a link, returns an empty string. Equivalent to
// www_match from the reference code.
func parseWWWAutolink(data string, position int) (Range, bool) {
// Check that this isn't part of another word
if position > 1 {
prevChar := data[position-1]
if !isWhitespaceByte(prevChar) && !isAllowedBeforeWWWLink(prevChar) {
return Range{}, false
}
}
// Check that this starts with www
if len(data)-position < 4 || !wwwAutoLinkRegex.MatchString(data[position:]) {
return Range{}, false
}
end := checkDomain(data[position:], false)
if end == 0 {
return Range{}, false
}
end += position
// Grab all text until the end of the string or the next whitespace character
for end < len(data) && !isWhitespaceByte(data[end]) {
end += 1
}
// Trim trailing punctuation
end = trimTrailingCharactersFromLink(data, position, end)
if position == end {
return Range{}, false
}
return Range{position, end}, true
}
func isAllowedBeforeWWWLink(c byte) bool {
switch c {
case '*', '_', '~', ')':
return true
}
return false
}
// Given a string with a : at the given position, tried to parse and return a range containing a URL scheme
// if one exists. If the text around the given position isn't a link, returns an empty string. Equivalent to
// url_match from the reference code.
func parseURLAutolink(data string, position int) (Range, bool) {
// Check that a :// exists. This doesn't match the clients that treat the slashes as optional.
if len(data)-position < 4 || data[position+1] != '/' || data[position+2] != '/' {
return Range{}, false
}
start := position - 1
for start > 0 && isAlphanumericByte(data[start-1]) {
start -= 1
}
if start < 0 || position >= len(data) {
return Range{}, false
}
// Ensure that the URL scheme is allowed and that at least one character after the scheme is valid.
scheme := data[start:position]
if !isSchemeAllowed(scheme) || !isValidHostCharacter(data[position+3:]) {
return Range{}, false
}
end := checkDomain(data[position+3:], true)
if end == 0 {
return Range{}, false
}
end += position
// Grab all text until the end of the string or the next whitespace character
for end < len(data) && !isWhitespaceByte(data[end]) {
end += 1
}
// Trim trailing punctuation
end = trimTrailingCharactersFromLink(data, start, end)
if start == end {
return Range{}, false
}
return Range{start, end}, true
}
func isSchemeAllowed(scheme string) bool {
// Note that this doesn't support the custom URL schemes implemented by the client
for _, allowed := range DefaultURLSchemes {
if strings.EqualFold(allowed, scheme) {
return true
}
}
return false
}
// Given a string starting with a URL, returns the number of valid characters that make up the URL's domain.
// Returns 0 if the string doesn't start with a domain name. allowShort determines whether or not the domain
// needs to contain a period to be considered valid. Equivalent to check_domain from the reference code.
func checkDomain(data string, allowShort bool) int {
foundUnderscore := false
foundPeriod := false
i := 1
for ; i < len(data)-1; i++ {
if data[i] == '_' {
foundUnderscore = true
break
} else if data[i] == '.' {
foundPeriod = true
} else if !isValidHostCharacter(data[i:]) && data[i] != '-' {
break
}
}
if foundUnderscore {
return 0
}
if allowShort {
// If allowShort is set, accept any string of valid domain characters
return i
}
// If allowShort isn't set, a valid domain just requires at least a single period. Note that this
// logic isn't entirely necessary because we already know the string starts with "www." when
// this is called from parseWWWAutolink
if foundPeriod {
return i
}
return 0
}
// Returns true if the provided link starts with a valid character for a domain name. Equivalent to
// is_valid_hostchar from the reference code.
func isValidHostCharacter(link string) bool {
c, _ := utf8.DecodeRuneInString(link)
if c == utf8.RuneError {
return false
}
return !unicode.IsSpace(c) && !unicode.IsPunct(c)
}
// Removes any trailing characters such as punctuation or stray brackets that shouldn't be part of the link.
// Returns a new end position for the link. Equivalent to autolink_delim from the reference code.
func trimTrailingCharactersFromLink(markdown string, start int, end int) int {
runes := []rune(markdown[start:end])
linkEnd := len(runes)
// Cut off the link before an open angle bracket if it contains one
for i, c := range runes {
if c == '<' {
linkEnd = i
break
}
}
for linkEnd > 0 {
c := runes[linkEnd-1]
if !canEndAutolink(c) {
// Trim trailing quotes, periods, etc
linkEnd = linkEnd - 1
} else if c == ';' {
// Trim a trailing HTML entity
newEnd := linkEnd - 2
for newEnd > 0 && ((runes[newEnd] >= 'a' && runes[newEnd] <= 'z') || (runes[newEnd] >= 'A' && runes[newEnd] <= 'Z')) {
newEnd -= 1
}
if newEnd < linkEnd-2 && runes[newEnd] == '&' {
linkEnd = newEnd
} else {
// This isn't actually an HTML entity, so just trim the semicolon
linkEnd = linkEnd - 1
}
} else if c == ')' {
// Only allow an autolink ending with a bracket if that bracket is part of a matching pair of brackets.
// If there are more closing brackets than opening ones, remove the extra bracket
numClosing := 0
numOpening := 0
// Examples (input text => output linked portion):
//
// http://www.pokemon.com/Pikachu_(Electric)
// => http://www.pokemon.com/Pikachu_(Electric)
//
// http://www.pokemon.com/Pikachu_((Electric)
// => http://www.pokemon.com/Pikachu_((Electric)
//
// http://www.pokemon.com/Pikachu_(Electric))
// => http://www.pokemon.com/Pikachu_(Electric)
//
// http://www.pokemon.com/Pikachu_((Electric))
// => http://www.pokemon.com/Pikachu_((Electric))
for i := 0; i < linkEnd; i++ {
if runes[i] == '(' {
numOpening += 1
} else if runes[i] == ')' {
numClosing += 1
}
}
if numClosing <= numOpening {
// There's fewer or equal closing brackets, so we've found the end of the link
break
}
linkEnd -= 1
} else {
// There's no special characters at the end of the link, so we're at the end
break
}
}
return start + len(string(runes[:linkEnd]))
}
func canEndAutolink(c rune) bool {
switch c {
case '?', '!', '.', ',', ':', '*', '_', '~', '\'', '"':
return false
}
return true
}