snapshot of https://github.com/mattermost/mattermost.git (master, 2026-09-16; blobs > 131072B omitted)

server/public/shared/markdown/autolink.go

@@ -0,0 +1,265 @@
+// 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 angle bracket if it contains one
+	for i, c := range runes {
+		if c == '<' || c == '>' {
+			linkEnd = i
+			break
+		}
+	}
+
+	numClosing := 0
+	numOpening := 0
+	for i := range linkEnd {
+		if runes[i] == '(' {
+			numOpening += 1
+		} else if runes[i] == ')' {
+			numClosing += 1
+		}
+	}
+
+	trimLinkEnd := func(newEnd int) {
+		for i := newEnd; i < linkEnd; i++ {
+			if runes[i] == '(' {
+				numOpening -= 1
+			} else if runes[i] == ')' {
+				numClosing -= 1
+			}
+		}
+		linkEnd = newEnd
+	}
+
+	for linkEnd > 0 {
+		c := runes[linkEnd-1]
+
+		if !canEndAutolink(c) {
+			// Trim trailing quotes, periods, etc
+			trimLinkEnd(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] == '&' {
+				trimLinkEnd(newEnd)
+			} else {
+				// This isn't actually an HTML entity, so just trim the semicolon
+				trimLinkEnd(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
+
+			// 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))
+
+			if numClosing <= numOpening {
+				// There's fewer or equal closing brackets, so we've found the end of the link
+				break
+			}
+
+			trimLinkEnd(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
+}