GoToSocial/internal/text/sanitize.go

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// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package text
import (
"html"
"regexp"
"strings"
"github.com/microcosm-cc/bluemonday"
)
// Regular HTML policy is an adapted version of the default
// bluemonday UGC policy, with some tweaks of our own.
// See: https://github.com/microcosm-cc/bluemonday#usage
var regular *bluemonday.Policy = func() *bluemonday.Policy {
p := bluemonday.NewPolicy()
// AllowStandardAttributes will enable "id", "title" and
// the language specific attributes "dir" and "lang" on
// all elements that are allowed
p.AllowStandardAttributes()
/*
LAYOUT AND FORMATTING
*/
// "aside" is permitted and takes no attributes.
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/aside
p.AllowElements("article", "aside")
// "details" is permitted, including the "open" attribute
// which can either be blank or the value "open".
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/details
p.AllowAttrs("open").Matching(regexp.MustCompile(`(?i)^(|open)$`)).OnElements("details")
// "section" is permitted and takes no attributes.
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/section
p.AllowElements("section")
// "summary" is permitted and takes no attributes.
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/summary
p.AllowElements("summary")
// "h1" through "h6" are permitted and take no attributes.
p.AllowElements("h1", "h2", "h3", "h4", "h5", "h6")
// "hgroup" is permitted and takes no attributes.
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/hgroup
p.AllowElements("hgroup")
// "blockquote" is permitted, including the "cite"
// attribute which must be a standard URL.
p.AllowAttrs("cite").OnElements("blockquote")
// "br" "div" "hr" "p" "span" "wbr" are permitted and take no attributes
p.AllowElements("br", "div", "hr", "p", "span", "wbr")
// The following are all inline phrasing elements:
p.AllowElements("abbr", "acronym", "cite", "code", "dfn", "em",
"figcaption", "mark", "s", "samp", "strong", "sub", "sup", "var")
// "q" is permitted and "cite" is a URL and handled by URL policies
p.AllowAttrs("cite").OnElements("q")
// "time" is permitted
p.AllowAttrs("datetime").Matching(bluemonday.ISO8601).OnElements("time")
// Block and inline elements that impart no
// semantic meaning but style the document.
// Underlines, italics, bold, strikethrough etc.
p.AllowElements("b", "i", "pre", "small", "strike", "tt", "u")
// "del" "ins" are permitted
p.AllowAttrs("cite").Matching(bluemonday.Paragraph).OnElements("del", "ins")
p.AllowAttrs("datetime").Matching(bluemonday.ISO8601).OnElements("del", "ins")
// Enable ordered, unordered, and definition lists.
p.AllowLists()
// Class needed on span for mentions, which look like this when assembled:
// `<span class="h-card"><a href="https://example.org/users/targetAccount" class="u-url mention">@<span>someusername</span></a></span>`
p.AllowAttrs("class").OnElements("span")
/*
LANGUAGE FORMATTING
*/
// "bdi" "bdo" are permitted on "dir".
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/dir
p.AllowAttrs("dir").Matching(bluemonday.Direction).OnElements("bdi", "bdo")
// "rp" "rt" "ruby" are permitted. See:
// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/rp
// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/rt
// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ruby
p.AllowElements("rp", "rt", "ruby")
/*
CODE BLOCKS
*/
// Permit language tags for code elements.
p.AllowAttrs("class").Matching(regexp.MustCompile("^language-[a-zA-Z0-9]+$")).OnElements("code")
// Don't sanitize HTML inside code blocks.
p.SkipElementsContent("code", "pre")
/*
LINKS AND LINK SAFETY.
*/
// Permit hyperlinks.
p.AllowAttrs("class", "href", "rel").OnElements("a")
// URLs must be parseable by net/url.Parse().
p.RequireParseableURLs(true)
// Most common URL schemes only.
p.AllowURLSchemes("mailto", "http", "https")
// Force rel="noreferrer".
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/noreferrer
p.RequireNoReferrerOnLinks(true)
// Add rel="nofollow" on all fully qualified (not relative) links.
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel#nofollow
p.RequireNoFollowOnFullyQualifiedLinks(true)
// Force crossorigin="anonymous"
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/crossorigin#anonymous
p.RequireCrossOriginAnonymous(true)
// Force target="_blank".
// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#target
p.AddTargetBlankToFullyQualifiedLinks(true)
return p
}()
// '[C]an be thought of as equivalent to stripping all HTML
// elements and their attributes as it has nothing on its allowlist.
// An example usage scenario would be blog post titles where HTML
// tags are not expected at all and if they are then the elements
// and the content of the elements should be stripped. This is a
// very strict policy.'
//
// Source: https://github.com/microcosm-cc/bluemonday#usage
var strict *bluemonday.Policy = bluemonday.StrictPolicy()
// removeHTML strictly removes *all* recognized
// HTML elements from the given string.
func removeHTML(in string) string {
return strict.Sanitize(in)
}
// SanitizeToHTML sanitizes only risky html elements
// from the given string, allowing safe ones through.
func SanitizeToHTML(in string) string {
return regular.Sanitize(in)
}
// SanitizeToPlaintext runs text through basic sanitization.
// This removes any html elements that were in the string,
// and returns clean plaintext.
func SanitizeToPlaintext(in string) string {
// Unescape first to catch any tricky critters.
content := html.UnescapeString(in)
// Remove all detected HTML.
content = removeHTML(content)
// Unescape again to return plaintext.
content = html.UnescapeString(content)
return strings.TrimSpace(content)
}