Source: helpers.go in package github.com/microcosm-cc/bluemonday

Copyright (c) 2014, David Kitchen <david@buro9.com> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of the organisation (Microcosm) nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


package bluemonday

import (
	"encoding/base64"
	"net/url"
	"regexp"
)

A selection of regular expressions that can be used as .Matching() rules on HTML attributes.

CellAlign handles the `align` attribute https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-align

	CellAlign = regexp.MustCompile(`(?i)^(center|justify|left|right|char)$`)

CellVerticalAlign handles the `valign` attribute https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-valign

	CellVerticalAlign = regexp.MustCompile(`(?i)^(baseline|bottom|middle|top)$`)

Direction handles the `dir` attribute https://developer.mozilla.org/en-US/docs/Web/HTML/Element/bdo#attr-dir

	Direction = regexp.MustCompile(`(?i)^(rtl|ltr)$`)

ImageAlign handles the `align` attribute on the `image` tag http://www.w3.org/MarkUp/Test/Img/imgtest.html

	ImageAlign = regexp.MustCompile(
		`(?i)^(left|right|top|texttop|middle|absmiddle|baseline|bottom|absbottom)$`,
	)

Integer describes whole positive integers (including 0) used in places like td.colspan https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-colspan

	Integer = regexp.MustCompile(`^[0-9]+$`)

ISO8601 according to the W3 group is only a subset of the ISO8601 standard: http://www.w3.org/TR/NOTE-datetime Used in places like time.datetime https://developer.mozilla.org/en-US/docs/Web/HTML/Element/time#attr-datetime Matches patterns: Year: YYYY (eg 1997) Year and month: YYYY-MM (eg 1997-07) Complete date: YYYY-MM-DD (eg 1997-07-16) Complete date plus hours and minutes: YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00) Complete date plus hours, minutes and seconds: YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00) Complete date plus hours, minutes, seconds and a decimal fraction of a second YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)

	ISO8601 = regexp.MustCompile(
		`^[0-9]{4}(-[0-9]{2}(-[0-9]{2}([ T][0-9]{2}(:[0-9]{2}){1,2}(.[0-9]{1,6})` +
			`?Z?([\+-][0-9]{2}:[0-9]{2})?)?)?)?$`,
	)

ListType encapsulates the common value as well as the latest spec values for lists https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ol#attr-type

	ListType = regexp.MustCompile(`(?i)^(circle|disc|square|a|A|i|I|1)$`)

SpaceSeparatedTokens is used in places like `a.rel` and the common attribute `class` which both contain space delimited lists of data tokens http://www.w3.org/TR/html-markup/datatypes.html#common.data.tokens-def Regexp: \p{L} matches unicode letters, \p{N} matches unicode numbers

	SpaceSeparatedTokens = regexp.MustCompile(`^([\s\p{L}\p{N}_-]+)$`)

Number is a double value used on HTML5 meter and progress elements http://www.whatwg.org/specs/web-apps/current-work/multipage/the-button-element.html#the-meter-element

	Number = regexp.MustCompile(`^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$`)

NumberOrPercent is used predominantly as units of measurement in width and height attributes https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#attr-height

	NumberOrPercent = regexp.MustCompile(`^[0-9]+[%]?$`)

Paragraph of text in an attribute such as *.'title', img.alt, etc https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-title Note that we are not allowing chars that could close tags like '>'

	Paragraph = regexp.MustCompile(`^[\p{L}\p{N}\s\-_',\[\]!\./\\\(\)]*$`)

dataURIImagePrefix is used by AllowDataURIImages to define the acceptable prefix of data URIs that contain common web image formats. This is not exported as it's not useful by itself, and only has value within the AllowDataURIImages func

	dataURIImagePrefix = regexp.MustCompile(
		`^image/(gif|jpeg|png|webp);base64,`,
	)
)

AllowStandardURLs is a convenience function that will enable rel="nofollow" on "a", "area" and "link" (if you have allowed those elements) and will ensure that the URL values are parseable and either relative or belong to the "mailto", "http", or "https" schemes

URLs must be parseable by net/url.Parse()

	p.RequireParseableURLs(true)

!url.IsAbs() is permitted

	p.AllowRelativeURLs(true)

Most common URL schemes only

	p.AllowURLSchemes("mailto", "http", "https")

For all anchors we will add rel="nofollow" if it does not already exist This applies to "a" "area" "link"

	p.RequireNoFollowOnLinks(true)
}

AllowStandardAttributes will enable "id", "title" and the language specific attributes "dir" and "lang" on all elements that are whitelisted

"dir" "lang" are permitted as both language attributes affect charsets and direction of text.

	p.AllowAttrs("dir").Matching(Direction).Globally()
	p.AllowAttrs(
		"lang",
	).Matching(regexp.MustCompile(`[a-zA-Z]{2,20}`)).Globally()

"id" is permitted. This is pretty much as some HTML elements require this to work well ("dfn" is an example of a "id" being value) This does create a risk that JavaScript and CSS within your web page might identify the wrong elements. Ensure that you select things accurately

	p.AllowAttrs("id").Matching(
		regexp.MustCompile(`[a-zA-Z0-9\:\-_\.]+`),
	).Globally()

"title" is permitted as it improves accessibility.

	p.AllowAttrs("title").Matching(Paragraph).Globally()
}

AllowStyling presently enables the class attribute globally. Note: When bluemonday ships a CSS parser and we can safely sanitise that, this will also allow sanitized styling of elements via the style attribute.

func (p *Policy) AllowStyling() {

"class" is permitted globally

	p.AllowAttrs("class").Matching(SpaceSeparatedTokens).Globally()
}

AllowImages enables the img element and some popular attributes. It will also ensure that URL values are parseable. This helper does not enable data URI images, for that you should also use the AllowDataURIImages() helper.

func (p *Policy) AllowImages() {

"img" is permitted

	p.AllowAttrs("align").Matching(ImageAlign).OnElements("img")
	p.AllowAttrs("alt").Matching(Paragraph).OnElements("img")
	p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("img")

Standard URLs enabled

	p.AllowStandardURLs()
	p.AllowAttrs("src").OnElements("img")
}

AllowDataURIImages permits the use of inline images defined in RFC2397 http://tools.ietf.org/html/rfc2397 http://en.wikipedia.org/wiki/Data_URI_scheme Images must have a mimetype matching: image/gif image/jpeg image/png image/webp NOTE: There is a potential security risk to allowing data URIs and you should only permit them on content you already trust. http://palizine.plynt.com/issues/2010Oct/bypass-xss-filters/ https://capec.mitre.org/data/definitions/244.html

func (p *Policy) AllowDataURIImages() {

URLs must be parseable by net/url.Parse()

	p.RequireParseableURLs(true)

Supply a function to validate images contained within data URI

	p.AllowURLSchemeWithCustomPolicy(
		"data",
		func(url *url.URL) (allowUrl bool) {
			if url.RawQuery != "" || url.Fragment != "" {
				return false
			}

			matched := dataURIImagePrefix.FindString(url.Opaque)
			if matched == "" {
				return false
			}

			_, err := base64.StdEncoding.DecodeString(url.Opaque[len(matched):])
			if err != nil {
				return false
			}

			return true
		},
	)
}

AllowLists will enabled ordered and unordered lists, as well as definition lists

"ol" "ul" are permitted

	p.AllowAttrs("type").Matching(ListType).OnElements("ol", "ul")

"li" is permitted

	p.AllowAttrs("type").Matching(ListType).OnElements("li")
	p.AllowAttrs("value").Matching(Integer).OnElements("li")

"dl" "dt" "dd" are permitted

	p.AllowElements("dl", "dt", "dd")
}

AllowTables will enable a rich set of elements and attributes to describe HTML tables

func (p *Policy) AllowTables() {

"table" is permitted

	p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("table")
	p.AllowAttrs("summary").Matching(Paragraph).OnElements("table")

"caption" is permitted

	p.AllowElements("caption")

"col" "colgroup" are permitted

	p.AllowAttrs("align").Matching(CellAlign).OnElements("col", "colgroup")
	p.AllowAttrs("height", "width").Matching(
		NumberOrPercent,
	).OnElements("col", "colgroup")
	p.AllowAttrs("span").Matching(Integer).OnElements("colgroup", "col")
	p.AllowAttrs("valign").Matching(
		CellVerticalAlign,
	).OnElements("col", "colgroup")

"thead" "tr" are permitted

	p.AllowAttrs("align").Matching(CellAlign).OnElements("thead", "tr")
	p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("thead", "tr")

"td" "th" are permitted

	p.AllowAttrs("abbr").Matching(Paragraph).OnElements("td", "th")
	p.AllowAttrs("align").Matching(CellAlign).OnElements("td", "th")
	p.AllowAttrs("colspan", "rowspan").Matching(Integer).OnElements("td", "th")
	p.AllowAttrs("headers").Matching(
		SpaceSeparatedTokens,
	).OnElements("td", "th")
	p.AllowAttrs("height", "width").Matching(
		NumberOrPercent,
	).OnElements("td", "th")
	p.AllowAttrs(
		"scope",
	).Matching(
		regexp.MustCompile(`(?i)(?:row|col)(?:group)?`),
	).OnElements("td", "th")
	p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("td", "th")
	p.AllowAttrs("nowrap").Matching(
		regexp.MustCompile(`(?i)|nowrap`),
	).OnElements("td", "th")

"tbody" "tfoot"

	p.AllowAttrs("align").Matching(CellAlign).OnElements("tbody", "tfoot")
	p.AllowAttrs("valign").Matching(
		CellVerticalAlign,
	).OnElements("tbody", "tfoot")