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298 lines
11 KiB
Go
298 lines
11 KiB
Go
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// Copyright (c) 2014, David Kitchen <david@buro9.com>
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// * Redistributions of source code must retain the above copyright notice, this
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// list of conditions and the following disclaimer.
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//
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// * Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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//
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// * Neither the name of the organisation (Microcosm) nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package bluemonday
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import (
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"encoding/base64"
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"net/url"
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"regexp"
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)
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// A selection of regular expressions that can be used as .Matching() rules on
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// HTML attributes.
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var (
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// CellAlign handles the `align` attribute
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-align
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CellAlign = regexp.MustCompile(`(?i)^(center|justify|left|right|char)$`)
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// CellVerticalAlign handles the `valign` attribute
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-valign
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CellVerticalAlign = regexp.MustCompile(`(?i)^(baseline|bottom|middle|top)$`)
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// Direction handles the `dir` attribute
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/bdo#attr-dir
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Direction = regexp.MustCompile(`(?i)^(rtl|ltr)$`)
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// ImageAlign handles the `align` attribute on the `image` tag
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// http://www.w3.org/MarkUp/Test/Img/imgtest.html
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ImageAlign = regexp.MustCompile(
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`(?i)^(left|right|top|texttop|middle|absmiddle|baseline|bottom|absbottom)$`,
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)
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// Integer describes whole positive integers (including 0) used in places
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// like td.colspan
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-colspan
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Integer = regexp.MustCompile(`^[0-9]+$`)
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// ISO8601 according to the W3 group is only a subset of the ISO8601
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// standard: http://www.w3.org/TR/NOTE-datetime
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//
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// Used in places like time.datetime
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/time#attr-datetime
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//
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// Matches patterns:
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// Year:
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// YYYY (eg 1997)
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// Year and month:
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// YYYY-MM (eg 1997-07)
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// Complete date:
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// YYYY-MM-DD (eg 1997-07-16)
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// Complete date plus hours and minutes:
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// YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00)
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// Complete date plus hours, minutes and seconds:
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// YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00)
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// Complete date plus hours, minutes, seconds and a decimal fraction of a
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// second
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// YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)
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ISO8601 = regexp.MustCompile(
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`^[0-9]{4}(-[0-9]{2}(-[0-9]{2}([ T][0-9]{2}(:[0-9]{2}){1,2}(.[0-9]{1,6})` +
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`?Z?([\+-][0-9]{2}:[0-9]{2})?)?)?)?$`,
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)
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// ListType encapsulates the common value as well as the latest spec
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// values for lists
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ol#attr-type
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ListType = regexp.MustCompile(`(?i)^(circle|disc|square|a|A|i|I|1)$`)
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// SpaceSeparatedTokens is used in places like `a.rel` and the common attribute
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// `class` which both contain space delimited lists of data tokens
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// http://www.w3.org/TR/html-markup/datatypes.html#common.data.tokens-def
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// Regexp: \p{L} matches unicode letters, \p{N} matches unicode numbers
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SpaceSeparatedTokens = regexp.MustCompile(`^([\s\p{L}\p{N}_-]+)$`)
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// Number is a double value used on HTML5 meter and progress elements
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// http://www.whatwg.org/specs/web-apps/current-work/multipage/the-button-element.html#the-meter-element
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Number = regexp.MustCompile(`^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$`)
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// NumberOrPercent is used predominantly as units of measurement in width
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// and height attributes
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#attr-height
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NumberOrPercent = regexp.MustCompile(`^[0-9]+[%]?$`)
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// Paragraph of text in an attribute such as *.'title', img.alt, etc
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-title
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// Note that we are not allowing chars that could close tags like '>'
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Paragraph = regexp.MustCompile(`^[\p{L}\p{N}\s\-_',\[\]!\./\\\(\)]*$`)
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// dataURIImagePrefix is used by AllowDataURIImages to define the acceptable
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// prefix of data URIs that contain common web image formats.
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//
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// This is not exported as it's not useful by itself, and only has value
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// within the AllowDataURIImages func
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dataURIImagePrefix = regexp.MustCompile(
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`^image/(gif|jpeg|png|webp);base64,`,
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)
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)
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// AllowStandardURLs is a convenience function that will enable rel="nofollow"
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// on "a", "area" and "link" (if you have allowed those elements) and will
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// ensure that the URL values are parseable and either relative or belong to the
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// "mailto", "http", or "https" schemes
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func (p *Policy) AllowStandardURLs() {
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// URLs must be parseable by net/url.Parse()
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p.RequireParseableURLs(true)
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// !url.IsAbs() is permitted
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p.AllowRelativeURLs(true)
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// Most common URL schemes only
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p.AllowURLSchemes("mailto", "http", "https")
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// For all anchors we will add rel="nofollow" if it does not already exist
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// This applies to "a" "area" "link"
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p.RequireNoFollowOnLinks(true)
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}
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// AllowStandardAttributes will enable "id", "title" and the language specific
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// attributes "dir" and "lang" on all elements that are whitelisted
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func (p *Policy) AllowStandardAttributes() {
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// "dir" "lang" are permitted as both language attributes affect charsets
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// and direction of text.
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p.AllowAttrs("dir").Matching(Direction).Globally()
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p.AllowAttrs(
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"lang",
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).Matching(regexp.MustCompile(`[a-zA-Z]{2,20}`)).Globally()
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// "id" is permitted. This is pretty much as some HTML elements require this
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// to work well ("dfn" is an example of a "id" being value)
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// This does create a risk that JavaScript and CSS within your web page
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// might identify the wrong elements. Ensure that you select things
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// accurately
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p.AllowAttrs("id").Matching(
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regexp.MustCompile(`[a-zA-Z0-9\:\-_\.]+`),
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).Globally()
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// "title" is permitted as it improves accessibility.
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p.AllowAttrs("title").Matching(Paragraph).Globally()
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}
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// AllowStyling presently enables the class attribute globally.
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//
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// Note: When bluemonday ships a CSS parser and we can safely sanitise that,
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// this will also allow sanitized styling of elements via the style attribute.
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func (p *Policy) AllowStyling() {
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// "class" is permitted globally
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p.AllowAttrs("class").Matching(SpaceSeparatedTokens).Globally()
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}
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// AllowImages enables the img element and some popular attributes. It will also
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// ensure that URL values are parseable. This helper does not enable data URI
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// images, for that you should also use the AllowDataURIImages() helper.
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func (p *Policy) AllowImages() {
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// "img" is permitted
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p.AllowAttrs("align").Matching(ImageAlign).OnElements("img")
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p.AllowAttrs("alt").Matching(Paragraph).OnElements("img")
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p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("img")
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// Standard URLs enabled
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p.AllowStandardURLs()
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p.AllowAttrs("src").OnElements("img")
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}
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// AllowDataURIImages permits the use of inline images defined in RFC2397
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// http://tools.ietf.org/html/rfc2397
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// http://en.wikipedia.org/wiki/Data_URI_scheme
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//
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// Images must have a mimetype matching:
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// image/gif
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// image/jpeg
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// image/png
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// image/webp
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//
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// NOTE: There is a potential security risk to allowing data URIs and you should
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// only permit them on content you already trust.
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// http://palizine.plynt.com/issues/2010Oct/bypass-xss-filters/
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// https://capec.mitre.org/data/definitions/244.html
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func (p *Policy) AllowDataURIImages() {
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// URLs must be parseable by net/url.Parse()
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p.RequireParseableURLs(true)
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// Supply a function to validate images contained within data URI
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p.AllowURLSchemeWithCustomPolicy(
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"data",
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func(url *url.URL) (allowUrl bool) {
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if url.RawQuery != "" || url.Fragment != "" {
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return false
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}
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matched := dataURIImagePrefix.FindString(url.Opaque)
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if matched == "" {
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return false
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}
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_, err := base64.StdEncoding.DecodeString(url.Opaque[len(matched):])
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if err != nil {
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return false
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}
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return true
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},
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)
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}
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// AllowLists will enabled ordered and unordered lists, as well as definition
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// lists
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func (p *Policy) AllowLists() {
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// "ol" "ul" are permitted
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p.AllowAttrs("type").Matching(ListType).OnElements("ol", "ul")
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// "li" is permitted
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p.AllowAttrs("type").Matching(ListType).OnElements("li")
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p.AllowAttrs("value").Matching(Integer).OnElements("li")
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// "dl" "dt" "dd" are permitted
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p.AllowElements("dl", "dt", "dd")
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}
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// AllowTables will enable a rich set of elements and attributes to describe
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// HTML tables
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func (p *Policy) AllowTables() {
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// "table" is permitted
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p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("table")
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p.AllowAttrs("summary").Matching(Paragraph).OnElements("table")
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// "caption" is permitted
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p.AllowElements("caption")
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// "col" "colgroup" are permitted
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p.AllowAttrs("align").Matching(CellAlign).OnElements("col", "colgroup")
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p.AllowAttrs("height", "width").Matching(
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NumberOrPercent,
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).OnElements("col", "colgroup")
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p.AllowAttrs("span").Matching(Integer).OnElements("colgroup", "col")
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p.AllowAttrs("valign").Matching(
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CellVerticalAlign,
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).OnElements("col", "colgroup")
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// "thead" "tr" are permitted
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p.AllowAttrs("align").Matching(CellAlign).OnElements("thead", "tr")
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p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("thead", "tr")
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// "td" "th" are permitted
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p.AllowAttrs("abbr").Matching(Paragraph).OnElements("td", "th")
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p.AllowAttrs("align").Matching(CellAlign).OnElements("td", "th")
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p.AllowAttrs("colspan", "rowspan").Matching(Integer).OnElements("td", "th")
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p.AllowAttrs("headers").Matching(
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SpaceSeparatedTokens,
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).OnElements("td", "th")
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p.AllowAttrs("height", "width").Matching(
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NumberOrPercent,
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).OnElements("td", "th")
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p.AllowAttrs(
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"scope",
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).Matching(
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regexp.MustCompile(`(?i)(?:row|col)(?:group)?`),
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).OnElements("td", "th")
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p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("td", "th")
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p.AllowAttrs("nowrap").Matching(
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regexp.MustCompile(`(?i)|nowrap`),
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).OnElements("td", "th")
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// "tbody" "tfoot"
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p.AllowAttrs("align").Matching(CellAlign).OnElements("tbody", "tfoot")
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p.AllowAttrs("valign").Matching(
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CellVerticalAlign,
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).OnElements("tbody", "tfoot")
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}
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