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Discourage using "out-of-container" relative URLs #1939

Merged
merged 15 commits into from
Dec 7, 2021
Merged

Discourage using "out-of-container" relative URLs #1939

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4082d35
Made the changes as discussed in the issue
iherman Nov 25, 2021
0534d02
markup error reported by check
iherman Nov 25, 2021
af87825
Doh. Still a markup error
iherman Nov 25, 2021
ea8b94d
Used the same verion of the algorithm
iherman Nov 26, 2021
6063289
minor changes on the explanations
iherman Nov 27, 2021
f6f6d21
Romain's first batch of comments
iherman Nov 30, 2021
3c95120
Second batch of romain's comments
iherman Nov 30, 2021
587f2b9
Minor editorial change, per Matt's comment
iherman Dec 2, 2021
7ef5dd9
Implementing the latest round of comments (https://github.com/w3c/epu…
iherman Dec 3, 2021
1d40e48
Merge branch 'main' into editorial/out-of-container-url-1912
iherman Dec 3, 2021
a1b71a7
Markup error sneaked in..
iherman Dec 3, 2021
6049f4d
Merge branch 'editorial/out-of-container-url-1912' of https://github.…
iherman Dec 3, 2021
9eaa337
Improved the note
iherman Dec 3, 2021
6d003f6
Latest comments of Romain
iherman Dec 4, 2021
e90a01f
Merge branch 'main' into editorial/out-of-container-url-1912
iherman Dec 7, 2021
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51 changes: 30 additions & 21 deletions epub33/core/index.html
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Expand Up @@ -5984,24 +5984,13 @@ <h4>URLs in the OCF Abstract Container</h4>

</div>

<p> In the <a>OCF Abstract Container</a>, when a file uses a URL string to reference another file in
the container, the string MUST be a
<a data-cite="url#path-relative-scheme-less-url-string">path-relative-scheme-less-URL string</a>,
<p>
A string is a <dfn id="dfn-valid-relative-container-url-string">valid-relative-container-URL-string</dfn> if it is
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a <a data-cite="url#path-relative-scheme-less-url-string">path-relative-scheme-less-URL string</a>,
optionally followed by <code>U+0023 (#)</code> and a
<a data-cite="url#url-fragment-string">URL-fragment string</a>.
<a data-cite="url#url-fragment-string">URL-fragment string</a>, and if the following steps return <var>true</var>:
</p>

<p class="note">
The properties of the <a>container root URL</a> are such that whatever the amount
of <a data-cite="url/#double-dot-path-segment">double-dot path segments</a> in a URL string (for
example, <code>../../../secret</code>), it is parsed to a <a>content URL</a> (and not "leak"
outside the container). This avoids potential run-time security issues.
Furthermore, the additional constraint and <a href="#algo-out-of-container">algorithm</a> below
ensure that such potentially problematic URLs can also be detected when checking the EPUB Document.
</p>

<p>To validate a URL string <var>url</var> found in the <a>OCF Abstract Container</a>, the following steps SHOULD return <var>true</var>:</p>

<ol class="algorithm" id="algo-out-of-container">
<li>
Set the <a>container root URL</a> to <code>https://a.example.org/A/</code>.
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Expand Down Expand Up @@ -6086,11 +6075,28 @@ <h4>URLs in the OCF Abstract Container</h4>
<li>Return <var>false</var>.</li>
</ol>

<p class="note">
For better interoperability with non-conforming or legacy Reading Systems and toolchains,
EPUB Creators should not use more <a data-cite="url/#double-dot-path-segment">double-dot path segments</a>
than needed to reach the target container file.
</p>
<p>
In the <a>OCF Abstract Container</a>, any URL string MUST be an <a data-cite="url#absolute-url-with-fragment-string">absolute-URL-with-fragment-string</a> or a <a>valid-relative-container-URL-string</a>.
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</p>

<div class="note">
<p>
The properties of the <a>container root URL</a> are such that whatever the amount
of <a data-cite="url#double-dot-path-segment">double-dot path segments</a> in a URL string (for
example, <code>../../../secret</code>), it is parsed to a <a>content URL</a> (and not "leak"
outside the container). This avoids potential run-time security issues.
The additional constraint on <a>valid-relative-container-URL-strings</a>
ensures that such potentially problematic URLs can also be detected when checking the EPUB Publication.
</p>


<p>
For better interoperability with non-conforming or legacy Reading Systems and toolchains,
EPUB Creators should not use more <a data-cite="url#double-dot-path-segment">double-dot path segments</a>
than needed to reach the target container file.
</p>

</div>

<aside class="example" title="Referencing a file in the same directory">
<p>In this example, the file <code>image1.jpg</code> is in the same directory as the <a>XHTML
Expand Down Expand Up @@ -6120,7 +6126,7 @@ <h4>URLs in the OCF Abstract Container</h4>
</pre>

<p>
A URL `../../../../EPUB/secret.xhtml` appearing in `content.xhtml` would be parsed by a Reading System into a <a>content URL</a> with a path `EPUB/secret.xhtml`, following the constraints on the <a>container root URL</a>. However, as the URL could be perceived as one of a resource outside the container, and create interoperability issues, it would be reported as a warning by a checker tool.
A URL `../../../../EPUB/secret.xhtml` appearing in `content.xhtml` would be parsed by a Reading System into a <a>content URL</a> with a path `EPUB/secret.xhtml`, following the constraints on the <a>container root URL</a>. However, as the URL could be perceived as one of a resource outside the container, and create interoperability issues; it would be reported as an error by a checker tool.
</p>
</aside>
</section>
Expand Down Expand Up @@ -10555,6 +10561,9 @@ <h2>Change Log</h2>
>Working Group's issue tracker</a>.</p>

<ul>

<li>03-Dec-2021: Remove the element-based restrictions on remote resources. See <a
href="https://github.com/w3c/epub-specs/issues/1913">issue 1913</a>.</li>
<li>26-Nov-2021: A requirement and an algorithm to detect out-of-container URLs has been added to the
specification. See <a href="https://github.com/w3c/epub-specs/issues/1912">issue 1912</a>
</li>
Expand Down