analytics/PlausibleWeb.Favicon.html
2023-10-13 16:38:53 +00:00

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<span translate="no">PlausibleWeb.Favicon</span>
<small class="app-vsn" translate="no">(Plausible v0.0.1)</small>
</h1>
<section id="moduledoc">
<p>A Plug that fetches favicon images from DuckDuckGo and returns them
to the Plausible frontend.</p><p>The proxying is there so we can reduce the number of third-party domains that
the browser clients need to connect to. Our goal is to have 0 third-party domain
connections on the website for privacy reasons.</p><p>This module also maps between categorized sources and their respective URLs for favicons.
What does that mean exactly? During ingestion we use <a href="PlausibleWeb.RefInspector.html#parse/1"><code class="inline">PlausibleWeb.RefInspector.parse/1</code></a> to
categorize our referrer sources like so:</p><p>google.com -&gt; Google
google.co.uk -&gt; Google
google.com.au -&gt; Google</p><p>So when we show Google as a source in the dashboard, the request to this plug will come as:
<a href="https://plausible/io/favicon/sources/Google">https://plausible/io/favicon/sources/Google</a></p><p>Now, when we want to show a favicon for Google, we need to convert Google -&gt; google.com or
some other hostname owned by Google:
<a href="https://icons.duckduckgo.com/ip3/google.com.ico">https://icons.duckduckgo.com/ip3/google.com.ico</a></p><p>The mapping from source category -&gt; source hostname is stored in &quot;priv/referer_favicon_domains.json&quot; and
managed by <a href="Mix.Tasks.GenerateReferrerFavicons.html#run/1"><code class="inline">Mix.Tasks.GenerateReferrerFavicons.run/1</code></a></p>
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Summary
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<div class="summary-functions summary">
<h2>
<a href="#functions">Functions</a>
</h2>
<div class="summary-row">
<div class="summary-signature">
<a href="#call/2" translate="no">call(conn, list)</a>
</div>
<div class="summary-synopsis"><p>Proxies HTTP request to DuckDuckGo favicon service. Swallows hop-by-hop HTTP
headers that should not be forwarded as defined in <a href="https://www.rfc-editor.org/rfc/rfc2616#section-13.5.1">RFC 2616</a></p></div>
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<a href="#init/1" translate="no">init(_)</a>
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</section>
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Functions
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<h1 class="signature" translate="no">call(conn, list)</h1>
<a href="https://github.com/plausible/analytics/blob/main/lib/plausible_web/plugs/favicon.ex#L82" class="icon-action" rel="help" title="View Source">
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<section class="docstring">
<p>Proxies HTTP request to DuckDuckGo favicon service. Swallows hop-by-hop HTTP
headers that should not be forwarded as defined in <a href="https://www.rfc-editor.org/rfc/rfc2616#section-13.5.1">RFC 2616</a></p><h2 id="call/2-placeholder" class="section-heading">
<a href="#call/2-placeholder">
<i class="ri-link-m" aria-hidden="true"></i>
Placeholder
</a>
</h2>
<p>Cases where we show a placeholder icon instead:</p><ol><li>In case of network error to DuckDuckGo</li><li>In case of non-2xx status code from DuckDuckGo</li><li>In case of broken image response body from DuckDuckGo</li></ol><p>I'm not sure why DDG sometimes returns a broken PNG image in their response
but we filter that out. When the icon request fails, we show a placeholder
favicon instead. The placeholder is an emoji from
<a href="https://favicon.io/emoji-favicons/">https://favicon.io/emoji-favicons/</a></p><p>DuckDuckGo favicon service has some issues with <a href="https://css-tricks.com/svg-favicons-and-all-the-fun-things-we-can-do-with-them/">SVG favicons</a>.
For some reason, they return them with <code class="inline">content-type=image/x-icon</code> whereas SVG
icons should be returned with <code class="inline">content-type=image/svg+xml</code>. This Plug detects
when the response body starts with <code class="inline">&lt;svg</code> and will override the <code class="inline">Content-Type</code>
to correct it.</p><h2 id="call/2-preventing-xss-vulnerabilities" class="section-heading">
<a href="#call/2-preventing-xss-vulnerabilities">
<i class="ri-link-m" aria-hidden="true"></i>
Preventing XSS vulnerabilities
</a>
</h2>
<p>SVGs may contain <code class="inline">&lt;script&gt;</code> tags, and as these SVGs come from external
sources, we need to prevent untrusted code from running on the browser.</p><ul><li><p>This Plug sets a strict <code class="inline">Content-Security-Policy</code> header telling the browser
not to run scripts.</p></li><li><p>This Plug sets <code class="inline">Content-Disposition=attachment</code> to prevent the SVG from
rendering when navigating to <code class="inline">/favicon/sources/:domain</code> directly.</p></li><li><p>Browsers do not execute scripts from <code class="inline">&lt;img&gt;</code> tags, therefore it is safe to
use <code class="inline">&lt;img src=&quot;https://plausible.io/favicon/sources/dummy.site&quot;&gt;&lt;/img&gt;</code></p></li></ul>
</section>
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<h1 class="signature" translate="no">init(_)</h1>
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