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diff --git a/latest/development/url_previews.html b/latest/development/url_previews.html new file mode 100644 index 0000000000..7189a53575 --- /dev/null +++ b/latest/development/url_previews.html @@ -0,0 +1,320 @@ +<!DOCTYPE HTML> +<html lang="en" class="sidebar-visible no-js light"> + <head> + <!-- Book generated using mdBook --> + <meta charset="UTF-8"> + <title>URL Previews - Synapse</title> + + + + + <!-- Custom HTML head --> + + + + <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> + <meta name="description" content=""> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <meta name="theme-color" content="#ffffff" /> + + + <link rel="icon" href="../favicon.svg"> + + + <link rel="shortcut icon" href="../favicon.png"> + + <link rel="stylesheet" href="../css/variables.css"> + <link rel="stylesheet" href="../css/general.css"> + <link rel="stylesheet" href="../css/chrome.css"> + + <link rel="stylesheet" href="../css/print.css" media="print"> + + + <!-- Fonts --> + <link rel="stylesheet" href="../FontAwesome/css/font-awesome.css"> + + <link rel="stylesheet" href="../fonts/fonts.css"> + + + <!-- Highlight.js Stylesheets --> + <link rel="stylesheet" href="../highlight.css"> + <link rel="stylesheet" href="../tomorrow-night.css"> + <link rel="stylesheet" href="../ayu-highlight.css"> + + <!-- Custom theme stylesheets --> + + <link rel="stylesheet" href="../docs/website_files/table-of-contents.css"> + + <link rel="stylesheet" href="../docs/website_files/remove-nav-buttons.css"> + + <link rel="stylesheet" href="../docs/website_files/indent-section-headers.css"> + + + + </head> + <body> + <!-- Provide site root to javascript --> + <script type="text/javascript"> + var path_to_root = "../"; + var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? 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</script> + + <!-- Hide / unhide sidebar before it is displayed --> + <script type="text/javascript"> + var html = document.querySelector('html'); + var sidebar = 'hidden'; + if (document.body.clientWidth >= 1080) { + try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } + sidebar = sidebar || 'visible'; + } + html.classList.remove('sidebar-visible'); + html.classList.add("sidebar-" + sidebar); + </script> + + <nav id="sidebar" class="sidebar" aria-label="Table of contents"> + <div class="sidebar-scrollbox"> + <ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="../welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="../postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="../reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="../setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="../turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="../delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a href="../upgrade.html">Upgrading between Synapse Versions</a></li><li class="chapter-item expanded "><a href="../MSC1711_certificates_FAQ.html">Upgrading from pre-Synapse 1.0</a></li><li class="chapter-item expanded affix "><li class="part-title">Usage</li><li class="chapter-item expanded "><a href="../federate.html">Federation</a></li><li class="chapter-item expanded "><a href="../usage/configuration/index.html">Configuration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../usage/configuration/homeserver_sample_config.html">Homeserver Sample Config File</a></li><li class="chapter-item expanded "><a href="../usage/configuration/logging_sample_config.html">Logging Sample Config File</a></li><li class="chapter-item expanded "><a href="../structured_logging.html">Structured Logging</a></li><li class="chapter-item expanded "><a href="../templates.html">Templates</a></li><li class="chapter-item expanded "><a href="../usage/configuration/user_authentication/index.html">User Authentication</a></li><li><ol class="section"><li class="chapter-item expanded "><div>Single-Sign On</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="../openid.html">OpenID Connect</a></li><li class="chapter-item expanded "><div>SAML</div></li><li class="chapter-item expanded "><div>CAS</div></li><li class="chapter-item expanded "><a href="../sso_mapping_providers.html">SSO Mapping Providers</a></li></ol></li><li class="chapter-item 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Replication</a></li></ol></li><li class="chapter-item expanded "><a href="../development/internal_documentation/index.html">Internal Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><div>Single Sign-On</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/saml.html">SAML</a></li><li class="chapter-item expanded "><a href="../development/cas.html">CAS</a></li></ol></li><li class="chapter-item expanded "><a href="../development/room-dag-concepts.html">Room DAG concepts</a></li><li class="chapter-item expanded "><div>State Resolution</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="../auth_chain_difference_algorithm.html">The Auth Chain Difference Algorithm</a></li></ol></li><li class="chapter-item expanded "><a href="../media_repository.html">Media Repository</a></li><li class="chapter-item expanded "><a href="../room_and_user_statistics.html">Room and User Statistics</a></li></ol></li><li class="chapter-item expanded "><div>Scripts</div></li><li class="chapter-item expanded affix "><li class="part-title">Other</li><li class="chapter-item expanded "><a href="../deprecation_policy.html">Dependency Deprecation Policy</a></li></ol> + </div> + <div id="sidebar-resize-handle" class="sidebar-resize-handle"></div> + </nav> + + <div id="page-wrapper" class="page-wrapper"> + + <div class="page"> + + <div id="menu-bar-hover-placeholder"></div> + <div id="menu-bar" class="menu-bar sticky bordered"> + <div class="left-buttons"> + <button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar"> + <i class="fa fa-bars"></i> + </button> + <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list"> + <i class="fa fa-paint-brush"></i> + </button> + <ul id="theme-list" 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(Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar"> + <i class="fa fa-search"></i> + </button> + + </div> + + <h1 class="menu-title">Synapse</h1> + + <div class="right-buttons"> + + <a href="../print.html" title="Print this book" aria-label="Print this book"> + <i id="print-button" class="fa fa-print"></i> + </a> + + + <a href="https://github.com/matrix-org/synapse" title="Git repository" aria-label="Git repository"> + <i id="git-repository-button" class="fa fa-github"></i> + </a> + + + <a href="https://github.com/matrix-org/synapse/edit/develop/docs/development/url_previews.md" title="Suggest an edit" aria-label="Suggest an edit"> + <i id="git-edit-button" class="fa fa-edit"></i> + </a> + + + </div> + </div> + + + <div id="search-wrapper" class="hidden"> + <form id="searchbar-outer" class="searchbar-outer"> + <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> + </form> + <div id="searchresults-outer" class="searchresults-outer hidden"> + <div id="searchresults-header" class="searchresults-header"></div> + <ul id="searchresults"> + </ul> + </div> + </div> + + + <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> + <script type="text/javascript"> + document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); + document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); + Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { + link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); + }); + </script> + + <div id="content" class="content"> + <main> + <!-- Page table of contents --> + <div class="sidetoc"> + <nav class="pagetoc"></nav> + </div> + + <h1 id="url-previews"><a class="header" href="#url-previews">URL Previews</a></h1> +<p>The <code>GET /_matrix/media/r0/preview_url</code> endpoint provides a generic preview API +for URLs which outputs <a href="https://ogp.me/">Open Graph</a> responses (with some Matrix +specific additions).</p> +<p>This does have trade-offs compared to other designs:</p> +<ul> +<li>Pros: +<ul> +<li>Simple and flexible; can be used by any clients at any point</li> +</ul> +</li> +<li>Cons: +<ul> +<li>If each homeserver provides one of these independently, all the HSes in a +room may needlessly DoS the target URI</li> +<li>The URL metadata must be stored somewhere, rather than just using Matrix +itself to store the media.</li> +<li>Matrix cannot be used to distribute the metadata between homeservers.</li> +</ul> +</li> +</ul> +<p>When Synapse is asked to preview a URL it does the following:</p> +<ol> +<li>Checks against a URL blacklist (defined as <code>url_preview_url_blacklist</code> in the +config).</li> +<li>Checks the in-memory cache by URLs and returns the result if it exists. (This +is also used to de-duplicate processing of multiple in-flight requests at once.)</li> +<li>Kicks off a background process to generate a preview: +<ol> +<li>Checks the database cache by URL and timestamp and returns the result if it +has not expired and was successful (a 2xx return code).</li> +<li>Checks if the URL matches an oEmbed pattern. If it does, fetch the oEmbed +response. If this is an image, replace the URL to fetch and continue. If +if it is HTML content, use the HTML as the document and continue.</li> +<li>If it doesn't match an oEmbed pattern, downloads the URL and stores it +into a file via the media storage provider and saves the local media +metadata.</li> +<li>If the media is an image: +<ol> +<li>Generates thumbnails.</li> +<li>Generates an Open Graph response based on image properties.</li> +</ol> +</li> +<li>If the media is HTML: +<ol> +<li>Decodes the HTML via the stored file.</li> +<li>Generates an Open Graph response from the HTML.</li> +<li>If an image exists in the Open Graph response: +<ol> +<li>Downloads the URL and stores it into a file via the media storage +provider and saves the local media metadata.</li> +<li>Generates thumbnails.</li> +<li>Updates the Open Graph response based on image properties.</li> +</ol> +</li> +</ol> +</li> +<li>Stores the result in the database cache.</li> +</ol> +</li> +<li>Returns the result.</li> +</ol> +<p>The in-memory cache expires after 1 hour.</p> +<p>Expired entries in the database cache (and their associated media files) are +deleted every 10 seconds. The default expiration time is 1 hour from download.</p> + + </main> + + <nav class="nav-wrapper" aria-label="Page navigation"> + <!-- Mobile navigation buttons --> + + <a rel="prev" href="../consent_tracking.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + + + + <a rel="next" href="../user_directory.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + + + <div style="clear: both"></div> + </nav> + </div> + </div> + + <nav class="nav-wide-wrapper" aria-label="Page navigation"> + + <a rel="prev" href="../consent_tracking.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + + + + <a rel="next" href="../user_directory.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + + </nav> + + </div> + + + + + + + + + <script type="text/javascript"> + window.playground_copyable = true; + </script> + + + + + + <script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script> + <script src="../mark.min.js" type="text/javascript" charset="utf-8"></script> + <script src="../searcher.js" type="text/javascript" charset="utf-8"></script> + + + <script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script> + <script src="../highlight.js" type="text/javascript" charset="utf-8"></script> + <script src="../book.js" type="text/javascript" charset="utf-8"></script> + + <!-- Custom JS scripts --> + + <script type="text/javascript" src="../docs/website_files/table-of-contents.js"></script> + + + + + </body> +</html> \ No newline at end of file |