2022-06-28 12:15:27 +00:00
<!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" >
2023-12-11 14:56:13 +00:00
< link rel = "stylesheet" href = "../docs/website_files/version-picker.css" >
2022-06-28 12:15:27 +00:00
< / 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 ? "navy" : "light";
< / script >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script type = "text/javascript" >
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script type = "text/javascript" >
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('light')
html.classList.add(theme);
html.classList.add('js');
< / 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 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/config_documentation.html" > Configuration Manual< / a > < / li > < 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 " > < a href = "../usage/configuration/user_authentication/single_sign_on/index.html" > Single-Sign On< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../openid.html" > OpenID Connect< / a > < / li > < li class = "chapter-item expanded " > < a href = "../usage/configuration/user_authentication/single_sign_on/saml.html" > SAML< / a > < / li > < li class = "chapter-item expanded " > < a href = "../usage/configuration/user_authentication/single_sign_on/cas.html" > CAS< / a > < / li > < li class = "chapter-item expanded " > < a href = "../sso_mapping_providers.html" > SSO Mapping Providers< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../password_auth_providers.html" > Password Auth Providers< / a > < / li > < li class = "chapter-item expanded " > < a href = "../jwt.html" > JSON Web Tokens< / a > < / li > < li class = "chapter-item expanded " > < a href = "../usage/configuration/user_authentication/refresh_tokens.html" > Refresh Tokens< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../CAPTCHA_SETUP.html" > Registration Captcha< / a > < / li > < li class = "chapter-item expanded " > < a href = "../application_services.html" > Application Services< / a > < / li > < li class = "chapter-item expanded " > < a href = "../server_notices.html" > Server Notices< / a > < / li > < li class = "chapter-item expanded " > < a href = "../consent_tracking.html" > Consent Tracking< / a > < / li > < li class = "chapter-item expanded " > < a href = "../development/url_previews.html" class = "active" > URL Previews< / a > < / li > < li class = "chapter-item expanded " > < a href = "../user_directory.html" > User Directory< / a > < / li > < li class = "chapter-item expanded " > < a href = "../message_retention_policies.html" > Message Retention Policies< / a > < / li > < li class = "chapter-item expanded " > < a href = "../modules/index.html" > Pluggable Modules< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../modules/writing_a_module.html" > Writing a module< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../modules/spam_checker_callbacks.html" > Spam checker callbacks< / a > < / li > < li class = "chapter-item expanded " > < a
< / 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" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "light" > Light (default)< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "ayu" > Ayu< / button > < / li >
< / ul >
< button id = "search-toggle" class = "icon-button" type = "button" title = "Search. (Shortkey: s)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "S" aria-controls = "searchbar" >
< i class = "fa fa-search" > < / i >
< / button >
2023-12-11 14:56:13 +00:00
< div class = "version-picker" >
< div class = "dropdown" >
< div class = "select" >
< span > < / span >
< i class = "fa fa-chevron-down" > < / i >
< / div >
< input type = "hidden" name = "version" >
< ul class = "dropdown-menu" >
<!-- Versions will be added dynamically in version - picker.js -->
< / ul >
< / div >
< / div >
2022-06-28 12:15:27 +00:00
< / 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 < a href = "https://oembed.com/" > oEmbed< / a > pattern. If it
does, update the URL to download.< / li >
< li > 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 a JSON oEmbed URL was found in the HTML via autodiscovery:
< ol >
< li > Downloads the URL and stores it into a file via the media storage provider
and saves the local media metadata.< / li >
< li > Convert the oEmbed response to an Open Graph response.< / li >
< li > Override any Open Graph data from the HTML with data from oEmbed.< / li >
< / ol >
< / 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 > If the media is JSON and an oEmbed URL was found:
< ol >
< li > Convert the oEmbed response to an Open Graph response.< / li >
< li > If a thumbnail or image is in the oEmbed 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 >
2023-12-11 14:56:13 +00:00
< script type = "text/javascript" src = "../docs/website_files/version-picker.js" > < / script >
< script type = "text/javascript" src = "../docs/website_files/version.js" > < / script >
2022-06-28 12:15:27 +00:00
< / body >
2023-12-11 14:56:13 +00:00
< / html >
