EchoHub/docs/auriondocs/Code/src/EchoHub.Server/Services/LinkEmbedService.cs.md

LinkEmbedService

File: src/EchoHub.Server/Services/LinkEmbedService.cs
Kind: class

public partial class LinkEmbedService

Detects URLs inside a message and attempts to build lightweight Open Graph-style preview data for each. Call TryGetEmbedsAsync when you need server-side preview cards for message text (for example, chat or activity feeds); the service will return a list of EmbedDto instances for URLs it successfully fetched and parsed, or null if no usable embeds were found. The method is resilient: it never throws to callers (failures are logged) and applies several safeguards (URI validation, scheme check, private-host blocking, content-type and size limits, timeout).

Remarks

LinkEmbedService is a focused utility for fetching and extracting minimal preview metadata from remote pages. It integrates with IHttpClientFactory (expects a named client "OgFetch") and logs issues through the injected ILogger<LinkEmbedService>. The implementation defends against common server-side preview hazards: it only allows absolute http/https URIs, rejects private/internal hosts via IsPrivateHost, enforces a read timeout using HubConstants.EmbedFetchTimeoutSeconds, and limits the amount of HTML read with HubConstants.EmbedMaxHtmlBytes. Parsing is performed by extracting Open Graph tags via ParseOgTags, falling back to the <title> tag (via TitleTagRegex), and optionally parsing a theme-color meta tag (via ParseThemeColor / ThemeColorRegex). Text fields are HTML-decoded and long descriptions are truncated to HubConstants.EmbedMaxDescriptionLength.

Notes

• The service expects a named IHttpClientFactory client called "OgFetch"; if that client is not registered or misconfigured the fetches will fail and be logged at debug level.
• Fetches are performed sequentially for each URL in TryGetEmbedsAsync, so large numbers of links or slow hosts may increase total latency; each fetch is nevertheless bounded by HubConstants.EmbedFetchTimeoutSeconds.
• HTML extraction relies on regex-based parsing (TitleTagRegex, ThemeColorRegex) and the ParseOgTags helper; this is intentionally pragmatic but may miss nonstandard or deeply nested metadata. The service also drops non-HTML responses, invalid URIs, non-HTTP(S) schemes, private hosts, and pages that lack any usable title or Open Graph title — in all those cases it returns null for that URL and proceeds without throwing.