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Content Delivery Architecture

This document describes how SkyCMS serves files, pages, and assets to site visitors — from blob storage through the application layer to CDN edge caches.

Audience: Developers

Delivery Paths

SkyCMS delivers content through three distinct paths:

Path Controller Purpose
/pub/* PubController Protected file serving with authentication
/* (static mode) StaticProxyController Pre-generated HTML from blob storage
Static files ASP.NET Middleware CSS, JS, and built-in assets from wwwroot

Protected File Serving (PubController)

The PubController serves files from blob storage with optional authentication and per-article authorization.

Request Flow

  1. A request to /pub/{path} is routed to PubController.Index().
  2. Cache headers are set based on authentication requirements.
  3. If authentication is required, the user's identity is validated.
  4. For article-specific paths (/pub/articles/{articleNumber}/*), per-article authorization is checked via AuthorizeUserForArticleQuery.
  5. The file is served from cache or blob storage.

Caching

  • In-memory cache: Files are cached for 4 minutes after first access.
  • Cache key: Generated per tenant and path by ICacheKeyProvider.GenerateFileKey(hostname, path).
  • ETag support: Storage ETags are converted to HTTP ETag headers for browser cache validation.

Cache Control Headers

Context Cache-Control
Authenticated content private, no-cache, no-store, must-revalidate
Public content public, max-age=3600

Editor vs. Publisher

Both the Editor and Publisher have their own PubController, both extending PubControllerBase:

Application Authentication
Editor Based on IEditorSettings.CosmosRequiresAuthentication
Publisher Based on SiteSettings.CosmosRequiresAuthentication; marked [AllowAnonymous] by default

Static File Serving (StaticProxyController)

In static mode (CosmosStaticWebPages = true), the StaticProxyController serves pre-generated HTML files from blob storage.

Request Flow

  1. The request path is normalized (root → index.html).
  2. Attempt to serve the exact file from storage (checking cache first).
  3. If no file found, check for SPA fallback.
  4. Return 404 if neither succeeds.

Cache TTLs

File Type Cache Duration
index.html 10 seconds
All other files 5 minutes

The short TTL for index.html ensures frequent content updates are reflected quickly while still providing caching benefits.

SPA Fallback Routing

For Single Page Application (SPA) deployments:

  1. The controller queries the database for ArticleType.SpaApp entries matching the requested URL.
  2. If a SPA is found at that path, the controller returns {path}/index.html instead of 404.
  3. SPA detection results are cached for 5 minutes.
  4. This allows client-side routing to work without server-side route definitions.

Static File Middleware

ASP.NET Core's static file middleware serves built-in assets (CSS, JS, images) from the wwwroot directory:

  • JavaScript files have explicit Content-Type: application/javascript headers.
  • Static files are served before controller routing in the middleware pipeline.

Middleware Order

Routing → CORS → Response Caching → Authentication → Authorization → Rate Limiter → Endpoints

Blob Storage Interface

All file serving goes through IStorageContext, which abstracts the underlying storage provider:

Method Returns Purpose
GetFileAsync(path) FileManagerEntry File metadata (name, size, content type, dates)
GetStreamAsync(path) Stream File content as a readable stream
BlobExistsAsync(path) bool Check if a file exists
GetFilesAndDirectories(path) List<FileManagerEntry> Directory listing

File Metadata

Each file entry includes:

  • Name — File name
  • Path — Full storage path
  • Size — Size in bytes
  • ContentType — MIME type
  • Extension — File extension
  • Created / Modified — Timestamps (UTC)

CDN Integration

When a CDN is configured, content delivery operates through two layers:

Visitor Request Path

Visitor → CDN Edge → Publisher → Blob Storage (or cache)
         (cached)    (origin)

Cache Invalidation

  • CDN cache is purged on publish/unpublish operations.
  • Purge failures do not block publishing — they only affect cache freshness.
  • Bulk static page generation triggers a full CDN purge.
  • Supported providers: Cloudflare, Azure CDN/Front Door, CloudFront, Sucuri.

Cache Key Isolation

Cache keys are scoped per tenant:

  • ICacheKeyProvider.GenerateFileKey(hostname, path) — File cache keys.
  • ICacheKeyProvider.GenerateSpaCheckKey(articleUrl) — SPA detection cache keys.

This ensures multi-tenant deployments have isolated caches.

Multi-Tenancy

  • Blob storage paths are scoped to the current tenant.
  • Cache keys include the tenant hostname.
  • CDN configuration and purge operations are per-tenant.
  • Authentication checks use the tenant's settings.
  • PubControllerBase injects scoped services that resolve to the current tenant.

See Also