aah Request Lifecycle

Incoming requests are handled by the server via routes. Each route describes an HTTP endpoint with a path, method, controller, and action. Each incoming request passes through a pre-defined list of steps, user-defined steps and optional server extension points.

It would be nice to have diagram to explain the Lifecycle. Later, will do my best.

Lifecycle

Lifecycle always reflects latest version flow.

  • Captures the request received time, used for server access log.
  • aah.Context is prepared for the request. i.e. parsing and creating ahttp.Request instance and ahttp.ResponseWriter instance.
  • Sets the Request ID header if enabled
  • OnRequest server extension point: Always called, the aah.Context object instance is passed via event data. aah.Context is decorated with SetURL and SetMethod methods. Calls to these methods will impact how the request is routed and can be used for rewrite rules.
    • Note: route is not evaluated at this point.
  • Route Lookup: Based on request path.
    • If it’s static file route then server process that request via http.ServeContent.
      • OnPreReply and OnAfterReply server extension points applicable to Static File delivery. does call .
    • If no route found then below one of the action performed based on request.
      • If Redirect Trailing Slash opportunity is found then server redirects that request to the new URL. It can be controlled via routes.conf.
      • It does HTTP auto OPTIONS. User defined OPTIONS take precedence over auto. It can be controlled via routes.conf.
      • It does HTTP auto 405 Method Not Allowed. It can be controlled via routes.conf.
      • Centralized Error Handler gets called with 404 status code.
    • Finally it skips to OnPreReply server extension point and writing response on the wire.
  • Route Found: aah.Context is updated with targeted controller and action information. Path Variables are parsed and available at this point via ctx.Req.
    • If controller or action is not found in the registry then
      • Centralized Error Handler gets called with 404 status code.
      • Flow skips to OnPreReply server extension point and writing response on the wire.
  • Parse Session Cookie if the session mode is stateful
  • Read and Parse Request
    • For GET method request parse Query parameters
    • For not GET method. Query parameters, Form, Multi-part based on content-type.
  • Anti-CSRF Protection - secret verification. Since v0.9
  • OnPreAuth server extension point. Since v0.7
  • Authenticate the incoming request. Since v0.7
  • Populates Authorization info into Subject. Since v0.7
  • Auto Check Authorization roles & permissions based on route authz configuration upcoming
  • OnPostAuth server extension point. Since v0.7
  • Validate request parameter values upcoming
  • User-defined middleware(s) execution (basically before m.Next(ctx) call).
  • Controller interceptor Before is called if exists.
  • Controller-Action interceptor Before<ActionName> is called if exists.
  • Targeted controller Action is called.
    • Auto Parse and Bind, know more
      • It sanitizes the request parameter to prevent XSS attacks, it’s highly recommended to use Since v0.8
  • Controller-Action interceptor After<ActionName> is called if exists.
  • Controller interceptor After is called if exists.
  • Controller interceptor Finally is called if exists. It is always executed.
  • Note: If any panic happens around controller action interceptor Panic is called on that controller.
  • User-defined middleware(s) execution (basically after m.Next(ctx) call).
  • If Reply is an Error type then Centralized Error Handler is called. Since v0.8
  • If the Response is already sent via ctx.Res and ctx.Reply().Done() is called then framework does not intervene with response, so request completes here.
  • Write Response Header(s) and set Cookies (session cookie, etc.)
  • If it’s a Redirect reply then framework redirects it.
  • Determines response content-type if it’s not set in the reply builder.
  • If it’s HTML content-type then
    • Finds a view based on namespace, controller & action along with master layout if it’s not overridden in the reply builder.
    • Populates view args with framework provided values.
  • Renders reply body based on content-type, if any errors it logs and sends meaningful error message.
  • If HTTP client supports the Gzip compression and it’s enabled in the config then Gzip response writer is used automatically. You have option to disable Gzip for particular via reply builder.
  • OnPreReply server extension point: Always called, you’re allowed to modified ctx.Reply() it will reflect on response. Except when-
    • ctx.Reply().Done() was called, refer godoc for more info.
  • Writing reply on the wire-
    • Response Status - default is 200 OK, if not provided.
    • Response body bytes.
  • OnAfterReply server extension point: Always called. Response is already written on the wire. Nothing we can do about the response, however context has a valuable information such as response bytes size, response status code, etc. Except when-
    • ctx.Reply().Done() was called, refer godoc for more info.
    • ctx.Reply().Redirect(...) was called.
  • Writes data to server access log, if enabled. Since v0.7
  • If its Multipart request with files, it does cleanup.

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