Why must a CONTEXT-bound service parameter be typed HTTPContext in EK9?

← Web Services · Ref: Q1329

The CONTEXT qualifier gives a service operation access to the request context (authenticated principal, security state, connection metadata), so the bound parameter MUST be typed HTTPContext. Binding :=: CONTEXT to a String (or any other type) triggers E07791 because the framework supplies a context object, not a parsed value.

CORRECT PATTERN

  info() as GET for :/data
    -> ctx as HTTPContext :=: CONTEXT

INCORRECT PATTERN

  info() as GET for :/data
    -> ctx as String :=: CONTEXT

Do not confuse CONTENT with CONTEXT. CONTENT binds the request body, which IS a String; CONTEXT binds request metadata, which is an HTTPContext. For individual request values use the specific access qualifiers (:=: QUERY, :=: PATH).

See Q202 for parameter binding. See Q868 for parameter type rules.

Example

defines module qa.webdeep.service.context.binding

  defines constant

    JSON_RESPONSE <- "application/json"

  defines service

    <?-
      Service using CONTEXT binding correctly: the parameter is typed
      HTTPContext, which is what the framework supplies for :=: CONTEXT.
    -?>
    InfoService :/info open

      info() as GET for :/data
        ->
          ctx as HTTPContext :=: CONTEXT
        <- response as HTTPResponse: (capturedCtx: ctx) with trait HTTPResponse
          override content()
            <- rtn as String: `{"hasContext": ${capturedCtx?}}`
          override status() as pure
            <- rtn as Integer: 200
          override contentType() as pure
            <- rtn as String: JSON_RESPONSE
          override cacheControl() as pure
            <- rtn as String: "no-cache"
          override contentLanguage() as pure
            <- rtn as String: "en"
          default operator ?

  defines application

    InfoApp
      register InfoService()

  defines program

    ContextBindingDemo()
      stdout <- Stdout()
      stdout.println("CONTEXT binds an HTTPContext (request metadata).")
      stdout.println("CONTENT binds a String (the request body).")

Common mistakes

E07791 — The CONTEXT qualifier supplies the request context object (principal, security state, connection metadata), so the parameter must be typed HTTPContext. Binding :=: CONTEXT to a String triggers E07791. CONTENT binds the body (a String); CONTEXT binds metadata (an HTTPContext) — do not confuse them. See ek9 -h E07791 for details.

Incorrect:

        -> ctx as String :=: CONTEXT

Correct:

->
          ctx as HTTPContext :=: CONTEXT

Coming from another language?

Java Spring: SecurityContextHolder / Principal injected as method args, validated only at runtime. C# ASP.NET: HttpContext available ambiently, no compile-time type checking of binding. Go: context.Context passed manually with no framework guard. EK9: the compiler enforces at compile time that a CONTEXT-bound parameter is exactly HTTPContext, eliminating mismatched-binding bugs before the service runs.

Keywords: HTTPContext, binding, service, E07791, CONTEXT, request, type, CONTENT