E12062: constraint reference must extend SecurityGate or CORSPolicy

What went wrong

A 'constrain by' clause references a type that exists but does not extend SecurityGate or CORSPolicy. Constraint references must be concrete implementations of one of these two abstract functions.

SecurityGate is an abstract function that receives an HTTPContext and returns an enriched context (or unset to reject). CORSPolicy is an abstract function that receives an Origin string and returns a Boolean (allow/reject).

Worked examples

The [EXAMPLE] section below shows a service constrained by a plain function that extends neither SecurityGate nor CORSPolicy, then by an 'ApiGate' that is a SecurityGate.

Rationale

The constraint system is strongly typed. Only functions that implement the SecurityGate or CORSPolicy contract can be used as constraints. This ensures the router can call them with the correct arguments and interpret their return values correctly.

How to fix it

Ensure the constraint reference extends the correct base: a security gate is a function that 'is SecurityGate' (it takes the HTTPContext and returns the context it lets through, unset to refuse), and a CORS policy is a function that 'is CORSPolicy' (it takes the request's origin and returns a Boolean). A plain function with the right-looking parameters is neither.

See also

• Security posture required: E12050
• Constraint type not resolved: E12060
• Duplicate constraint role: E12064
• SecurityGate abstract function: ek9 -h SecurityGate
• CORSPolicy abstract function: ek9 -h CORSPolicy
• Compilable examples: ek9 -q 1294 (What types are valid in a constrain by clause?) ek9 -q 1293 (What happens when a constrain by reference cannot be re...) ek9 -q 1295 (Why does constrain by X and Y fail when both extend Sec...) ek9 -q 1292 (How does service security posture work with 'open' and ...)

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E12062: constraint reference must extend SecurityGate or CORSPolicy

#!ek9
defines module error.e12062.bad

  defines function

    NotAGate() as pure
      <- rtn as String: "not a security gate"

  defines service

    InvalidConstraint for :/api constrain by NotAGate
      health() as GET for :/status
        <- response as HTTPResponse: () with trait of HTTPResponse
          override status() as pure
            <- rtn as Integer: 200
          override content()
            <- rtn as Bytes: Bytes().withUtf8("ok")
          override contentType() as pure
            <- rtn as String: "text/plain"
          default operator ?

Fixed: Constrain by a function that is a SecurityGate

#!ek9
defines module error.e12062.good

  defines function

    ApiGate is SecurityGate
      -> context as HTTPContext
      <- rtn as HTTPContext: context

  defines service

    GatedService for :/api constrain by ApiGate

      health() as GET for :/status
        <- response as HTTPResponse: () with trait of HTTPResponse
          override status() as pure
            <- rtn as Integer: 200
          override content()
            <- rtn as Bytes: Bytes().withUtf8("ok")
          override contentType() as pure
            <- rtn as String: "text/plain"
          default operator ?

Questions and answers

These Q&A entries show E12062 and its fix:

• Q1294: What types are valid in a constrain by clause?