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GenericInterceptor type

An interceptor function to be invoked in a chain for the given context. It serves as the base interface for various types of interceptors, such as method invocation interceptor or request/response processing interceptor.


export type GenericInterceptor<C extends Context = Context> = (context: C, next: Next) => ValueOrPromise<NonVoid>;

References: Context, Next, ValueOrPromise, NonVoid


We choose NonVoid as the return type to avoid possible bugs that an interceptor forgets to return the value from next(). For example, the code below will fail to compile.

const myInterceptor: Interceptor = async (ctx, next) {
  // preprocessing
  // ...

  // There is a subtle bug that the result from `next()` is not further
  // returned back to the upstream interceptors
  const result = await next();

  // postprocessing
  // ...
  // We must have `return ...` here
  // either return `result` or another value if the interceptor decides to
  // have its own response