OpenAPI validator middleware should throw a custom error

[mkurapov]

Context

While working on

• Standardize Open Payment errors rafiki#1905

in Rafiki, I discovered that the OpenAPI validator middleware uses the ctx.throw method directly when handling errors:

open-payments/packages/openapi/src/middleware.ts

Lines 29 to 38 in d365729

	} catch (err) {
	if (err instanceof Koa.HttpError) {
	throw err
	} else if (isValidationError(err)) {
	ctx.throw(err.status ?? 500, err.errors[0])
	} else {
	console.log('err=', err)
	ctx.throw(500)
	}
	}

If we want to use a custom error (like the planned OpenPaymentsServer error in Rafiki) this prevents us from writing a general error error handler at the beginning of the middleware chain, since this middleware will always throw ctx.throw(500) for something other than a Koa.HttpError (and have a busy console.error log as well, without control over it).

By throwing a custom error instead of a ctx.throw, we can directly determine whether the particular Koa error came from this validation middleware or not, allowing us to be more explicit in how we handle the error and how we log the contents of the error.

Todos

• Have the OpenAPI middleware throw a custom error (e.g. OpenAPIValidatorMiddlewareError)