override the match function in createHandler class.

[mswjs]

override the match function in createHandler class.

[ingmothman]

WOW, thank for the quick response. I will upgrade and let you know.
Thanks.

[kettanaito]

Hello, @osmancode. That sounds like a great suggestion.

Technically, it should be possible to achieve this at the moment by using a wildcard ('*') to match all resources, and providing a header presence check:

import { composeMocks, rest } from 'msw'

const { start } = composeMocks(
  rest.get('*', (req, res, { json }) => {
    if (req.headers['X-Mock-Response']) {
      // In case the header is present, mock the response
      return res(json({ mocked: true }))
    }

    // Perform the original request otherwise
    return fetch(req)
  })
)

start()

I am not fully sure about the fetch() part, as the recommended way to get the original response. However, that's how it's achieved in the Mock Service Worker.

Implementation details

I think it would be suitable to adjust the call signature of the handler functions passed to composeMocks to be more generic, while those handlers grouped under the rest namespace would be a high-order functions with certain predicates built in (matching a fixed method and URL path). Referring to this interface:

https://github.com/open-draft/msw/blob/3bb93d7d53c7d8334f2b432a0ddf8384d2648af3/src/handlers/createHandler.ts#L32

1. Schema entry getter (handler) should be a function of request that returns Boolean (actual request match verdict) and executes a resolver function when the request matches. Generally, I see no reason for the schema entry to assume any kind of matching, which would allow to provide a custom handler exactly how you require.

type SchemaEntryGetter = (req: Request, handler: ResponseHandler) => Boolean

2. Standard rest namespace method then could be implemented as abstractions over the aforementioned generic schema entry getter function. Here's a basic schematics:

// rest.ts
export const get = (mask: Mask, handler: ResponseHandler): SchemaEntryGetter => {
  return (req) => {
    // each of the "rest[abc]" methods can be generated, as they follow the same
    // request method matching wrapper on top of a resolver execution.
    if (req.method === 'GET' && internalMatchMask(mask, req.url)) {
      resolver(...)
    }
  }
}

3. The usage of custom handlers would look roughly as follows:

import { SchemaEntryGetter, ResponseHandler, composeMocks } from 'msw'

const handleRequestGroup = (handler: ResponseHandler): SchemaEntryGetter => {
  return (req, res, context) => {
    if (req.headers['X-Mock-Response']) {
      handler(req, res, context)
    }
  }
}

const { start } = composeMocks(
  handleRequestGroup((req, res, { json }) => {
    res(json({ mocked: true })
  })
)

start()

[kettanaito]

I've added the support for this. Please see how to declare custom request handler.

Please update to [email protected] to have this support. Let me know if this solves the issue for you.

[kettanaito]

@osmancode, hi! Please, did those changes help you achieve what you wanted?