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API Config

It's frequently useful to have a way to store and access state in our handlers. For example, we might want to keep track of the number of requests we've received, or we may want to pass around credentials to an API.

Assignment

The product managers at Chirpy want to know how many requests are being made to serve our homepage - in essence, they want to know how many people are viewing the site!

They have asked for a simple HTTP endpoint they can hit to get the number of requests that have been processed. It will return the count as plain text in the response body.

For now, they just want the number of requests that have been processed since the last time the server was started, we don't need to worry about saving the data between restarts.

Steps

Create a type in src/config.ts that will hold any stateful, in-memory data we'll need to keep track of. In our case, we just need to keep track of the number of requests we've received.

type APIConfig = {
  fileserverHits: number;
};

Create a config object in src/config.ts that will hold the stateful data. Import this config wherever you need to access or modify the state.

Use .js extensions when importing files. We're using a bare-bones setup without a bundler, so Node can't import .ts. For example: import './config.js'.

Next, write a new middleware that increments fileserverHits every time it's called.

function middlewareMetricsInc(req: Request, res: Response, next: NextFunction) {
  // ...
}

Where Gophers have to worry about atomicity and multiple goroutines accessing a single object, JavaScript enjoyers get a perk from JavaScript being single-threaded.

Register that handler in the express app on the /app path. Make sure the middleware runs before serving the files.
Create a new handler that writes the number of requests that have been counted as plain text in this format to the HTTP response:

Hits: x

Where x is the number of requests that have been processed. Just import the same config object and access the fileserverHits property.

Register that handler in the express app on the /metrics path.
Finally, create and register a handler on the /reset path that, when hit, will reset your fileserverHits back to 0.

It should follow the same design as the previous handlers.

Run and submit the CLI tests.