Angular HttpClient - Handle empty and non-empty responses

Question

Assuming we have http: HttpClient, I would like to provide a service call wrapper method as follows:

public async post<T>(url: string, body: any): Promise<T> {
    // do some stuff

    const response = await this.http.post<T>(url, body, this.options).toPromise();

    // do more stuff

    return response
}

This works as expected for any T except void. The behavior I was hoping for (and am still looking to implement) is to not return any value (Promise<void>) when the server returns no response. I'm now wondering what the best way to implement this is without having a different function for empty response bodies.

I assume there's no way to disambiguate based on the generic type? I tried looking for ways to do that, but it seems there's no way to do it, which makes sense given what TypeScript does and how it works. Fwiw, the type would be available at the call-site (as in, I would be calling that method as service.post<void>(...) in the case I expect an empty response body).

One thing I was wondering is if I could always make it return a string (responseType: "text") and then parse the JSON manually. Then I could check the status and response string, if they were 200 and "" respectively I would know that I can return undefined. If that was the right way to go (and I'm not sure that it is) there are a few questions I have:

Would manually parsing the JSON have a performance drawback?
What method should I use to parse it? What does the HttpClient use?
How would I make sure that error handling works the same as if it happened from within the HttpClient.post method? Ideally I wouldn't want it to deviate from the error mechanism inside of HttpClient.post.

Or is there another simple way that I'm missing to implement the desired method? Are any of my assumptions false?

Not related, but is there a reason for making this a Promise, instead of using just the observables you get? — AVJT82
– AVJT82, Commented Feb 9, 2019 at 13:38
I just like promises more. I'm mainly a C# programmer and async/await fit my mental model very well, I find it easier to think with them compared to observables. It's not set in stone and if it would somehow help with this I wouldn't mind changing it, but as you said it's probably unrelated to my issue. — Stjepan Bakrac
– Stjepan Bakrac, Commented Feb 9, 2019 at 13:42
have you found way around it? I am also stuck on this issue. — chintan adatiya
– chintan adatiya, Commented Mar 5, 2019 at 14:45
@chintanadatiya Only what I mentioned in the answer below. I don't know of another way to get what I wanted. — Stjepan Bakrac
– Stjepan Bakrac, Commented Mar 5, 2019 at 18:14

Stjepan Bakrac · Accepted Answer · 2019-02-09 18:54:26Z

5

As it turns out this is only an issue if the server returns 200. If the server returns the "no content" status 204 (which is appropriate for an empty response body) then post returns null. I would have preferred undefined to distinguish from an actual null JSON response (since null is a valid JSON token), but it is what it is, and what it is is good enough for me.

answered Feb 9, 2019 at 18:54

Stjepan Bakrac

1,16212 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

smnbbrv Over a year ago

This does not answer your own question, so it should not be posted as answer IMO

Stjepan Bakrac Over a year ago

I admit it may not sound obvious from the question, but the entire question revolved around http.post erroring on <void>. But it does not error if the server returns 204, which seems to be the intended way to use the API. It may not answer the question, but it makes the question irrelevant. What is the correct thing to do? Delete the question? Close it?

Collectives™ on Stack Overflow

Angular HttpClient - Handle empty and non-empty responses

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related