Request Interceptors (can make pr)

[nhtyy]

Coming from Axios, when sending http requests that require some type of header computed at runtime the interceptors can be useful

for instance an auth header that includes the current timestamp

while you can add headers on a RequestBuilder, its kind of difficult to extract information from the actual request, mostly because the fields/useful fns are private, and nothing implements the copy trait

for context heres an example of something i need to do

X-HMAC is defined as the time current unix timestamp, + path + (if applicable the JSON string of) body
and
X-TIMESTAMP is just the timestamp

while i could do

async fn call_api(url: String, params:(String, String)) {
     // gather all information for header here
     let hmac = ....
     Client.get(url, &["set"]).query(params).headers(("X_HMAC", hmac)).headers(("X-TIMESTAMP", timestamp)).send().await;
}

instead of doing all this work before each call instead im just doing a request builder doing a .build() to get the request and extracting the data from the request and computing the headers

/// (timestamp, hmac)
fn req_headers(builder: reqwest::RequestBuilder) -> (String, String) {
    let req = builder.build()

    // extract data and compute hmac

  (timestamp, hmac)
}

async fn call_api(url: String, params:(String, String)) {
     let (timestamp, hmac) = req_headers(Client.get(url, &["set"]).query(params).build());
     Client.get(url, &["set"]).query(params).headers(("X_HMAC", hmac)).headers(("X-TIMESTAMP", timestamp)).send().await;
}

so im left with a request object (which contains all the information i need), but i cant go back into a builder because the fields and the new function is private

idea: make these fields and functions public, and add an interceptor field to a RequestBuilder, that gets called in .send()

pub struct RequestBuilder {
    pub client: Client,
    pub request: crate::Result<Request>,
    pub interceptor: Option<fn(RequestBuilder) -> RequestBuilder>
}

by making the Request field public and implementing clone, I can extract the info and add the headers on multiple routes with a single function defintion

this behaviour should be specific to the Client instance (ie interceptors are defined when the client is instantiated)

[nhtyy]

https://axios-http.com/docs/interceptors

[nhtyy]

#1745

[nhtyy]

started initial PR, while async impl can work, it needs to be reflected across blocking & wasm

[ducaale]

@nuhhtyy While reqwest doesn't support middleware/interceptor, you can use the reqwest_middleware crate or even implement your own solution. Either way, I think you should definitely check this great post on middlewares and reqwest.