reqwest-chain

Apply custom criteria to any reqwest response, deciding when and how to retry.

reqwest-chain builds on reqwest-middleware, to allow you to focus on your core logic without the boilerplate.

Use case

This crate is a more general framework than reqwest-retry. It allows inspection of:

• The result of the previous request
• The state of the retry chain
• The global state of your middleware

Based on this information, it allows updating any aspect of the next request.

If all you need is a simple retry, you should use reqwest-retry.

Getting started

See the tests directory for several examples.

You should implement Chainer for your middleware struct. This uses the chain method to make a decision after each request respones:

• If another request is required, update the previous request to form the next request in the chain, and return Ok(None).
• If the response is ready, return it inside Ok(Some(response)).
• If an error occurs and you cannot continue, return Err(error).

Below is the initial use case; refresh some authorization credential on request failure.

use reqwest::{header::{AUTHORIZATION, HeaderValue}, StatusCode};
use reqwest_chain::{Chainer, ChainMiddleware};
use reqwest_middleware::{ClientBuilder, ClientWithMiddleware, Error};

// Mimic some external function that returns a valid token.
fn fetch_token() -> String {
    "valid-token".to_string()
}

struct FetchTokenMiddleware;

#[async_trait::async_trait]
impl Chainer for FetchTokenMiddleware {
    // We don't need it here, but you can choose to keep track of state between
    // chained retries.
    type State = ();

    async fn chain(
        &self,
        result: Result<reqwest::Response, Error>,
        _state: &mut Self::State,
        request: &mut reqwest::Request,
    ) -> Result<Option<reqwest::Response>, Error> {
        let response = result?;
        if response.status() != StatusCode::UNAUTHORIZED {
            return Ok(Some(response))
        };
        request.headers_mut().insert(
            AUTHORIZATION,
            HeaderValue::from_str(&format!("Bearer {}", fetch_token())).expect("invalid header value"),
        );
        Ok(None)
    }
}

async fn run() {
    let client = ClientBuilder::new(reqwest::Client::new())
        .with(ChainMiddleware::new(FetchTokenMiddleware))
        .build();

    client
        .get("https://example.org")
        // If this request fails, this will be automatically retried with an
        // updated header value.
        .header(AUTHORIZATION, "Bearer expired-token")
        .send()
        .await
        .unwrap();
}

Thanks

Many thanks to the prior work in this area, namely:

• reqwest-middleware for the underlying framework
• reqwest-retry for inspiration