Reqwest request not getting my reqwest::Client's default headers

2 min read 06-10-2024

Reqwest request not getting my reqwest::Client's default headers

Why Your Reqwest Requests Aren't Getting Your Default Headers

Ever find yourself scratching your head when your Reqwest Client's default headers don't seem to be applied to every request? It's a common frustration, especially when you're expecting consistency in your API calls. Let's break down why this might happen and how to ensure your headers stick.

The Scenario: Missing Default Headers

Imagine this code snippet:

use reqwest::Client;

#[tokio::main]
async fn main() {
    let client = Client::new();
    let mut headers = reqwest::header::HeaderMap::new();
    headers.insert(
        reqwest::header::AUTHORIZATION,
        reqwest::header::HeaderValue::from_static("Bearer my-token"),
    );
    client.default_headers_mut().extend(headers);

    // You expect this request to include the Authorization header
    let response = client.get("https://api.example.com/users").send().await;
    
    // But it doesn't!
    println!("{:?}", response.unwrap().headers()); 
}

You've meticulously set up your Client with a default Authorization header, but when you make a request, it's missing. What's going on?

The Explanation: Mutable vs. Immutable

The culprit is the way reqwest::Client handles its default headers. While you can modify them using default_headers_mut(), this is a temporary change. When you create a new request, the Client clones its internal state, including the headers, making them immutable for that specific request.

This behavior is intended to prevent accidental modification of headers across requests. Think of it as a way to ensure each request maintains its own distinct identity.

The Solution: Persistence Through Methods

So, how do you ensure your default headers are always present? The key is to leverage methods that modify the request itself:

use reqwest::Client;

#[tokio::main]
async fn main() {
    let client = Client::new();
    let mut headers = reqwest::header::HeaderMap::new();
    headers.insert(
        reqwest::header::AUTHORIZATION,
        reqwest::header::HeaderValue::from_static("Bearer my-token"),
    );
    client.default_headers_mut().extend(headers);

    // Modify the request directly
    let response = client
        .get("https://api.example.com/users")
        .headers(headers.clone())
        .send()
        .await;
    
    // Now the headers are present!
    println!("{:?}", response.unwrap().headers());
}

By using the headers method, you explicitly add the headers to the request itself, overriding any cloned defaults and ensuring your Authorization header is included.

Additional Tips

Predefined Headers: Reqwest offers convenience methods like bearer_auth for common scenarios:

let response = client
     .get("https://api.example.com/users")
     .bearer_auth("my-token")
     .send()
     .await;

Request Builder Pattern: The Client methods like get, post, etc. return a RequestBuilder allowing you to chain multiple modifications (including headers) before sending.

Conclusion

Understanding the mutable and immutable nature of Reqwest's headers is essential for consistent API interactions. By leveraging request-specific modification methods like headers or convenience methods like bearer_auth, you can reliably include your default headers in every request.

Happy coding!