reqwest-rewire

reqwest-rewire is a lightweight wrapper around reqwest that transparently rewrites outgoing request URLs based on user-defined rules.

It is designed primarily for testing and local development, allowing you to redirect HTTP requests to mock servers without changing application code.

Installation

[dependencies]
reqwest-rewire = "0.2"

Motivation

In many applications, you want to:

• Use real APIs in production
• Redirect those same calls to mock servers in tests
• Avoid changing request code just to mock HTTP

reqwest-rewire solves this by acting as a rewiring layer in front of reqwest.

Core Concept

You define a set of redirect rules:

https://real-api.com/api/
→ http://localhost:3000/api-mock/

Any request matching the left-hand side is transparently rewritten before being sent.

The most specific rule always wins.

Usage

1. Use the TestableClient trait or reqwest_rewire::Client enum

Your application code depends on a trait, not a concrete client:

    use reqwest_rewire::TestableClient;

    fn fetch_data(client: Box<dyn TestableClient>) {
        client
            .get("https://real-api.com/api/users")
            .send()
            .unwrap();
    }

You can also use the Client enum, which has two states:

enum Client {
    ReqwestClient(reqwest::Client),
    TestClient(RewireClient),
}

It does implement the TestableClient trait, but it allows you to use it instead of dynamic object:

    use reqwest_rewire;

    fn fetch_data(client: reqwest_rewire::Client) { // No Box<dyn ...>
        client
            .get("https://real-api.com/api/users")
            .send()
            .unwrap();
    }

2. Use reqwest::Client in production

    let client = reqwest::Client::new();
    fetch_data(&client);

3. Use RewireClient in tests

    use std::collections::HashMap;
    use reqwest_rewire::RewireClient;

    let mut redirects = HashMap::new();
    redirects.insert(
        "https://real-api.com/api/".to_string(),
        "http://localhost:3000/api-mock/".to_string(),
    );

    let client = RewireClient::new(redirects);

    fetch_data(&client);

No application code changes required 🎉

Rewrite Behavior

• URLs are parsed using url::Url
• Rewrites match on:
  • scheme
  • host
  • path prefix
• The rule with the longest matching path is selected
• Query strings and fragments are preserved
• Invalid URLs fall back to the original request

Example

Request:
https://real-api.com/api/v1/users?id=42

Rule:
https://real-api.com/api/
→ http://localhost:3000/api-mock/

Result:
http://localhost:3000/api-mock/v1/users?id=42

Non-Goals

• HTTP mocking or response stubbing
• Network interception or proxying
• Wildcard URLs (* is not valid in URLs)

For full HTTP mocking, consider tools like wiremock, mockito, or httpmock.

Testing Philosophy

reqwest-rewire is intentionally minimal:

• It rewrites requests
• It does not alter responses
• It does not simulate servers

This makes it ideal as a composable building block in larger test setups.

API Stability

• The crate follows semantic versioning
• 0.x releases may introduce breaking changes
• 1.0 will guarantee API stability

License

Licensed under either of:

• Apache License, Version 2.0
• MIT License

You may choose either.

Contributing

Issues, ideas, and pull requests are welcome!
Please open an issue before making large changes.