Reqwest doesn't protect agains incorrect usage of HTTP verbs

[Pzixel]

Most of existing HTTP client implementation have safeguards against incorrect usage of HTTP verbs. For example, following JS code:

fetch('https://jsonplaceholder.typicode.com/posts/1', {
    method: 'GET',
    body: JSON.stringify({a: 1}),
}).then((response) => {
    console.log(response);
});

Raises an error: TypeError: Request with GET/HEAD method cannot have body.

Most of clients in other languages do this as well.

It makes sense if following Rust code was also producing an error:

use url::Url;

#[tokio::main]
async fn main() {
    let url = Url::parse("https://jsonplaceholder.typicode.com/posts/1").unwrap();
    let client = reqwest::Client::new();
    let res = client.get(url).json(&serde_json::json!({"a": 1})).send().await.unwrap().text().await.unwrap();
    println!("{}", res);
}

The specification is pretty much against allowing such code to be executed:

9.3.1. GET A client SHOULD NOT generate content in a GET request unless it is made directly to an origin server that has previously indicated, in or out of band, that such a request has a purpose and will be adequately supported. An origin server SHOULD NOT rely on private agreements to receive content, since participants in HTTP communication are often unaware of intermediaries along the request chain.

While it might be valuable to keep a backdoor for extremely rare cases where server violates HTTP semantic and requires such requests, I think it is worth making this an error by-default.

I can work on an implementation if overall idea is supported by crate maintainers.