"iron::Modifier<Response> is not implemented" while trying to set content-type on response using iron and mime

Question

I am trying to run the examples from the book Programming Rust published by O'Reilly and I am stuck at making the following code compile successfully:

Cargo.toml

[package]
name = "gcd-online"
version = "0.1.0"
authors = ["Jignesh Gohel <abc@example.com>"]
edition = "2018"

[dependencies]
iron = "0.6.0"
mime = "0.3.12"
router = "0.6.0"
urlencoded = "0.6.0"

/src/main.rs

extern crate iron;
extern crate mime;

use iron::prelude::*;
use iron::status;

fn main() {
    println!("Serving on http://localhost:3000...");
    Iron::new(get_form).http("localhost:3000").unwrap();
}


fn get_form(_request: &mut Request) -> IronResult<Response> {
    let mut response = Response::new();

    response.set_mut(status::Ok);
    response.set_mut(mime::TEXT_HTML_UTF_8);
    response.set_mut(r#"
        <title>GCD Calculator</title>
        <form action="/gcd" method="post">
            <input type="text" name="n" />
            <input type="text" name="m" />
            <button type="submit">Compute GCD</button>
        </form>
    "#);

    Ok(response)
}

Output

   Compiling gcd-online v0.1.0 (~/oreilly-programming-rust-book-examples/chapter-1/gcd-online)                                                          
error[E0277]: the trait bound `mime::Mime: iron::modifier::Modifier<iron::Response>` is not satisfied                                                                           
  --> src/main.rs:17:14                                                                                                                                                         
   |                                                                                                                                                                            
17 |     response.set_mut(mime::TEXT_HTML_UTF_8);                                                                                                                               
   |              ^^^^^^^ the trait `iron::modifier::Modifier<iron::Response>` is not implemented for `mime::Mime`

My Cargo.toml uses latest version of dependencies, however book author uses following versions

[dependencies]
iron = "0.5.1"
mime = "0.2.3"
router = "0.5.1"
urlencoded = "0.5.0"

and as part of which author used following code

#[macro_use] extern crate mime;

fn get_form(_request: &mut Request) -> IronResult<Response> {
    let mut response = Response::new();

    response.set_mut(mime!(Text/Html; Charset=Utf8));

    Ok(response)
}

I think the difference in versions is what is causing the compilation error.

I tried to go through the docs of the iron and mime crates but I couldn't figure out how to get past this error.

Answer 1

As you've noticed, newest versions of mime and iron are not compatible with the example code from the book. The issue was raised on the official book's repository.

You could use the old mime crate, but in the long run it would be best to use mime from the iron crate as explained in the docs.

For iron 0.6.0 you can replace the faulty line:

response.set_mut(mime::TEXT_HTML_UTF_8);

or

response.set_mut(mime!(Text/Html; Charset=Utf8));

with one of the following:

response.headers.set(iron::headers::ContentType("text/html; charset=utf-8".parse::<iron::mime::Mime>().unwrap()));

or

response.headers.set(iron::headers::ContentType(
    iron::mime::Mime(
        iron::mime::TopLevel::Text,
        iron::mime::SubLevel::Html,
            vec![(iron::mime::Attr::Charset, iron::mime::Value::Utf8)])
    )
);