Into types

[yoshuawuyts]

This makes creating Request and Response easier by taking auto-converting arguments:

Example

let mut res = Response::new(200)?;
let mut res = Response::new(StatusCode::NotFound)?;

let url = Url::parse("https://example.com")?;
let mut req = Request::new(Method::Get, url)?;

let url = Url::parse("https://example.com")?;
let mut req = Request::new("GET", url)?;

Caveats

Unfortunately TryFrom is not yet implemented for url, so I've filed servo/rust-url#568. A workaround for this would be to implement this using new types so we can implement the trait ourselves. This would then enable us to write:

let mut res = Response::new(200)?;
let mut req = Request::new("GET", "https://example.com")?;

[rylev]

Hmmm it feels weird that an operation that you know will not fail returns a Result. Response::new(StatusCode::NotFound) will not fail but because of new being able to take arbitrary u16s it now must return a Result. This makes sense but is strange. Would the following work and be acceptable?

Response::new(404.try_into()?);

[yoshuawuyts]

@rylev heh, I mean it could work of course, but I'd like us to try the other version first. The reason why I'm going down this path is because I'm feeling quite inspired by how Rust does handles sockets. If you think of it it's extremely flexible but also ergonomic. The following are all valid:

TcpStream::connect("127.0.0.1:80")?;
TcpStream::connect("localhost:80")?;
TcpStream::connect(("127.0.0.1", 80))?;
TcpStream::connect((Ipv4Addr::LOCALHOST, 80))?;
TcpStream::connect(["127.0.0.1:80", "127.0.0.1:81", "127.0.0.1:82"])?;
TcpStream::connect(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1))?;
TcpStream::connect(Ipv4Addr::new(127, 0, 0, 1))?;

And all of the values passed in can in turn be constructed from other values. I've got a hunch that if we can provide flexibility at this API layer and propagate it, people will come to appreciate it quite a bit. Of course it's not certain, but I'd like for us to try if possible.

[rylev]

@yoshuawuyts and I have decided to close this PR because it's offering a bit too high level of an API that would be more appropriate for higher level crates.