Switch to reqwest for proxy support

[gregjopa]

This PR changes the http library from attohttpc to reqwest for proxy support to resolve #798.

The reqwest library supports proxies by default and can be set using environment variables. Ex:

export https_proxy=http://proxy.giantcorp.com:8080/
# uses the proxy
volta install npm@latest

[gregjopa]

I struggled with this code here. The goal is to make a blocking request and get both the response body and also the response headers which is needed lower in the file. Let me know if there's a better approach.

[charlespierce]

Yeah, the lack of a way to destructure the Response makes this tricky. I think the easiest approach might be to determine the expires string before reading the data with something like:

let expires = if let Ok(expires_header) = response.headers().decode::<Expires>() {
    expires_header.to_string()
} else {
    let expiry_date = SystemTime::now() + Duration::from_secs(max_age(&response).into());
    HttpDate::from(expiry_date).to_string()
};

Then we can use:

let response_text = response.text().with_context(registry_fetch_error("Node", url))?;

Here, and finally do write!(expiry_file, "{}", expires).with_context(...) at the end of the file. So we calculate everything we need from the response first, then consume it to get the raw text, and then use the pre-calculated bit later on when we need it.

[charlespierce]

Thanks for this @gregjopa! I'll take a look later today!

[charlespierce]

This is great @gregjopa, thanks! A couple of comments on making sure to preserve the existing error behavior and a slightly modified approach to the destructuring problem you noted in node/resolve.rs

[charlespierce]

Yeah, the lack of a way to destructure the Response makes this tricky. I think the easiest approach might be to determine the expires string before reading the data with something like:

let expires = if let Ok(expires_header) = response.headers().decode::<Expires>() {
    expires_header.to_string()
} else {
    let expiry_date = SystemTime::now() + Duration::from_secs(max_age(&response).into());
    HttpDate::from(expiry_date).to_string()
};

Then we can use:

let response_text = response.text().with_context(registry_fetch_error("Node", url))?;

Here, and finally do write!(expiry_file, "{}", expires).with_context(...) at the end of the file. So we calculate everything we need from the response first, then consume it to get the raw text, and then use the pre-calculated bit later on when we need it.

[gregjopa]

Thanks for the feedback @charlespierce! Your detailed comments are helping me learn Rust 😄 I think I was able to address everything. Please have another look.

[charlespierce]

This looks great, thanks @gregjopa!

While I'm sad to lose the binary-size improvements from using attohttpc, I don't find any significant difference in the startup time for the hot-path shims, so it doesn't appear to impact the performance at all.