Display implementation for Error is unergonomic

[netvl]

I found that there is no simple way to get a detailed message of an error without direct matching on Error variants, or without using Debug, because the Display impl for Error ignores the message:

impl fmt::Display for Error {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        write!(fmt, "HTTP/2 Error: {}", self.description())
    }
}

impl StdError for Error {
    fn description(&self) -> &str {
        match *self {
            ...
            Error::Other(_) => "An unknown error",
        }
    }
    ....
}

This interferes with generic error handling using libraries like failure - you cannot easily present a generic error to the user if it contains httpbis::error::Error. For example, suppose I have code like this (using rust-grpc):

fn start_server(config: Config) -> Result<(), failure::Error> {
    let mut server_builder = grpc::ServerBuilder::new_plain();
    server_builder.http.set_addr(&config.address).context("Failed to set address")?;
    ...
}

set_addr returns httpbis::error::Error, and it may fail if e.g. hostname in the address resolves to many addresses. If I use this code and I try to print the error chain when the address is incorrect, I get this:

% ./target/debug/iprlist server
[E] [iprlist] Failed to set address
[E] [iprlist]   HTTP/2 Error: An unknown error

which is completely opaque and user-unfriendly. And there is no simple way to show a more detailed error message, because the httpbis error is wrapped into failure::Context and failure::Error, and it would require downcasting and matching on all httpbis::error::Error enum variants to get a proper error message. Moreover, as far as I can see, this is not limited to the Error::Other variant - variants like Error::IoError are also displayed without any details.

In my opinion, the Display impl should display the underlying error, if there is any, instead of forwarding to description().