actix-web/guide/src/qs_13.md

# HTTP/2.0

Actix web automatically upgrades connections to *HTTP/2.0* if possible.

## Negotiation

*HTTP/2.0* protocol over tls without prior knowledge requires
[tls alpn](https://tools.ietf.org/html/rfc7301).

> Currently, only `rust-openssl` has support.

`alpn` negotiation requires enabling the feature. When enabled, `HttpServer` provides the
[serve_tls](../actix_web/struct.HttpServer.html#method.serve_tls) method.

```toml
[dependencies]
actix-web = { version = "0.3.3", features=["alpn"] }
openssl = { version="0.10", features = ["v110"] }
```

```rust,ignore
use std::fs::File;
use actix_web::*;
use openssl::ssl::{SslMethod, SslAcceptor, SslFiletype};

fn main() {
    // load ssl keys
    let mut builder = SslAcceptor::mozilla_intermediate(SslMethod::tls()).unwrap();
    builder.set_private_key_file("key.pem", SslFiletype::PEM).unwrap();
    builder.set_certificate_chain_file("cert.pem").unwrap();

    HttpServer::new(
        || App::new()
            .resource("/index.html", |r| r.f(index)))
        .bind("127.0.0.1:8080").unwrap();
        .serve_ssl(builder).unwrap();
}
```

Upgrades to *HTTP/2.0* schema described in
[rfc section 3.2](https://http2.github.io/http2-spec/#rfc.section.3.2) is not supported.
Starting *HTTP/2* with prior knowledge is supported for both clear text connection
and tls connection. [rfc section 3.4](https://http2.github.io/http2-spec/#rfc.section.3.4)

> Check out [examples/tls](https://github.com/actix/actix-web/tree/master/examples/tls)
> for a concrete example.