turn_rs/processor/
binding.rs

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use super::{Context, Response};
use crate::{StunClass, SOFTWARE};

use bytes::BytesMut;
use faster_stun::attribute::*;
use faster_stun::*;

/// process binding request
///
/// [rfc8489](https://tools.ietf.org/html/rfc8489)
///
/// In the Binding request/response transaction, a Binding request is
/// sent from a STUN client to a STUN server.  When the Binding request
/// arrives at the STUN server, it may have passed through one or more
/// NATs between the STUN client and the STUN server (in Figure 1, there
/// are two such NATs).  As the Binding request message passes through a
/// NAT, the NAT will modify the source transport address (that is, the
/// source IP address and the source port) of the packet.  As a result,
/// the source transport address of the request received by the server
/// will be the public IP address and port created by the NAT closest to
/// the server.  This is called a "reflexive transport address".  The
/// STUN server copies that source transport address into an XOR-MAPPED-
/// ADDRESS attribute in the STUN Binding response and sends the Binding
/// response back to the STUN client.  As this packet passes back through
/// a NAT, the NAT will modify the destination transport address in the
/// IP header, but the transport address in the XOR-MAPPED-ADDRESS
/// attribute within the body of the STUN response will remain untouched.
/// In this way, the client can learn its reflexive transport address
/// allocated by the outermost NAT with respect to the STUN server.
pub fn process<'a>(
    ctx: Context,
    payload: MessageReader,
    bytes: &'a mut BytesMut,
) -> Result<Option<Response<'a>>, StunError> {
    let method = Method::Binding(Kind::Response);
    let mut pack = MessageWriter::extend(method, &payload, bytes);
    pack.append::<XorMappedAddress>(ctx.addr);
    pack.append::<MappedAddress>(ctx.addr);
    pack.append::<ResponseOrigin>(*ctx.env.external.as_ref());
    pack.append::<Software>(SOFTWARE);
    pack.flush(None)?;
    ctx.env.observer.binding(&ctx.addr);
    Ok(Some(Response::new(bytes, StunClass::Msg, None, None)))
}