net.peer.* vs net.host.*

[garthk]

lib/opentelemetry_plug.ex reads wrong to me:

    attributes = [{"http.target", conn.request_path},
                  {"http.host",  conn.host},
                  {"http.scheme",  conn.scheme},
                  {"http.user_agent", user_agent},
                  {"http.method", conn.method},
                  {"net.peer.ip", to_string(:inet_parse.ntoa(peer_ip))},
                  {"net.peer.port", adapter.peer_data.port},
                  {"net.peer.name", host},
                  {"net.transport", "IP.TCP"},
                  {"net.host.ip", to_string(:inet_parse.ntoa(conn.remote_ip))},
                  {"net.host.port", conn.port} | optional_attributes(conn)
                  # {"net.host.name", HostName}
                 ]

vs the semantic conventions spec:

Attribute name	Notes and examples
net.transport	Transport protocol used. See note below.
net.peer.ip	Remote address of the peer (dotted decimal for IPv4 or RFC5952 for IPv6)
net.peer.port	Remote port number as an integer. E.g., 80.
net.peer.name	Remote hostname or similar, see note below.
net.host.ip	Like net.peer.ip but for the host IP. Useful in case of a multi-IP host.
net.host.port	Like net.peer.port but for the host port.
net.host.name	Local hostname or similar, see note below.

… and the semantic conventions for HTTP spec, from which I lack the time to extract the right bit, and Plug.Conn:

remote_ip - the IP of the client, example: {151, 236, 219, 228}. This field is meant to be overwritten by plugs that understand e.g. the X-Forwarded-For header or HAProxy's PROXY protocol. It defaults to peer's IP

If conn.remote_ip has the apparent client IP address from X-Forwarded-For, that should go in http.client_ip, which you did by other means, not in net.host.ip. So there'll be some cleaning up in there.

[garthk]

I've raised elixir-plug/plug#948 to see if we can get the sock out of conn.adapter via official means rather than rummaging, matching the use of Plug.Conn.get_peer_data/1 in #4.

[garthk]

Aah, I get it now. "host" != "server". For spans sent by an HTTP client, the HTTP client is the host and the HTTP server is the peer. For spans sent by an HTTP server, the HTTP client is the peer and the HTTP server is the host.