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The message-of-the-day (MOTD) extension is a lightweight, one-way communication channel from server to client. During the Wisp v2 handshake the server encodes an arbitrary UTF-8 string into the extension payload. After the mux is created, the client can read that string from the negotiated extension list. The extension carries no client payload; only the server sends data.

​
Extension details

FieldValue
Extension ID0x04
Extension structMotdProtocolExtension
Builder enumMotdProtocolExtensionBuilder
Feature gatenone (always available)
DirectionServer → Client only

​
Server setup

Use the Server variant of MotdProtocolExtensionBuilder and pass the MOTD string. 
use wisp_mux::extensions::{
    motd::MotdProtocolExtensionBuilder,
    AnyProtocolExtensionBuilder,
};

let motd = "Welcome to my Wisp server v1.2.3".to_string();

let extensions: Vec<AnyProtocolExtensionBuilder> = vec![
    AnyProtocolExtensionBuilder::new(MotdProtocolExtensionBuilder::Server(motd)),
];
MotdProtocolExtensionBuilder::new_server(motd) is an equivalent constructor that may be more readable in longer builder chains.

​
Client setup

Use the Client variant to tell the library to capture the MOTD string during the handshake. No credentials or configuration are needed. 
use wisp_mux::extensions::{
    motd::MotdProtocolExtensionBuilder,
    AnyProtocolExtensionBuilder,
};

let extensions: Vec<AnyProtocolExtensionBuilder> = vec![
    AnyProtocolExtensionBuilder::new(MotdProtocolExtensionBuilder::Client),
];

​
Reading the MOTD after connection

After ClientMux::new completes, call mux.get_extensions().find_extension::<MotdProtocolExtension>(). The motd field on the returned struct contains the server’s message. On the client side motd is populated from the wire; on the server side it remains an empty string. 
use wisp_mux::extensions::{
    ProtocolExtensionListExt,
    motd::MotdProtocolExtension,
};

let motd_text = mux
    .get_extensions()
    .find_extension::<MotdProtocolExtension>()
    .map(|x| x.motd.clone());

println!("Server MOTD: {:?}", motd_text);

​
Full example (from simple-wisp-client)

The snippet below is adapted from simple-wisp-client and shows how MOTD parsing integrates with a full connection setup that may also enable UDP and authentication extensions. 
use wisp_mux::{
    extensions::{
        motd::{MotdProtocolExtension, MotdProtocolExtensionBuilder},
        AnyProtocolExtensionBuilder, ProtocolExtensionListExt,
    },
    ClientMux, WispV2Handshake,
};

let mut extensions: Vec<AnyProtocolExtensionBuilder> = Vec::new();

// Enable MOTD capture when --motd flag is set
if opts.motd {
    extensions.push(AnyProtocolExtensionBuilder::new(
        MotdProtocolExtensionBuilder::Client,
    ));
}

let (mux, fut) = ClientMux::new(rx, tx, Some(WispV2Handshake::new(extensions)))
    .await?
    .with_required_extensions(&[]) // MOTD is informational — don't require it
    .await?;

// Read the MOTD; returns None if the server did not send one
let motd_extension = mux
    .get_extensions()
    .find_extension::<MotdProtocolExtension>();

println!(
    "connected, was_downgraded={}, extensions={:?}, motd={:?}",
    mux.was_downgraded(),
    mux.get_extensions()
        .iter()
        .map(|x| x.get_id())
        .collect::<Vec<_>>(),
    motd_extension.map(|x| x.motd.clone()),
);

​
epoxy-server MOTD configuration

When using epoxy-server, the MOTD is set to the server’s version string by default. You can override it via the motd_extension key in the server configuration file. Set motd_extension to an empty string to disable the extension entirely.
The MOTD extension is purely informational. It is safe to include MotdProtocolExtensionBuilder::Client on every connection without calling with_required_extensions for its ID — the library will simply not populate motd if the server chose not to send it.

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