You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: map.rs
    path of file: ./repos/iroh/iroh-net/src/derp
    
    the code of the file until where you have to start completion: //! based on tailscale/tailcfg/derpmap.go

use std::{collections::BTreeMap, fmt, sync::Arc};

use anyhow::{ensure, Result};
use serde::{Deserialize, Serialize};

use crate::defaults::DEFAULT_DERP_STUN_
    
    pub fn default_from_node(url: DerpUrl, stun_port: u16) -> Self {
        let mut nodes = BTreeMap::new();
        nodes.insert(
            url.clone(),
            DerpNode {
                url,
                stun_only: false,
                stun_port,
            }
            .into(),
        );

        DerpMap {
            nodes: Arc::new(nodes),
        }
    }