fips/src/config/transport.rs

//! Transport configuration types.
//!
//! Generic transport instance handling (single vs. named) and
//! transport-specific configuration structs.

use std::collections::HashMap;

use serde::{Deserialize, Serialize};

/// Default UDP bind address.
const DEFAULT_UDP_BIND_ADDR: &str = "0.0.0.0:4000";

/// Default UDP MTU (IPv6 minimum).
const DEFAULT_UDP_MTU: u16 = 1280;

/// Default UDP receive buffer size (2 MB).
const DEFAULT_UDP_RECV_BUF: usize = 2 * 1024 * 1024;

/// Default UDP send buffer size (2 MB).
const DEFAULT_UDP_SEND_BUF: usize = 2 * 1024 * 1024;

/// UDP transport instance configuration.
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct UdpConfig {
    /// Bind address (`bind_addr`). Defaults to "0.0.0.0:4000".
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub bind_addr: Option<String>,

    /// UDP MTU (`mtu`). Defaults to 1280 (IPv6 minimum).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub mtu: Option<u16>,

    /// UDP receive buffer size in bytes (`recv_buf_size`). Defaults to 2 MB.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub recv_buf_size: Option<usize>,

    /// UDP send buffer size in bytes (`send_buf_size`). Defaults to 2 MB.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub send_buf_size: Option<usize>,
}

impl UdpConfig {
    /// Get the bind address, using default if not configured.
    pub fn bind_addr(&self) -> &str {
        self.bind_addr.as_deref().unwrap_or(DEFAULT_UDP_BIND_ADDR)
    }

    /// Get the UDP MTU, using default if not configured.
    pub fn mtu(&self) -> u16 {
        self.mtu.unwrap_or(DEFAULT_UDP_MTU)
    }

    /// Get the receive buffer size, using default if not configured.
    pub fn recv_buf_size(&self) -> usize {
        self.recv_buf_size.unwrap_or(DEFAULT_UDP_RECV_BUF)
    }

    /// Get the send buffer size, using default if not configured.
    pub fn send_buf_size(&self) -> usize {
        self.send_buf_size.unwrap_or(DEFAULT_UDP_SEND_BUF)
    }
}

/// Transport instances - either a single config or named instances.
///
/// Allows both simple single-instance config:
/// ```yaml
/// transports:
///   udp:
///     bind_addr: "0.0.0.0:4000"
/// ```
///
/// And multiple named instances:
/// ```yaml
/// transports:
///   udp:
///     main:
///       bind_addr: "0.0.0.0:4000"
///     backup:
///       bind_addr: "192.168.1.100:4001"
/// ```
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(untagged)]
pub enum TransportInstances<T> {
    /// Single unnamed instance (config fields directly under transport type).
    Single(T),
    /// Multiple named instances.
    Named(HashMap<String, T>),
}

impl<T> TransportInstances<T> {
    /// Get the number of instances.
    pub fn len(&self) -> usize {
        match self {
            TransportInstances::Single(_) => 1,
            TransportInstances::Named(map) => map.len(),
        }
    }

    /// Check if there are no instances.
    pub fn is_empty(&self) -> bool {
        match self {
            TransportInstances::Single(_) => false,
            TransportInstances::Named(map) => map.is_empty(),
        }
    }

    /// Iterate over all instances as (name, config) pairs.
    ///
    /// Single instances have `None` as the name.
    /// Named instances have `Some(name)`.
    pub fn iter(&self) -> impl Iterator<Item = (Option<&str>, &T)> {
        match self {
            TransportInstances::Single(config) => {
                vec![(None, config)].into_iter()
            }
            TransportInstances::Named(map) => {
                map.iter()
                    .map(|(k, v)| (Some(k.as_str()), v))
                    .collect::<Vec<_>>()
                    .into_iter()
            }
        }
    }
}

impl<T> Default for TransportInstances<T> {
    fn default() -> Self {
        TransportInstances::Named(HashMap::new())
    }
}

/// Transports configuration section.
///
/// Each transport type can have either a single instance (config directly
/// under the type name) or multiple named instances.
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct TransportsConfig {
    /// UDP transport instances.
    #[serde(default, skip_serializing_if = "is_transport_empty")]
    pub udp: TransportInstances<UdpConfig>,

    // Future transport types:
    // #[serde(default, skip_serializing_if = "is_transport_empty")]
    // pub tcp: TransportInstances<TcpConfig>,
    //
    // #[serde(default, skip_serializing_if = "is_transport_empty")]
    // pub tor: TransportInstances<TorConfig>,
}

/// Helper for skip_serializing_if on TransportInstances.
fn is_transport_empty<T>(instances: &TransportInstances<T>) -> bool {
    instances.is_empty()
}

impl TransportsConfig {
    /// Check if any transports are configured.
    pub fn is_empty(&self) -> bool {
        self.udp.is_empty()
        // && self.tcp.is_empty()
        // && self.tor.is_empty()
    }

    /// Merge another TransportsConfig into this one.
    ///
    /// Non-empty transport sections from `other` replace those in `self`.
    pub fn merge(&mut self, other: TransportsConfig) {
        if !other.udp.is_empty() {
            self.udp = other.udp;
        }
        // Future: same for tcp, tor, etc.
    }
}