do smarter IP deserialization

src/app/widgets.rs

@@ -147,7 +147,7 @@ impl Widget for &mut App {
                     buf,
                 );
                 network_info(
-                    &self.service.config.local_ip_addr.unwrap_or([0u8; 4].into()),
+                    &self.service.config.local_ip_addr,
                     footer_left.inner(footer_margin),
                     buf,
                 );

src/config.rs

@@ -9,7 +9,7 @@ use figment::{
     providers::{Format, Serialized, Toml},
 };
 use local_ip_address::local_ip;
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
 
 use crate::{
     DEFAULT_PORT, MULTICAST_IP,
@@ -22,8 +22,8 @@ pub struct Config {
     pub multicast_addr: SocketAddrV4,
     pub download_dir: PathBuf,
     pub data_dir: PathBuf,
-    #[serde(skip_serializing)]
-    pub local_ip_addr: Option<Ipv4Addr>,
+    #[serde(deserialize_with = "deserialize_local_addr")]
+    pub local_ip_addr: Ipv4Addr,
     pub device: Device,
 }
 
@@ -33,7 +33,7 @@ impl Default for Config {
             multicast_addr: SocketAddrV4::new(MULTICAST_IP, DEFAULT_PORT),
             download_dir: Default::default(),
             data_dir: Default::default(),
-            local_ip_addr: None,
+            local_ip_addr: Ipv4Addr::from_bits(0),
             device: Default::default(),
         }
     }
@@ -47,10 +47,6 @@ impl Config {
         let config_file = dirs.config_dir().join("jocalsend.toml");
         let data_dir = dirs.data_local_dir().join("jocalsend");
 
-        let IpAddr::V4(local_ip_addr) = local_ip()? else {
-            return Err(LocalSendError::IPv6Unsupported);
-        };
-
         let key = data_dir.join("key.pem");
         let cert = data_dir.join("cert.pem");
         let fingerprint = if data_dir.exists() {
@@ -67,8 +63,8 @@ impl Config {
 
         let config = Self {
             multicast_addr: SocketAddrV4::new(MULTICAST_IP, DEFAULT_PORT),
+            local_ip_addr: get_local_ip_addr(),
             download_dir,
-            local_ip_addr: Some(local_ip_addr),
             data_dir,
             device: Device {
                 alias: rustix::system::uname()
@@ -80,7 +76,7 @@ impl Config {
             },
         };
 
-        let mut config = if !config_file.exists() {
+        let config = if !config_file.exists() {
             log::info!("creating config file at {config_file:?}");
             std::fs::write(&config_file, toml::to_string(&config)?)?;
             config
@@ -92,10 +88,6 @@ impl Config {
                 .map_err(Box::new)? // boxed because the error size from figment is large
         };
 
-        if config.local_ip_addr.is_none() {
-            config.local_ip_addr = Some(local_ip_addr);
-        }
-
         log::info!("using config: {config:?}");
 
         Ok(config)
@@ -118,3 +110,17 @@ fn gen_ssl(key: &Path, cert: &Path) -> Result<String> {
     std::fs::write(cert, cert_text)?;
     Ok(sha256::digest(key_text))
 }
+
+fn deserialize_local_addr<'de, D>(_: D) -> std::result::Result<Ipv4Addr, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    Ok(get_local_ip_addr())
+}
+
+fn get_local_ip_addr() -> Ipv4Addr {
+    let IpAddr::V4(local_ip_addr) = local_ip().unwrap_or(IpAddr::V4(Ipv4Addr::from_bits(0))) else {
+        panic!("IPv6 is unsupported");
+    };
+    local_ip_addr
+}