Use MaxMindDb and thiserror.

src/lib.rs

@@ -1,17 +1,32 @@
 use std::net::IpAddr;
 
 /// Allows geo-locating IPs and keeps analytics.
-pub struct Locat {}
+pub struct Locat {
+    geoip: maxminddb::Reader<Vec<u8>>,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("maxminddb error: {0}")]
+    MaxMindDb(#[from] maxminddb::MaxMindDBError),
+}
 
 impl Locat {
-    pub fn new(_geoip_country_db_path: &str, _analytics_db_path: &str) -> Self {
-        // TODO: read geoip db, create analytics db
-        Self {}
+    pub fn new(geoip_country_db_path: &str, _analytics_db_path: &str) -> Result<Self, Error> {
+        // Todo: create analytics db.
+
+        Ok(Self {
+            geoip: maxminddb::Reader::open_readfile(geoip_country_db_path)?,
+        })
     }
 
     /// Converts an address to an ISO 3166-1 alpha-2 country code.
-    pub fn ip_to_iso_code(&self, _addr: IpAddr) -> Option<&str> {
-        None
+    pub fn ip_to_iso_code(&self, addr: IpAddr) -> Option<&str> {
+        self.geoip
+            .lookup::<maxminddb::geoip2::Country>(addr)
+            .ok()?
+            .country?
+            .iso_code
     }
 
     /// Returns a map of country codes to number of requests.