create tmp cache directory if one is not specified

config/default.toml

@@ -1,6 +1,6 @@
 debug = true
 source_code = "https://github.com/realaravinth/libmedium"
-cache = "/var/lib/libmedium"
+#cache = "/var/lib/libmedium"
 
 [server]
 # The port at which you want authentication to listen to

src/data.rs

@@ -44,7 +44,7 @@ pub type AppData = web::Data<Data>;
 
 impl Data {
     pub fn new() -> AppData {
-        let path = Path::new(&SETTINGS.cache).join("posts_cache");
+        let path = Path::new(SETTINGS.cache.as_ref().unwrap()).join("posts_cache");
         let cache = sled::open(path).unwrap();
         let posts = cache.open_tree("posts").unwrap();
         AppData::new(Self {

src/settings.rs

@@ -42,7 +42,7 @@ impl Server {
 #[derive(Debug, Clone, Deserialize)]
 pub struct Settings {
     pub debug: bool,
-    pub cache: String,
+    pub cache: Option<String>,
     pub server: Server,
     pub source_code: String,
 }
@@ -82,14 +82,26 @@ impl Settings {
             Err(e) => warn!("couldn't interpret PORT: {}", e),
         }
 
-        let settings: Settings = s.try_into()?;
+        let mut settings: Settings = s.try_into()?;
 
-        let cache_path = Path::new(&settings.cache);
+        if settings.cache.is_none() {
+            let tmp = env::temp_dir().join("libmedium_cache_path");
+            if !tmp.exists() {
+                fs::create_dir_all(&tmp).unwrap()
+            }
+            settings.cache = Some(tmp.to_str().unwrap().to_string())
+        }
+
+        let cache_path = settings.cache.as_ref().unwrap();
+        let cache_path = Path::new(&cache_path);
         if !cache_path.exists() {
             fs::create_dir(&cache_path).unwrap();
         }
         if !cache_path.is_dir() {
-            panic!("Cache path {} must be a directory", &settings.cache);
+            panic!(
+                "Cache path {} must be a directory",
+                &settings.cache.as_ref().unwrap()
+            );
         }
         Ok(settings)
     }