add way to supply downloaded file name, expose whether it's cached in return value

src/lib.rs

@@ -170,21 +170,34 @@ impl Downloader {
         }
     }
 
-    pub fn get(&self, url: &str) -> PathBuf {
+    pub fn get(&self, url: &str) -> DownloaderResult {
+        let filename = url.get((url.rfind('/').expect("not a valid url") + 1..)).expect("failed to parse filename");
+        self.get_to(url, filename)
+    }
+
+    pub fn get_to(&self, url: &str, filename: &str) -> DownloaderResult {
         if !self.cache.exists() {
             create_dir_all(self.cache.as_path()).expect("failed to create cache directory");
         }
 
-        let filename = url.get((url.rfind('/').expect("not a valid url") + 1..)).expect("failed to parse filename");
         let mut out_path = self.cache.clone();
         out_path.push(filename);
 
-        if !out_path.exists() {
+        let was_cached = out_path.exists();
+        if !was_cached {
             let mut result = reqwest::get(url).expect("failed to download url");
             let mut file = File::create(out_path.as_path()).expect("failed to open file");
             copy(&mut result, &mut file).expect("failed to write file");
         }
 
-        out_path
+        DownloaderResult {
+            out_path: out_path,
+            was_cached: was_cached
+        }
     }
 }
+
+pub struct DownloaderResult {
+    pub out_path: PathBuf,
+    pub was_cached: bool
+}