Allow file to be borrowed

symphonia-core/src/io/mod.rs

@@ -74,6 +74,33 @@ impl MediaSource for std::fs::File {
     }
 }
 
+impl<'a> MediaSource for &'a mut std::fs::File {
+    /// Returns if the `std::io::File` backing the `MediaSource` is seekable.
+    ///
+    /// Note: This operation involves querying the underlying file descriptor for information and
+    /// may be moderately expensive. Therefore it is recommended to cache this value if used often.
+    fn is_seekable(&self) -> bool {
+        // If the file's metadata is available, and the file is a regular file (i.e., not a FIFO,
+        // etc.), then the MediaSource will be seekable. Otherwise assume it is not. Note that
+        // metadata() follows symlinks.
+        match self.metadata() {
+            Ok(metadata) => metadata.is_file(),
+            _ => false,
+        }
+    }
+
+    /// Returns the length in bytes of the `std::io::File` backing the `MediaSource`.
+    ///
+    /// Note: This operation involves querying the underlying file descriptor for information and
+    /// may be moderately expensive. Therefore it is recommended to cache this value if used often.
+    fn byte_len(&self) -> Option<u64> {
+        match self.metadata() {
+            Ok(metadata) => Some(metadata.len()),
+            _ => None,
+        }
+    }
+}
+
 impl<T: std::convert::AsRef<[u8]> + Send + Sync> MediaSource for io::Cursor<T> {
     /// Always returns true since a `io::Cursor<u8>` is always seekable.
     fn is_seekable(&self) -> bool {