Fix panic reading MP3 files with no MPEG frames

src/mp3/read.rs

@@ -96,13 +96,6 @@ where
 					// We have found the first frame
 					break;
 				}
-
-				// The search for sync bits was unsuccessful
-				return Err(FileDecodingError::new(
-					FileType::MP3,
-					"File contains an invalid frame",
-				)
-				.into());
 			},
 		}
 	}
@@ -140,6 +133,13 @@ where
 	file.last_frame_offset = reader.stream_position()?;
 
 	file.properties = if read_properties {
+		if first_frame_header.is_none() {
+			// The search for sync bits was unsuccessful
+			return Err(
+				FileDecodingError::new(FileType::MP3, "File contains an invalid frame").into(),
+			);
+		}
+
 		// Safe to unwrap, since we return early if no frame is found
 		let first_frame_header = first_frame_header.unwrap();
 
@@ -172,3 +172,20 @@ where
 
 	Ok(file)
 }
+
+#[cfg(test)]
+mod tests {
+	use crate::file::AudioFile;
+	use crate::mp3::Mp3File;
+	use std::fs::File;
+
+	#[test]
+	fn issue_39() {
+		// MP3 file that only consists of an ID3v2 tag
+		assert!(Mp3File::read_from(
+			&mut File::open("tests/files/assets/issue_39.mp3").unwrap(),
+			true,
+		)
+		.is_err());
+	}
+}