Add UnitResponse for commands without response payload

src/lib.rs

@@ -4,7 +4,7 @@ mod error;
 use error::{Error, MpdResult};
 use itertools::Itertools;
 mod structs;
-pub use structs::{Position, State, Stats, Status, Track};
+pub use structs::{Position, State, Stats, Status, Track, UnitResponse};
 
 /// some unprintable character to separate repeated keys
 const SEPARATOR: char = '\x02';
@@ -288,7 +288,8 @@ artists: 2841
 albums: 2455
 songs: 40322
 db_playtime: 11620284
-db_update: 1588433046";
+db_update: 1588433046
+OK";
     let s: Stats = deserialize_response(input_str.lines()).unwrap();
     assert_eq!(
       s,
@@ -303,4 +304,18 @@ db_update: 1588433046";
       }
     );
   }
+
+  #[test]
+  fn de_unit_response_test() {
+    let success = "OK";
+    let r: Result<UnitResponse, _> = deserialize_response(success.lines());
+    assert_eq!(r, Ok(UnitResponse {}));
+
+    let failure = r#"ACK [2@0] {consume} wrong number of arguments for "consume""#;
+    let r: Result<UnitResponse, _> = deserialize_response(failure.lines());
+    assert_eq!(
+      r,
+      Err(error::Error::from_str(r#"[2@0] {consume} wrong number of arguments for "consume""#))
+    );
+  }
 }

src/structs.rs

@@ -47,6 +47,11 @@ pub struct Track {
   pub composer:                   Option<String>,
 }
 
+/// An empty struct that can be used as the response data for commands that only ever return `OK`
+/// or an error message, e.g. `consume` or other boolean toggles.
+#[derive(Deserialize, PartialEq, Debug)]
+pub struct UnitResponse {}
+
 /// The position of an item in a list with an optional total length.
 /// Can be used for e.g. track number,
 /// where `Position { 3, 12 }` represents track 3 of a CD with 12 tracks,