Add playlist info

This is also the first occurence of multiple structs in one response.
The Itertools.batching approach seems to work quite well.

src/lib.rs

@@ -2,6 +2,7 @@ use serde::de;
 use std::collections::HashMap;
 mod error;
 use error::{Error, MpdResult};
+use itertools::Itertools;
 mod structs;
 pub use structs::{Position, Status, Track};
 
@@ -34,6 +35,34 @@ pub fn deserialize_response<'a, I: Iterator<Item = &'a str>, T: de::DeserializeO
   Ok(envy::from_iter(map).unwrap())
 }
 
+pub fn read_playlist_info<'a, I: Iterator<Item = &'a str>>(input: I) -> MpdResult<Vec<Track>> {
+  input
+    .peekable()
+    .batching(|it| {
+      let mut v = match it.next() {
+        // if the playlist is empty or we’ve reached the end,
+        // the response is only the `OK` line.
+        Some("OK") => return None,
+        // otherwise this is the file attribute and thus the first key-value of this track
+        Some(s) => vec![s],
+        _ => return None,
+      };
+      // Only peek here in case we encounter the `file:` line which we still need for the next track.
+      while let Some(l) = it.peek() {
+        if l.starts_with("file:") {
+          return Some(v);
+        }
+        if l.starts_with("OK") {
+          return Some(v);
+        }
+        v.push(it.next().unwrap());
+      }
+      None
+    })
+    .map(|b| deserialize_response(b.into_iter()))
+    .collect()
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;
@@ -186,4 +215,69 @@ OK";
       }
     );
   }
+  #[test]
+  fn de_playlist_test() {
+    let input_str = "file: 137 A New World.mp3
+Last-Modified: 2018-03-07T13:11:43Z
+Artist: Arata Iiyoshi
+Title: A New World
+Album: Pokemon Mystery Dungeon: Explorers of Sky
+duration: 225.802
+Pos: 1000
+Id: 6365
+file: 139 Thoughts For Friends.mp3
+Last-Modified: 2018-03-07T13:11:43Z
+Artist: Arata Iiyoshi
+Title: Thoughts For Friends
+Album: Pokemon Mystery Dungeon: Explorers of Sky
+duration: 66.560
+Pos: 1001
+Id: 6366
+file: 140 A Message On the Wind.mp3
+Last-Modified: 2018-03-07T13:11:43Z
+Artist: Arata Iiyoshi
+Title: A Message On the Wind
+Album: Pokemon Mystery Dungeon: Explorers of Sky
+duration: 50.155
+Pos: 1002
+Id: 6367
+OK";
+    let queue = read_playlist_info(input_str.lines());
+    let first_track = Track {
+      file: "137 A New World.mp3".into(),
+      title: Some("A New World".into()),
+      artist: Some("Arata Iiyoshi".into()),
+      album: Some("Pokemon Mystery Dungeon: Explorers of Sky".into()),
+      last_modified: Some(DateTime::parse_from_rfc3339("2018-03-07T13:11:43Z").unwrap()),
+      duration: Some(Duration::from_secs_f64(225.802)),
+      pos: 1000,
+      id: 6365,
+      ..Track::default()
+    };
+    assert_eq!(
+      queue,
+      Ok(vec![
+        first_track.clone(),
+        Track {
+          file: "139 Thoughts For Friends.mp3".into(),
+          title: Some("Thoughts For Friends".into()),
+          duration: Some(Duration::from_secs_f64(66.56)),
+          pos: 1001,
+          id: 6366,
+          ..first_track.clone()
+        },
+        Track {
+          file: "140 A Message On the Wind.mp3".into(),
+          title: Some("A Message On the Wind".into()),
+          duration: Some(Duration::from_secs_f64(50.155)),
+          pos: 1002,
+          id: 6367,
+          ..first_track
+        },
+      ])
+    );
+
+    let queue = read_playlist_info("OK".lines());
+    assert_eq!(queue, Ok(vec![]));
+  }
 }