Modify Keys and Events to detect Esc key presses (#45)

* modify Keys and Events to detect Esc key presses

The strategy used here is to read two bytes at a time, going on the
assumption that escape sequences will consist of multi byte reads and
solitary Esc key presses will consist of single byte reads.

Tests had to be modified to account for these new multi byte reads by
including dummy bytes when a single byte was previously expected.

Fixes ticki/termion#43

* expand keys example to include Esc key presses

* add test for Esc key press

examples/keys.rs

@@ -23,6 +23,7 @@ fn main() {
             Key::Char(c) => println!("{}", c),
             Key::Alt(c) => println!("^{}", c),
             Key::Ctrl(c) => println!("*{}", c),
+            Key::Esc => println!("ESC"),
             Key::Left => println!("←"),
             Key::Right => println!("→"),
             Key::Up => println!("↑"),

src/event.rs

@@ -90,6 +90,8 @@ pub enum Key {
     Ctrl(char),
     /// Null byte.
     Null,
+    /// Esc key.
+    Esc,
 
     #[allow(missing_docs)]
     #[doc(hidden)]

src/input.rs

@@ -7,11 +7,11 @@ use event::{parse_event, Event, Key};
 use raw::IntoRawMode;
 
 /// An iterator over input keys.
-pub struct Keys<I> {
-    iter: Events<I>,
+pub struct Keys<R> {
+    iter: Events<R>,
 }
 
-impl<I: Iterator<Item = Result<u8, io::Error>>> Iterator for Keys<I> {
+impl<R: Read> Iterator for Keys<R> {
     type Item = Result<Key, io::Error>;
 
     fn next(&mut self) -> Option<Result<Key, io::Error>> {
@@ -27,29 +27,59 @@ impl<I: Iterator<Item = Result<u8, io::Error>>> Iterator for Keys<I> {
 }
 
 /// An iterator over input events.
-pub struct Events<I> {
-    bytes: I,
+pub struct Events<R> {
+    source: R,
+    leftover: Option<u8>,
 }
 
-impl<I: Iterator<Item = Result<u8, io::Error>>> Iterator for Events<I> {
+impl<R: Read> Iterator for Events<R> {
     type Item = Result<Event, io::Error>;
 
     fn next(&mut self) -> Option<Result<Event, io::Error>> {
-        let iter = &mut self.bytes;
-        match iter.next() {
-            Some(item) => Some(parse_event(item, iter).or(Ok(Event::Unsupported))),
-            None => None,
+        let mut source = &mut self.source;
+
+        if let Some(c) = self.leftover {
+            // we have a leftover byte, use it
+            self.leftover = None;
+            return Some(parse_event(Ok(c), &mut source.bytes()).or(Ok(Event::Unsupported)));
         }
+
+        // Here we read two bytes at a time. We need to distinguish between single ESC key presses,
+        // and escape sequences (which start with ESC or a x1B byte). The idea is that if this is
+        // an escape sequence, we will read multiple bytes (the first byte being ESC) but if this
+        // is a single ESC keypress, we will only read a single byte.
+        let mut buf = [0u8; 2];
+        let res = match source.read(&mut buf) {
+            Ok(0) => return None,
+            Ok(1) => match buf[0] {
+                b'\x1B' => Ok(Event::Key(Key::Esc)),
+                c => parse_event(Ok(c), &mut source.bytes()),
+            },
+            Ok(2) => {
+                if buf[0] != b'\x1B' {
+                    // this is not an escape sequence, but we read two bytes, save the second byte
+                    // for later
+                    self.leftover = Some(buf[1]);
+                }
+
+                let mut iter = buf[1..2].iter().map(|c| Ok(*c)).chain(source.bytes());
+                parse_event(Ok(buf[0]), &mut iter)
+            }
+            Ok(_) => unreachable!(),
+            Err(e) => Err(e),
+        };
+
+        Some(res.or(Ok(Event::Unsupported)))
     }
 }
 
 /// Extension to `Read` trait.
 pub trait TermRead {
     /// An iterator over input events.
-    fn events(self) -> Events<io::Bytes<Self>> where Self: Sized;
+    fn events(self) -> Events<Self> where Self: Sized;
 
     /// An iterator over key inputs.
-    fn keys(self) -> Keys<io::Bytes<Self>> where Self: Sized;
+    fn keys(self) -> Keys<Self> where Self: Sized;
 
     /// Read a line.
     ///
@@ -68,12 +98,13 @@ pub trait TermRead {
 }
 
 impl<R: Read> TermRead for R {
-    fn events(self) -> Events<io::Bytes<R>> {
+    fn events(self) -> Events<Self> {
         Events {
-            bytes: self.bytes(),
+            source: self,
+            leftover: None,
         }
     }
-    fn keys(self) -> Keys<io::Bytes<R>> {
+    fn keys(self) -> Keys<Self> {
         Keys {
             iter: self.events(),
         }
@@ -213,6 +244,13 @@ mod test {
         assert!(st.next().is_none());
     }
 
+    #[test]
+    fn test_esc_key() {
+        let mut st = b"\x1B".keys();
+        assert_eq!(st.next().unwrap().unwrap(), Key::Esc);
+        assert!(st.next().is_none());
+    }
+
     fn line_match(a: &str, b: Option<&str>) {
         let mut sink = io::sink();