Create tokio-codec (#360)

Create a new tokio-codec crate with many of the contents of
`tokio_io::codec`.

tokio-codec/src/lines_codec.rs

@@ -0,0 +1,89 @@
+use bytes::{BufMut, BytesMut};
+use tokio_io::_tokio_codec::{Encoder, Decoder};
+use std::{io, str};
+
+/// A simple `Codec` implementation that splits up data into lines.
+#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct LinesCodec {
+    // Stored index of the next index to examine for a `\n` character.
+    // This is used to optimize searching.
+    // For example, if `decode` was called with `abc`, it would hold `3`,
+    // because that is the next index to examine.
+    // The next time `decode` is called with `abcde\n`, the method will
+    // only look at `de\n` before returning.
+    next_index: usize,
+}
+
+impl LinesCodec {
+    /// Returns a `LinesCodec` for splitting up data into lines.
+    pub fn new() -> LinesCodec {
+        LinesCodec { next_index: 0 }
+    }
+}
+
+fn utf8(buf: &[u8]) -> Result<&str, io::Error> {
+    str::from_utf8(buf).map_err(|_|
+        io::Error::new(
+            io::ErrorKind::InvalidData,
+            "Unable to decode input as UTF8"))
+}
+
+fn without_carriage_return(s: &[u8]) -> &[u8] {
+    if let Some(&b'\r') = s.last() {
+        &s[..s.len() - 1]
+    } else {
+        s
+    }
+}
+
+impl Decoder for LinesCodec {
+    type Item = String;
+    type Error = io::Error;
+
+    fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<String>, io::Error> {
+        if let Some(newline_offset) =
+            buf[self.next_index..].iter().position(|b| *b == b'\n')
+        {
+            let newline_index = newline_offset + self.next_index;
+            let line = buf.split_to(newline_index + 1);
+            let line = &line[..line.len()-1];
+            let line = without_carriage_return(line);
+            let line = utf8(line)?;
+            self.next_index = 0;
+            Ok(Some(line.to_string()))
+        } else {
+            self.next_index = buf.len();
+            Ok(None)
+        }
+    }
+
+    fn decode_eof(&mut self, buf: &mut BytesMut) -> Result<Option<String>, io::Error> {
+        Ok(match self.decode(buf)? {
+            Some(frame) => Some(frame),
+            None => {
+                // No terminating newline - return remaining data, if any
+                if buf.is_empty() || buf == &b"\r"[..] {
+                    None
+                } else {
+                    let line = buf.take();
+                    let line = without_carriage_return(&line);
+                    let line = utf8(line)?;
+                    self.next_index = 0;
+                    Some(line.to_string())
+                }
+            }
+        })
+    }
+}
+
+impl Encoder for LinesCodec {
+    type Item = String;
+    type Error = io::Error;
+
+    fn encode(&mut self, line: String, buf: &mut BytesMut) -> Result<(), io::Error> {
+        buf.reserve(line.len() + 1);
+        buf.put(line);
+        buf.put_u8(b'\n');
+        Ok(())
+    }
+}