add mark/reset feature to ByteBuf and RingBuf

test/test_byte_buf.rs

@@ -30,6 +30,10 @@ pub fn test_byte_buf_read_write() {
     let mut buf = buf.flip();
     let mut dst = [0; 5];
 
+    buf.mark();
+    assert_eq!(5, buf.read(&mut dst[..]).unwrap());
+    assert_eq!(b"hello", &dst);
+    buf.reset();
     assert_eq!(5, buf.read(&mut dst[..]).unwrap());
     assert_eq!(b"hello", &dst);
 

test/test_ring.rs

@@ -19,9 +19,16 @@ pub fn test_initial_buf_empty() {
     assert_eq!(buf.bytes(), [1, 2, 3]);
 
     let mut out = [0u8; 3];
+
+    buf.mark();
     let bytes_read = buf.read(&mut out[..]).unwrap();;
     assert_eq!(bytes_read, 3);
     assert_eq!(out, [1, 2, 3]);
+    buf.reset();
+    let bytes_read = buf.read(&mut out[..]).unwrap();;
+    assert_eq!(bytes_read, 3);
+    assert_eq!(out, [1, 2, 3]);
+
     assert_eq!(MutBuf::remaining(&buf), 16);
     assert_eq!(Buf::remaining(&buf), 0);
 }
@@ -39,6 +46,11 @@ fn test_wrapping_write() {
     let bytes_written = buf.write(&[23;8][..]).unwrap();
     assert_eq!(bytes_written, 8);
 
+    buf.mark();
+    let bytes_read = buf.read(&mut out[..]).unwrap();
+    assert_eq!(bytes_read, 10);
+    assert_eq!(out, [42, 42, 23, 23, 23, 23, 23, 23, 23, 23]);
+    buf.reset();
     let bytes_read = buf.read(&mut out[..]).unwrap();
     assert_eq!(bytes_read, 10);
     assert_eq!(out, [42, 42, 23, 23, 23, 23, 23, 23, 23, 23]);
@@ -64,3 +76,16 @@ fn test_io_write_and_read() {
     assert_eq!(bytes_read, 8);
     assert_eq!(out, [2;8]);
 }
+
+#[test]
+#[should_panic]
+fn test_wrap_reset() {
+    use std::io::{Read, Write};
+
+    let mut buf = RingBuf::new(8);
+    buf.write(&[1, 2, 3, 4, 5, 6, 7]).unwrap();
+    buf.mark();
+    buf.read(&mut [0; 4]).unwrap();
+    buf.write(&[1, 2, 3, 4]).unwrap();
+    buf.reset();
+}