Implement buffer traits on Vec<u8>, &[u8], Cursor

src/buf/byte.rs

@@ -9,6 +9,9 @@ use std::{cmp, ptr};
  */
 
 /// A `Buf` backed by a contiguous region of memory.
+///
+/// This `Buf` is better suited for cases where there is a clear delineation
+/// between reading and writing.
 pub struct ByteBuf {
     mem: alloc::MemRef,
     cap: u32,

src/buf/mod.rs

@@ -9,7 +9,7 @@ pub use self::ring::RingBuf;
 pub use self::slice::{SliceBuf, MutSliceBuf};
 
 use {BufError, RopeBuf};
-use std::{cmp, fmt, io, ptr};
+use std::{cmp, fmt, io, ptr, usize};
 
 /// A trait for values that provide sequential read access to bytes.
 pub trait Buf {
@@ -312,6 +312,77 @@ impl fmt::Debug for Box<Buf+'static> {
     }
 }
 
+impl Buf for io::Cursor<Vec<u8>> {
+    fn remaining(&self) -> usize {
+        self.get_ref().len() - self.position() as usize
+    }
+
+    fn bytes(&self) -> &[u8] {
+        let pos = self.position() as usize;
+        &(&self.get_ref())[pos..]
+    }
+
+    fn advance(&mut self, cnt: usize) {
+        let pos = self.position() as usize;
+        let pos = cmp::min(self.get_ref().len(), pos + cnt);
+        self.set_position(pos as u64);
+    }
+}
+
+impl MutBuf for Vec<u8> {
+    fn remaining(&self) -> usize {
+        usize::MAX - self.len()
+    }
+
+    fn advance(&mut self, cnt: usize) {
+        let len = self.len() + cnt;
+
+        if len > self.capacity() {
+            // Reserve additional
+            // TODO: Should this case panic?
+            let cap = self.capacity();
+            self.reserve(cap - len);
+        }
+
+        unsafe {
+            self.set_len(len);
+        }
+    }
+
+    fn mut_bytes(&mut self) -> &mut [u8] {
+        use std::slice;
+
+        if self.capacity() == self.len() {
+            self.reserve(64); // Grow the vec
+        }
+
+        let cap = self.capacity();
+        let len = self.len();
+
+        unsafe {
+            let ptr = self.as_mut_ptr();
+            &mut slice::from_raw_parts_mut(ptr, cap)[len..]
+        }
+    }
+}
+
+impl<'a> Buf for io::Cursor<&'a [u8]> {
+    fn remaining(&self) -> usize {
+        self.get_ref().len() - self.position() as usize
+    }
+
+    fn bytes(&self) -> &[u8] {
+        let pos = self.position() as usize;
+        &(&self.get_ref())[pos..]
+    }
+
+    fn advance(&mut self, cnt: usize) {
+        let pos = self.position() as usize;
+        let pos = cmp::min(self.get_ref().len(), pos + cnt);
+        self.set_position(pos as u64);
+    }
+}
+
 /*
  *
  * ===== Read impls =====

src/buf/ring.rs

@@ -9,6 +9,8 @@ enum Mark {
 /// Buf backed by a continous chunk of memory. Maintains a read cursor and a
 /// write cursor. When reads and writes reach the end of the allocated buffer,
 /// wraps around to the start.
+///
+/// This type is suited for use cases where reads and writes are intermixed.
 pub struct RingBuf {
     ptr: alloc::MemRef,  // Pointer to the memory
     cap: usize,          // Capacity of the buffer
@@ -19,6 +21,7 @@ pub struct RingBuf {
 
 // TODO: There are most likely many optimizations that can be made
 impl RingBuf {
+    /// Allocates a new `RingBuf` with the specified capacity.
     pub fn new(mut capacity: usize) -> RingBuf {
         // Handle the 0 length buffer case
         if capacity == 0 {
@@ -45,14 +48,17 @@ impl RingBuf {
         }
     }
 
+    /// Returns `true` if the buf cannot accept any further writes.
     pub fn is_full(&self) -> bool {
         self.cap == self.len
     }
 
+    /// Returns `true` if the buf cannot accept any further reads.
     pub fn is_empty(&self) -> bool {
         self.len == 0
     }
 
+    /// Returns the number of bytes that the buf can hold.
     pub fn capacity(&self) -> usize {
         self.cap
     }
@@ -85,10 +91,12 @@ impl RingBuf {
         }
     }
 
+    /// Returns the number of bytes remaining to read.
     fn read_remaining(&self) -> usize {
         self.len
     }
 
+    /// Returns the remaining write capacity until which the buf becomes full.
     fn write_remaining(&self) -> usize {
         self.cap - self.len
     }

test/test_buf.rs

@@ -0,0 +1,48 @@
+use bytes::{Buf, MutBuf, MutBufExt};
+use std::usize;
+use std::io::{Cursor};
+
+#[test]
+pub fn test_fresh_cursor_vec() {
+    let mut buf = Cursor::new(b"hello".to_vec());
+
+    assert_eq!(buf.remaining(), 5);
+    assert_eq!(buf.bytes(), b"hello");
+
+    buf.advance(2);
+
+    assert_eq!(buf.remaining(), 3);
+    assert_eq!(buf.bytes(), b"llo");
+
+    buf.advance(3);
+
+    assert_eq!(buf.remaining(), 0);
+    assert_eq!(buf.bytes(), b"");
+
+    buf.advance(1);
+
+    assert_eq!(buf.remaining(), 0);
+    assert_eq!(buf.bytes(), b"");
+}
+
+#[test]
+pub fn test_vec_as_mut_buf() {
+    let mut buf = vec![];
+
+    assert_eq!(buf.remaining(), usize::MAX);
+    assert_eq!(buf.mut_bytes().len(), 64);
+
+    buf.write(&b"zomg"[..]).unwrap();
+
+    assert_eq!(&buf, b"zomg");
+
+    assert_eq!(buf.remaining(), usize::MAX - 4);
+    assert_eq!(buf.capacity(), 64);
+
+    for _ in 0..16 {
+        buf.write(&b"zomg"[..]).unwrap();
+    }
+
+    assert_eq!(buf.len(), 68);
+    assert_eq!(buf.capacity(), 128);
+}