Decoders return the number of bytes that they read

Closes #35

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bincode"
-version = "0.1.3"
+version = "0.2.0"
 authors = ["Ty Overby <ty@pre-alpha.com>", "Francesco Mazzoli <f@mazzo.li>"]
 
 repository = "https://github.com/TyOverby/bincode"

examples/basic.rs

@@ -24,7 +24,7 @@ fn main() {
     // 8 bytes for the length of the vector, 4 bytes per float.
     assert_eq!(encoded.len(), 8 + 4 * 4);
 
-    let decoded: World = bincode::decode(&encoded[..]).unwrap();
+    let (decoded, _): (World, _) = bincode::decode(&encoded[..]).unwrap();
 
     assert!(world == decoded);
 }

src/lib.rs

@@ -18,7 +18,7 @@
 //!     let limit = bincode::SizeLimit::Bounded(20);
 //!
 //!     let encoded: Vec<u8> = bincode::encode(&target, limit).unwrap();
-//!     let decoded: Option<String> = bincode::decode(&encoded[..]).unwrap();
+//!     let (decoded, len): (Option<String>, u64) = bincode::decode(&encoded[..]).unwrap();
 //!     assert_eq!(target, decoded);
 //! }
 //! ```
@@ -95,9 +95,12 @@ pub fn encode<T: Encodable>(t: &T, size_limit: SizeLimit) -> EncodingResult<Vec<
 
 /// Decodes a slice of bytes into an object.
 ///
-/// This method does not have a size-limit because if you already have the bytes
-/// in memory, then you don't gain anything by having a limiter.
-pub fn decode<T: Decodable>(b: &[u8]) -> DecodingResult<T> {
+/// If successful, this function returns the decoded object along with the number
+/// of bytes that were read.
+///
+/// This method does not have a size-limit because with all the bytes contiguous
+/// in memory, then nothing is gained by having a limiter.
+pub fn decode<T: Decodable>(b: &[u8]) -> DecodingResult<(T, u64)> {
     let mut b = b;
     decode_from(&mut b, SizeLimit::Infinite)
 }
@@ -125,7 +128,8 @@ pub fn encode_into<T: Encodable, W: Write>(t: &T,
     t.encode(&mut writer::EncoderWriter::new(w))
 }
 
-/// Decoes an object directly from a `Buffer`ed Reader.
+/// Decodes an object directly from a `Read`er.  If successful, returns the
+/// decoded object and the number of bytes read out of the `Read`er.
 ///
 /// If the provided `SizeLimit` is reached, the decode will bail immediately.
 /// A SizeLimit can help prevent an attacker from flooding your server with
@@ -134,8 +138,11 @@ pub fn encode_into<T: Encodable, W: Write>(t: &T,
 /// If this returns an `DecodingError`, assume that the buffer that you passed
 /// in is in an invalid state, as the error could be returned during any point
 /// in the reading.
-pub fn decode_from<R: Read, T: Decodable>(r: &mut R, size_limit: SizeLimit) -> DecodingResult<T> {
-    Decodable::decode(&mut reader::DecoderReader::new(r, size_limit))
+pub fn decode_from<R: Read, T: Decodable>(r: &mut R, size_limit: SizeLimit) -> DecodingResult<(T, u64)> {
+    let mut decoder_reader = reader::DecoderReader::new(r, size_limit);
+    let value = try!(Decodable::decode(&mut decoder_reader));
+    let bytes_read = decoder_reader.bytes_read();
+    Ok((value, bytes_read))
 }
 
 

src/reader.rs

@@ -114,6 +114,10 @@ impl<'a, R: Read> DecoderReader<'a, R> {
             read: 0
         }
     }
+
+    pub fn bytes_read(&self) -> u64 {
+        self.read
+    }
 }
 
 impl <'a, A> DecoderReader<'a, A> {

src/test.rs

@@ -20,14 +20,14 @@ fn the_same<V>(element: V)
         let rf = RefBox::new(v);
 
         let encoded = encode(&rf, Infinite).unwrap();
-        let decoded: RefBox<'static, V> = decode(&encoded[..]).unwrap();
+        let (decoded, _): (RefBox<'static, V>, _) = decode(&encoded[..]).unwrap();
 
         decoded.take().deref() == v
     }
 
     let size = encoded_size(&element);
     let encoded = encode(&element, Infinite).unwrap();
-    let decoded = decode(&encoded[..]).unwrap();
+    let (decoded, _) = decode(&encoded[..]).unwrap();
     assert!(element == decoded);
     assert!(size == encoded.len() as u64);
     assert!(ref_box_correct(&element))
@@ -206,12 +206,12 @@ fn decoding_errors() {
 fn too_big_decode() {
     let encoded = vec![0,0,0,3];
     let mut encoded_ref = &encoded[..];
-    let decoded: Result<u32, _> = decode_from(&mut encoded_ref, Bounded(3));
+    let decoded: Result<(u32, _), _> = decode_from(&mut encoded_ref, Bounded(3));
     assert!(decoded.is_err());
 
     let encoded = vec![0,0,0,3];
     let mut encoded_ref = &encoded[..];
-    let decoded: Result<u32, _> = decode_from(&mut encoded_ref, Bounded(4));
+    let decoded: Result<(u32, _), _> = decode_from(&mut encoded_ref, Bounded(4));
     assert!(decoded.is_ok());
 }
 
@@ -219,9 +219,9 @@ fn too_big_decode() {
 fn too_big_char_decode() {
     let encoded = vec![0x41];
     let mut encoded_ref = &encoded[..];
-    let decoded: Result<char, _> = decode_from(&mut encoded_ref, Bounded(1));
+    let decoded: Result<(char, _), _> = decode_from(&mut encoded_ref, Bounded(1));
     assert!(decoded.is_ok());
-    assert_eq!(decoded.unwrap(), 'A');
+    assert_eq!(decoded.unwrap().0, 'A');
 }
 
 #[test]
@@ -268,9 +268,9 @@ fn test_refbox() {
     // Test 1
     {
         let encoded = encode(&Message::M1(RefBox::new(&large_object)), Infinite).unwrap();
-        let decoded: Message<'static> = decode(&encoded[..]).unwrap();
+        let decoded: (Message<'static>, _) = decode(&encoded[..]).unwrap();
 
-        match decoded {
+        match decoded.0 {
             Message::M1(b) => assert!(b.take().deref() == &large_object),
             _ => assert!(false)
         }
@@ -279,9 +279,9 @@ fn test_refbox() {
     // Test 2
     {
         let encoded = encode(&Message::M2(RefBox::new(&large_map)), Infinite).unwrap();
-        let decoded: Message<'static> = decode(&encoded[..]).unwrap();
+        let decoded: (Message<'static>, _) = decode(&encoded[..]).unwrap();
 
-        match decoded {
+        match decoded.0 {
             Message::M2(b) => assert!(b.take().deref() == &large_map),
             _ => assert!(false)
         }