[Breaking change] Made all decode_from_slice also return the number of bytes read

benches/varint.rs

@@ -14,7 +14,7 @@ fn slice_varint_u8(c: &mut Criterion) {
 
     c.bench_function("slice_varint_u8", |b| {
         b.iter(|| {
-            let _: Vec<u8> = bincode::decode_from_slice(&bytes, config).unwrap();
+            let _: (Vec<u8>, usize) = bincode::decode_from_slice(&bytes, config).unwrap();
         })
     });
 }
@@ -30,7 +30,7 @@ fn slice_varint_u16(c: &mut Criterion) {
 
     c.bench_function("slice_varint_u16", |b| {
         b.iter(|| {
-            let _: Vec<u16> = bincode::decode_from_slice(&bytes, config).unwrap();
+            let _: (Vec<u8>, usize) = bincode::decode_from_slice(&bytes, config).unwrap();
         })
     });
 }
@@ -46,7 +46,7 @@ fn slice_varint_u32(c: &mut Criterion) {
 
     c.bench_function("slice_varint_u32", |b| {
         b.iter(|| {
-            let _: Vec<u32> = bincode::decode_from_slice(&bytes, config).unwrap();
+            let _: (Vec<u16>, usize) = bincode::decode_from_slice(&bytes, config).unwrap();
         })
     });
 }
@@ -62,7 +62,7 @@ fn slice_varint_u64(c: &mut Criterion) {
 
     c.bench_function("slice_varint_u64", |b| {
         b.iter(|| {
-            let _: Vec<u64> = bincode::decode_from_slice(&bytes, config).unwrap();
+            let _: (Vec<u64>, usize) = bincode::decode_from_slice(&bytes, config).unwrap();
         })
     });
 }

derive/src/parse/generics.rs

@@ -122,6 +122,7 @@ impl Generics {
 }
 
 #[derive(Debug)]
+#[allow(clippy::enum_variant_names)]
 enum Generic {
     Lifetime(Lifetime),
     Simple(SimpleGeneric),

readme.md

@@ -53,9 +53,10 @@ fn main() {
     // The 4 floats are encoded in 4 bytes each.
     assert_eq!(encoded.len(), 1 + 4 * 4);
 
-    let decoded: World = bincode::decode_from_slice(&encoded[..], config).unwrap();
+    let (decoded, len): (World, usize) = bincode::decode_from_slice(&encoded[..], config).unwrap();
 
     assert_eq!(world, decoded);
+    assert_eq!(len, encoded.len()); // read all bytes
 }
 ```
 

src/de/impl_core.rs

@@ -1,4 +1,5 @@
 #![allow(unused_unsafe)]
+#![allow(clippy::needless_borrow)]
 
 //! Contains implementations for rust core that have not been stabilized
 //!

src/de/read.rs

@@ -61,7 +61,7 @@ pub trait BorrowReader<'storage>: Reader {
 
 /// A reader type for `&[u8]` slices. Implements both [Reader] and [BorrowReader], and thus can be used for borrowed data.
 pub struct SliceReader<'storage> {
-    slice: &'storage [u8],
+    pub(crate) slice: &'storage [u8],
 }
 
 impl<'storage> SliceReader<'storage> {

src/features/serde/de_owned.rs

@@ -5,20 +5,22 @@ use crate::{
 };
 use serde_incl::de::*;
 
-/// Decode an owned type from the given slice.
+/// Decode an owned type from the given slice. Will return the decoded type `T` as well as the amount of bytes that were read.
 ///
 /// Note that this does not work with borrowed types like `&str` or `&[u8]`. For that use [decode_borrowed_from_slice].
 ///
 /// [decode_borrowed_from_slice]: fn.decode_borrowed_from_slice.html
-pub fn decode_from_slice<T, C>(slice: &[u8], config: C) -> Result<T, DecodeError>
+pub fn decode_from_slice<T, C>(slice: &[u8], config: C) -> Result<(T, usize), DecodeError>
 where
     T: DeserializeOwned,
     C: Config,
 {
     let reader = crate::de::read::SliceReader::new(slice);
     let mut decoder = crate::de::DecoderImpl::new(reader, config);
     let serde_decoder = SerdeDecoder { de: &mut decoder };
-    T::deserialize(serde_decoder)
+    let result = T::deserialize(serde_decoder)?;
+    let bytes_read = slice.len() - decoder.reader().slice.len();
+    Ok((result, bytes_read))
 }
 
 pub(crate) struct SerdeDecoder<'a, DE: Decoder> {

src/lib.rs

@@ -49,7 +49,7 @@
 //!
 //! // Decoding works the same as encoding.
 //! // The trait used is `de::Decode`, and can also be automatically implemented with the `derive` feature.
-//! let decoded: (u8, u32, i128, char, [u8; 4]) = bincode::decode_from_slice(slice, Configuration::standard()).unwrap();
+//! let decoded: (u8, u32, i128, char, [u8; 4]) = bincode::decode_from_slice(slice, Configuration::standard()).unwrap().0;
 //!
 //! assert_eq!(decoded, input);
 //! ```
@@ -67,7 +67,7 @@ mod features;
 pub(crate) mod utils;
 pub(crate) mod varint;
 
-use de::read::Reader;
+use de::{read::Reader, Decoder};
 use enc::write::Writer;
 pub use features::*;
 
@@ -120,10 +120,12 @@ pub fn encode_into_writer<E: enc::Encode, W: Writer, C: Config>(
 pub fn decode_from_slice<'a, D: de::BorrowDecode<'a>, C: Config>(
     src: &'a [u8],
     config: C,
-) -> Result<D, error::DecodeError> {
+) -> Result<(D, usize), error::DecodeError> {
     let reader = de::read::SliceReader::new(src);
     let mut decoder = de::DecoderImpl::<_, C>::new(reader, config);
-    D::borrow_decode(&mut decoder)
+    let result = D::borrow_decode(&mut decoder)?;
+    let bytes_read = src.len() - decoder.reader().slice.len();
+    Ok((result, bytes_read))
 }
 
 /// Attempt to decode a given type `D` from the given [Reader].

tests/alloc.rs

@@ -44,9 +44,11 @@ fn test_vec() {
     let vec = bincode::encode_to_vec(Foo { a: 5, b: 10 }, Configuration::standard()).unwrap();
     assert_eq!(vec, &[5, 10]);
 
-    let foo: Foo = bincode::decode_from_slice(&vec, Configuration::standard()).unwrap();
+    let (foo, len): (Foo, usize) =
+        bincode::decode_from_slice(&vec, Configuration::standard()).unwrap();
     assert_eq!(foo.a, 5);
     assert_eq!(foo.b, 10);
+    assert_eq!(len, 2);
 }
 
 #[test]

tests/basic_types.rs

@@ -136,9 +136,10 @@ fn test_slice() {
     bincode::encode_into_slice(input, &mut buffer, Configuration::standard()).unwrap();
     assert_eq!(&buffer[..8], &[7, 1, 2, 3, 4, 5, 6, 7]);
 
-    let output: &[u8] =
+    let (output, len): (&[u8], usize) =
         bincode::decode_from_slice(&mut buffer[..8], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, 8);
 }
 
 #[test]
@@ -148,18 +149,20 @@ fn test_option_slice() {
     let n = bincode::encode_into_slice(input, &mut buffer, Configuration::standard()).unwrap();
     assert_eq!(&buffer[..n], &[1, 7, 1, 2, 3, 4, 5, 6, 7]);
 
-    let output: Option<&[u8]> =
+    let (output, len): (Option<&[u8]>, usize) =
         bincode::decode_from_slice(&buffer[..n], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, n);
 
     let mut buffer = [0u8; 32];
     let input: Option<&[u8]> = None;
     let n = bincode::encode_into_slice(input, &mut buffer, Configuration::standard()).unwrap();
     assert_eq!(&buffer[..n], &[0]);
 
-    let output: Option<&[u8]> =
+    let (output, len): (Option<&[u8]>, usize) =
         bincode::decode_from_slice(&buffer[..n], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, n);
 }
 
 #[test]
@@ -172,9 +175,10 @@ fn test_str() {
         &[11, 72, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]
     );
 
-    let output: &str =
+    let (output, len): (&str, usize) =
         bincode::decode_from_slice(&mut buffer[..12], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, 12);
 }
 
 #[test]
@@ -187,18 +191,20 @@ fn test_option_str() {
         &[1, 11, 72, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]
     );
 
-    let output: Option<&str> =
+    let (output, len): (Option<&str>, usize) =
         bincode::decode_from_slice(&buffer[..n], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, n);
 
     let mut buffer = [0u8; 32];
     let input: Option<&str> = None;
     let n = bincode::encode_into_slice(input, &mut buffer, Configuration::standard()).unwrap();
     assert_eq!(&buffer[..n], &[0]);
 
-    let output: Option<&str> =
+    let (output, len): (Option<&str>, usize) =
         bincode::decode_from_slice(&buffer[..n], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, n);
 }
 
 #[test]
@@ -208,7 +214,8 @@ fn test_array() {
     bincode::encode_into_slice(input, &mut buffer, Configuration::standard()).unwrap();
     assert_eq!(&buffer[..10], &[10, 20, 30, 40, 50, 60, 70, 80, 90, 100]);
 
-    let output: [u8; 10] =
+    let (output, len): ([u8; 10], usize) =
         bincode::decode_from_slice(&mut buffer[..10], Configuration::standard()).unwrap();
     assert_eq!(input, output);
+    assert_eq!(len, 10);
 }

tests/derive.rs

@@ -64,8 +64,10 @@ fn test_decode() {
         c: 1024u32,
     };
     let slice = [5, 10, 251, 0, 4];
-    let result: Test2<u32> = bincode::decode_from_slice(&slice, Configuration::standard()).unwrap();
+    let (result, len): (Test2<u32>, usize) =
+        bincode::decode_from_slice(&slice, Configuration::standard()).unwrap();
     assert_eq!(result, start);
+    assert_eq!(len, 5);
 }
 
 #[test]
@@ -79,8 +81,11 @@ fn test_encode_decode_str() {
     let mut slice = [0u8; 100];
 
     let len = bincode::encode_into_slice(&start, &mut slice, Configuration::standard()).unwrap();
-    let end: Test3 = bincode::decode_from_slice(&slice[..len], Configuration::standard()).unwrap();
+    assert_eq!(len, 21);
+    let (end, len): (Test3, usize) =
+        bincode::decode_from_slice(&slice[..len], Configuration::standard()).unwrap();
     assert_eq!(end, start);
+    assert_eq!(len, 21);
 }
 
 #[test]
@@ -97,9 +102,10 @@ fn test_encode_tuple() {
 fn test_decode_tuple() {
     let start = TestTupleStruct(5, 10, 1024);
     let mut slice = [5, 10, 251, 0, 4];
-    let result: TestTupleStruct =
+    let (result, len): (TestTupleStruct, usize) =
         bincode::decode_from_slice(&mut slice, Configuration::standard()).unwrap();
     assert_eq!(result, start);
+    assert_eq!(len, 5);
 }
 
 #[test]
@@ -116,9 +122,10 @@ fn test_encode_enum_struct_variant() {
 fn test_decode_enum_struct_variant() {
     let start = TestEnum::Bar { name: 5u32 };
     let mut slice = [1, 5];
-    let result: TestEnum =
+    let (result, len): (TestEnum, usize) =
         bincode::decode_from_slice(&mut slice, Configuration::standard()).unwrap();
     assert_eq!(result, start);
+    assert_eq!(len, 2);
 }
 
 #[test]
@@ -135,9 +142,10 @@ fn test_encode_enum_tuple_variant() {
 fn test_decode_enum_unit_variant() {
     let start = TestEnum::Foo;
     let mut slice = [0];
-    let result: TestEnum =
+    let (result, len): (TestEnum, usize) =
         bincode::decode_from_slice(&mut slice, Configuration::standard()).unwrap();
     assert_eq!(result, start);
+    assert_eq!(len, 1);
 }
 
 #[test]
@@ -154,9 +162,10 @@ fn test_encode_enum_unit_variant() {
 fn test_decode_enum_tuple_variant() {
     let start = TestEnum::Baz(5, 10, 1024);
     let mut slice = [2, 5, 10, 251, 0, 4];
-    let result: TestEnum =
+    let (result, len): (TestEnum, usize) =
         bincode::decode_from_slice(&mut slice, Configuration::standard()).unwrap();
     assert_eq!(result, start);
+    assert_eq!(len, 6);
 }
 
 #[derive(bincode::Decode, bincode::Encode, PartialEq, Eq, Debug)]
@@ -185,7 +194,9 @@ fn test_c_style_enum() {
     assert_eq!(ser(CStyleEnum::E), 6);
 
     fn de(num: u8) -> Result<CStyleEnum, bincode::error::DecodeError> {
-        bincode::decode_from_slice(&[num], Configuration::standard())
+        let (result, len) = bincode::decode_from_slice(&[num], Configuration::standard())?;
+        assert_eq!(len, 1);
+        Ok(result)
     }
 
     fn expected_err(idx: u32) -> Result<CStyleEnum, bincode::error::DecodeError> {

tests/issues/issue_431.rs

@@ -26,7 +26,9 @@ fn test() {
     };
     let vec = bincode::encode_to_vec(&t, Configuration::standard()).unwrap();
 
-    let decoded: T<String> = bincode::decode_from_slice(&vec, Configuration::standard()).unwrap();
+    let (decoded, len): (T<String>, usize) =
+        bincode::decode_from_slice(&vec, Configuration::standard()).unwrap();
 
     assert_eq!(t, decoded);
+    assert_eq!(len, 12);
 }

tests/serde.rs

@@ -28,10 +28,11 @@ fn test_serde_round_trip() {
     let bytes =
         bincode::encode_to_vec(SerdeRoundtrip { a: 15, b: 15 }, Configuration::standard()).unwrap();
     assert_eq!(bytes, &[15, 15]);
-    let result: SerdeRoundtrip =
+    let (result, len): (SerdeRoundtrip, usize) =
         bincode::decode_from_slice(&bytes, Configuration::standard()).unwrap();
     assert_eq!(result.a, 15);
     assert_eq!(result.b, 15);
+    assert_eq!(len, 2);
 }
 
 #[derive(Serialize, Deserialize, PartialEq, Debug)]
@@ -115,7 +116,7 @@ fn test_serialize_deserialize_owned_data() {
 
     assert_eq!(result, expected);
 
-    let output: SerdeWithOwnedData =
+    let (output, len): (SerdeWithOwnedData, usize) =
         bincode::serde::decode_from_slice(&result, Configuration::standard()).unwrap();
     assert_eq!(
         SerdeWithOwnedData {
@@ -124,6 +125,7 @@ fn test_serialize_deserialize_owned_data() {
         },
         output
     );
+    assert_eq!(len, 13);
 }
 
 #[cfg(feature = "derive")]
@@ -154,24 +156,33 @@ mod derive {
 
     #[test]
     fn test_serde_derive() {
-        fn test_encode_decode<T>(start: T)
+        fn test_encode_decode<T>(start: T, expected_len: usize)
         where
             T: bincode::Encode + bincode::Decode + PartialEq + core::fmt::Debug,
         {
             let mut slice = [0u8; 100];
             let len =
                 bincode::encode_into_slice(&start, &mut slice, Configuration::standard()).unwrap();
+            assert_eq!(len, expected_len);
             let slice = &slice[..len];
-            let result: T = bincode::decode_from_slice(&slice, Configuration::standard()).unwrap();
+            let (result, len): (T, usize) =
+                bincode::decode_from_slice(&slice, Configuration::standard()).unwrap();
 
             assert_eq!(start, result);
+            assert_eq!(len, expected_len);
         }
-        test_encode_decode(StructWithSerde {
-            serde: SerdeType { a: 5 },
-        });
-        test_encode_decode(EnumWithSerde::Unit(SerdeType { a: 5 }));
-        test_encode_decode(EnumWithSerde::Struct {
-            serde: SerdeType { a: 5 },
-        });
+        test_encode_decode(
+            StructWithSerde {
+                serde: SerdeType { a: 5 },
+            },
+            1,
+        );
+        test_encode_decode(EnumWithSerde::Unit(SerdeType { a: 5 }), 2);
+        test_encode_decode(
+            EnumWithSerde::Struct {
+                serde: SerdeType { a: 5 },
+            },
+            2,
+        );
     }
 }