Added an option to encode a fixed array length or to skip it

src/config.rs

@@ -12,7 +12,10 @@
 //!     .with_little_endian()
 //!     // pick one of:
 //!     .with_variable_int_encoding()
-//!     .with_fixed_int_encoding();
+//!     .with_fixed_int_encoding()
+//!     // pick one of:
+//!     .skip_fixed_array_length()
+//!     .write_fixed_array_length();
 //! ```
 //!
 //! See [Config] for more information on the configuration options.
@@ -26,12 +29,15 @@ use core::marker::PhantomData;
 ///
 /// - [with_little_endian] and [with_big_endian]
 /// - [with_fixed_int_encoding] and [with_variable_int_encoding]
+/// - [skip_fixed_array_length] and [write_fixed_array_length]
 ///
 ///
 /// [with_little_endian]: #method.with_little_endian
 /// [with_big_endian]: #method.with_big_endian
 /// [with_fixed_int_encoding]: #method.with_fixed_int_encoding
 /// [with_variable_int_encoding]: #method.with_variable_int_encoding
+/// [skip_fixed_array_length]: #method.skip_fixed_array_length
+/// [write_fixed_array_length]: #method.write_fixed_array_length
 pub trait Config: InternalConfig {
     /// Makes bincode encode all integer types in big endian.
     fn with_big_endian(self) -> BigEndian<Self> {
@@ -97,6 +103,16 @@ pub trait Config: InternalConfig {
     fn with_fixed_int_encoding(self) -> Fixint<Self> {
         Fixint { _pd: PhantomData }
     }
+
+    /// Skip writing the length of fixed size arrays (`[u8; N]`) before writing the array
+    fn skip_fixed_array_length(self) -> SkipFixedArrayLength<Self> {
+        SkipFixedArrayLength { _pd: PhantomData }
+    }
+
+    /// Write the length of fixed size arrays (`[u8; N]`) before writing the array
+    fn write_fixed_array_length(self) -> WriteFixedArrayLength<Self> {
+        WriteFixedArrayLength { _pd: PhantomData }
+    }
 }
 
 impl<T: InternalConfig> Config for T {}
@@ -104,6 +120,7 @@ impl<T: InternalConfig> Config for T {}
 /// The default config. By default this will be:
 /// - Little endian
 /// - Variable int encoding
+/// - Skip fixed array length
 #[derive(Copy, Clone)]
 pub struct Default;
 
@@ -112,6 +129,7 @@ impl InternalConfig for Default {
     const INT_ENCODING: IntEncoding = IntEncoding::Variable;
     const LIMIT: Option<u64> = None;
     const ALLOW_TRAILING: bool = true;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = true;
 }
 
 #[doc(hidden)]
@@ -125,6 +143,7 @@ impl<C: InternalConfig> InternalConfig for BigEndian<C> {
     const INT_ENCODING: IntEncoding = C::INT_ENCODING;
     const LIMIT: Option<u64> = C::LIMIT;
     const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = C::SKIP_FIXED_ARRAY_LENGTH;
 }
 
 #[doc(hidden)]
@@ -138,6 +157,7 @@ impl<C: InternalConfig> InternalConfig for LittleEndian<C> {
     const INT_ENCODING: IntEncoding = C::INT_ENCODING;
     const LIMIT: Option<u64> = C::LIMIT;
     const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = C::SKIP_FIXED_ARRAY_LENGTH;
 }
 
 #[doc(hidden)]
@@ -151,6 +171,7 @@ impl<C: InternalConfig> InternalConfig for Fixint<C> {
     const INT_ENCODING: IntEncoding = IntEncoding::Fixed;
     const LIMIT: Option<u64> = C::LIMIT;
     const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = C::SKIP_FIXED_ARRAY_LENGTH;
 }
 
 #[doc(hidden)]
@@ -164,6 +185,35 @@ impl<C: InternalConfig> InternalConfig for Varint<C> {
     const INT_ENCODING: IntEncoding = IntEncoding::Variable;
     const LIMIT: Option<u64> = C::LIMIT;
     const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = C::SKIP_FIXED_ARRAY_LENGTH;
+}
+
+#[doc(hidden)]
+#[derive(Copy, Clone)]
+pub struct SkipFixedArrayLength<C: Config> {
+    _pd: PhantomData<C>,
+}
+
+impl<C: InternalConfig> InternalConfig for SkipFixedArrayLength<C> {
+    const ENDIAN: Endian = C::ENDIAN;
+    const INT_ENCODING: IntEncoding = C::INT_ENCODING;
+    const LIMIT: Option<u64> = C::LIMIT;
+    const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = true;
+}
+
+#[doc(hidden)]
+#[derive(Copy, Clone)]
+pub struct WriteFixedArrayLength<C: Config> {
+    _pd: PhantomData<C>,
+}
+
+impl<C: InternalConfig> InternalConfig for WriteFixedArrayLength<C> {
+    const ENDIAN: Endian = C::ENDIAN;
+    const INT_ENCODING: IntEncoding = C::INT_ENCODING;
+    const LIMIT: Option<u64> = C::LIMIT;
+    const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+    const SKIP_FIXED_ARRAY_LENGTH: bool = false;
 }
 
 mod internal {
@@ -172,6 +222,7 @@ mod internal {
         const INT_ENCODING: IntEncoding;
         const LIMIT: Option<u64>;
         const ALLOW_TRAILING: bool;
+        const SKIP_FIXED_ARRAY_LENGTH: bool;
     }
 
     #[derive(PartialEq, Eq)]
@@ -194,5 +245,6 @@ mod internal {
         const INT_ENCODING: IntEncoding = C::INT_ENCODING;
         const LIMIT: Option<u64> = C::LIMIT;
         const ALLOW_TRAILING: bool = C::ALLOW_TRAILING;
+        const SKIP_FIXED_ARRAY_LENGTH: bool = C::SKIP_FIXED_ARRAY_LENGTH;
     }
 }

src/de/decoder.rs

@@ -228,6 +228,15 @@ impl<'a, 'de, R: Reader<'de>, C: Config> Decode for &'a mut Decoder<R, C> {
 
     fn decode_array<const N: usize>(&mut self) -> Result<[u8; N], DecodeError> {
         let mut array = [0u8; N];
+        if !C::SKIP_FIXED_ARRAY_LENGTH {
+            let length = self.decode_usize()?;
+            if length != N {
+                return Err(DecodeError::ArrayLengthMismatch {
+                    found: length,
+                    required: N,
+                });
+            }
+        }
         self.reader.read(&mut array)?;
         Ok(array)
     }

src/enc/encoder.rs

@@ -195,6 +195,9 @@ impl<'a, W: Writer, C: Config> Encode for &'a mut Encoder<W, C> {
     }
 
     fn encode_array<const N: usize>(&mut self, val: [u8; N]) -> Result<(), EncodeError> {
+        if !C::SKIP_FIXED_ARRAY_LENGTH {
+            self.encode_usize(N)?;
+        }
         self.writer.write(&val)
     }
 

src/error.rs

@@ -52,6 +52,14 @@ pub enum DecodeError {
 
     /// The decoder tried to decode a `bool` and failed. The given value is what is actually read.
     InvalidBooleanValue(u8),
+
+    /// The decoder tried to decode an array of length `required`, but the binary data contained an array of length `found`.
+    ArrayLengthMismatch {
+        /// The length of the array required by the rust type.
+        required: usize,
+        /// The length of the array found in the binary format.
+        found: usize,
+    },
 }
 
 /// Integer types. Used by [DecodeError]. These types have no purpose other than being shown in errors.

tests/basic_types.rs

@@ -11,7 +11,7 @@ where
         + 'static,
     C: Config,
 {
-    let mut buffer = [0u8; 32];
+    let mut buffer = [0u8; 1024];
     let len = bincode::encode_into_slice_with_config(element.clone(), &mut buffer, config).unwrap();
     println!(
         "{:?}: {:?} ({:?})",
@@ -32,27 +32,62 @@ where
         + Clone
         + 'static,
 {
+    // A matrix of each different config option possible
     the_same_with_config(
         element.clone(),
         config::Default
             .with_little_endian()
-            .with_fixed_int_encoding(),
+            .with_fixed_int_encoding()
+            .skip_fixed_array_length(),
     );
     the_same_with_config(
         element.clone(),
-        config::Default.with_big_endian().with_fixed_int_encoding(),
+        config::Default
+            .with_big_endian()
+            .with_fixed_int_encoding()
+            .skip_fixed_array_length(),
     );
     the_same_with_config(
         element.clone(),
         config::Default
             .with_little_endian()
-            .with_variable_int_encoding(),
+            .with_variable_int_encoding()
+            .skip_fixed_array_length(),
+    );
+    the_same_with_config(
+        element.clone(),
+        config::Default
+            .with_big_endian()
+            .with_variable_int_encoding()
+            .skip_fixed_array_length(),
+    );
+    the_same_with_config(
+        element.clone(),
+        config::Default
+            .with_little_endian()
+            .with_fixed_int_encoding()
+            .write_fixed_array_length(),
+    );
+    the_same_with_config(
+        element.clone(),
+        config::Default
+            .with_big_endian()
+            .with_fixed_int_encoding()
+            .write_fixed_array_length(),
+    );
+    the_same_with_config(
+        element.clone(),
+        config::Default
+            .with_little_endian()
+            .with_variable_int_encoding()
+            .write_fixed_array_length(),
     );
     the_same_with_config(
         element,
         config::Default
             .with_big_endian()
-            .with_variable_int_encoding(),
+            .with_variable_int_encoding()
+            .write_fixed_array_length(),
     );
 }
 
@@ -95,6 +130,27 @@ fn test_numbers() {
     the_same((1u8, 2u8, 3u8, 4u8, 5u8, 6u8));
     the_same((1u8, 2u8, 3u8, 4u8, 5u8, 6u8, 7u8));
     the_same((1u8, 2u8, 3u8, 4u8, 5u8, 6u8, 7u8, 8u8));
+
+    // arrays
+    #[rustfmt::skip]
+    the_same([
+        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
+        17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,
+        33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
+        49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64,
+        65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,
+        81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96,
+        97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112,
+        113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128,
+        129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144,
+        145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160,
+        161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176,
+        177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192,
+        193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208,
+        209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224,
+        225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240,
+        241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255
+    ]);
 }
 
 #[test]