From e414cabd33c4a3c21c24df2063672058632b5bfe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lena=20Hellstr=C3=B6m?= <lena@stygian.nexus>
Date: Mon, 20 Sep 2021 16:35:36 +0200
Subject: [PATCH] Add derive for Decodeable

---
 derive/src/derive_struct.rs | 29 ++++++++++++++++++++++++++++-
 src/de/mod.rs               | 26 ++++++++++++++++++++------
 tests/derive.rs             | 21 ++++++++++++++++++++-
 3 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/derive/src/derive_struct.rs b/derive/src/derive_struct.rs
index 1668657..5680850 100644
--- a/derive/src/derive_struct.rs
+++ b/derive/src/derive_struct.rs
@@ -63,6 +63,33 @@ impl DeriveStruct {
     }
 
     pub fn to_decodable(self) -> Result<TokenStream> {
-        unimplemented!()
+        let DeriveStruct {
+            name,
+            generics,
+            fields,
+        } = self;
+
+        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+        let fields = fields
+            .into_iter()
+            .map(|field| {
+                quote! {
+                    #field: bincode::de::Decodable::decode(&mut decoder)?,
+                }
+            })
+            .collect::<Vec<_>>();
+
+        let result = quote! {
+            impl #impl_generics bincode::de::Decodable for #name #ty_generics #where_clause {
+                fn decode<D: bincode::de::Decode>(mut decoder: D) -> Result<#name #ty_generics, bincode::error::DecodeError> {
+                    Ok(#name {
+                        #(#fields)*
+                    })
+                }
+
+            }
+        };
+        Ok(result.into())
     }
 }
diff --git a/src/de/mod.rs b/src/de/mod.rs
index 0295e58..8ee5567 100644
--- a/src/de/mod.rs
+++ b/src/de/mod.rs
@@ -1,7 +1,7 @@
 use core::marker::PhantomData;
 
 use crate::{
-    config::{Config, Endian},
+    config::{Config, Endian, IntEncoding},
     error::DecodeError,
 };
 use read::Reader;
@@ -33,12 +33,26 @@ impl<'de, R: Reader<'de>, C: Config> Decoder<R, C> {
 
 impl<'a, 'de, R: Reader<'de>, C: Config> Decode for &'a mut Decoder<R, C> {
     fn decode_u32(&mut self) -> Result<u32, DecodeError> {
-        let mut bytes = [0u8; 4];
+        Ok(match C::INT_ENCODING {
+            IntEncoding::Variable => crate::varint::varint_decode_u32(&mut self.reader, C::ENDIAN)?,
+            IntEncoding::Fixed => {
+                let mut bytes = [0u8; 4];
 
-        self.reader.read(bytes.as_mut())?;
-        Ok(match C::ENDIAN {
-            Endian::Little => u32::from_le_bytes(bytes),
-            Endian::Big => u32::from_be_bytes(bytes),
+                self.reader.read(bytes.as_mut())?;
+                match C::ENDIAN {
+                    Endian::Little => u32::from_le_bytes(bytes),
+                    Endian::Big => u32::from_be_bytes(bytes),
+                }
+            }
         })
     }
 }
+
+impl<'a, T> Decode for &'a mut T
+where
+    T: Decode,
+{
+    fn decode_u32(&mut self) -> Result<u32, DecodeError> {
+        T::decode_u32(self)
+    }
+}
diff --git a/tests/derive.rs b/tests/derive.rs
index 155925b..27c23f3 100644
--- a/tests/derive.rs
+++ b/tests/derive.rs
@@ -1,4 +1,4 @@
-use bincode::enc::Encodeable;
+use bincode::{de::Decodable, enc::Encodeable};
 
 #[derive(bincode::Encodable, PartialEq, Debug)]
 pub struct Test<T: Encodeable> {
@@ -7,6 +7,13 @@ pub struct Test<T: Encodeable> {
     c: u8,
 }
 
+#[derive(bincode::Decodable, PartialEq, Debug, Eq)]
+pub struct Test2<T: Decodable> {
+    a: T,
+    b: u32,
+    c: u32,
+}
+
 #[test]
 fn test_encodable() {
     let start = Test {
@@ -19,3 +26,15 @@ fn test_encodable() {
     assert_eq!(bytes_written, 3);
     assert_eq!(&slice[..bytes_written], &[10, 10, 20]);
 }
+
+#[test]
+fn test_decodable() {
+    let start = Test2 {
+        a: 5u32,
+        b: 10u32,
+        c: 1024u32,
+    };
+    let mut slice = [5, 10, 251, 0, 4];
+    let result: Test2<u32> = bincode::decode(&mut slice).unwrap();
+    assert_eq!(result, start);
+}