der_derive: add DecodeValue, EncodeValue macros (#1722)

* der_derive: add SequenceDecode, SequenceEncode macros

* der_derive: rename macros to DecodeValue, EncodeValue

Author: dishmaker

der/src/lib.rs

@@ -385,7 +385,7 @@ pub use crate::{
 pub use crate::{asn1::Any, document::Document};
 
 #[cfg(feature = "derive")]
-pub use der_derive::{BitString, Choice, Enumerated, Sequence, ValueOrd};
+pub use der_derive::{BitString, Choice, DecodeValue, EncodeValue, Enumerated, Sequence, ValueOrd};
 
 #[cfg(feature = "flagset")]
 pub use flagset;

der/tests/derive.rs

@@ -735,6 +735,56 @@ mod sequence {
     }
 }
 
+/// Custom derive test cases for the `EncodeValue` macro.
+mod encode_value {
+    use der::{Encode, EncodeValue, FixedTag, Tag};
+    use hex_literal::hex;
+
+    #[derive(EncodeValue, Default, Eq, PartialEq, Debug)]
+    #[asn1(tag_mode = "IMPLICIT")]
+    pub struct EncodeOnlyCheck<'a> {
+        #[asn1(type = "OCTET STRING", context_specific = "5")]
+        pub field: &'a [u8],
+    }
+    impl FixedTag for EncodeOnlyCheck<'_> {
+        const TAG: Tag = Tag::Sequence;
+    }
+
+    #[test]
+    fn sequence_encode_only_to_der() {
+        let obj = EncodeOnlyCheck {
+            field: &[0x33, 0x44],
+        };
+
+        let der_encoded = obj.to_der().unwrap();
+
+        assert_eq!(der_encoded, hex!("30 04 85 02 33 44"));
+    }
+}
+
+/// Custom derive test cases for the `DecodeValue` macro.
+mod decode_value {
+    use der::{Decode, DecodeValue, FixedTag, Tag};
+    use hex_literal::hex;
+
+    #[derive(DecodeValue, Default, Eq, PartialEq, Debug)]
+    #[asn1(tag_mode = "IMPLICIT")]
+    pub struct DecodeOnlyCheck<'a> {
+        #[asn1(type = "OCTET STRING", context_specific = "5")]
+        pub field: &'a [u8],
+    }
+    impl FixedTag for DecodeOnlyCheck<'_> {
+        const TAG: Tag = Tag::Sequence;
+    }
+
+    #[test]
+    fn sequence_decode_only_from_der() {
+        let obj = DecodeOnlyCheck::from_der(&hex!("30 04 85 02 33 44")).unwrap();
+
+        assert_eq!(obj.field, &[0x33, 0x44]);
+    }
+}
+
 /// Custom derive test cases for the `BitString` macro.
 #[cfg(feature = "std")]
 mod bitstring {

der_derive/src/lib.rs

@@ -261,7 +261,7 @@ pub fn derive_enumerated(input: TokenStream) -> TokenStream {
     }
 }
 
-/// Derive the [`Sequence`][1] trait on a `struct`.
+/// Derive the [`DecodeValue`][1], [`EncodeValue`][2], [`Sequence`][3] traits on a `struct`.
 ///
 /// This custom derive macro can be used to automatically impl the
 /// `Sequence` trait for any struct which can be decoded/encoded as an
@@ -289,16 +289,42 @@ pub fn derive_enumerated(input: TokenStream) -> TokenStream {
 ///
 /// # `#[asn1(type = "...")]` attribute
 ///
-/// See [toplevel documentation for the `der_derive` crate][2] for more
+/// See [toplevel documentation for the `der_derive` crate][4] for more
 /// information about the `#[asn1]` attribute.
 ///
-/// [1]: https://docs.rs/der/latest/der/trait.Sequence.html
-/// [2]: https://docs.rs/der_derive/
+/// [1]: https://docs.rs/der/latest/der/trait.DecodeValue.html
+/// [2]: https://docs.rs/der/latest/der/trait.EncodeValue.html
+/// [3]: https://docs.rs/der/latest/der/trait.Sequence.html
+/// [4]: https://docs.rs/der_derive/
 #[proc_macro_derive(Sequence, attributes(asn1))]
 pub fn derive_sequence(input: TokenStream) -> TokenStream {
     let input = parse_macro_input!(input as DeriveInput);
     match DeriveSequence::new(input) {
-        Ok(t) => t.to_tokens().into(),
+        Ok(t) => t.to_tokens_all().into(),
+        Err(e) => e.to_compile_error().into(),
+    }
+}
+
+/// Derive the [`EncodeValue`][1] trait on a `struct`.
+///
+/// [1]: https://docs.rs/der/latest/der/trait.EncodeValue.html
+#[proc_macro_derive(EncodeValue, attributes(asn1))]
+pub fn derive_sequence_encode(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    match DeriveSequence::new(input) {
+        Ok(t) => t.to_tokens_encode().into(),
+        Err(e) => e.to_compile_error().into(),
+    }
+}
+
+/// Derive the [`DecodeValue`][1] trait on a `struct`.
+///
+/// [1]: https://docs.rs/der/latest/der/trait.DecodeValue.html
+#[proc_macro_derive(DecodeValue, attributes(asn1))]
+pub fn derive_sequence_decode(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    match DeriveSequence::new(input) {
+        Ok(t) => t.to_tokens_decode().into(),
         Err(e) => e.to_compile_error().into(),
     }
 }

der_derive/src/sequence.rs

@@ -7,7 +7,7 @@ use crate::{ErrorType, TypeAttrs, default_lifetime};
 use field::SequenceField;
 use proc_macro2::TokenStream;
 use quote::{ToTokens, quote};
-use syn::{DeriveInput, GenericParam, Generics, Ident, LifetimeParam};
+use syn::{DeriveInput, GenericParam, Generics, Ident, Lifetime, LifetimeParam};
 
 /// Derive the `Sequence` trait for a struct
 pub(crate) struct DeriveSequence {
@@ -51,13 +51,10 @@ impl DeriveSequence {
         })
     }
 
-    /// Lower the derived output into a [`TokenStream`].
-    pub fn to_tokens(&self) -> TokenStream {
-        let ident = &self.ident;
+    /// Use the first lifetime parameter as lifetime for Decode/Encode lifetime
+    /// if none found, add one.
+    fn calc_lifetime(&self) -> (Generics, Lifetime) {
         let mut generics = self.generics.clone();
-
-        // Use the first lifetime parameter as lifetime for Decode/Encode lifetime
-        // if none found, add one.
         let lifetime = generics
             .lifetimes()
             .next()
@@ -69,23 +66,39 @@ impl DeriveSequence {
                     .insert(0, GenericParam::Lifetime(LifetimeParam::new(lt.clone())));
                 lt
             });
-
         // We may or may not have inserted a lifetime.
+        (generics, lifetime)
+    }
+
+    /// Lower the derived output into a [`TokenStream`] for Sequence trait impl.
+    pub fn to_tokens_sequence_trait(&self) -> TokenStream {
+        let ident = &self.ident;
+
+        let (der_generics, lifetime) = self.calc_lifetime();
+
         let (_, ty_generics, where_clause) = self.generics.split_for_impl();
-        let (impl_generics, _, _) = generics.split_for_impl();
+        let (impl_generics, _, _) = der_generics.split_for_impl();
+
+        quote! {
+            impl #impl_generics ::der::Sequence<#lifetime> for #ident #ty_generics #where_clause {}
+        }
+    }
+
+    /// Lower the derived output into a [`TokenStream`] for DecodeValue trait impl.
+    pub fn to_tokens_decode(&self) -> TokenStream {
+        let ident = &self.ident;
+
+        let (der_generics, lifetime) = self.calc_lifetime();
+
+        let (_, ty_generics, where_clause) = self.generics.split_for_impl();
+        let (impl_generics, _, _) = der_generics.split_for_impl();
 
         let mut decode_body = Vec::new();
         let mut decode_result = Vec::new();
-        let mut encoded_lengths = Vec::new();
-        let mut encode_fields = Vec::new();
 
         for field in &self.fields {
             decode_body.push(field.to_decode_tokens());
             decode_result.push(&field.ident);
-
-            let field = field.to_encode_tokens();
-            encoded_lengths.push(quote!(#field.encoded_len()?));
-            encode_fields.push(quote!(#field.encode(writer)?;));
         }
 
         let error = self.error.to_token_stream();
@@ -109,6 +122,26 @@ impl DeriveSequence {
                     })
                 }
             }
+        }
+    }
+
+    /// Lower the derived output into a [`TokenStream`] for EncodeValue trait impl.
+    pub fn to_tokens_encode(&self) -> TokenStream {
+        let ident = &self.ident;
+
+        let (_, ty_generics, where_clause) = self.generics.split_for_impl();
+        let (impl_generics, _, _) = self.generics.split_for_impl();
+
+        let mut encoded_lengths = Vec::new();
+        let mut encode_fields = Vec::new();
+
+        for field in &self.fields {
+            let field = field.to_encode_tokens();
+            encoded_lengths.push(quote!(#field.encoded_len()?));
+            encode_fields.push(quote!(#field.encode(writer)?;));
+        }
+
+        quote! {
 
             impl #impl_generics ::der::EncodeValue for #ident #ty_generics #where_clause {
                 fn value_len(&self) -> ::der::Result<::der::Length> {
@@ -127,8 +160,22 @@ impl DeriveSequence {
                     Ok(())
                 }
             }
+        }
+    }
 
-            impl #impl_generics ::der::Sequence<#lifetime> for #ident #ty_generics #where_clause {}
+    /// Lower the derived output into a [`TokenStream`] for trait impls:
+    /// - EncodeValue
+    /// - DecodeValue
+    /// - Sequence
+    pub fn to_tokens_all(&self) -> TokenStream {
+        let decode_tokens = self.to_tokens_decode();
+        let encode_tokens = self.to_tokens_encode();
+        let sequence_trait_tokens = self.to_tokens_sequence_trait();
+
+        quote! {
+            #decode_tokens
+            #encode_tokens
+            #sequence_trait_tokens
         }
     }
 }