ssh-encoding: add derive feature + extend derive functionallity

ssh-derive/src/attributes.rs

@@ -0,0 +1,97 @@
+use proc_macro2::TokenStream;
+use quote::quote;
+
+pub(crate) struct ContainerAttributes {
+    pub(crate) length_prefixed: bool,
+    pub(crate) discriminant_type: Option<TokenStream>,
+}
+
+impl TryFrom<&syn::DeriveInput> for ContainerAttributes {
+    type Error = syn::Error;
+
+    fn try_from(input: &syn::DeriveInput) -> Result<Self, Self::Error> {
+        let mut length_prefixed = false;
+        let mut discriminant_type = None;
+        for attr in &input.attrs {
+            if attr.path().is_ident("ssh") {
+                attr.parse_nested_meta(|meta| {
+                    // #[ssh(length_prefixed)]
+                    if meta.path.is_ident("length_prefixed") {
+                        length_prefixed = true;
+                    } else {
+                        return Err(syn::Error::new_spanned(meta.path, "unknown attribute"));
+                    }
+                    Ok(())
+                })?;
+            } else if attr.path().is_ident("repr") {
+                attr.parse_nested_meta(|meta| {
+                    // #[repr(u8)]  or similar
+                    // https://doc.rust-lang.org/reference/type-layout.html#primitive-representations
+                    if meta.path.is_ident("u8") {
+                        discriminant_type = Some(quote! {u8});
+                    } else if meta.path.is_ident("u16") {
+                        discriminant_type = Some(quote! {u16});
+                    } else if meta.path.is_ident("u32") {
+                        discriminant_type = Some(quote! {u32});
+                    } else if meta.path.is_ident("u64") {
+                        discriminant_type = Some(quote! {u64});
+                    } else if meta.path.is_ident("u128") {
+                        discriminant_type = Some(quote! {u128});
+                    } else if meta.path.is_ident("usize") {
+                        discriminant_type = Some(quote! {usize});
+                    } else if meta.path.is_ident("i8") {
+                        discriminant_type = Some(quote! {i8});
+                    } else if meta.path.is_ident("i16") {
+                        discriminant_type = Some(quote! {i16});
+                    } else if meta.path.is_ident("i32") {
+                        discriminant_type = Some(quote! {i32});
+                    } else if meta.path.is_ident("i64") {
+                        discriminant_type = Some(quote! {i64});
+                    } else if meta.path.is_ident("i128") {
+                        discriminant_type = Some(quote! {i128});
+                    } else if meta.path.is_ident("isize") {
+                        discriminant_type = Some(quote! {isize});
+                    } else {
+                        return Err(syn::Error::new_spanned(
+                            meta.path,
+                            "unsupported repr for deriving Encode/Decode, must be a primitive integer type",
+                        ));
+                    }
+                    Ok(())
+                })?;
+            }
+        }
+
+        Ok(Self {
+            length_prefixed,
+            discriminant_type,
+        })
+    }
+}
+
+pub(crate) struct FieldAttributes {
+    pub(crate) length_prefixed: bool,
+}
+
+impl TryFrom<&syn::Field> for FieldAttributes {
+    type Error = syn::Error;
+
+    fn try_from(field: &syn::Field) -> Result<Self, Self::Error> {
+        let mut length_prefixed = false;
+        for attr in &field.attrs {
+            if attr.path().is_ident("ssh") {
+                attr.parse_nested_meta(|meta| {
+                    // #[ssh(length_prefixed)]
+                    if meta.path.is_ident("length_prefixed") {
+                        length_prefixed = true;
+                    } else {
+                        return Err(syn::Error::new_spanned(meta.path, "unknown attribute"));
+                    }
+                    Ok(())
+                })?;
+            }
+        }
+
+        Ok(Self { length_prefixed })
+    }
+}