der: add test for application tags

Author: dishmaker

der/src/asn1/application.rs

@@ -19,3 +19,30 @@ pub type ApplicationExplicitRef<'a, const TAG: u16, T> =
 /// Application class, reference, IMPLICIT
 pub type ApplicationImplicitRef<'a, const TAG: u16, T> =
     CustomClassImplicitRef<'a, TAG, T, CLASS_APPLICATION>;
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used)]
+mod tests {
+    use crate::{
+        asn1::{context_specific::ContextSpecificExplicit, OctetStringRef},
+        Decode, Encode,
+    };
+    use hex_literal::hex;
+
+    #[test]
+    fn round_trip() {
+        const EXAMPLE_BYTES: &[u8] = &hex!(
+            "A2 06"
+            "04 04"
+            "01020304"
+        );
+
+        let field =
+            ContextSpecificExplicit::<2, OctetStringRef<'_>>::from_der(EXAMPLE_BYTES).unwrap();
+        assert_eq!(field.value, OctetStringRef::new(&[1, 2, 3, 4]).unwrap());
+
+        let mut buf = [0u8; 128];
+        let encoded = field.encode_to_slice(&mut buf).unwrap();
+        assert_eq!(encoded, EXAMPLE_BYTES);
+    }
+}

der/src/asn1/context_specific.rs

@@ -22,28 +22,6 @@ pub type ContextSpecificExplicitRef<'a, const TAG: u16, T> =
 pub type ContextSpecificImplicitRef<'a, const TAG: u16, T> =
     CustomClassImplicitRef<'a, TAG, T, CLASS_CONTEXT_SPECIFIC>;
 
-// pub fn decode_implicit<'a, R: Reader<'a>, T: Tagged + DecodeValue<'a>>(
-//     number: TagNumber,
-//     reader: &mut R,
-// ) -> Result<Option<T>, T::Error> {
-//     match AnyCustomClassImplicit::decode_skipping(Class::ContextSpecific, number, reader) {
-//         Ok(Some(custom)) => Ok(Some(custom.value)),
-//         Ok(None) => Ok(None),
-//         Err(err) => Err(err),
-//     }
-// }
-
-// pub fn decode_explicit<'a, R: Reader<'a>, T: Decode<'a>>(
-//     number: TagNumber,
-//     reader: &mut R,
-// ) -> Result<Option<T>, T::Error> {
-//     match AnyCustomClassExplicit::decode_skipping(Class::ContextSpecific, number, reader) {
-//         Ok(Some(custom)) => Ok(Some(custom.value)),
-//         Ok(None) => Ok(None),
-//         Err(err) => Err(err),
-//     }
-// }
-
 #[cfg(test)]
 #[allow(clippy::unwrap_used)]
 mod tests {

der/src/asn1/private.rs

@@ -80,7 +80,6 @@ mod tests {
     use crate::{asn1::BitStringRef, Decode, Encode, SliceReader};
     use hex_literal::hex;
 
-    // Public key data from `pkcs8` crate's `ed25519-pkcs8-v2.der`
     const EXAMPLE_BYTES: &[u8] =
         &hex!("E123032100A3A7EAE3A8373830BC47E1167BC50E1DB551999651E0E2DC587623438EAC3F31");
 

der/src/tag.rs

@@ -377,6 +377,7 @@ fn parse_parts<'a, R: Reader<'a>>(first_byte: u8, reader: &mut R) -> Result<(boo
     Err(Error::new(ErrorKind::TagNumberInvalid, reader.position()))
 }
 
+/// Length of encoded tag depends only on number it encodes
 fn tag_length(tag_number: u16) -> Length {
     if tag_number <= 30 {
         Length::ONE
@@ -389,6 +390,21 @@ fn tag_length(tag_number: u16) -> Length {
     }
 }
 
+fn tag_class_number_bytes(
+    class: Class,
+    tag_number: TagNumber,
+    constructed: bool,
+    buf: &mut [u8; Tag::MAX_SIZE],
+) -> &[u8] {
+    let mut first_byte = class as u8;
+    if constructed {
+        first_byte |= CONSTRUCTED_FLAG;
+    }
+    let num = tag_number.value();
+    tag_number_bytes(first_byte, num, buf)
+}
+
+/// Tag contains class bits, constructed flag and number
 #[allow(clippy::cast_possible_truncation)]
 fn tag_number_bytes(first_byte: u8, num: u16, buf: &mut [u8; Tag::MAX_SIZE]) -> &[u8] {
     if num <= 30 {
@@ -418,14 +434,9 @@ impl Encode for Tag {
     }
 
     fn encode(&self, writer: &mut impl Writer) -> Result<()> {
-        let mut first_byte = self.class() as u8;
-        if self.is_constructed() {
-            first_byte |= CONSTRUCTED_FLAG;
-        }
-        let num = self.number().value();
-
         let mut buf = [0u8; Tag::MAX_SIZE];
-        let tag_bytes = tag_number_bytes(first_byte, num, &mut buf);
+        let tag_bytes =
+            tag_class_number_bytes(self.class(), self.number(), self.is_constructed(), &mut buf);
         writer.write(tag_bytes)
     }
 }
@@ -499,7 +510,10 @@ impl fmt::Display for Tag {
 
 impl fmt::Debug for Tag {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "Tag(0x{:02x}: {})", self.number().value(), self)
+        let mut buf = [0u8; Tag::MAX_SIZE];
+        let tag_bytes =
+            tag_class_number_bytes(self.class(), self.number(), self.is_constructed(), &mut buf);
+        write!(f, "Tag({:02X?}: {})", tag_bytes, self)
     }
 }