gss-api: change NegHints::hint_name to GeneralStringRef type (#1779)

* der: add minimal GeneralStringRef type

Co-authored-by: Arthur Gautier <superbaloo+registrations.github@superbaloo.net>

Author: dishmaker

der/src/asn1.rs

@@ -11,6 +11,7 @@ mod bmp_string;
 mod boolean;
 mod choice;
 mod context_specific;
+mod general_string;
 mod generalized_time;
 mod ia5_string;
 mod integer;
@@ -35,6 +36,7 @@ pub use self::{
     bit_string::{BitStringIter, BitStringRef},
     choice::Choice,
     context_specific::{ContextSpecific, ContextSpecificRef},
+    general_string::GeneralStringRef,
     generalized_time::GeneralizedTime,
     ia5_string::Ia5StringRef,
     integer::{int::IntRef, uint::UintRef},

der/src/asn1/general_string.rs

@@ -0,0 +1,36 @@
+use crate::{BytesRef, DecodeValue, EncodeValue, FixedTag, Header, Length, Reader, Tag, Writer};
+
+/// This is currently `&[u8]` internally, as `GeneralString` is not fully implemented yet
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct GeneralStringRef<'a> {
+    /// Raw contents, unchecked
+    inner: BytesRef<'a>,
+}
+impl<'a> GeneralStringRef<'a> {
+    /// This is currently `&[u8]` internally, as `GeneralString` is not fully implemented yet
+    pub fn as_bytes(&self) -> &'a [u8] {
+        self.inner.as_slice()
+    }
+}
+
+impl FixedTag for GeneralStringRef<'_> {
+    const TAG: Tag = Tag::GeneralString;
+}
+impl<'a> DecodeValue<'a> for GeneralStringRef<'a> {
+    type Error = crate::Error;
+
+    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self, Self::Error> {
+        Ok(Self {
+            inner: BytesRef::decode_value(reader, header)?,
+        })
+    }
+}
+impl EncodeValue for GeneralStringRef<'_> {
+    fn value_len(&self) -> crate::Result<Length> {
+        self.inner.value_len()
+    }
+
+    fn encode_value(&self, encoder: &mut impl Writer) -> crate::Result<()> {
+        self.inner.encode_value(encoder)
+    }
+}

gss-api/src/negotiation.rs

@@ -1,7 +1,7 @@
 //! Negotiation-related types
 use der::{
-    AnyRef, Choice, Enumerated, Sequence,
-    asn1::{BitString, OctetStringRef},
+    Choice, Enumerated, Sequence,
+    asn1::{BitString, GeneralStringRef, OctetStringRef},
 };
 
 use crate::MechType;
@@ -295,14 +295,8 @@ pub enum NegState {
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Sequence)]
 pub struct NegHints<'a> {
     /// SHOULD<5> contain the string "not_defined_in_RFC4178@please_ignore".
-    /// This is currently `AnyRef` as `GeneralString` is not part of the `der` crate
-    #[asn1(
-        context_specific = "0",
-        optional = "true",
-        tag_mode = "IMPLICIT",
-        constructed = "true"
-    )]
-    pub hint_name: Option<AnyRef<'a>>, // TODO: GeneralString
+    #[asn1(context_specific = "0", optional = "true")]
+    pub hint_name: Option<GeneralStringRef<'a>>,
 
     /// Never present. MUST be omitted by the sender. Note that the encoding rules, as specified in [X690], require that this structure not be present at all, not just be zero.
     ///
@@ -389,7 +383,7 @@ mod tests {
         );
         assert_eq!(
             b"not_defined_in_RFC4178@please_ignore",
-            &neg_token.neg_hints.unwrap().hint_name.unwrap().value()[2..]
+            &neg_token.neg_hints.unwrap().hint_name.unwrap().as_bytes()
         );
     }