Make TagNumber support tags beyond 30.

der/src/asn1/context_specific.rs

@@ -89,9 +89,7 @@ impl<T> ContextSpecific<T> {
         F: FnOnce(&mut R) -> Result<Self, E>,
         E: From<Error>,
     {
-        while let Some(octet) = reader.peek_byte() {
-            let tag = Tag::try_from(octet)?;
-
+        while let Some(tag) = Tag::peek_optional(reader)? {
             if !tag.is_context_specific() || (tag.number() > tag_number) {
                 break;
             } else if tag.number() == tag_number {

der/src/asn1/optional.rs

@@ -10,8 +10,8 @@ where
     type Error = T::Error;
 
     fn decode<R: Reader<'a>>(reader: &mut R) -> Result<Option<T>, Self::Error> {
-        if let Some(byte) = reader.peek_byte() {
-            if T::can_decode(Tag::try_from(byte)?) {
+        if let Some(tag) = Tag::peek_optional(reader)? {
+            if T::can_decode(tag) {
                 return T::decode(reader).map(Some);
             }
         }

der/src/encode.rs

@@ -73,7 +73,7 @@ where
 {
     /// Compute the length of this value in bytes when encoded as ASN.1 DER.
     fn encoded_len(&self) -> Result<Length> {
-        self.value_len().and_then(|len| len.for_tlv())
+        self.value_len().and_then(|len| len.for_tlv(self.tag()))
     }
 
     /// Encode this value as ASN.1 DER using the provided [`Writer`].

der/src/header.rs

@@ -15,7 +15,7 @@ pub struct Header {
 
 impl Header {
     /// Maximum number of DER octets a header can be in this crate.
-    pub(crate) const MAX_SIZE: usize = 1 + Length::MAX_SIZE;
+    pub(crate) const MAX_SIZE: usize = Tag::MAX_SIZE + Length::MAX_SIZE;
 
     /// Create a new [`Header`] from a [`Tag`] and a specified length.
     ///

der/src/length.rs

@@ -1,6 +1,6 @@
 //! Length calculations for encoded ASN.1 DER values
 
-use crate::{Decode, DerOrd, Encode, Error, ErrorKind, Reader, Result, SliceWriter, Writer};
+use crate::{Decode, DerOrd, Encode, Error, ErrorKind, Reader, Result, SliceWriter, Tag, Writer};
 use core::{
     cmp::Ordering,
     fmt,
@@ -51,8 +51,8 @@ impl Length {
 
     /// Get the length of DER Tag-Length-Value (TLV) encoded data if `self`
     /// is the length of the inner "value" portion of the message.
-    pub fn for_tlv(self) -> Result<Self> {
-        Self::ONE + self.encoded_len()? + self
+    pub fn for_tlv(self, tag: Tag) -> Result<Self> {
+        tag.encoded_len()? + self.encoded_len()? + self
     }
 
     /// Perform saturating addition of two lengths.

der/src/reader.rs

@@ -115,13 +115,10 @@ pub trait Reader<'r>: Sized {
         Header::peek(self)
     }
 
-    /// Peek at the next byte in the reader.
+    /// Peek at the next tag in the reader.
     #[deprecated(since = "0.8.0-rc.1", note = "use `Tag::peek` instead")]
     fn peek_tag(&self) -> Result<Tag, Error> {
-        match self.peek_byte() {
-            Some(byte) => byte.try_into(),
-            None => Err(Error::incomplete(self.input_len())),
-        }
+        Tag::peek(self)
     }
 
     /// Read a single byte.