use updated base64

This takes advantage of the recent update to the base64 crate.

We've also removed our custom error type in favor of using the base64
error type directly.

tower-sessions-core/src/session.rs

@@ -4,13 +4,14 @@ use std::{
  fmt::{self, Display},
  hash::Hash,
  result,
- str::FromStr,
+ str::{self, FromStr},
  sync::{
  atomic::{self, AtomicBool},
  Arc,
  },
 };
 
+use base64::{engine::general_purpose::URL_SAFE_NO_PAD, DecodeError, Engine as _};
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use serde_json::Value;
 use time::{Duration, OffsetDateTime};
@@ -870,42 +871,31 @@ impl Default for Id {
 
 impl Display for Id {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- use base64::{engine::general_purpose::URL_SAFE_NO_PAD, Engine as _};
-
- let mut encoded = [0u8; 22];
+ let mut encoded = [0; 22];
  URL_SAFE_NO_PAD
  .encode_slice(self.0.to_le_bytes(), &mut encoded)
  .expect("Encoded ID must be exactly 22 bytes");
- let encoded = std::str::from_utf8(&encoded).expect("Encoded ID must be valid UTF-8");
+ let encoded = str::from_utf8(&encoded).expect("Encoded ID must be valid UTF-8");
 
  f.write_str(encoded)
  }
 }
 
 impl FromStr for Id {
- type Err = IdError;
+ type Err = base64::DecodeSliceError;
 
  fn from_str(s: &str) -> result::Result<Self, Self::Err> {
- use base64::{engine::general_purpose::URL_SAFE_NO_PAD, Engine as _};
-
- let mut decoded = [0u8; 22];
- URL_SAFE_NO_PAD.decode_slice(s.as_bytes(), &mut decoded)?;
- // N.B. The last six bytes will be zeroes.
- let id_bytes: [u8; 16] = decoded[..16].try_into().map_err(|_| Self::Err::Length)?;
+ let mut decoded = [0; 16];
+ let bytes_decoded = URL_SAFE_NO_PAD.decode_slice(s.as_bytes(), &mut decoded)?;
+ if bytes_decoded != 16 {
+  let err = DecodeError::InvalidLength(bytes_decoded);
+  return Err(base64::DecodeSliceError::DecodeError(err));
+ }
 
- Ok(Self(i128::from_le_bytes(id_bytes)))
+ Ok(Self(i128::from_le_bytes(decoded)))
  }
 }
 
-#[derive(Debug, thiserror::Error)]
-pub enum IdError {
- #[error(transparent)]
- DecodeSlice(#[from] base64::DecodeSliceError),
-
- #[error("Provided base64 string is not composed of exactly 128-bytes")]
- Length,
-}
-
 /// Record type that's appropriate for encoding and decoding sessions to and
 /// from session stores.
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]