webauthn_rp

bin.rs (28095B)

---

 use super::{
     super::super::bin::{
         Decode, DecodeBuffer, EncDecErr, Encode, EncodeBuffer, EncodeBufferFallible as _,
     },
     Aaguid, Attestation, AuthenticationExtensionsPrfOutputs, AuthenticatorAttachment,
     AuthenticatorExtensionOutputMetadata, AuthenticatorExtensionOutputStaticState, Backup,
     ClientExtensionsOutputsMetadata, ClientExtensionsOutputsStaticState, CompressedP256PubKey,
     CompressedP384PubKey, CompressedPubKey, CredentialPropertiesOutput, CredentialProtectionPolicy,
     DynamicState, Ed25519PubKey, FourToSixtyThree, Metadata, ResidentKeyRequirement, RsaPubKey,
     StaticState, UncompressedP256PubKey, UncompressedP384PubKey, UncompressedPubKey,
 };
 use core::{
     convert::Infallible,
     error::Error,
     fmt::{self, Display, Formatter},
 };
 use p256::{
     NistP256,
     elliptic_curve::{Curve, generic_array::typenum::ToInt as _},
 };
 use p384::NistP384;
 impl EncodeBuffer for CredentialProtectionPolicy {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         match *self {
             Self::None => 0u8,
             Self::UserVerificationOptional => 1,
             Self::UserVerificationOptionalWithCredentialIdList => 2,
             Self::UserVerificationRequired => 3,
         }
         .encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for CredentialProtectionPolicy {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         u8::decode_from_buffer(data).and_then(|val| match val {
             0 => Ok(Self::None),
             1 => Ok(Self::UserVerificationOptional),
             2 => Ok(Self::UserVerificationOptionalWithCredentialIdList),
             3 => Ok(Self::UserVerificationRequired),
             _ => Err(EncDecErr),
         })
     }
 }
 impl EncodeBuffer for ResidentKeyRequirement {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         match *self {
             Self::Required => 0u8,
             Self::Discouraged => 1,
             Self::Preferred => 2,
         }
         .encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for ResidentKeyRequirement {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         u8::decode_from_buffer(data).and_then(|val| match val {
             0 => Ok(Self::Required),
             1 => Ok(Self::Discouraged),
             2 => Ok(Self::Preferred),
             _ => Err(EncDecErr),
         })
     }
 }
 impl EncodeBuffer for Ed25519PubKey<&[u8]> {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         // We don't rely on `[u8]::encode_into_buffer` since
         // we always know the `slice` has length 32; thus
         // we want to "pretend" this is an array (i.e., don't encode the length).
         buffer.extend_from_slice(self.0);
     }
 }
 impl<'a> DecodeBuffer<'a> for Ed25519PubKey<[u8; ed25519_dalek::PUBLIC_KEY_LENGTH]> {
     type Err = EncDecErr;
     // We don't verify `Self` is in fact "valid" (i.e., we don't call
     // [`Self::validate`]) since that's expensive and an error will
     // happen later during authentication anyway. Note even if we did,
     // that wouldn't detect a public key that was altered in persistent
     // storage in such a way that it's still valid; thus there is no
     // benefit in performing "expensive" validation checks.
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         <[u8; ed25519_dalek::PUBLIC_KEY_LENGTH]>::decode_from_buffer(data).map(Self)
     }
 }
 impl EncodeBuffer for UncompressedP256PubKey<'_> {
     #[expect(clippy::indexing_slicing, reason = "comment justifies its correctness")]
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         /// Number of bytes the y-coordinate takes.
         const Y_LEN: usize = <NistP256 as Curve>::FieldBytesSize::INT;
         /// The index of the least significant byte of the y-coordinate.
         const ODD_BYTE_INDEX: usize = Y_LEN - 1;
         // We don't rely on `[u8]::encode_into_buffer` since
         // we always know the `slice` has length 32; thus
         // we want to "pretend" this is an array (i.e., don't encode the length).
         buffer.extend_from_slice(self.0);
         // `self.1.len() == 32` and `ODD_BYTE_INDEX == 31`, so indexing is fine.
         (self.1[ODD_BYTE_INDEX] & 1 == 1).encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for CompressedP256PubKey<[u8; <NistP256 as Curve>::FieldBytesSize::INT]> {
     type Err = EncDecErr;
     // We don't verify `Self` is in fact "valid" (i.e., we don't call
     // [`Self::validate`]) since that's expensive and an error will
     // happen later during authentication anyway. Note even if we did,
     // that wouldn't detect a public key that was altered in persistent
     // storage in such a way that it's still valid; thus there is no
     // benefit in performing "expensive" validation checks.
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         <[u8; <NistP256 as Curve>::FieldBytesSize::INT]>::decode_from_buffer(data)
             .and_then(|x| bool::decode_from_buffer(data).map(|y_is_odd| Self { x, y_is_odd }))
     }
 }
 impl EncodeBuffer for UncompressedP384PubKey<'_> {
     #[expect(clippy::indexing_slicing, reason = "comment justifies its correctness")]
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         /// Number of bytes the y-coordinate takes.
         const Y_LEN: usize = <NistP384 as Curve>::FieldBytesSize::INT;
         /// The index of the least significant byte of the y-coordinate.
         const ODD_BYTE_INDEX: usize = Y_LEN - 1;
         // We don't rely on `[u8]::encode_into_buffer` since
         // we always know the `slice` has length 48; thus
         // we want to "pretend" this is an array (i.e., don't encode the length).
         buffer.extend_from_slice(self.0);
         // `self.1.len() == 48` and `ODD_BYTE_INDEX == 47`, so indexing is fine.
         (self.1[ODD_BYTE_INDEX] & 1 == 1).encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for CompressedP384PubKey<[u8; <NistP384 as Curve>::FieldBytesSize::INT]> {
     type Err = EncDecErr;
     // We don't verify `Self` is in fact "valid" (i.e., we don't call
     // [`Self::validate`]) since that's expensive and an error will
     // happen later during authentication anyway. Note even if we did,
     // that wouldn't detect a public key that was altered in persistent
     // storage in such a way that it's still valid; thus there is no
     // benefit in performing "expensive" validation checks.
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         // Only `array`s that implement `Default` implement `DecodeBuffer`;
         // thus we must manually implement it.
         let mut x = [0; <NistP384 as Curve>::FieldBytesSize::INT];
         data.split_at_checked(x.len())
             .ok_or(EncDecErr)
             .and_then(|(x_slice, rem)| {
                 *data = rem;
                 bool::decode_from_buffer(data).map(|y_is_odd| {
                     x.copy_from_slice(x_slice);
                     Self { x, y_is_odd }
                 })
             })
     }
 }
 impl EncodeBuffer for RsaPubKey<&[u8]> {
     #[expect(clippy::unreachable, reason = "we want to crash when there is a bug")]
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         // Max length is 2048, so this won't error.
         self.0
             .encode_into_buffer(buffer)
             .unwrap_or_else(|_e| unreachable!("there is a bug in [u8]::encode_into_buffer"));
         self.1.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for RsaPubKey<Vec<u8>> {
     type Err = EncDecErr;
     // We don't verify `Self` is in fact "valid" (i.e., we don't call
     // [`Self::validate`]) since that's expensive and an error will
     // happen later during authentication anyway. Note even if we did,
     // that wouldn't detect a public key that was altered in persistent
     // storage in such a way that it's still valid; thus there is no
     // benefit in performing "expensive" validation checks.
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         Vec::decode_from_buffer(data).and_then(|n| {
             u32::decode_from_buffer(data)
                 .and_then(|e| Self::try_from((n, e)).map_err(|_e| EncDecErr))
         })
     }
 }
 impl EncodeBuffer for UncompressedPubKey<'_> {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         match *self {
             Self::Ed25519(key) => {
                 0u8.encode_into_buffer(buffer);
                 key.encode_into_buffer(buffer);
             }
             Self::P256(key) => {
                 1u8.encode_into_buffer(buffer);
                 key.encode_into_buffer(buffer);
             }
             Self::P384(key) => {
                 2u8.encode_into_buffer(buffer);
                 key.encode_into_buffer(buffer);
             }
             Self::Rsa(key) => {
                 3u8.encode_into_buffer(buffer);
                 key.encode_into_buffer(buffer);
             }
         }
     }
 }
 impl<'a> DecodeBuffer<'a>
     for CompressedPubKey<
         [u8; ed25519_dalek::PUBLIC_KEY_LENGTH],
         [u8; <NistP256 as Curve>::FieldBytesSize::INT],
         [u8; <NistP384 as Curve>::FieldBytesSize::INT],
         Vec<u8>,
     >
 {
     type Err = EncDecErr;
     // We don't verify `Self` is in fact "valid" (i.e., we don't call
     // [`Self::validate`]) since that's expensive and an error will
     // happen later during authentication anyway. Note even if we did,
     // that wouldn't detect a public key that was altered in persistent
     // storage in such a way that it's still valid; thus there is no
     // benefit in performing "expensive" validation checks.
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         u8::decode_from_buffer(data).and_then(|val| match val {
             0 => Ed25519PubKey::decode_from_buffer(data).map(Self::Ed25519),
             1 => CompressedP256PubKey::decode_from_buffer(data).map(Self::P256),
             2 => CompressedP384PubKey::decode_from_buffer(data).map(Self::P384),
             3 => RsaPubKey::decode_from_buffer(data).map(Self::Rsa),
             _ => Err(EncDecErr),
         })
     }
 }
 impl EncodeBuffer for AuthenticatorExtensionOutputStaticState {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.cred_protect.encode_into_buffer(buffer);
         self.hmac_secret.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for AuthenticatorExtensionOutputStaticState {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         CredentialProtectionPolicy::decode_from_buffer(data).and_then(|cred_protect| {
             Option::decode_from_buffer(data).map(|hmac_secret| Self {
                 cred_protect,
                 hmac_secret,
             })
         })
     }
 }
 impl EncodeBuffer for Attestation {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         match *self {
             Self::None => 0u8,
             Self::Surrogate => 1,
         }
         .encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for Attestation {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         u8::decode_from_buffer(data).and_then(|val| match val {
             0 => Ok(Self::None),
             1 => Ok(Self::Surrogate),
             _ => Err(EncDecErr),
         })
     }
 }
 impl EncodeBuffer for Aaguid<'_> {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         buffer.extend_from_slice(self.0);
     }
 }
 /// Owned version of [`Aaguid`] that exists for [`MetadataOwned::aaguid`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct AaguidOwned(pub [u8; super::AAGUID_LEN]);
 impl<'a: 'b, 'b> From<&'a AaguidOwned> for Aaguid<'b> {
     #[inline]
     fn from(value: &'a AaguidOwned) -> Self {
         Self(value.0.as_slice())
     }
 }
 impl<'a> DecodeBuffer<'a> for AaguidOwned {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         <[u8; super::AAGUID_LEN]>::decode_from_buffer(data).map(Self)
     }
 }
 impl EncodeBuffer for FourToSixtyThree {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.into_u8().encode_into_buffer(buffer);
     }
 }
 impl EncodeBuffer for AuthenticatorExtensionOutputMetadata {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.min_pin_length.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for FourToSixtyThree {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         u8::decode_from_buffer(data).and_then(|val| Self::from_u8(val).ok_or(EncDecErr))
     }
 }
 impl<'a> DecodeBuffer<'a> for AuthenticatorExtensionOutputMetadata {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         Option::decode_from_buffer(data).map(|min_pin_length| Self { min_pin_length })
     }
 }
 impl EncodeBuffer for CredentialPropertiesOutput {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.rk.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for CredentialPropertiesOutput {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         Option::decode_from_buffer(data).map(|rk| Self { rk })
     }
 }
 impl EncodeBuffer for AuthenticationExtensionsPrfOutputs {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.enabled.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for AuthenticationExtensionsPrfOutputs {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         bool::decode_from_buffer(data).map(|enabled| Self { enabled })
     }
 }
 impl EncodeBuffer for ClientExtensionsOutputsMetadata {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.cred_props.encode_into_buffer(buffer);
     }
 }
 impl EncodeBuffer for ClientExtensionsOutputsStaticState {
     fn encode_into_buffer(&self, buffer: &mut Vec<u8>) {
         self.prf.encode_into_buffer(buffer);
     }
 }
 impl<'a> DecodeBuffer<'a> for ClientExtensionsOutputsMetadata {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         Option::decode_from_buffer(data).map(|cred_props| Self { cred_props })
     }
 }
 impl<'a> DecodeBuffer<'a> for ClientExtensionsOutputsStaticState {
     type Err = EncDecErr;
     fn decode_from_buffer(data: &mut &'a [u8]) -> Result<Self, Self::Err> {
         Option::decode_from_buffer(data).map(|prf| Self { prf })
     }
 }
 impl Encode for Metadata<'_> {
     type Output<'a>
         = Vec<u8>
     where
         Self: 'a;
     type Err = Infallible;
     #[inline]
     fn encode(&self) -> Result<Self::Output<'_>, Self::Err> {
         // Length of the anticipated most common output:
         // * 1 for `Attestation`
         // * 16 for `Aaguid`.
         // * 1 or 2 for `AuthenticatorExtensionOutputMetadata` where we assume 1 is the most common
         // * 1–3 for `ClientExtensionsOutputsMetadata` where we assume 1 is the most common
         // * 1 for `ResidentKeyRequirement`
         let mut buffer = Vec::with_capacity(1 + 16 + 1 + 1 + 1);
         self.attestation.encode_into_buffer(&mut buffer);
         self.aaguid.encode_into_buffer(&mut buffer);
         self.extensions.encode_into_buffer(&mut buffer);
         self.client_extension_results
             .encode_into_buffer(&mut buffer);
         self.resident_key.encode_into_buffer(&mut buffer);
         Ok(buffer)
     }
 }
 /// Owned version of [`Metadata`] that exists to [`Self::decode`] the output of [`Metadata::encode`].
 #[derive(Clone, Copy, Debug)]
 pub struct MetadataOwned {
     /// [`Metadata::attestation`].
     pub attestation: Attestation,
     /// [`Metadata::aaguid`].
     pub aaguid: AaguidOwned,
     /// [`Metadata::extensions`].
     pub extensions: AuthenticatorExtensionOutputMetadata,
     /// [`Metadata::client_extension_results`].
     pub client_extension_results: ClientExtensionsOutputsMetadata,
     /// [`Metadata::resident_key`].
     pub resident_key: ResidentKeyRequirement,
 }
 impl<'a: 'b, 'b> From<&'a MetadataOwned> for Metadata<'b> {
     #[inline]
     fn from(value: &'a MetadataOwned) -> Self {
         Self {
             attestation: value.attestation,
             aaguid: (&value.aaguid).into(),
             extensions: value.extensions,
             client_extension_results: value.client_extension_results,
             resident_key: value.resident_key,
         }
     }
 }
 /// Error returned from [`MetadataOwned::decode`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum DecodeMetadataOwnedErr {
     /// Variant returned when [`MetadataOwned::attestation`] could not be decoded.
     Attestation,
     /// Variant returned when [`MetadataOwned::aaguid`] could not be decoded.
     Aaguid,
     /// Variant returned when [`MetadataOwned::extensions`] could not be decoded.
     Extensions,
     /// Variant returned when [`MetadataOwned::client_extension_results`] could not be decoded.
     ClientExtensionResults,
     /// Variant returned when [`MetadataOwned::resident_key`] could not be decoded.
     ResidentKey,
     /// Variant returned when [`MetadataOwned`] was decoded with trailing data.
     TrailingData,
 }
 impl Display for DecodeMetadataOwnedErr {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_str(match *self {
             Self::Attestation => "attestation could not be decoded",
             Self::Aaguid => "aaguid could not be decoded",
             Self::Extensions => "extensions could not be decoded",
             Self::ClientExtensionResults => "client_extension_results could not be decoded",
             Self::ResidentKey => "resident_key could not be decoded",
             Self::TrailingData => "trailing data existed after decoding MetadataOwned",
         })
     }
 }
 impl Error for DecodeMetadataOwnedErr {}
 impl Decode for MetadataOwned {
     type Input<'a> = &'a [u8];
     type Err = DecodeMetadataOwnedErr;
     #[inline]
     fn decode(mut input: Self::Input<'_>) -> Result<Self, Self::Err> {
         Attestation::decode_from_buffer(&mut input)
             .map_err(|_e| DecodeMetadataOwnedErr::Attestation)
             .and_then(|attestation| {
                 AaguidOwned::decode_from_buffer(&mut input)
                     .map_err(|_e| DecodeMetadataOwnedErr::Aaguid)
                     .and_then(|aaguid| {
                         AuthenticatorExtensionOutputMetadata::decode_from_buffer(&mut input)
                             .map_err(|_e| DecodeMetadataOwnedErr::Extensions)
                             .and_then(|extensions| {
                                 ClientExtensionsOutputsMetadata::decode_from_buffer(&mut input)
                                     .map_err(|_e| DecodeMetadataOwnedErr::ClientExtensionResults)
                                     .and_then(|client_extension_results| {
                                         ResidentKeyRequirement::decode_from_buffer(&mut input)
                                             .map_err(|_e| DecodeMetadataOwnedErr::ResidentKey)
                                             .and_then(|resident_key| {
                                                 if input.is_empty() {
                                                     Ok(Self {
                                                         attestation,
                                                         aaguid,
                                                         extensions,
                                                         client_extension_results,
                                                         resident_key,
                                                     })
                                                 } else {
                                                     Err(DecodeMetadataOwnedErr::TrailingData)
                                                 }
                                             })
                                     })
                             })
                     })
             })
     }
 }
 impl Encode for StaticState<UncompressedPubKey<'_>> {
     type Output<'a>
         = Vec<u8>
     where
         Self: 'a;
     type Err = Infallible;
     /// Transforms `self` into a `Vec` that can subsequently be [`StaticState::decode`]d into a [`StaticState`] of
     /// [`CompressedPubKey`].
     #[expect(
         clippy::arithmetic_side_effects,
         reason = "comment justifies its correctness"
     )]
     #[inline]
     fn encode(&self) -> Result<Self::Output<'_>, Self::Err> {
         let mut buffer = Vec::with_capacity(
             // The maximum value is 1 + 2 + 2048 + 4 + 1 + 1 + 1 + 1 + 1 = 2060 so overflow cannot happen.
             // `key.0.len() <= MAX_RSA_N_BYTES` which is 2048.
             match self.credential_public_key {
                 UncompressedPubKey::Ed25519(_) => 33,
                 UncompressedPubKey::P256(_) => 34,
                 UncompressedPubKey::P384(_) => 50,
                 UncompressedPubKey::Rsa(key) => 1 + 2 + key.0.len() + 4,
             } + 1
                 + 1
                 + usize::from(self.extensions.hmac_secret.is_some())
                 + 1
                 + usize::from(self.client_extension_results.prf.is_some()),
         );
         self.credential_public_key.encode_into_buffer(&mut buffer);
         self.extensions.encode_into_buffer(&mut buffer);
         self.client_extension_results
             .encode_into_buffer(&mut buffer);
         Ok(buffer)
     }
 }
 /// Error returned from [`StaticState::decode`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum DecodeStaticStateErr {
     /// Variant returned when [`StaticState::credential_public_key`] could not be decoded.
     CredentialPublicKey,
     /// Variant returned when [`StaticState::extensions`] could not be decoded.
     Extensions,
     /// Variant returned when [`StaticState::client_extension_results`] could not be decoded.
     ClientExtensionResults,
     /// Variant returned when there was trailing data after decoding a [`StaticState`].
     TrailingData,
 }
 impl Display for DecodeStaticStateErr {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_str(match *self {
             Self::CredentialPublicKey => "credential_public_key could not be decoded",
             Self::Extensions => "extensions could not be decoded",
             Self::ClientExtensionResults => "client_extension_results could not be decoded",
             Self::TrailingData => "there was trailing data after decoding a StaticState",
         })
     }
 }
 impl Error for DecodeStaticStateErr {}
 impl Decode
     for StaticState<
         CompressedPubKey<
             [u8; ed25519_dalek::PUBLIC_KEY_LENGTH],
             [u8; <NistP256 as Curve>::FieldBytesSize::INT],
             [u8; <NistP384 as Curve>::FieldBytesSize::INT],
             Vec<u8>,
         >,
     >
 {
     type Input<'a> = &'a [u8];
     type Err = DecodeStaticStateErr;
     /// Interprets `input` as the [`StaticState::Output`] of [`StaticState::encode`].
     #[inline]
     fn decode(mut input: Self::Input<'_>) -> Result<Self, Self::Err> {
         CompressedPubKey::decode_from_buffer(&mut input)
             .map_err(|_e| DecodeStaticStateErr::CredentialPublicKey)
             .and_then(|credential_public_key| {
                 AuthenticatorExtensionOutputStaticState::decode_from_buffer(&mut input)
                     .map_err(|_e| DecodeStaticStateErr::Extensions)
                     .and_then(|extensions| {
                         ClientExtensionsOutputsStaticState::decode_from_buffer(&mut input)
                             .map_err(|_e| DecodeStaticStateErr::ClientExtensionResults)
                             .and_then(|client_extension_results| {
                                 if input.is_empty() {
                                     Ok(Self {
                                         credential_public_key,
                                         extensions,
                                         client_extension_results,
                                     })
                                 } else {
                                     Err(DecodeStaticStateErr::TrailingData)
                                 }
                             })
                     })
             })
     }
 }
 impl Encode for DynamicState {
     type Output<'a>
         = [u8; 7]
     where
         Self: 'a;
     type Err = Infallible;
     #[expect(
         clippy::little_endian_bytes,
         reason = "need cross-platform correctness"
     )]
     #[inline]
     fn encode(&self) -> Result<Self::Output<'_>, Self::Err> {
         let mut buffer = [
             u8::from(self.user_verified),
             match self.backup {
                 Backup::NotEligible => 0,
                 Backup::Eligible => 1,
                 Backup::Exists => 2,
             },
             0,
             0,
             0,
             0,
             match self.authenticator_attachment {
                 AuthenticatorAttachment::None => 0,
                 AuthenticatorAttachment::Platform => 1,
                 AuthenticatorAttachment::CrossPlatform => 2,
             },
         ];
         buffer[2..6].copy_from_slice(self.sign_count.to_le_bytes().as_slice());
         Ok(buffer)
     }
 }
 /// Error returned from [`DynamicState::decode`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum DecodeDynamicStateErr {
     /// Variant returned when [`DynamicState::user_verified`] could not be decoded.
     UserVerified,
     /// Variant returned when [`DynamicState::backup`] could not be decoded.
     Backup,
     /// Variant returned when [`DynamicState::sign_count`] could not be decoded.
     SignCount,
     /// Variant returned when [`DynamicState::authenticator_attachment`] could not be decoded.
     AuthenticatorAttachment,
 }
 impl Display for DecodeDynamicStateErr {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_str(match *self {
             Self::UserVerified => "user_verified could not be decoded",
             Self::Backup => "backup could not be decoded",
             Self::SignCount => "sign_count could not be decoded",
             Self::AuthenticatorAttachment => "authenticator_attachment could not be decoded",
         })
     }
 }
 impl Error for DecodeDynamicStateErr {}
 impl Decode for DynamicState {
     type Input<'a> = [u8; 7];
     type Err = DecodeDynamicStateErr;
     #[expect(
         clippy::panic_in_result_fn,
         reason = "want to crash when there is a bug"
     )]
     #[inline]
     fn decode(input: Self::Input<'_>) -> Result<Self, Self::Err> {
         let mut buffer = input.as_slice();
         bool::decode_from_buffer(&mut buffer)
             .map_err(|_e| DecodeDynamicStateErr::UserVerified)
             .and_then(|user_verified| {
                 Backup::decode_from_buffer(&mut buffer)
                     .map_err(|_e| DecodeDynamicStateErr::Backup)
                     .and_then(|backup| {
                         u32::decode_from_buffer(&mut buffer)
                             .map_err(|_e| DecodeDynamicStateErr::SignCount)
                             .and_then(|sign_count| {
                                 AuthenticatorAttachment::decode_from_buffer(&mut buffer)
                                     .map_err(|_e| DecodeDynamicStateErr::AuthenticatorAttachment)
                                     .map(|authenticator_attachment| {
                                         assert!(
                                             buffer.is_empty(),
                                             "there is a bug in DynamicState::decode"
                                         );
                                         Self {
                                             user_verified,
                                             backup,
                                             sign_count,
                                             authenticator_attachment,
                                         }
                                     })
                             })
                     })
             })
     }
 }