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Diffstat (limited to 'vendor/base64/src/engine/general_purpose/mod.rs')
| -rw-r--r-- | vendor/base64/src/engine/general_purpose/mod.rs | 352 |
1 files changed, 352 insertions, 0 deletions
diff --git a/vendor/base64/src/engine/general_purpose/mod.rs b/vendor/base64/src/engine/general_purpose/mod.rs new file mode 100644 index 00000000..6fe95809 --- /dev/null +++ b/vendor/base64/src/engine/general_purpose/mod.rs @@ -0,0 +1,352 @@ +//! Provides the [GeneralPurpose] engine and associated config types. +use crate::{ + alphabet, + alphabet::Alphabet, + engine::{Config, DecodeMetadata, DecodePaddingMode}, + DecodeSliceError, +}; +use core::convert::TryInto; + +pub(crate) mod decode; +pub(crate) mod decode_suffix; + +pub use decode::GeneralPurposeEstimate; + +pub(crate) const INVALID_VALUE: u8 = 255; + +/// A general-purpose base64 engine. +/// +/// - It uses no vector CPU instructions, so it will work on any system. +/// - It is reasonably fast (~2-3GiB/s). +/// - It is not constant-time, though, so it is vulnerable to timing side-channel attacks. For loading cryptographic keys, etc, it is suggested to use the forthcoming constant-time implementation. + +#[derive(Debug, Clone)] +pub struct GeneralPurpose { + encode_table: [u8; 64], + decode_table: [u8; 256], + config: GeneralPurposeConfig, +} + +impl GeneralPurpose { + /// Create a `GeneralPurpose` engine from an [Alphabet]. + /// + /// While not very expensive to initialize, ideally these should be cached + /// if the engine will be used repeatedly. + pub const fn new(alphabet: &Alphabet, config: GeneralPurposeConfig) -> Self { + Self { + encode_table: encode_table(alphabet), + decode_table: decode_table(alphabet), + config, + } + } +} + +impl super::Engine for GeneralPurpose { + type Config = GeneralPurposeConfig; + type DecodeEstimate = GeneralPurposeEstimate; + + fn internal_encode(&self, input: &[u8], output: &mut [u8]) -> usize { + let mut input_index: usize = 0; + + const BLOCKS_PER_FAST_LOOP: usize = 4; + const LOW_SIX_BITS: u64 = 0x3F; + + // we read 8 bytes at a time (u64) but only actually consume 6 of those bytes. Thus, we need + // 2 trailing bytes to be available to read.. + let last_fast_index = input.len().saturating_sub(BLOCKS_PER_FAST_LOOP * 6 + 2); + let mut output_index = 0; + + if last_fast_index > 0 { + while input_index <= last_fast_index { + // Major performance wins from letting the optimizer do the bounds check once, mostly + // on the output side + let input_chunk = + &input[input_index..(input_index + (BLOCKS_PER_FAST_LOOP * 6 + 2))]; + let output_chunk = + &mut output[output_index..(output_index + BLOCKS_PER_FAST_LOOP * 8)]; + + // Hand-unrolling for 32 vs 16 or 8 bytes produces yields performance about equivalent + // to unsafe pointer code on a Xeon E5-1650v3. 64 byte unrolling was slightly better for + // large inputs but significantly worse for 50-byte input, unsurprisingly. I suspect + // that it's a not uncommon use case to encode smallish chunks of data (e.g. a 64-byte + // SHA-512 digest), so it would be nice if that fit in the unrolled loop at least once. + // Plus, single-digit percentage performance differences might well be quite different + // on different hardware. + + let input_u64 = read_u64(&input_chunk[0..]); + + output_chunk[0] = self.encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize]; + output_chunk[1] = self.encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize]; + output_chunk[2] = self.encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize]; + output_chunk[3] = self.encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize]; + output_chunk[4] = self.encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize]; + output_chunk[5] = self.encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize]; + output_chunk[6] = self.encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize]; + output_chunk[7] = self.encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize]; + + let input_u64 = read_u64(&input_chunk[6..]); + + output_chunk[8] = self.encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize]; + output_chunk[9] = self.encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize]; + output_chunk[10] = self.encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize]; + output_chunk[11] = self.encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize]; + output_chunk[12] = self.encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize]; + output_chunk[13] = self.encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize]; + output_chunk[14] = self.encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize]; + output_chunk[15] = self.encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize]; + + let input_u64 = read_u64(&input_chunk[12..]); + + output_chunk[16] = self.encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize]; + output_chunk[17] = self.encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize]; + output_chunk[18] = self.encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize]; + output_chunk[19] = self.encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize]; + output_chunk[20] = self.encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize]; + output_chunk[21] = self.encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize]; + output_chunk[22] = self.encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize]; + output_chunk[23] = self.encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize]; + + let input_u64 = read_u64(&input_chunk[18..]); + + output_chunk[24] = self.encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize]; + output_chunk[25] = self.encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize]; + output_chunk[26] = self.encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize]; + output_chunk[27] = self.encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize]; + output_chunk[28] = self.encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize]; + output_chunk[29] = self.encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize]; + output_chunk[30] = self.encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize]; + output_chunk[31] = self.encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize]; + + output_index += BLOCKS_PER_FAST_LOOP * 8; + input_index += BLOCKS_PER_FAST_LOOP * 6; + } + } + + // Encode what's left after the fast loop. + + const LOW_SIX_BITS_U8: u8 = 0x3F; + + let rem = input.len() % 3; + let start_of_rem = input.len() - rem; + + // start at the first index not handled by fast loop, which may be 0. + + while input_index < start_of_rem { + let input_chunk = &input[input_index..(input_index + 3)]; + let output_chunk = &mut output[output_index..(output_index + 4)]; + + output_chunk[0] = self.encode_table[(input_chunk[0] >> 2) as usize]; + output_chunk[1] = self.encode_table + [((input_chunk[0] << 4 | input_chunk[1] >> 4) & LOW_SIX_BITS_U8) as usize]; + output_chunk[2] = self.encode_table + [((input_chunk[1] << 2 | input_chunk[2] >> 6) & LOW_SIX_BITS_U8) as usize]; + output_chunk[3] = self.encode_table[(input_chunk[2] & LOW_SIX_BITS_U8) as usize]; + + input_index += 3; + output_index += 4; + } + + if rem == 2 { + output[output_index] = self.encode_table[(input[start_of_rem] >> 2) as usize]; + output[output_index + 1] = + self.encode_table[((input[start_of_rem] << 4 | input[start_of_rem + 1] >> 4) + & LOW_SIX_BITS_U8) as usize]; + output[output_index + 2] = + self.encode_table[((input[start_of_rem + 1] << 2) & LOW_SIX_BITS_U8) as usize]; + output_index += 3; + } else if rem == 1 { + output[output_index] = self.encode_table[(input[start_of_rem] >> 2) as usize]; + output[output_index + 1] = + self.encode_table[((input[start_of_rem] << 4) & LOW_SIX_BITS_U8) as usize]; + output_index += 2; + } + + output_index + } + + fn internal_decoded_len_estimate(&self, input_len: usize) -> Self::DecodeEstimate { + GeneralPurposeEstimate::new(input_len) + } + + fn internal_decode( + &self, + input: &[u8], + output: &mut [u8], + estimate: Self::DecodeEstimate, + ) -> Result<DecodeMetadata, DecodeSliceError> { + decode::decode_helper( + input, + estimate, + output, + &self.decode_table, + self.config.decode_allow_trailing_bits, + self.config.decode_padding_mode, + ) + } + + fn config(&self) -> &Self::Config { + &self.config + } +} + +/// Returns a table mapping a 6-bit index to the ASCII byte encoding of the index +pub(crate) const fn encode_table(alphabet: &Alphabet) -> [u8; 64] { + // the encode table is just the alphabet: + // 6-bit index lookup -> printable byte + let mut encode_table = [0_u8; 64]; + { + let mut index = 0; + while index < 64 { + encode_table[index] = alphabet.symbols[index]; + index += 1; + } + } + + encode_table +} + +/// Returns a table mapping base64 bytes as the lookup index to either: +/// - [INVALID_VALUE] for bytes that aren't members of the alphabet +/// - a byte whose lower 6 bits are the value that was encoded into the index byte +pub(crate) const fn decode_table(alphabet: &Alphabet) -> [u8; 256] { + let mut decode_table = [INVALID_VALUE; 256]; + + // Since the table is full of `INVALID_VALUE` already, we only need to overwrite + // the parts that are valid. + let mut index = 0; + while index < 64 { + // The index in the alphabet is the 6-bit value we care about. + // Since the index is in 0-63, it is safe to cast to u8. + decode_table[alphabet.symbols[index] as usize] = index as u8; + index += 1; + } + + decode_table +} + +#[inline] +fn read_u64(s: &[u8]) -> u64 { + u64::from_be_bytes(s[..8].try_into().unwrap()) +} + +/// Contains configuration parameters for base64 encoding and decoding. +/// +/// ``` +/// # use base64::engine::GeneralPurposeConfig; +/// let config = GeneralPurposeConfig::new() +/// .with_encode_padding(false); +/// // further customize using `.with_*` methods as needed +/// ``` +/// +/// The constants [PAD] and [NO_PAD] cover most use cases. +/// +/// To specify the characters used, see [Alphabet]. +#[derive(Clone, Copy, Debug)] +pub struct GeneralPurposeConfig { + encode_padding: bool, + decode_allow_trailing_bits: bool, + decode_padding_mode: DecodePaddingMode, +} + +impl GeneralPurposeConfig { + /// Create a new config with `padding` = `true`, `decode_allow_trailing_bits` = `false`, and + /// `decode_padding_mode = DecodePaddingMode::RequireCanonicalPadding`. + /// + /// This probably matches most people's expectations, but consider disabling padding to save + /// a few bytes unless you specifically need it for compatibility with some legacy system. + pub const fn new() -> Self { + Self { + // RFC states that padding must be applied by default + encode_padding: true, + decode_allow_trailing_bits: false, + decode_padding_mode: DecodePaddingMode::RequireCanonical, + } + } + + /// Create a new config based on `self` with an updated `padding` setting. + /// + /// If `padding` is `true`, encoding will append either 1 or 2 `=` padding characters as needed + /// to produce an output whose length is a multiple of 4. + /// + /// Padding is not needed for correct decoding and only serves to waste bytes, but it's in the + /// [spec](https://datatracker.ietf.org/doc/html/rfc4648#section-3.2). + /// + /// For new applications, consider not using padding if the decoders you're using don't require + /// padding to be present. + pub const fn with_encode_padding(self, padding: bool) -> Self { + Self { + encode_padding: padding, + ..self + } + } + + /// Create a new config based on `self` with an updated `decode_allow_trailing_bits` setting. + /// + /// Most users will not need to configure this. It's useful if you need to decode base64 + /// produced by a buggy encoder that has bits set in the unused space on the last base64 + /// character as per [forgiving-base64 decode](https://infra.spec.whatwg.org/#forgiving-base64-decode). + /// If invalid trailing bits are present and this is `true`, those bits will + /// be silently ignored, else `DecodeError::InvalidLastSymbol` will be emitted. + pub const fn with_decode_allow_trailing_bits(self, allow: bool) -> Self { + Self { + decode_allow_trailing_bits: allow, + ..self + } + } + + /// Create a new config based on `self` with an updated `decode_padding_mode` setting. + /// + /// Padding is not useful in terms of representing encoded data -- it makes no difference to + /// the decoder if padding is present or not, so if you have some un-padded input to decode, it + /// is perfectly fine to use `DecodePaddingMode::Indifferent` to prevent errors from being + /// emitted. + /// + /// However, since in practice + /// [people who learned nothing from BER vs DER seem to expect base64 to have one canonical encoding](https://eprint.iacr.org/2022/361), + /// the default setting is the stricter `DecodePaddingMode::RequireCanonicalPadding`. + /// + /// Or, if "canonical" in your circumstance means _no_ padding rather than padding to the + /// next multiple of four, there's `DecodePaddingMode::RequireNoPadding`. + pub const fn with_decode_padding_mode(self, mode: DecodePaddingMode) -> Self { + Self { + decode_padding_mode: mode, + ..self + } + } +} + +impl Default for GeneralPurposeConfig { + /// Delegates to [GeneralPurposeConfig::new]. + fn default() -> Self { + Self::new() + } +} + +impl Config for GeneralPurposeConfig { + fn encode_padding(&self) -> bool { + self.encode_padding + } +} + +/// A [GeneralPurpose] engine using the [alphabet::STANDARD] base64 alphabet and [PAD] config. +pub const STANDARD: GeneralPurpose = GeneralPurpose::new(&alphabet::STANDARD, PAD); + +/// A [GeneralPurpose] engine using the [alphabet::STANDARD] base64 alphabet and [NO_PAD] config. +pub const STANDARD_NO_PAD: GeneralPurpose = GeneralPurpose::new(&alphabet::STANDARD, NO_PAD); + +/// A [GeneralPurpose] engine using the [alphabet::URL_SAFE] base64 alphabet and [PAD] config. +pub const URL_SAFE: GeneralPurpose = GeneralPurpose::new(&alphabet::URL_SAFE, PAD); + +/// A [GeneralPurpose] engine using the [alphabet::URL_SAFE] base64 alphabet and [NO_PAD] config. +pub const URL_SAFE_NO_PAD: GeneralPurpose = GeneralPurpose::new(&alphabet::URL_SAFE, NO_PAD); + +/// Include padding bytes when encoding, and require that they be present when decoding. +/// +/// This is the standard per the base64 RFC, but consider using [NO_PAD] instead as padding serves +/// little purpose in practice. +pub const PAD: GeneralPurposeConfig = GeneralPurposeConfig::new(); + +/// Don't add padding when encoding, and require no padding when decoding. +pub const NO_PAD: GeneralPurposeConfig = GeneralPurposeConfig::new() + .with_encode_padding(false) + .with_decode_padding_mode(DecodePaddingMode::RequireNone); |