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Diffstat (limited to 'vendor/base64/src/read/decoder.rs')
| -rw-r--r-- | vendor/base64/src/read/decoder.rs | 335 |
1 files changed, 335 insertions, 0 deletions
diff --git a/vendor/base64/src/read/decoder.rs b/vendor/base64/src/read/decoder.rs new file mode 100644 index 00000000..781f6f88 --- /dev/null +++ b/vendor/base64/src/read/decoder.rs @@ -0,0 +1,335 @@ +use crate::{engine::Engine, DecodeError, DecodeSliceError, PAD_BYTE}; +use std::{cmp, fmt, io}; + +// This should be large, but it has to fit on the stack. +pub(crate) const BUF_SIZE: usize = 1024; + +// 4 bytes of base64 data encode 3 bytes of raw data (modulo padding). +const BASE64_CHUNK_SIZE: usize = 4; +const DECODED_CHUNK_SIZE: usize = 3; + +/// A `Read` implementation that decodes base64 data read from an underlying reader. +/// +/// # Examples +/// +/// ``` +/// use std::io::Read; +/// use std::io::Cursor; +/// use base64::engine::general_purpose; +/// +/// // use a cursor as the simplest possible `Read` -- in real code this is probably a file, etc. +/// let mut wrapped_reader = Cursor::new(b"YXNkZg=="); +/// let mut decoder = base64::read::DecoderReader::new( +/// &mut wrapped_reader, +/// &general_purpose::STANDARD); +/// +/// // handle errors as you normally would +/// let mut result = Vec::new(); +/// decoder.read_to_end(&mut result).unwrap(); +/// +/// assert_eq!(b"asdf", &result[..]); +/// +/// ``` +pub struct DecoderReader<'e, E: Engine, R: io::Read> { + engine: &'e E, + /// Where b64 data is read from + inner: R, + + /// Holds b64 data read from the delegate reader. + b64_buffer: [u8; BUF_SIZE], + /// The start of the pending buffered data in `b64_buffer`. + b64_offset: usize, + /// The amount of buffered b64 data after `b64_offset` in `b64_len`. + b64_len: usize, + /// Since the caller may provide us with a buffer of size 1 or 2 that's too small to copy a + /// decoded chunk in to, we have to be able to hang on to a few decoded bytes. + /// Technically we only need to hold 2 bytes, but then we'd need a separate temporary buffer to + /// decode 3 bytes into and then juggle copying one byte into the provided read buf and the rest + /// into here, which seems like a lot of complexity for 1 extra byte of storage. + decoded_chunk_buffer: [u8; DECODED_CHUNK_SIZE], + /// Index of start of decoded data in `decoded_chunk_buffer` + decoded_offset: usize, + /// Length of decoded data after `decoded_offset` in `decoded_chunk_buffer` + decoded_len: usize, + /// Input length consumed so far. + /// Used to provide accurate offsets in errors + input_consumed_len: usize, + /// offset of previously seen padding, if any + padding_offset: Option<usize>, +} + +// exclude b64_buffer as it's uselessly large +impl<'e, E: Engine, R: io::Read> fmt::Debug for DecoderReader<'e, E, R> { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + f.debug_struct("DecoderReader") + .field("b64_offset", &self.b64_offset) + .field("b64_len", &self.b64_len) + .field("decoded_chunk_buffer", &self.decoded_chunk_buffer) + .field("decoded_offset", &self.decoded_offset) + .field("decoded_len", &self.decoded_len) + .field("input_consumed_len", &self.input_consumed_len) + .field("padding_offset", &self.padding_offset) + .finish() + } +} + +impl<'e, E: Engine, R: io::Read> DecoderReader<'e, E, R> { + /// Create a new decoder that will read from the provided reader `r`. + pub fn new(reader: R, engine: &'e E) -> Self { + DecoderReader { + engine, + inner: reader, + b64_buffer: [0; BUF_SIZE], + b64_offset: 0, + b64_len: 0, + decoded_chunk_buffer: [0; DECODED_CHUNK_SIZE], + decoded_offset: 0, + decoded_len: 0, + input_consumed_len: 0, + padding_offset: None, + } + } + + /// Write as much as possible of the decoded buffer into the target buffer. + /// Must only be called when there is something to write and space to write into. + /// Returns a Result with the number of (decoded) bytes copied. + fn flush_decoded_buf(&mut self, buf: &mut [u8]) -> io::Result<usize> { + debug_assert!(self.decoded_len > 0); + debug_assert!(!buf.is_empty()); + + let copy_len = cmp::min(self.decoded_len, buf.len()); + debug_assert!(copy_len > 0); + debug_assert!(copy_len <= self.decoded_len); + + buf[..copy_len].copy_from_slice( + &self.decoded_chunk_buffer[self.decoded_offset..self.decoded_offset + copy_len], + ); + + self.decoded_offset += copy_len; + self.decoded_len -= copy_len; + + debug_assert!(self.decoded_len < DECODED_CHUNK_SIZE); + + Ok(copy_len) + } + + /// Read into the remaining space in the buffer after the current contents. + /// Must only be called when there is space to read into in the buffer. + /// Returns the number of bytes read. + fn read_from_delegate(&mut self) -> io::Result<usize> { + debug_assert!(self.b64_offset + self.b64_len < BUF_SIZE); + + let read = self + .inner + .read(&mut self.b64_buffer[self.b64_offset + self.b64_len..])?; + self.b64_len += read; + + debug_assert!(self.b64_offset + self.b64_len <= BUF_SIZE); + + Ok(read) + } + + /// Decode the requested number of bytes from the b64 buffer into the provided buffer. It's the + /// caller's responsibility to choose the number of b64 bytes to decode correctly. + /// + /// Returns a Result with the number of decoded bytes written to `buf`. + /// + /// # Panics + /// + /// panics if `buf` is too small + fn decode_to_buf(&mut self, b64_len_to_decode: usize, buf: &mut [u8]) -> io::Result<usize> { + debug_assert!(self.b64_len >= b64_len_to_decode); + debug_assert!(self.b64_offset + self.b64_len <= BUF_SIZE); + debug_assert!(!buf.is_empty()); + + let b64_to_decode = &self.b64_buffer[self.b64_offset..self.b64_offset + b64_len_to_decode]; + let decode_metadata = self + .engine + .internal_decode( + b64_to_decode, + buf, + self.engine.internal_decoded_len_estimate(b64_len_to_decode), + ) + .map_err(|dse| match dse { + DecodeSliceError::DecodeError(de) => { + match de { + DecodeError::InvalidByte(offset, byte) => { + match (byte, self.padding_offset) { + // if there was padding in a previous block of decoding that happened to + // be correct, and we now find more padding that happens to be incorrect, + // to be consistent with non-reader decodes, record the error at the first + // padding + (PAD_BYTE, Some(first_pad_offset)) => { + DecodeError::InvalidByte(first_pad_offset, PAD_BYTE) + } + _ => { + DecodeError::InvalidByte(self.input_consumed_len + offset, byte) + } + } + } + DecodeError::InvalidLength(len) => { + DecodeError::InvalidLength(self.input_consumed_len + len) + } + DecodeError::InvalidLastSymbol(offset, byte) => { + DecodeError::InvalidLastSymbol(self.input_consumed_len + offset, byte) + } + DecodeError::InvalidPadding => DecodeError::InvalidPadding, + } + } + DecodeSliceError::OutputSliceTooSmall => { + unreachable!("buf is sized correctly in calling code") + } + }) + .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?; + + if let Some(offset) = self.padding_offset { + // we've already seen padding + if decode_metadata.decoded_len > 0 { + // we read more after already finding padding; report error at first padding byte + return Err(io::Error::new( + io::ErrorKind::InvalidData, + DecodeError::InvalidByte(offset, PAD_BYTE), + )); + } + } + + self.padding_offset = self.padding_offset.or(decode_metadata + .padding_offset + .map(|offset| self.input_consumed_len + offset)); + self.input_consumed_len += b64_len_to_decode; + self.b64_offset += b64_len_to_decode; + self.b64_len -= b64_len_to_decode; + + debug_assert!(self.b64_offset + self.b64_len <= BUF_SIZE); + + Ok(decode_metadata.decoded_len) + } + + /// Unwraps this `DecoderReader`, returning the base reader which it reads base64 encoded + /// input from. + /// + /// Because `DecoderReader` performs internal buffering, the state of the inner reader is + /// unspecified. This function is mainly provided because the inner reader type may provide + /// additional functionality beyond the `Read` implementation which may still be useful. + pub fn into_inner(self) -> R { + self.inner + } +} + +impl<'e, E: Engine, R: io::Read> io::Read for DecoderReader<'e, E, R> { + /// Decode input from the wrapped reader. + /// + /// Under non-error circumstances, this returns `Ok` with the value being the number of bytes + /// written in `buf`. + /// + /// Where possible, this function buffers base64 to minimize the number of read() calls to the + /// delegate reader. + /// + /// # Errors + /// + /// Any errors emitted by the delegate reader are returned. Decoding errors due to invalid + /// base64 are also possible, and will have `io::ErrorKind::InvalidData`. + fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { + if buf.is_empty() { + return Ok(0); + } + + // offset == BUF_SIZE when we copied it all last time + debug_assert!(self.b64_offset <= BUF_SIZE); + debug_assert!(self.b64_offset + self.b64_len <= BUF_SIZE); + debug_assert!(if self.b64_offset == BUF_SIZE { + self.b64_len == 0 + } else { + self.b64_len <= BUF_SIZE + }); + + debug_assert!(if self.decoded_len == 0 { + // can be = when we were able to copy the complete chunk + self.decoded_offset <= DECODED_CHUNK_SIZE + } else { + self.decoded_offset < DECODED_CHUNK_SIZE + }); + + // We shouldn't ever decode into decoded_buffer when we can't immediately write at least one + // byte into the provided buf, so the effective length should only be 3 momentarily between + // when we decode and when we copy into the target buffer. + debug_assert!(self.decoded_len < DECODED_CHUNK_SIZE); + debug_assert!(self.decoded_len + self.decoded_offset <= DECODED_CHUNK_SIZE); + + if self.decoded_len > 0 { + // we have a few leftover decoded bytes; flush that rather than pull in more b64 + self.flush_decoded_buf(buf) + } else { + let mut at_eof = false; + while self.b64_len < BASE64_CHUNK_SIZE { + // Copy any bytes we have to the start of the buffer. + self.b64_buffer + .copy_within(self.b64_offset..self.b64_offset + self.b64_len, 0); + self.b64_offset = 0; + + // then fill in more data + let read = self.read_from_delegate()?; + if read == 0 { + // we never read into an empty buf, so 0 => we've hit EOF + at_eof = true; + break; + } + } + + if self.b64_len == 0 { + debug_assert!(at_eof); + // we must be at EOF, and we have no data left to decode + return Ok(0); + }; + + debug_assert!(if at_eof { + // if we are at eof, we may not have a complete chunk + self.b64_len > 0 + } else { + // otherwise, we must have at least one chunk + self.b64_len >= BASE64_CHUNK_SIZE + }); + + debug_assert_eq!(0, self.decoded_len); + + if buf.len() < DECODED_CHUNK_SIZE { + // caller requested an annoyingly short read + // have to write to a tmp buf first to avoid double mutable borrow + let mut decoded_chunk = [0_u8; DECODED_CHUNK_SIZE]; + // if we are at eof, could have less than BASE64_CHUNK_SIZE, in which case we have + // to assume that these last few tokens are, in fact, valid (i.e. must be 2-4 b64 + // tokens, not 1, since 1 token can't decode to 1 byte). + let to_decode = cmp::min(self.b64_len, BASE64_CHUNK_SIZE); + + let decoded = self.decode_to_buf(to_decode, &mut decoded_chunk[..])?; + self.decoded_chunk_buffer[..decoded].copy_from_slice(&decoded_chunk[..decoded]); + + self.decoded_offset = 0; + self.decoded_len = decoded; + + // can be less than 3 on last block due to padding + debug_assert!(decoded <= 3); + + self.flush_decoded_buf(buf) + } else { + let b64_bytes_that_can_decode_into_buf = (buf.len() / DECODED_CHUNK_SIZE) + .checked_mul(BASE64_CHUNK_SIZE) + .expect("too many chunks"); + debug_assert!(b64_bytes_that_can_decode_into_buf >= BASE64_CHUNK_SIZE); + + let b64_bytes_available_to_decode = if at_eof { + self.b64_len + } else { + // only use complete chunks + self.b64_len - self.b64_len % 4 + }; + + let actual_decode_len = cmp::min( + b64_bytes_that_can_decode_into_buf, + b64_bytes_available_to_decode, + ); + self.decode_to_buf(actual_decode_len, buf) + } + } + } +} |