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Diffstat (limited to 'third_party/rust/base64/src/write/encoder.rs')
| -rw-r--r-- | third_party/rust/base64/src/write/encoder.rs | 381 |
1 files changed, 381 insertions, 0 deletions
diff --git a/third_party/rust/base64/src/write/encoder.rs b/third_party/rust/base64/src/write/encoder.rs new file mode 100644 index 0000000000..4bb57eb065 --- /dev/null +++ b/third_party/rust/base64/src/write/encoder.rs @@ -0,0 +1,381 @@ +use crate::encode::encode_to_slice; +use crate::{encode_config_slice, Config}; +use std::{ + cmp, fmt, + io::{ErrorKind, Result, Write}, +}; + +pub(crate) const BUF_SIZE: usize = 1024; +/// The most bytes whose encoding will fit in `BUF_SIZE` +const MAX_INPUT_LEN: usize = BUF_SIZE / 4 * 3; +// 3 bytes of input = 4 bytes of base64, always (because we don't allow line wrapping) +const MIN_ENCODE_CHUNK_SIZE: usize = 3; + +/// A `Write` implementation that base64 encodes data before delegating to the wrapped writer. +/// +/// Because base64 has special handling for the end of the input data (padding, etc), there's a +/// `finish()` method on this type that encodes any leftover input bytes and adds padding if +/// appropriate. It's called automatically when deallocated (see the `Drop` implementation), but +/// any error that occurs when invoking the underlying writer will be suppressed. If you want to +/// handle such errors, call `finish()` yourself. +/// +/// # Examples +/// +/// ``` +/// use std::io::Write; +/// +/// // use a vec as the simplest possible `Write` -- in real code this is probably a file, etc. +/// let mut enc = base64::write::EncoderWriter::new(Vec::new(), base64::STANDARD); +/// +/// // handle errors as you normally would +/// enc.write_all(b"asdf").unwrap(); +/// +/// // could leave this out to be called by Drop, if you don't care +/// // about handling errors or getting the delegate writer back +/// let delegate = enc.finish().unwrap(); +/// +/// // base64 was written to the writer +/// assert_eq!(b"YXNkZg==", &delegate[..]); +/// +/// ``` +/// +/// # Panics +/// +/// Calling `write()` (or related methods) or `finish()` after `finish()` has completed without +/// error is invalid and will panic. +/// +/// # Errors +/// +/// Base64 encoding itself does not generate errors, but errors from the wrapped writer will be +/// returned as per the contract of `Write`. +/// +/// # Performance +/// +/// It has some minor performance loss compared to encoding slices (a couple percent). +/// It does not do any heap allocation. +pub struct EncoderWriter<W: Write> { + config: Config, + /// Where encoded data is written to. It's an Option as it's None immediately before Drop is + /// called so that finish() can return the underlying writer. None implies that finish() has + /// been called successfully. + delegate: Option<W>, + /// Holds a partial chunk, if any, after the last `write()`, so that we may then fill the chunk + /// with the next `write()`, encode it, then proceed with the rest of the input normally. + extra_input: [u8; MIN_ENCODE_CHUNK_SIZE], + /// How much of `extra` is occupied, in `[0, MIN_ENCODE_CHUNK_SIZE]`. + extra_input_occupied_len: usize, + /// Buffer to encode into. May hold leftover encoded bytes from a previous write call that the underlying writer + /// did not write last time. + output: [u8; BUF_SIZE], + /// How much of `output` is occupied with encoded data that couldn't be written last time + output_occupied_len: usize, + /// panic safety: don't write again in destructor if writer panicked while we were writing to it + panicked: bool, +} + +impl<W: Write> fmt::Debug for EncoderWriter<W> { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + write!( + f, + "extra_input: {:?} extra_input_occupied_len:{:?} output[..5]: {:?} output_occupied_len: {:?}", + self.extra_input, + self.extra_input_occupied_len, + &self.output[0..5], + self.output_occupied_len + ) + } +} + +impl<W: Write> EncoderWriter<W> { + /// Create a new encoder that will write to the provided delegate writer `w`. + pub fn new(w: W, config: Config) -> EncoderWriter<W> { + EncoderWriter { + config, + delegate: Some(w), + extra_input: [0u8; MIN_ENCODE_CHUNK_SIZE], + extra_input_occupied_len: 0, + output: [0u8; BUF_SIZE], + output_occupied_len: 0, + panicked: false, + } + } + + /// Encode all remaining buffered data and write it, including any trailing incomplete input + /// triples and associated padding. + /// + /// Once this succeeds, no further writes or calls to this method are allowed. + /// + /// This may write to the delegate writer multiple times if the delegate writer does not accept + /// all input provided to its `write` each invocation. + /// + /// If you don't care about error handling, it is not necessary to call this function, as the + /// equivalent finalization is done by the Drop impl. + /// + /// Returns the writer that this was constructed around. + /// + /// # Errors + /// + /// The first error that is not of `ErrorKind::Interrupted` will be returned. + pub fn finish(&mut self) -> Result<W> { + // If we could consume self in finish(), we wouldn't have to worry about this case, but + // finish() is retryable in the face of I/O errors, so we can't consume here. + if self.delegate.is_none() { + panic!("Encoder has already had finish() called") + }; + + self.write_final_leftovers()?; + + let writer = self.delegate.take().expect("Writer must be present"); + + Ok(writer) + } + + /// Write any remaining buffered data to the delegate writer. + fn write_final_leftovers(&mut self) -> Result<()> { + if self.delegate.is_none() { + // finish() has already successfully called this, and we are now in drop() with a None + // writer, so just no-op + return Ok(()); + } + + self.write_all_encoded_output()?; + + if self.extra_input_occupied_len > 0 { + let encoded_len = encode_config_slice( + &self.extra_input[..self.extra_input_occupied_len], + self.config, + &mut self.output[..], + ); + + self.output_occupied_len = encoded_len; + + self.write_all_encoded_output()?; + + // write succeeded, do not write the encoding of extra again if finish() is retried + self.extra_input_occupied_len = 0; + } + + Ok(()) + } + + /// Write as much of the encoded output to the delegate writer as it will accept, and store the + /// leftovers to be attempted at the next write() call. Updates `self.output_occupied_len`. + /// + /// # Errors + /// + /// Errors from the delegate writer are returned. In the case of an error, + /// `self.output_occupied_len` will not be updated, as errors from `write` are specified to mean + /// that no write took place. + fn write_to_delegate(&mut self, current_output_len: usize) -> Result<()> { + self.panicked = true; + let res = self + .delegate + .as_mut() + .expect("Writer must be present") + .write(&self.output[..current_output_len]); + self.panicked = false; + + res.map(|consumed| { + debug_assert!(consumed <= current_output_len); + + if consumed < current_output_len { + self.output_occupied_len = current_output_len.checked_sub(consumed).unwrap(); + // If we're blocking on I/O, the minor inefficiency of copying bytes to the + // start of the buffer is the least of our concerns... + // Rotate moves more than we need to, but copy_within isn't stabilized yet. + self.output.rotate_left(consumed); + } else { + self.output_occupied_len = 0; + } + }) + } + + /// Write all buffered encoded output. If this returns `Ok`, `self.output_occupied_len` is `0`. + /// + /// This is basically write_all for the remaining buffered data but without the undesirable + /// abort-on-`Ok(0)` behavior. + /// + /// # Errors + /// + /// Any error emitted by the delegate writer abort the write loop and is returned, unless it's + /// `Interrupted`, in which case the error is ignored and writes will continue. + fn write_all_encoded_output(&mut self) -> Result<()> { + while self.output_occupied_len > 0 { + let remaining_len = self.output_occupied_len; + match self.write_to_delegate(remaining_len) { + // try again on interrupts ala write_all + Err(ref e) if e.kind() == ErrorKind::Interrupted => {} + // other errors return + Err(e) => return Err(e), + // success no-ops because remaining length is already updated + Ok(_) => {} + }; + } + + debug_assert_eq!(0, self.output_occupied_len); + Ok(()) + } +} + +impl<W: Write> Write for EncoderWriter<W> { + /// Encode input and then write to the delegate writer. + /// + /// Under non-error circumstances, this returns `Ok` with the value being the number of bytes + /// of `input` consumed. The value may be `0`, which interacts poorly with `write_all`, which + /// interprets `Ok(0)` as an error, despite it being allowed by the contract of `write`. See + /// <https://github.com/rust-lang/rust/issues/56889> for more on that. + /// + /// If the previous call to `write` provided more (encoded) data than the delegate writer could + /// accept in a single call to its `write`, the remaining data is buffered. As long as buffered + /// data is present, subsequent calls to `write` will try to write the remaining buffered data + /// to the delegate and return either `Ok(0)` -- and therefore not consume any of `input` -- or + /// an error. + /// + /// # Errors + /// + /// Any errors emitted by the delegate writer are returned. + fn write(&mut self, input: &[u8]) -> Result<usize> { + if self.delegate.is_none() { + panic!("Cannot write more after calling finish()"); + } + + if input.is_empty() { + return Ok(0); + } + + // The contract of `Write::write` places some constraints on this implementation: + // - a call to `write()` represents at most one call to a wrapped `Write`, so we can't + // iterate over the input and encode multiple chunks. + // - Errors mean that "no bytes were written to this writer", so we need to reset the + // internal state to what it was before the error occurred + + // before reading any input, write any leftover encoded output from last time + if self.output_occupied_len > 0 { + let current_len = self.output_occupied_len; + return self + .write_to_delegate(current_len) + // did not read any input + .map(|_| 0); + } + + debug_assert_eq!(0, self.output_occupied_len); + + // how many bytes, if any, were read into `extra` to create a triple to encode + let mut extra_input_read_len = 0; + let mut input = input; + + let orig_extra_len = self.extra_input_occupied_len; + + let mut encoded_size = 0; + // always a multiple of MIN_ENCODE_CHUNK_SIZE + let mut max_input_len = MAX_INPUT_LEN; + + // process leftover un-encoded input from last write + if self.extra_input_occupied_len > 0 { + debug_assert!(self.extra_input_occupied_len < 3); + if input.len() + self.extra_input_occupied_len >= MIN_ENCODE_CHUNK_SIZE { + // Fill up `extra`, encode that into `output`, and consume as much of the rest of + // `input` as possible. + // We could write just the encoding of `extra` by itself but then we'd have to + // return after writing only 4 bytes, which is inefficient if the underlying writer + // would make a syscall. + extra_input_read_len = MIN_ENCODE_CHUNK_SIZE - self.extra_input_occupied_len; + debug_assert!(extra_input_read_len > 0); + // overwrite only bytes that weren't already used. If we need to rollback extra_len + // (when the subsequent write errors), the old leading bytes will still be there. + self.extra_input[self.extra_input_occupied_len..MIN_ENCODE_CHUNK_SIZE] + .copy_from_slice(&input[0..extra_input_read_len]); + + let len = encode_to_slice( + &self.extra_input[0..MIN_ENCODE_CHUNK_SIZE], + &mut self.output[..], + self.config.char_set.encode_table(), + ); + debug_assert_eq!(4, len); + + input = &input[extra_input_read_len..]; + + // consider extra to be used up, since we encoded it + self.extra_input_occupied_len = 0; + // don't clobber where we just encoded to + encoded_size = 4; + // and don't read more than can be encoded + max_input_len = MAX_INPUT_LEN - MIN_ENCODE_CHUNK_SIZE; + + // fall through to normal encoding + } else { + // `extra` and `input` are non empty, but `|extra| + |input| < 3`, so there must be + // 1 byte in each. + debug_assert_eq!(1, input.len()); + debug_assert_eq!(1, self.extra_input_occupied_len); + + self.extra_input[self.extra_input_occupied_len] = input[0]; + self.extra_input_occupied_len += 1; + return Ok(1); + }; + } else if input.len() < MIN_ENCODE_CHUNK_SIZE { + // `extra` is empty, and `input` fits inside it + self.extra_input[0..input.len()].copy_from_slice(input); + self.extra_input_occupied_len = input.len(); + return Ok(input.len()); + }; + + // either 0 or 1 complete chunks encoded from extra + debug_assert!(encoded_size == 0 || encoded_size == 4); + debug_assert!( + // didn't encode extra input + MAX_INPUT_LEN == max_input_len + // encoded one triple + || MAX_INPUT_LEN == max_input_len + MIN_ENCODE_CHUNK_SIZE + ); + + // encode complete triples only + let input_complete_chunks_len = input.len() - (input.len() % MIN_ENCODE_CHUNK_SIZE); + let input_chunks_to_encode_len = cmp::min(input_complete_chunks_len, max_input_len); + debug_assert_eq!(0, max_input_len % MIN_ENCODE_CHUNK_SIZE); + debug_assert_eq!(0, input_chunks_to_encode_len % MIN_ENCODE_CHUNK_SIZE); + + encoded_size += encode_to_slice( + &input[..(input_chunks_to_encode_len)], + &mut self.output[encoded_size..], + self.config.char_set.encode_table(), + ); + + // not updating `self.output_occupied_len` here because if the below write fails, it should + // "never take place" -- the buffer contents we encoded are ignored and perhaps retried + // later, if the consumer chooses. + + self.write_to_delegate(encoded_size) + // no matter whether we wrote the full encoded buffer or not, we consumed the same + // input + .map(|_| extra_input_read_len + input_chunks_to_encode_len) + .map_err(|e| { + // in case we filled and encoded `extra`, reset extra_len + self.extra_input_occupied_len = orig_extra_len; + + e + }) + } + + /// Because this is usually treated as OK to call multiple times, it will *not* flush any + /// incomplete chunks of input or write padding. + /// # Errors + /// + /// The first error that is not of [`ErrorKind::Interrupted`] will be returned. + fn flush(&mut self) -> Result<()> { + self.write_all_encoded_output()?; + self.delegate + .as_mut() + .expect("Writer must be present") + .flush() + } +} + +impl<W: Write> Drop for EncoderWriter<W> { + fn drop(&mut self) { + if !self.panicked { + // like `BufWriter`, ignore errors during drop + let _ = self.write_final_leftovers(); + } + } +} |