Struct base64::write::EncoderWriter

[+] Show declaration

pub struct EncoderWriter<W: Write> { /* fields omitted */ }

[−] Expand description

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.

Implementations

impl<W: Write> EncoderWriter<W>[−]

pub fn new(w: W, config: Config) -> EncoderWriter<W>[−]

Create a new encoder that will write to the provided delegate writer w.

pub fn finish(&mut self) -> Result<W>[−]

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.

Trait Implementations

impl<W: Write> Debug for EncoderWriter<W>[+]

[+] Show hidden undocumented items

fn fmt(&self, f: &mut Formatter<'_>) -> Result[−]

Formats the value using the given formatter.

impl<W: Write> Drop for EncoderWriter<W>[+]

[+] Show hidden undocumented items

fn drop(&mut self)[−]

Executes the destructor for this type.

impl<W: Write> Write for EncoderWriter<W>[+]

[+] Show hidden undocumented items

fn write(&mut self, input: &[u8]) -> Result<usize>[−]

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 flush(&mut self) -> Result<()>[−]

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.

pub fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>[−]

Like write, except that it writes from a slice of buffers.

pub fn is_write_vectored(&self) -> bool[−]

🔬 This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

pub fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>[−]

Attempts to write an entire buffer into this writer.

pub fn write_all_vectored(
    &mut self,
    bufs: &mut [IoSlice<'_>]
) -> Result<(), Error>[−]

🔬 This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>[−]

Writes a formatted string into this writer, returning any error encountered.

pub fn by_ref(&mut self) -> &mut Self[−]

Creates a “by reference” adaptor for this instance of Write.