Struct SyncStream 

pub struct SyncStream<S> { /* private fields */ }

Available on crate features compat and io only.

A growable buffered stream adapter that bridges async I/O with sync traits.

Buffer Growth Strategy

• Read buffer: Grows as needed to accommodate incoming data, up to max_buffer_size
• Write buffer: Grows as needed for outgoing data, up to max_buffer_size
• Both buffers shrink back to base_capacity when fully consumed and capacity exceeds 4x base

Usage Pattern

The sync Read and Write implementations will return WouldBlock errors when buffers need servicing via the async methods:

• Call fill_read_buf() when Read::read() returns WouldBlock
• Call flush_write_buf() when Write::write() returns WouldBlock

Note on flush()

The Write::flush() method intentionally returns Ok(()) without checking if there’s buffered data. This is for compatibility with libraries like tungstenite that call flush() after every write. Actual flushing happens via the async flush_write_buf() method.

Implementations

impl<S> SyncStream<S>

pub fn new(stream: S) -> SyncStream<S>

Creates a new SyncStream with default buffer sizes.

• Base capacity: 8KiB
• Max buffer size: 64MiB

pub fn with_capacity(base_capacity: usize, stream: S) -> SyncStream<S>

Creates a new SyncStream with a custom base capacity.

The maximum buffer size defaults to 64MiB.

pub fn with_limits( base_capacity: usize, max_buffer_size: usize, stream: S, ) -> SyncStream<S>

Creates a new SyncStream with custom base capacity and maximum buffer size.

pub fn get_ref(&self) -> &S

Returns a reference to the underlying stream.

pub fn get_mut(&mut self) -> &mut S

Returns a mutable reference to the underlying stream.

pub fn into_inner(self) -> S

Consumes the SyncStream, returning the underlying stream.

Any buffered data is discarded. Use into_parts if you need to preserve unread data.

pub fn into_parts(self) -> (S, Vec<u8>)

Consumes the SyncStream, returning the underlying stream and any unread buffered data.

If the read buffer is currently lent to an IO operation, the returned Vec will be empty.

pub fn is_eof(&self) -> bool

Returns true if the stream has reached EOF.

pub fn read_buf_uninit( &mut self, buf: &mut [MaybeUninit<u8>], ) -> Result<usize, Error>

Pull some bytes from this source into the specified buffer.

pub fn has_pending_write(&self) -> bool

Returns true if there is pending data in the write buffer that needs to be flushed.

impl<S> SyncStream<S>

where S: AsyncRead,

pub async fn fill_read_buf(&mut self) -> Result<usize, Error>

Fills the read buffer by reading from the underlying async stream.

This method:

1. Compacts the buffer if there’s unconsumed data
2. Ensures there’s space for at least base_capacity more bytes
3. Reads data from the underlying stream
4. Returns the number of bytes read (0 indicates EOF)

Errors

Returns an error if:

• The read buffer has reached max_buffer_size
• The underlying stream returns an error

impl<S> SyncStream<S>

where S: AsyncWrite,

pub async fn flush_write_buf(&mut self) -> Result<usize, Error>

Flushes the write buffer to the underlying async stream.

This method:

1. Writes all buffered data to the underlying stream
2. Calls flush() on the underlying stream
3. Returns the total number of bytes flushed

On error, any unwritten data remains in the buffer and can be retried.

Errors

Returns an error if the underlying stream returns an error. In this case, the buffer retains any data that wasn’t successfully written.

Trait Implementations

impl<S> BufRead for SyncStream<S>

fn fill_buf(&mut self) -> Result<&[u8], Error>

Returns the contents of the internal buffer, filling it with more data, via Read methods, if empty.

fn consume(&mut self, amt: usize)

Marks the given amount of additional bytes from the internal buffer as having been read. Subsequent calls to read only return bytes that have not been marked as read.

fn has_data_left(&mut self) -> Result<bool, Error>

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

Checks if there is any data left to be read.

fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes into buf until the delimiter byte or EOF is reached.

fn skip_until(&mut self, byte: u8) -> Result<usize, Error>

Skips all bytes until the delimiter byte or EOF is reached.

fn read_line(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until a newline (the 0xA byte) is reached, and append them to the provided String buffer.

fn split(self, byte: u8) -> Split<Self>

where Self: Sized,

Returns an iterator over the contents of this reader split on the byte byte.

fn lines(self) -> Lines<Self>

where Self: Sized,

Returns an iterator over the lines of this reader.

impl<S> Debug for SyncStream<S>

where S: Debug,

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

Formats the value using the given formatter.

impl<S> Read for SyncStream<S>

fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>

Reads data from the internal buffer.

Returns WouldBlock if the buffer is empty and not at EOF, indicating that fill_read_buf() should be called.

fn read_buf(&mut self, buf: BorrowedCursor<'_, u8>) -> Result<(), Error>

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

Pull some bytes from this source into the specified buffer.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

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

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until EOF in this source, appending them to buf.

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

Reads the exact number of bytes required to fill buf.

fn read_buf_exact( &mut self, cursor: BorrowedCursor<'_, u8>, ) -> Result<(), Error>

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

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

fn read_array<const N: usize>(&mut self) -> Result<[u8; N], Error>

where Self: Sized,

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

Read and return a fixed array of bytes from this source.

fn read_le<T>(&mut self) -> Result<T, Error>

where T: FromEndianBytes, Self: Sized,

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

Read and return a type (e.g. an integer) in little-endian order.

fn read_be<T>(&mut self) -> Result<T, Error>

where T: FromEndianBytes, Self: Sized,

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

Read and return a type (e.g. an integer) in big-endian order.

impl<S> Splittable for SyncStream<S>

where S: Splittable,

type ReadHalf = SyncStreamReadHalf<<S as Splittable>::ReadHalf>

The type of the read half, which normally implements AsyncRead or AsyncReadAt.

type WriteHalf = SyncStreamWriteHalf<<S as Splittable>::WriteHalf>

The type of the write half, which normally implements AsyncWrite or AsyncWriteAt.

fn split( self, ) -> (<SyncStream<S> as Splittable>::ReadHalf, <SyncStream<S> as Splittable>::WriteHalf)

Consumes self and returns a tuple containing separate read and write halves.

impl<S> Write for SyncStream<S>

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

Writes data to the internal buffer.

Returns WouldBlock if the buffer needs flushing or has reached max capacity. In the latter case, it may write partial data before returning WouldBlock.

fn flush(&mut self) -> Result<(), Error>

Returns Ok(()) without checking for buffered data.

Important: This does NOT actually flush data to the underlying stream. This behavior is intentional for compatibility with libraries like tungstenite that call flush() after every write operation. The actual async flush happens when flush_write_buf() is called.

This prevents spurious errors in sync code that expects flush() to succeed after successfully buffering data.

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

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

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.

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

Attempts to write an entire buffer into this writer.

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.

fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error>

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

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

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