9.5 KiB
fwd
import "github.com/philhofer/fwd"
Overview
Package fwd provides a buffered reader and writer. Each has methods that help improve the encoding/decoding performance of some binary protocols.
The Writer and Reader type provide similar
functionality to their counterparts in bufio, plus
a few extra utility methods that simplify read-ahead
and write-ahead. I wrote this package to improve serialization
performance for github.com/tinylib/msgp,
where it provided about a 2x speedup over bufio for certain
workloads. However, care must be taken to understand the semantics of the
extra methods provided by this package, as they allow
the user to access and manipulate the buffer memory
directly.
The extra methods for fwd.Reader are Peek, Skip
and Next. (*fwd.Reader).Peek, unlike (*bufio.Reader).Peek,
will re-allocate the read buffer in order to accommodate arbitrarily
large read-ahead. (*fwd.Reader).Skip skips the next n bytes
in the stream, and uses the io.Seeker interface if the underlying
stream implements it. (*fwd.Reader).Next returns a slice pointing
to the next n bytes in the read buffer (like Peek), but also
increments the read position. This allows users to process streams
in arbitrary block sizes without having to manage appropriately-sized
slices. Additionally, obviating the need to copy the data from the
buffer to another location in memory can improve performance dramatically
in CPU-bound applications.
fwd.Writer only has one extra method, which is (*fwd.Writer).Next, which
returns a slice pointing to the next n bytes of the writer, and increments
the write position by the length of the returned slice. This allows users
to write directly to the end of the buffer.
Portability
Because it uses the unsafe package, there are theoretically no promises about forward or backward portability.
To stay compatible with tinygo 0.32, unsafestr() has been updated to use unsafe.Slice() as suggested by https://tinygo.org/docs/guides/compatibility, which also required bumping go.mod to require at least go 1.20.
Index
- Constants
- type Reader
- func NewReader(r io.Reader) *Reader
- func NewReaderBuf(r io.Reader, buf []byte) *Reader
- func NewReaderSize(r io.Reader, n int) *Reader
- func (r *Reader) BufferSize() int
- func (r *Reader) Buffered() int
- func (r *Reader) Next(n int) ([]byte, error)
- func (r *Reader) Peek(n int) ([]byte, error)
- func (r *Reader) Read(b []byte) (int, error)
- func (r *Reader) ReadByte() (byte, error)
- func (r *Reader) ReadFull(b []byte) (int, error)
- func (r *Reader) Reset(rd io.Reader)
- func (r *Reader) Skip(n int) (int, error)
- func (r *Reader) WriteTo(w io.Writer) (int64, error)
- type Writer
- func NewWriter(w io.Writer) *Writer
- func NewWriterBuf(w io.Writer, buf []byte) *Writer
- func NewWriterSize(w io.Writer, n int) *Writer
- func (w *Writer) BufferSize() int
- func (w *Writer) Buffered() int
- func (w *Writer) Flush() error
- func (w *Writer) Next(n int) ([]byte, error)
- func (w *Writer) ReadFrom(r io.Reader) (int64, error)
- func (w *Writer) Write(p []byte) (int, error)
- func (w *Writer) WriteByte(b byte) error
- func (w *Writer) WriteString(s string) (int, error)
Constants
const (
// DefaultReaderSize is the default size of the read buffer
DefaultReaderSize = 2048
)
const (
// DefaultWriterSize is the
// default write buffer size.
DefaultWriterSize = 2048
)
type Reader
type Reader struct {
// contains filtered or unexported fields
}
Reader is a buffered look-ahead reader
func NewReader
func NewReader(r io.Reader) *Reader
NewReader returns a new *Reader that reads from 'r'
func NewReaderSize
func NewReaderSize(r io.Reader, n int) *Reader
NewReaderSize returns a new *Reader that reads from 'r' and has a buffer size 'n'
func (*Reader) BufferSize
func (r *Reader) BufferSize() int
BufferSize returns the total size of the buffer
func (*Reader) Buffered
func (r *Reader) Buffered() int
Buffered returns the number of bytes currently in the buffer
func (*Reader) Next
func (r *Reader) Next(n int) ([]byte, error)
Next returns the next 'n' bytes in the stream. Unlike Peek, Next advances the reader position. The returned bytes point to the same data as the buffer, so the slice is only valid until the next reader method call. An EOF is considered an unexpected error. If an the returned slice is less than the length asked for, an error will be returned, and the reader position will not be incremented.
func (*Reader) Peek
func (r *Reader) Peek(n int) ([]byte, error)
Peek returns the next 'n' buffered bytes, reading from the underlying reader if necessary. It will only return a slice shorter than 'n' bytes if it also returns an error. Peek does not advance the reader. EOF errors are not returned as io.ErrUnexpectedEOF.
func (*Reader) Read
func (r *Reader) Read(b []byte) (int, error)
Read implements io.Reader.
func (*Reader) ReadByte
func (r *Reader) ReadByte() (byte, error)
ReadByte implements io.ByteReader.
func (*Reader) ReadFull
func (r *Reader) ReadFull(b []byte) (int, error)
ReadFull attempts to read len(b) bytes into 'b'. It returns the number of bytes read into 'b', and an error if it does not return len(b). EOF is considered an unexpected error.
func (*Reader) Reset
func (r *Reader) Reset(rd io.Reader)
Reset resets the underlying reader and the read buffer.
func (*Reader) Skip
func (r *Reader) Skip(n int) (int, error)
Skip moves the reader forward 'n' bytes. Returns the number of bytes skipped and any errors encountered. It is analogous to Seek(n, 1). If the underlying reader implements io.Seeker, then that method will be used to skip forward.
If the reader encounters
an EOF before skipping 'n' bytes, it
returns io.ErrUnexpectedEOF. If the
underlying reader implements io.Seeker, then
those rules apply instead. (Many implementations
will not return io.EOF until the next call
to Read).
func (*Reader) WriteTo
func (r *Reader) WriteTo(w io.Writer) (int64, error)
WriteTo implements io.WriterTo.
type Writer
type Writer struct {
// contains filtered or unexported fields
}
Writer is a buffered writer
func NewWriter
func NewWriter(w io.Writer) *Writer
NewWriter returns a new writer
that writes to 'w' and has a buffer
that is DefaultWriterSize bytes.
func NewWriterBuf
func NewWriterBuf(w io.Writer, buf []byte) *Writer
NewWriterBuf returns a new writer that writes to 'w' and has 'buf' as a buffer. 'buf' is not used when has smaller capacity than 18, custom buffer is allocated instead.
func NewWriterSize
func NewWriterSize(w io.Writer, n int) *Writer
NewWriterSize returns a new writer that writes to 'w' and has a buffer size 'n'.
func (*Writer) BufferSize
func (w *Writer) BufferSize() int
BufferSize returns the maximum size of the buffer.
func (*Writer) Buffered
func (w *Writer) Buffered() int
Buffered returns the number of buffered bytes in the reader.
func (*Writer) Flush
func (w *Writer) Flush() error
Flush flushes any buffered bytes to the underlying writer.
func (*Writer) Next
func (w *Writer) Next(n int) ([]byte, error)
Next returns the next 'n' free bytes
in the write buffer, flushing the writer
as necessary. Next will return io.ErrShortBuffer
if 'n' is greater than the size of the write buffer.
Calls to 'next' increment the write position by
the size of the returned buffer.
func (*Writer) ReadFrom
func (w *Writer) ReadFrom(r io.Reader) (int64, error)
ReadFrom implements io.ReaderFrom
func (*Writer) Write
func (w *Writer) Write(p []byte) (int, error)
Write implements io.Writer
func (*Writer) WriteByte
func (w *Writer) WriteByte(b byte) error
WriteByte implements io.ByteWriter
func (*Writer) WriteString
func (w *Writer) WriteString(s string) (int, error)
WriteString is analogous to Write, but it takes a string.
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