/
decoder_reader.go
172 lines (149 loc) · 4.88 KB
/
decoder_reader.go
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package encoding
import (
"errors"
"io"
"golang.org/x/text/transform"
)
// Other than resetting r.err and r.transformComplete in Read() this
// was copied from x/text
func newDecoder(t transform.Transformer) *Decoder {
return &Decoder{Transformer: t}
}
// A Decoder converts bytes to UTF-8. It implements transform.Transformer.
//
// Transforming source bytes that are not of that encoding will not result in an
// error per se. Each byte that cannot be transcoded will be represented in the
// output by the UTF-8 encoding of '\uFFFD', the replacement rune.
type Decoder struct {
transform.Transformer
// This forces external creators of Decoders to use names in struct
// initializers, allowing for future extensibility without having to break
// code.
_ struct{}
}
// Bytes converts the given encoded bytes to UTF-8. It returns the converted
// bytes or nil, err if any error occurred.
func (d *Decoder) Bytes(b []byte) ([]byte, error) {
b, _, err := transform.Bytes(d, b)
if err != nil {
return nil, err
}
return b, nil
}
// String converts the given encoded string to UTF-8. It returns the converted
// string or "", err if any error occurred.
func (d *Decoder) String(s string) (string, error) {
s, _, err := transform.String(d, s)
if err != nil {
return "", err
}
return s, nil
}
// Reader wraps another Reader to decode its bytes.
//
// The Decoder may not be used for any other operation as long as the returned
// Reader is in use.
func (d *Decoder) Reader(r io.Reader) io.Reader {
return NewReader(r, d)
}
// Reader wraps another io.Reader by transforming the bytes read.
type Reader struct {
r io.Reader
t transform.Transformer
err error
// dst[dst0:dst1] contains bytes that have been transformed by t but
// not yet copied out via Read.
dst []byte
dst0, dst1 int
// src[src0:src1] contains bytes that have been read from r but not
// yet transformed through t.
src []byte
src0, src1 int
// transformComplete is whether the transformation is complete,
// regardless of whether or not it was successful.
transformComplete bool
}
var (
// ErrShortDst means that the destination buffer was too short to
// receive all of the transformed bytes.
ErrShortDst = errors.New("transform: short destination buffer")
// ErrShortSrc means that the source buffer has insufficient data to
// complete the transformation.
ErrShortSrc = errors.New("transform: short source buffer")
// errInconsistentByteCount means that Transform returned success (nil
// error) but also returned nSrc inconsistent with the src argument.
errInconsistentByteCount = errors.New("transform: inconsistent byte count returned")
)
const defaultBufSize = 4096
// NewReader returns a new Reader that wraps r by transforming the bytes read
// via t. It calls Reset on t.
func NewReader(r io.Reader, t transform.Transformer) *Reader {
t.Reset()
return &Reader{
r: r,
t: t,
dst: make([]byte, defaultBufSize),
src: make([]byte, defaultBufSize),
}
}
// Read implements the io.Reader interface.
func (r *Reader) Read(p []byte) (int, error) {
// Clear previous errors so a Read can be performed even if the last call
// returned EOF.
r.err = nil
r.transformComplete = false
n := 0
for {
// Copy out any transformed bytes and return the final error if we are done.
if r.dst0 != r.dst1 {
n = copy(p, r.dst[r.dst0:r.dst1])
r.dst0 += n
if r.dst0 == r.dst1 && r.transformComplete {
return n, r.err
}
return n, nil
} else if r.transformComplete {
return 0, r.err
}
// Try to transform some source bytes, or to flush the transformer if we
// are out of source bytes. We do this even if r.r.Read returned an error.
// As the io.Reader documentation says, "process the n > 0 bytes returned
// before considering the error".
if r.src0 != r.src1 || r.err != nil {
var err error
r.dst0 = 0
r.dst1, n, err = r.t.Transform(r.dst, r.src[r.src0:r.src1], r.err == io.EOF)
r.src0 += n
switch {
case err == nil:
if r.src0 != r.src1 {
r.err = errInconsistentByteCount
}
// The Transform call was successful; we are complete if we
// cannot read more bytes into src.
r.transformComplete = r.err != nil
continue
case err == ErrShortDst && (r.dst1 != 0 || n != 0):
// Make room in dst by copying out, and try again.
continue
case err == ErrShortSrc && r.src1-r.src0 != len(r.src) && r.err == nil:
// Read more bytes into src via the code below, and try again.
default:
r.transformComplete = true
// The reader error (r.err) takes precedence over the
// transformer error (err) unless r.err is nil or io.EOF.
if r.err == nil || r.err == io.EOF {
r.err = err
}
continue
}
}
// Move any untransformed source bytes to the start of the buffer
// and read more bytes.
if r.src0 != 0 {
r.src0, r.src1 = 0, copy(r.src, r.src[r.src0:r.src1])
}
n, r.err = r.r.Read(r.src[r.src1:])
r.src1 += n
}
}