goext/dataext/bufferedReadCloser.go

package dataext

import (
	"errors"
	"io"
)

type brcMode int

const (
	modeSourceReading  brcMode = 0
	modeSourceFinished brcMode = 1
	modeBufferReading  brcMode = 2
	modeBufferFinished brcMode = 3
)

type BufferedReadCloser interface {
	io.ReadCloser
	BufferedAll() ([]byte, error)
	Reset() error
}

type bufferedReadCloser struct {
	buffer []byte
	inner  io.ReadCloser
	mode   brcMode
	off    int
}

func NewBufferedReadCloser(sub io.ReadCloser) BufferedReadCloser {
	return &bufferedReadCloser{
		buffer: make([]byte, 0, 1024),
		inner:  sub,
		mode:   modeSourceReading,
		off:    0,
	}
}

func (b *bufferedReadCloser) Read(p []byte) (int, error) {
	switch b.mode {
	case modeSourceReading:
		n, err := b.inner.Read(p)
		if n > 0 {
			b.buffer = append(b.buffer, p[0:n]...)
		}

		if err == io.EOF {
			b.mode = modeSourceFinished
		}

		return n, err

	case modeSourceFinished:
		return 0, io.EOF

	case modeBufferReading:

		if len(b.buffer) <= b.off {
			b.mode = modeBufferFinished
			if len(p) == 0 {
				return 0, nil
			}
			return 0, io.EOF
		}

		n := copy(p, b.buffer[b.off:])
		b.off += n
		return n, nil

	case modeBufferFinished:
		return 0, io.EOF

	default:
		return 0, errors.New("object in undefined status")
	}
}

func (b *bufferedReadCloser) Close() error {
	switch b.mode {
	case modeSourceReading:
		_, err := b.BufferedAll()
		if err != nil {
			return err
		}
		err = b.inner.Close()
		if err != nil {
			return err
		}
		b.mode = modeSourceFinished
		return nil

	case modeSourceFinished:
		return nil

	case modeBufferReading:
		b.mode = modeBufferFinished
		return nil

	case modeBufferFinished:
		return nil

	default:
		return errors.New("object in undefined status")
	}

}

func (b *bufferedReadCloser) BufferedAll() ([]byte, error) {
	switch b.mode {
	case modeSourceReading:
		arr := make([]byte, 1024)
		for b.mode == modeSourceReading {
			_, err := b.Read(arr)
			if err != nil && err != io.EOF {
				return nil, err
			}
		}
		if err := b.Reset(); err != nil {
			return nil, err
		}
		return b.buffer, nil

	case modeSourceFinished:
		return b.buffer, nil

	case modeBufferReading:
		return b.buffer, nil

	case modeBufferFinished:
		return b.buffer, nil

	default:
		return nil, errors.New("object in undefined status")
	}
}

// Reset resets the buffer to the beginning of the buffer.
// If the original source is partially read, we will finish reading it and fill our buffer
func (b *bufferedReadCloser) Reset() error {
	switch b.mode {
	case modeSourceReading:
		if b.off == 0 {
			return nil // nobody has read anything yet
		}
		err := b.Close()
		if err != nil {
			return err
		}
		b.mode = modeBufferReading
		b.off = 0
		return nil

	case modeSourceFinished:
		err := b.Close()
		if err != nil {
			return err
		}
		b.mode = modeBufferReading
		b.off = 0
		return nil

	case modeBufferReading:
		fallthrough
	case modeBufferFinished:
		b.mode = modeBufferReading
		b.off = 0
		return nil

	default:
		return errors.New("object in undefined status")
	}
}