rclone/vendor/github.com/aws/aws-sdk-go/service/s3/s3crypto/helper.go

package s3crypto

import (
	"errors"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"

	"github.com/aws/aws-sdk-go/aws/request"
)

func getWriterStore(req *request.Request, path string, useTempFile bool) (io.ReadWriteSeeker, error) {
	if !useTempFile {
		return &bytesReadWriteSeeker{}, nil
	}
	// Create temp file to be used later for calculating the SHA256 header
	f, err := ioutil.TempFile(path, "")
	if err != nil {
		return nil, err
	}

	req.Handlers.Send.PushBack(func(r *request.Request) {
		// Close the temp file and cleanup
		f.Close()
		fpath := filepath.Join(path, f.Name())
		os.Remove(fpath)
	})
	return f, nil
}

type bytesReadWriteSeeker struct {
	buf []byte
	i   int64
}

// Copied from Go stdlib bytes.Reader
func (ws *bytesReadWriteSeeker) Read(b []byte) (int, error) {
	if ws.i >= int64(len(ws.buf)) {
		return 0, io.EOF
	}
	n := copy(b, ws.buf[ws.i:])
	ws.i += int64(n)
	return n, nil
}

func (ws *bytesReadWriteSeeker) Write(b []byte) (int, error) {
	ws.buf = append(ws.buf, b...)
	return len(b), nil
}

// Copied from Go stdlib bytes.Reader
func (ws *bytesReadWriteSeeker) Seek(offset int64, whence int) (int64, error) {
	var abs int64
	switch whence {
	case 0:
		abs = offset
	case 1:
		abs = int64(ws.i) + offset
	case 2:
		abs = int64(len(ws.buf)) + offset
	default:
		return 0, errors.New("bytes.Reader.Seek: invalid whence")
	}
	if abs < 0 {
		return 0, errors.New("bytes.Reader.Seek: negative position")
	}
	ws.i = abs
	return abs, nil
}