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package common
/*
Copied from https://ixday.github.io/post/golang-cancel-copy/
*/
import (
"context"
"io"
"os"
)
// CopyToFileWithBuffer copies data from io.Reader to os.File with given buffer and read chunk size.
// The reader and file won't be closed.
// If syncFile is set, the file will be synced after every read.
func CopyToFileWithBuffer(
ctx context.Context,
out *os.File,
in io.Reader,
buffer []byte,
chunkSize int,
syncFile bool,
) (written int64, err error) {
bufSize := len(buffer)
off := 0 // offset to the end of data in buffer
nRead := 0 // how many bytes were read in the last read
defer func() {
if off+nRead > 0 {
// write unwritten data in buffer
nWrite, _ := out.Write(buffer[:off+nRead])
written += int64(nWrite)
if syncFile {
_ = out.Sync()
}
}
}()
for {
select {
case <-ctx.Done():
err = ctx.Err()
return
default:
nRead, err = in.Read(buffer[off:Min[int](off+chunkSize, bufSize)])
if err != nil {
return
}
off += nRead
if off == bufSize {
// buffer is full
var nWritten int
nWritten, err = out.Write(buffer)
if err != nil {
return
}
if syncFile {
err = out.Sync()
if err != nil {
return
}
}
written += int64(nWritten)
off = 0
}
}
}
}
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