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package common
/*
Copied from https://ixday.github.io/post/golang-cancel-copy/
*/
import (
"context"
"io"
)
// here is some syntax sugar inspired by the Tomas Senart's video,
// it allows me to inline the Reader interface
type readerFunc func(p []byte) (n int, err error)
func (rf readerFunc) Read(p []byte) (n int, err error) { return rf(p) }
// Copy slightly modified function signature:
// - context has been added in order to propagate cancellation
// - (undo by Keuin) I do not return the number of bytes written, has it is not useful in my use case
func Copy(ctx context.Context, out io.Writer, in io.Reader) (written int64, err error) {
// Copy will call the Reader and Writer interface multiple time, in order
// to copy by chunk (avoiding loading the whole file in memory).
// I insert the ability to cancel before read time as it is the earliest
// possible in the call process.
written, err = io.Copy(out, readerFunc(func(p []byte) (int, error) {
// golang non-blocking channel: https://gobyexample.com/non-blocking-channel-operations
select {
// if context has been canceled
case <-ctx.Done():
// stop process and propagate "context canceled" error
return 0, ctx.Err()
default:
// otherwise just run default io.Reader implementation
return in.Read(p)
}
}))
return
}
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