func ExampleWithTimeout() {
// Pass a context with a timeout to tell a blocking function that it
// should abandon its work after the timeout elapses.
ctx, _ := context.WithTimeout(context.Background(), 100*time.Millisecond)
select {
case <-time.After(200 * time.Millisecond):
fmt.Println("overslept")
case <-ctx.Done():
fmt.Println(ctx.Err()) // prints "context deadline exceeded"
}
// Output:
// context deadline exceeded
}
func TestCancelReadCloser(t *testing.T) {
ctx, _ := context.WithTimeout(context.Background(), 100*time.Millisecond)
cancelReadCloser := NewCancelReadCloser(ctx, ioutil.NopCloser(&perpetualReader{}))
for {
var buf [128]byte
_, err := cancelReadCloser.Read(buf[:])
if err == context.DeadlineExceeded {
break
} else if err != nil {
t.Fatalf("got unexpected error: %v", err)
}
}
}
// NewCancelReadCloser creates a wrapper that closes the ReadCloser when the
// context is cancelled. The returned io.ReadCloser must be closed when it is
// no longer needed.
func NewCancelReadCloser(ctx context.Context, in io.ReadCloser) io.ReadCloser {
pR, pW := io.Pipe()
// Create a context used to signal when the pipe is closed
doneCtx, cancel := context.WithCancel(context.Background())
p := &cancelReadCloser{
cancel: cancel,
pR: pR,
pW: pW,
}
go func() {
_, err := io.Copy(pW, in)
select {
case <-ctx.Done():
// If the context was closed, p.closeWithError
// was already called. Calling it again would
// change the error that Read returns.
default:
p.closeWithError(err)
}
in.Close()
}()
go func() {
for {
select {
case <-ctx.Done():
p.closeWithError(ctx.Err())
case <-doneCtx.Done():
return
}
}
}()
return p
}