dualfroz
ae63f3a6f0
errors.As calls SignalError.As when it cannot match the concrete type directly, e.g. for `var target SignalError; errors.As(err, &target)`. The previous implementation matched target's type and returned true but never wrote to it, so callers got a successful errors.As result with a zero-valued SignalError and no indication the signal was lost. Add a regression test asserting the target is actually populated.
101 lines
3.0 KiB
Go
101 lines
3.0 KiB
Go
package run
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import (
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"context"
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"errors"
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"fmt"
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"os"
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"os/signal"
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)
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// ContextHandler returns an actor, i.e. an execute and interrupt func, that
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// terminates when the provided context is canceled.
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func ContextHandler(ctx context.Context) (execute func() error, interrupt func(error)) {
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ctx, cancel := context.WithCancel(ctx)
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return func() error {
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<-ctx.Done()
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return ctx.Err()
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}, func(error) {
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cancel()
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}
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}
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// SignalHandler returns an actor, i.e. an execute and interrupt func, that
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// terminates with ErrSignal when the process receives one of the provided
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// signals, or with ctx.Error() when the parent context is canceled. If no
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// signals are provided, the actor will terminate on any signal, per
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// [signal.Notify].
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func SignalHandler(ctx context.Context, signals ...os.Signal) (execute func() error, interrupt func(error)) {
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ctx, cancel := context.WithCancel(ctx)
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return func() error {
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testc := getTestSigChan(ctx)
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sigc := make(chan os.Signal, 1)
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signal.Notify(sigc, signals...)
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defer signal.Stop(sigc)
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select {
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case sig := <-testc:
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return &SignalError{Signal: sig}
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case sig := <-sigc:
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return &SignalError{Signal: sig}
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case <-ctx.Done():
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return ctx.Err()
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}
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}, func(error) {
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cancel()
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}
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}
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type testSigChanKey struct{}
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func getTestSigChan(ctx context.Context) <-chan os.Signal {
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c, _ := ctx.Value(testSigChanKey{}).(<-chan os.Signal) // can be nil
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return c
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}
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func putTestSigChan(ctx context.Context, c <-chan os.Signal) context.Context {
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return context.WithValue(ctx, testSigChanKey{}, c)
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}
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// SignalError is returned by the signal handler's execute function when it
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// terminates due to a received signal.
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//
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// SignalError has a design error that impacts comparison with errors.As.
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// Callers should prefer using errors.Is(err, ErrSignal) to check for signal
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// errors, and should only use errors.As in the rare case that they need to
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// program against the specific os.Signal value.
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type SignalError struct {
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Signal os.Signal
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}
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// Error implements the error interface.
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//
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// It was a design error to define this method on a value receiver rather than a
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// pointer receiver. For compatibility reasons it won't be changed.
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func (e SignalError) Error() string {
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return fmt.Sprintf("received signal %s", e.Signal)
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}
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// Is addresses a design error in the SignalError type, so that errors.Is with
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// ErrSignal will return true.
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func (e SignalError) Is(err error) bool {
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return errors.Is(err, ErrSignal)
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}
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// As fixes a design error in the SignalError type, so that errors.As with the
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// literal `&SignalError{}` will return true and, per the errors.As contract,
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// populate target with the underlying signal.
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//
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// errors.As requires target to be a non-nil pointer, so the only target type
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// that can actually be assigned here is *SignalError.
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func (e SignalError) As(target interface{}) bool {
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t, ok := target.(*SignalError)
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if !ok {
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return false
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}
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*t = e
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return true
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}
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// ErrSignal is returned by SignalHandler when a signal triggers termination.
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var ErrSignal = errors.New("signal error")
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