dolmen-go / contextio

Context-aware I/O streams (Writer, Reader) for Go

contextio - Context-aware I/O streams for Go

Author: @dolmen (Olivier Mengué).

Example

go test -run ExampleWriter

func main() {
	// interrupt context after 500ms
	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
	defer cancel()
	// interrupt context with SIGTERM (CTRL+C)
	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, os.Interrupt)
	go func() {
		<-sigs
		cancel()
	}()

	f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

	// Writer that fails when context is canceled
	out := contextio.NewWriter(ctx, f)

	// Infinite loop. Will only be interrupted once write fails.
	for {
		if _, err := out.Write([]byte{'a', 'b', 'c'}); err != nil {
			fmt.Println("Err:", err)
			break
		}
	}

	fmt.Println("Closing.")
}

See Also

• github.com/jbenet/go-context/io Context-aware reader and writer
• github.com/northbright/ctx/ctxcopy Context-aware io.Copy
• gitlab.com/streamy/concon Context-aware net.Conn

contextio's Issues

Cancel reader when read is blocking

I tried to solve a simular problem then your reader. But I work with streams, that can block for a long time. Here is a short example:

func main() {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	scanner := bufio.NewScanner(contextio.NewReader(ctx, os.Stdin))
	for scanner.Scan() {
		fmt.Println(scanner.Text())
	}
	if err := scanner.Err(); err != nil {
		log.Fatalf("Error reading from stdin: %v", err)
	}
}

This program is similar to cat but (should) stop after 5 seconds. Every line to type in stdin is printed back to stdout.

But if you stop typing before the 5 seconds are over, the program does not exists.

I don't know if this kind of problem is out of scope of tihs repo. For every one how is locking for a solution, here is a reader that stops a call to Read(), even when the input source is blocking:

type reader struct {
	ctx context.Context
	r   io.Reader
}

func NewReader(ctx context.Context, r io.Reader) io.Reader {
	return &reader{ctx, r}
}

func (r *reader) Read(p []byte) (n int, err error) {
	wait := make(chan struct{})

	go func() {
		n, err = r.r.Read(p)
		close(wait)
	}()

	select {
	case <-wait:
	case <-r.ctx.Done():
		err = io.EOF
	}
	return n, err
}

Release this module

This is a very useful module and it would be great if it had an official golang release for easy integration with dependabot. Would it be possible to tag the module with a SemVer version e.g. v1.0.0?

Add more tests

Use tools from package testing/iotest to write more tests.

First milestone: 100% coverage.