sse support

internal/server/sse/sse.go

@@ -0,0 +1,120 @@
+package sse
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"net/http"
+	"sync"
+)
+
+type (
+	Queue struct {
+		in  chan Event
+		out map[int]chan Event
+
+		ctx    context.Context
+		cancel context.CancelFunc
+
+		lock   sync.Mutex
+		prevID int
+	}
+
+	Event struct {
+		Type string
+		Data []byte
+	}
+)
+
+func NewQueue() *Queue {
+	ctx, cancel := context.WithCancel(context.Background())
+	return &Queue{
+		in:  make(chan Event),
+		out: make(map[int]chan Event),
+
+		ctx:    ctx,
+		cancel: cancel,
+	}
+}
+
+func (q *Queue) Start(ctx context.Context) error {
+	defer q.cancel()
+
+	for {
+		select {
+		case <-ctx.Done():
+			// we're done piping events
+			return nil
+		case e := <-q.in:
+			// share event will all subscribers
+			q.lock.Lock()
+			for _, out := range q.out {
+				out <- e
+			}
+			q.lock.Unlock()
+		}
+	}
+}
+
+func (q *Queue) Listen(ctx context.Context, fn func(context.Context, *Event) error) error {
+	// create new out pipe and append it to the queue
+
+	out := make(chan Event, 1)
+
+	q.lock.Lock()
+	q.prevID += 1
+	id := q.prevID
+	q.out[id] = out
+	q.lock.Unlock()
+
+	// delete the pipe when done listening
+	defer func() {
+		q.lock.Lock()
+		delete(q.out, id)
+		q.lock.Unlock()
+	}()
+
+	for {
+		select {
+		case <-q.ctx.Done():
+			// queue is shut down
+			return nil
+		case <-ctx.Done():
+			// done listening to events
+			return nil
+		case e := <-out:
+			// pass event to the caller
+			if err := fn(ctx, &e); err != nil {
+				return err
+			}
+		}
+	}
+}
+
+func (q *Queue) Send(ctx context.Context, eventType string, data []byte) error {
+	select {
+	case <-q.ctx.Done():
+		// the queue has closed
+		return fmt.Errorf("event queue closed: %w", q.ctx.Err())
+	case <-ctx.Done():
+		// sender ran out of time
+		return fmt.Errorf("provided context canceled: %w", ctx.Err())
+		// push the event onto the queue
+	case q.in <- Event{
+		Type: eventType,
+		Data: data,
+	}:
+	}
+
+	return nil
+}
+
+func (e *Event) Write(w http.ResponseWriter) {
+	fmt.Fprintf(
+		w,
+		"event: %s\ndata: %s\n\n",
+		e.Type,
+		bytes.ReplaceAll(e.Data, []byte("\n"), []byte(" ")),
+	)
+	w.(http.Flusher).Flush()
+}