wip: prepare to implement server-sent events for image download progress

api/events/events.go

@@ -0,0 +1,18 @@
+package events
+
+import (
+	"io"
+
+	"github.com/a-h/templ"
+)
+
+type Event interface {
+	templ.Component
+	// Event returns the event name
+	Event() string
+	// SerializeTo writes the event data to the writer.
+	//
+	// SerializeTo must not write multiple linebreaks (single linebreak is fine)
+	// in succession to the writer since it will mess up SSE events.
+	SerializeTo(w io.Writer) error
+}

api/events/image_download_start.go

@@ -0,0 +1,56 @@
+package events
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+)
+
+type ImageDownloadEvent string
+
+const (
+	ImageDownloadStart    ImageDownloadEvent = "image.download.start"
+	ImageDownloadEnd      ImageDownloadEvent = "image.download.end"
+	ImageDownloadError    ImageDownloadEvent = "image.download.error"
+	ImageDownloadProgress ImageDownloadEvent = "image.download.progress"
+)
+
+type ImageDownload struct {
+	EventKind     ImageDownloadEvent `json:"event"`
+	ImageURL      string             `json:"image_url"`
+	ImageHeight   int64              `json:"image_height"`
+	ImageWidth    int64              `json:"image_width"`
+	ContentLength int64              `json:"content_length"`
+	Downloaded    int64              `json:"downloaded"`
+	Subreddit     string             `json:"subreddit"`
+	PostURL       string             `json:"post_url"`
+	PostName      string             `json:"post_name"`
+	PostTitle     string             `json:"post_title"`
+	Error         error              `json:"error"`
+}
+
+// Render the template.
+func (im ImageDownload) Render(ctx context.Context, w io.Writer) error {
+	panic("not implemented") // TODO: Implement
+}
+
+// Event returns the event name
+func (im ImageDownload) Event() string {
+	return "image.download"
+}
+
+// SerializeTo writes the event data to the writer.
+//
+// SerializeTo must not write multiple linebreaks (single linebreak is fine)
+// in succession to the writer since it will mess up SSE events.
+func (im ImageDownload) SerializeTo(w io.Writer) error {
+	return json.NewEncoder(w).Encode(im)
+}
+
+type ImageDownloadSubreddit struct {
+	ImageDownload
+}
+
+func (im ImageDownloadSubreddit) Event() string {
+	return string(im.EventKind) + "." + im.Subreddit
+}

server/routes/events/download_simple.go

@@ -0,0 +1,46 @@
+package events
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"github.com/tigorlazuardi/redmage/pkg/log"
+)
+
+func (handler *Handler) SimpleDownloadEvent(rw http.ResponseWriter, r *http.Request) {
+	ctx, span := tracer.Start(r.Context(), "*Routes.EventsAPI")
+	defer span.End()
+
+	flush, ok := rw.(http.Flusher)
+	if !ok {
+		rw.WriteHeader(http.StatusInternalServerError)
+		_ = json.NewEncoder(rw).Encode(map[string]string{"error": "response writer does not support streaming"})
+		return
+	}
+
+	log.New(ctx).Info("new simple event stream connection", "user_agent", r.UserAgent())
+
+	rw.Header().Set("Content-Type", "text/event-stream")
+	rw.Header().Set("Cache-Control", "no-cache")
+	rw.Header().Set("Connection", "keep-alive")
+	rw.WriteHeader(200)
+	flush.Flush()
+
+	ev, close := handler.Subscribe()
+	defer close()
+
+	for {
+		select {
+		case <-r.Context().Done():
+			log.New(ctx).Info("simple event stream connection closed", "user_agent", r.UserAgent())
+			return
+		case event := <-ev:
+			msg := event.Event()
+			if _, err := fmt.Fprintf(rw, "event: %s\ndata: %s\n\n", msg, msg); err != nil {
+				return
+			}
+			flush.Flush()
+		}
+	}
+}

server/routes/events/events.go

@@ -0,0 +1,17 @@
+package events
+
+import (
+	"github.com/teivah/broadcast"
+	"github.com/tigorlazuardi/redmage/api/events"
+	"github.com/tigorlazuardi/redmage/config"
+)
+
+type Handler struct {
+	Config    *config.Config
+	Broadcast *broadcast.Relay[events.Event]
+}
+
+func (handler *Handler) Subscribe() (<-chan events.Event, func()) {
+	listener := handler.Broadcast.Listener(10)
+	return listener.Ch(), listener.Close
+}

server/routes/events/trace.go

@@ -0,0 +1,5 @@
+package events
+
+import "go.opentelemetry.io/otel"
+
+var tracer = otel.Tracer("server/routes/events")

views/components/progress/image_download.templ

@@ -0,0 +1,23 @@
+package progress
+
+type ImageDownloadStartData struct {
+	ID        string
+	Subreddit string
+	PostURL   string
+	PostName  string
+	PostTitle string
+}
+
+templ ImageDownloadStart(data ImageDownloadStartData) {
+}
+
+type ImageDownloadEndData struct {
+	ID        string
+	Subreddit string
+	PostURL   string
+	PostName  string
+	PostTitle string
+}
+
+templ ImageDownloadEnd(data ImageDownloadEndData) {
+}