feat(dev-server): Support polling API (#466)

implement /sdk/latest-all

internal/dev_server/sdk/polling.go

@@ -0,0 +1,24 @@
+package sdk
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/pkg/errors"
+)
+
+func LatestAll(w http.ResponseWriter, r *http.Request) {
+	ctx := r.Context()
+	allFlags, err := GetAllFlagsFromContext(ctx)
+	if err != nil {
+		WriteError(ctx, w, errors.Wrap(err, "failed to get flag state"))
+		return
+	}
+	serverFlags := ServerAllPayloadFromFlagsState(allFlags)
+	enc := json.NewEncoder(w)
+	err = enc.Encode(serverFlags.Data)
+	if err != nil {
+		WriteError(ctx, w, errors.Wrap(err, "failed to encode response"))
+		return
+	}
+}

internal/dev_server/sdk/routes.go

@@ -20,6 +20,7 @@ func BindRoutes(router *mux.Router) {
 	router.HandleFunc("/mobile/events/diagnostic", DevNull)
 
 	router.Handle("/all", GetProjectKeyFromAuthorizationHeader(http.HandlerFunc(StreamServerAllPayload)))
+	router.Handle("/sdk/latest-all", GetProjectKeyFromAuthorizationHeader(http.HandlerFunc(LatestAll)))
 
 	router.PathPrefix("/sdk/flags/{flagKey}").
 		Methods(http.MethodGet).