added subscription.Message.WriteSSE method

tools/subscriptions/message_test.go

@@ -0,0 +1,25 @@
+package subscriptions_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/pocketbase/pocketbase/tools/subscriptions"
+)
+
+func TestMessageWrite(t *testing.T) {
+	m := subscriptions.Message{
+		Name: "test_name",
+		Data: []byte("test_data"),
+	}
+
+	var sb strings.Builder
+
+	m.WriteSSE(&sb, "test_id")
+
+	expected := "id:test_id\nevent:test_name\ndata:test_data\n\n"
+
+	if v := sb.String(); v != expected {
+		t.Fatalf("Expected writer content\n%q\ngot\n%q", expected, v)
+	}
+}