make initial version configurable

cmd/check/main.go

@@ -35,7 +35,7 @@ func main() {
 		response = append(response, *req.Version)
 	} else if !req.Source.NoInitialVersion {
 		response = append(response, resource.Version{
-			Version: "mirror",
+			Version: req.Source.InitialVersion(),
 		})
 	}
 

types.go

@@ -1,13 +1,27 @@
 package resource
 
+const DefaultInitialVersion = "mirror"
+
 type Source struct {
 	// fetch the resource itself as an image
 	MirrorSelf bool `json:"mirror_self"`
 
+	// initial version that the mirrored resource image should emit from /check
+	// (default: 'mirror')
+	RawInitialVersion string `json:"mirrored_version"`
+
 	// don't emit an initial version; useful for testing pipeline triggering
 	NoInitialVersion bool `json:"no_initial_version"`
 }
 
+func (s Source) InitialVersion() string {
+	if s.RawInitialVersion == "" {
+		return DefaultInitialVersion
+	}
+
+	return s.RawInitialVersion
+}
+
 type Version struct {
 	Version string `json:"version"`
 }