Phase 3: OpenSubsonic core (response envelope, error codes 42-44, getOpenSubsonicExtensions) and apiKeyAuthentication extension with tokenInfo, web API key management

internal/subsonic/extensions.go

@@ -0,0 +1,48 @@
+package subsonic
+
+import "sort"
+
+func init() {
+	register("getOpenSubsonicExtensions", handleGetOpenSubsonicExtensions)
+}
+
+// extensionRegistry lists every OpenSubsonic extension VibeSonic
+// actually implements and has tests for. Advertising an extension here
+// is a promise the corresponding endpoint(s) really work — never add an
+// entry just because a route exists. Each feature file registers its
+// own entry via registerExtension() in its init().
+var extensionRegistry = map[string][]int{}
+
+func registerExtension(name string, versions ...int) {
+	if _, exists := extensionRegistry[name]; exists {
+		panic("subsonic: duplicate extension registration for " + name)
+	}
+	extensionRegistry[name] = versions
+}
+
+func supportedExtensions() []OpenSubsonicExtension {
+	names := make([]string, 0, len(extensionRegistry))
+	for n := range extensionRegistry {
+		names = append(names, n)
+	}
+	sort.Strings(names)
+	out := make([]OpenSubsonicExtension, 0, len(names))
+	for _, n := range names {
+		out = append(out, OpenSubsonicExtension{Name: n, Versions: extensionRegistry[n]})
+	}
+	return out
+}
+
+// hasExtension reports whether ext (any version) is advertised — used
+// where a feature is fully optional and we want to fail closed if it
+// were ever unregistered.
+func hasExtension(name string) bool {
+	_, ok := extensionRegistry[name]
+	return ok
+}
+
+func handleGetOpenSubsonicExtensions(rc *Context) *apiError {
+	rc.Response = newResponse()
+	rc.Response.OpenSubsonicExtensions = supportedExtensions()
+	return nil
+}