Phase 2: Subsonic REST API framework (auth, response formatting, error handling, routing) plus user permission model

internal/subsonic/router.go

@@ -0,0 +1,92 @@
+package subsonic
+
+import (
+	"net/http"
+	"strings"
+)
+
+type handlerFunc func(rc *Context) *apiError
+
+// registry maps a bare endpoint name (no "/rest/" prefix, no ".view"
+// suffix) to its handler. Populated by init()-time registrations in each
+// endpoint group's file (system.go, browsing.go, ...) via register().
+var registry = map[string]handlerFunc{}
+
+func register(name string, fn handlerFunc) {
+	if _, exists := registry[name]; exists {
+		panic("subsonic: duplicate handler registration for " + name)
+	}
+	registry[name] = fn
+}
+
+// Router returns the /rest/* handler. All authentication, protocol
+// version validation, parameter parsing, and response formatting is
+// centralized here — individual endpoint handlers never touch any of it
+// themselves, and never write directly to the ResponseWriter except the
+// small set of binary/streaming endpoints (stream, download, hls,
+// getCoverArt, getAvatar, getCaptions) which set rc.Handled.
+func (s *Server) Router() http.Handler {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/rest/", s.dispatch)
+	return mux
+}
+
+func (s *Server) dispatch(w http.ResponseWriter, r *http.Request) {
+	name := strings.TrimPrefix(r.URL.Path, "/rest/")
+	name = strings.TrimSuffix(name, ".view")
+	if name == "" {
+		http.NotFound(w, r)
+		return
+	}
+
+	// Subsonic clients may send parameters via query string or (for
+	// endpoints with large/binary bodies, or just by client preference)
+	// POST form encoding; ParseForm merges both into r.Form.
+	if err := r.ParseForm(); err != nil {
+		writeResponse(w, "xml", "", errorResponse(newError(ErrGeneric, "could not parse request")))
+		return
+	}
+	p := params{values: r.Form}
+
+	format := p.Get("f")
+	if format == "" {
+		format = "xml"
+	}
+	callback := p.Get("callback")
+	if format == "jsonp" && !jsonpCallbackRE.MatchString(callback) {
+		// A malformed/malicious callback name must never reach the
+		// response body; fail the request instead of sanitizing it.
+		writeResponse(w, "json", "", errorResponse(newError(ErrGeneric, "invalid callback parameter")))
+		return
+	}
+
+	handler, ok := registry[name]
+	if !ok {
+		writeResponse(w, format, callback, errorResponse(newError(ErrNotFound, "Unknown Subsonic API endpoint: "+name)))
+		return
+	}
+
+	if verr := checkVersion(p.Get("v")); verr != nil {
+		writeResponse(w, format, callback, errorResponse(verr))
+		return
+	}
+
+	user, aerr := authenticate(s.DB, s.EncryptionKey, p)
+	if aerr != nil {
+		writeResponse(w, format, callback, errorResponse(aerr))
+		return
+	}
+
+	rc := &Context{W: w, R: r, Server: s, User: user, Params: p, Format: format, Callback: callback}
+	if herr := handler(rc); herr != nil {
+		writeResponse(w, format, callback, errorResponse(herr))
+		return
+	}
+	if rc.Handled {
+		return
+	}
+	if rc.Response == nil {
+		rc.Response = newResponse()
+	}
+	writeResponse(w, format, callback, rc.Response)
+}