[client] mobile MDM bridge — iOS + Android setMDMPolicyFetcher entrypoint

client/android/mdm.go

@@ -0,0 +1,79 @@
+//go:build android
+
+package android
+
+import (
+	"encoding/json"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/mdm"
+)
+
+// PolicyFetcher is the mobile-side bridge for the MDM managed-config
+// snapshot. The native layer (Kotlin) implements this and registers
+// the instance via SetMobilePolicyFetcher at app start. Every
+// invocation must read the current RestrictionsManager state and
+// return the result as a JSON-encoded map[string]any string.
+//
+// JSON is used because gomobile does not support map[string]any
+// crossing the JNI boundary — the adapter on the Go side parses the
+// string back into the map[string]any expected by mdm.LoadPolicy.
+//
+// Return value contract:
+//   - "" (empty)         : interpreted as "no MDM source / no managed keys"
+//   - "{}"               : managed config explicitly empty
+//   - "{...}"            : JSON object with key/value pairs
+//   - malformed JSON     : logged and treated as empty
+type PolicyFetcher interface {
+	FetchJSON() string
+}
+
+// jsonFetcherAdapter wraps a gomobile-exposed PolicyFetcher into the
+// internal mdm.PolicyFetcher interface, taking care of JSON decoding
+// on every Fetch.
+type jsonFetcherAdapter struct {
+	inner PolicyFetcher
+}
+
+func (a *jsonFetcherAdapter) Fetch() map[string]any {
+	raw := a.inner.FetchJSON()
+	if raw == "" {
+		return nil
+	}
+	var out map[string]any
+	if err := json.Unmarshal([]byte(raw), &out); err != nil {
+		log.Warnf("MDM mobile fetcher: invalid JSON payload from native: %v", err)
+		return nil
+	}
+	return out
+}
+
+// SetMobilePolicyFetcher registers the native-provided MDM policy
+// fetcher. Call exactly once from the gomobile-init code (Kotlin
+// Application.onCreate) before the daemon starts. Passing nil
+// effectively disables MDM enforcement on this build.
+func SetMobilePolicyFetcher(p PolicyFetcher) {
+	if p == nil {
+		mdm.SetMobilePolicyFetcher(nil)
+		return
+	}
+	mdm.SetMobilePolicyFetcher(&jsonFetcherAdapter{inner: p})
+}
+
+// OnMDMPolicyChanged is the mobile entry point the native layer calls
+// when the OS broadcasts a managed-config change
+// (ACTION_APPLICATION_RESTRICTIONS_CHANGED on Android,
+// UserDefaults.didChangeNotification on iOS). The hook cancels the
+// current engine context so the current Run() returns; the native
+// loop is expected to re-invoke Run() afterwards, which re-reads
+// the config (including the fresh MDM overlay via the registered
+// PolicyFetcher).
+//
+// No payload is passed — the OS notification only signals "something
+// changed"; the actual values are read on-demand by the next
+// loadPlatformPolicy call inside Config.apply.
+func (c *Client) OnMDMPolicyChanged() {
+	log.Info("MDM policy change signaled by native; stopping engine to restart with fresh config")
+	c.Stop()
+}

client/mdm/policy_mobile.go

@@ -2,13 +2,41 @@
 
 package mdm
 
-// loadPlatformPolicy is unused on mobile: the native layer (Swift on iOS,
-// Kotlin/Java on Android) reads the OS managed-config store and pushes the
-// resulting dictionary in-process via a gomobile entry point that lands in
-// Phase 5 / Phase 6. The stub keeps the package compilable for mobile
-// builds and returns (nil, nil) — the platform-absent sentinel that
-// LoadPolicy in policy.go treats as "no MDM source present".
+// PolicyFetcher is the bridge between Go and the mobile native layer
+// (Kotlin/Java on Android, Swift on iOS). The native layer registers
+// an implementation at gomobile init via SetMobilePolicyFetcher;
+// thereafter every call to loadPlatformPolicy delegates to the
+// registered fetcher, which reads the OS-native managed-config store
+// (RestrictionsManager on Android, com.apple.configuration.managed
+// UserDefaults on iOS) and returns the current snapshot.
+//
+// Set-once at init, never mutated at runtime → no synchronisation
+// required for the read path. The native layer must register before
+// any Go code starts polling or processing MDM events.
+type PolicyFetcher interface {
+	Fetch() map[string]any
+}
+
+var fetcher PolicyFetcher
+
+// SetMobilePolicyFetcher registers the native-provided fetcher. Call
+// exactly once from the gomobile init code (Kotlin Application.onCreate
+// / Swift AppDelegate) before the daemon starts. Passing nil disables
+// MDM enforcement on this build (loadPlatformPolicy returns
+// (nil, nil) — the platform-absent sentinel that LoadPolicy treats as
+// "no MDM source present").
+func SetMobilePolicyFetcher(p PolicyFetcher) {
+	fetcher = p
+}
+
+// loadPlatformPolicy delegates to the native-provided fetcher. Returns
+// (nil, nil) — the platform-absent sentinel — when no fetcher has been
+// registered yet, so the package behaves identically to a desktop
+// device without an MDM source.
 func loadPlatformPolicy() (map[string]any, error) {
-	//nolint:nilnil // (nil, nil) is the documented platform-absent sentinel; see LoadPolicy.
-	return nil, nil
+	if fetcher == nil {
+		//nolint:nilnil // (nil, nil) is the documented platform-absent sentinel; see LoadPolicy.
+		return nil, nil
+	}
+	return fetcher.Fetch(), nil
 }