fusebox: add Storage{At,De}tached signals

Prior to this commit, the FuseBoxReverseService had {At,De}tachStorage
methods. These (1-to-1) methods still exist after this commit, but the
equivalent (1-to-N) signals enable experimenting with simplifying or
even removing the FuseBoxReverseService interface, which would allow the
FuseBoxService to serve multiple clients simultaneously, not just one.

Bug: 1249754
Change-Id: Icb96fa01a4613f4701ce599d720263b211c2f8d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3826416
Reviewed-by: Ben Reich <benreich@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1034936}

chrome/browser/ash/dbus/fusebox_service_provider.cc

@@ -136,7 +136,7 @@ void ReplyToStat(dbus::MethodCall* method_call,
 
 }  // namespace
 
-FuseBoxServiceProvider::FuseBoxServiceProvider() = default;
+FuseBoxServiceProvider::FuseBoxServiceProvider() : server_(this) {}
 
 FuseBoxServiceProvider::~FuseBoxServiceProvider() = default;
 
@@ -146,6 +146,7 @@ void FuseBoxServiceProvider::Start(scoped_refptr<dbus::ExportedObject> object) {
     return;
   }
 
+  exported_object_ = object;
   object->ExportMethod(fusebox::kFuseBoxServiceInterface, fusebox::kCloseMethod,
                        base::BindRepeating(&FuseBoxServiceProvider::Close,
                                            weak_ptr_factory_.GetWeakPtr()),
@@ -169,6 +170,29 @@ void FuseBoxServiceProvider::Start(scoped_refptr<dbus::ExportedObject> object) {
                        base::BindOnce(&OnExportedCallback));
 }
 
+void FuseBoxServiceProvider::OnRegisterFSURLPrefix(const std::string& subdir) {
+  if (!exported_object_) {
+    return;
+  }
+  dbus::Signal signal(fusebox::kFuseBoxServiceInterface,
+                      fusebox::kStorageAttachedSignal);
+  dbus::MessageWriter writer(&signal);
+  writer.AppendString(subdir);
+  exported_object_->SendSignal(&signal);
+}
+
+void FuseBoxServiceProvider::OnUnregisterFSURLPrefix(
+    const std::string& subdir) {
+  if (!exported_object_) {
+    return;
+  }
+  dbus::Signal signal(fusebox::kFuseBoxServiceInterface,
+                      fusebox::kStorageDetachedSignal);
+  dbus::MessageWriter writer(&signal);
+  writer.AppendString(subdir);
+  exported_object_->SendSignal(&signal);
+}
+
 void FuseBoxServiceProvider::Close(
     dbus::MethodCall* method_call,
     dbus::ExportedObject::ResponseSender sender) {

chrome/browser/ash/dbus/fusebox_service_provider.h

@@ -16,8 +16,8 @@ namespace ash {
 
 // FuseBoxServiceProvider implements the org.chromium.FuseBoxService D-Bus
 // interface.
-class FuseBoxServiceProvider
-    : public CrosDBusService::ServiceProviderInterface {
+class FuseBoxServiceProvider : public CrosDBusService::ServiceProviderInterface,
+                               public fusebox::Server::Delegate {
  public:
   FuseBoxServiceProvider();
   FuseBoxServiceProvider(const FuseBoxServiceProvider&) = delete;
@@ -28,6 +28,10 @@ class FuseBoxServiceProvider
   void Start(scoped_refptr<dbus::ExportedObject> object) override;
 
  private:
+  // fusebox::Server::Delegate overrides:
+  void OnRegisterFSURLPrefix(const std::string& subdir) override;
+  void OnUnregisterFSURLPrefix(const std::string& subdir) override;
+
   // D-Bus methods.
   //
   // In terms of semantics, they're roughly equivalent to the C standard
@@ -44,6 +48,7 @@ class FuseBoxServiceProvider
   void Stat(dbus::MethodCall* method_call,
             dbus::ExportedObject::ResponseSender sender);
 
+  scoped_refptr<dbus::ExportedObject> exported_object_;
   fusebox::Server server_;
 
   // base::WeakPtr{this} factory.

chrome/browser/ash/fusebox/fusebox_server.cc

@@ -264,7 +264,7 @@ Server* Server::GetInstance() {
   return g_server_instance;
 }
 
-Server::Server() {
+Server::Server(Delegate* delegate) : delegate_(delegate) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   DCHECK(!g_server_instance);
   g_server_instance = this;
@@ -300,6 +300,9 @@ void Server::RegisterFSURLPrefix(const std::string& subdir,
   std::string trimmed =
       std::string(base::TrimString(fs_url_prefix, "/", base::TRIM_TRAILING));
   prefix_map_.insert({subdir, PrefixMapEntry(trimmed, read_only)});
+  if (delegate_) {
+    delegate_->OnRegisterFSURLPrefix(subdir);
+  }
 }
 
 void Server::UnregisterFSURLPrefix(const std::string& subdir) {
@@ -309,6 +312,9 @@ void Server::UnregisterFSURLPrefix(const std::string& subdir) {
   if (iter != prefix_map_.end()) {
     prefix_map_.erase(iter);
   }
+  if (delegate_) {
+    delegate_->OnUnregisterFSURLPrefix(subdir);
+  }
 }
 
 void Server::Close(std::string fs_url_as_string, CloseCallback callback) {

chrome/browser/ash/fusebox/fusebox_server.h

@@ -16,10 +16,19 @@ namespace fusebox {
 
 class Server {
  public:
+  struct Delegate {
+    // These methods cause D-Bus signals to be sent that a storage unit (as
+    // named by the "subdir" in "/media/fuse/fusebox/subdir") has been attached
+    // or detached.
+    virtual void OnRegisterFSURLPrefix(const std::string& subdir) = 0;
+    virtual void OnUnregisterFSURLPrefix(const std::string& subdir) = 0;
+  };
+
   // Returns a pointer to the global Server instance.
   static Server* GetInstance();
 
-  Server();
+  // The delegate should live longer than the server.
+  explicit Server(Delegate* delegate);
   Server(const Server&) = delete;
   Server& operator=(const Server&) = delete;
   ~Server();
@@ -99,6 +108,7 @@ class Server {
   using PrefixMap = std::map<std::string, PrefixMapEntry>;
 
  private:
+  Delegate* delegate_;
   fusebox::MonikerMap moniker_map_;
   PrefixMap prefix_map_;
 };