backend: Add a signal emitter

A mechanism to allow emitting signals without exposing DBus internals.
Portals implementations should store the emitter in set_signal_emitter
and can then be used to emit the signals supported by the portal.

backend-demo/src/settings.rs

@@ -1,7 +1,10 @@
-use std::collections::HashMap;
+use std::{collections::HashMap, sync::Arc};
 
 use ashpd::{
-    backend::{request::RequestImpl, settings::SettingsImpl},
+    backend::{
+        request::RequestImpl,
+        settings::{SettingsImpl, SettingsSignalEmitter},
+    },
     desktop::settings::{ColorScheme, Namespace, APPEARANCE_NAMESPACE, COLOR_SCHEME_KEY},
     zbus::zvariant::OwnedValue,
     PortalError,
@@ -11,6 +14,8 @@ use async_trait::async_trait;
 #[derive(Default, Clone)]
 pub struct Settings {
     color_scheme: ColorScheme,
+    // The signal emitter allows dispatching changed events without exposing DBus internals
+    signal_emitter: Option<Arc<dyn SettingsSignalEmitter>>,
 }
 
 #[async_trait]
@@ -45,4 +50,8 @@ impl SettingsImpl for Settings {
             )))
         }
     }
+
+    fn set_signal_emitter(&mut self, signal_emitter: Arc<dyn SettingsSignalEmitter>) {
+        self.signal_emitter.replace(signal_emitter);
+    }
 }

src/backend/background.rs

@@ -47,6 +47,11 @@ pub enum AutoStartFlags {
     DBusActivation = 1,
 }
 
+#[async_trait]
+pub trait BackgroundSignalEmitter: Send + Sync {
+    async fn emit_changed(&self) -> zbus::Result<()>;
+}
+
 #[async_trait]
 pub trait BackgroundImpl: RequestImpl {
     async fn get_app_state(&self) -> Result<HashMap<AppID, AppState>, PortalError>;
@@ -61,6 +66,9 @@ pub trait BackgroundImpl: RequestImpl {
         commandline: Vec<String>,
         flags: BitFlags<AutoStartFlags>,
     ) -> Result<bool, PortalError>;
+
+    // Set the signal emitter, allowing to notify of changes.
+    fn set_signal_emitter(&mut self, signal_emitter: Arc<dyn BackgroundSignalEmitter>);
 }
 
 pub(crate) struct BackgroundInterface {
@@ -82,6 +90,13 @@ impl BackgroundInterface {
     }
 }
 
+#[async_trait]
+impl BackgroundSignalEmitter for BackgroundInterface {
+    async fn emit_changed(&self) -> zbus::Result<()> {
+        self.changed().await
+    }
+}
+
 #[zbus::interface(name = "org.freedesktop.impl.portal.Background")]
 impl BackgroundInterface {
     #[zbus(property(emits_changed_signal = "const"), name = "version")]

src/backend/permission_store.rs

@@ -9,6 +9,18 @@ use crate::{
     AppID, PortalError,
 };
 
+#[async_trait]
+pub trait PermissionStoreEmitter: Send + Sync {
+    async fn emit_document_changed(
+        &self,
+        table: &str,
+        id: DocumentID,
+        deleted: bool,
+        data: Value<'_>,
+        permissions: HashMap<AppID, Vec<Permission>>,
+    ) -> zbus::Result<()>;
+}
+
 #[async_trait]
 pub trait PermissionStoreImpl: Send + Sync {
     async fn lookup(
@@ -60,6 +72,9 @@ pub trait PermissionStoreImpl: Send + Sync {
         id: DocumentID,
         app: AppID,
     ) -> Result<(), PortalError>;
+
+    // Set the signal emitter, allowing to notify of changes.
+    fn set_signal_emitter(&mut self, signal_emitter: Arc<dyn PermissionStoreEmitter>);
 }
 
 pub(crate) struct PermissionStoreInterface {
@@ -97,6 +112,21 @@ impl PermissionStoreInterface {
     }
 }
 
+#[async_trait]
+impl PermissionStoreEmitter for PermissionStoreInterface {
+    async fn emit_document_changed(
+        &self,
+        table: &str,
+        id: DocumentID,
+        deleted: bool,
+        data: Value<'_>,
+        permissions: HashMap<AppID, Vec<Permission>>,
+    ) -> zbus::Result<()> {
+        self.document_changed(table, id, deleted, data, permissions)
+            .await
+    }
+}
+
 #[zbus::interface(name = "org.freedesktop.impl.portal.PermissionStore")]
 impl PermissionStoreInterface {
     #[zbus(property(emits_changed_signal = "const"), name = "version")]

src/backend/settings.rs

@@ -15,6 +15,14 @@ use crate::{
     PortalError,
 };
 
+#[async_trait]
+pub trait SettingsSignalEmitter: Send + Sync {
+    async fn emit_changed(&self, namespace: &str, key: &str, value: Value<'_>) -> zbus::Result<()>;
+    async fn emit_contrast_changed(&self, contrast: Contrast) -> zbus::Result<()>;
+    async fn emit_accent_color_changed(&self, color: Color) -> zbus::Result<()>;
+    async fn emit_color_scheme_changed(&self, scheme: ColorScheme) -> zbus::Result<()>;
+}
+
 #[async_trait]
 pub trait SettingsImpl: Send + Sync {
     async fn read_all(
@@ -23,6 +31,9 @@ pub trait SettingsImpl: Send + Sync {
     ) -> Result<HashMap<String, Namespace>, PortalError>;
 
     async fn read(&self, namespace: &str, key: &str) -> Result<OwnedValue, PortalError>;
+
+    // Set the signal emitter, allowing to notify of changes.
+    fn set_signal_emitter(&mut self, signal_emitter: Arc<dyn SettingsSignalEmitter>);
 }
 
 pub(crate) struct SettingsInterface {
@@ -71,6 +82,25 @@ impl SettingsInterface {
     }
 }
 
+#[async_trait]
+impl SettingsSignalEmitter for SettingsInterface {
+    async fn emit_changed(&self, namespace: &str, key: &str, value: Value<'_>) -> zbus::Result<()> {
+        self.changed(namespace, key, value).await
+    }
+
+    async fn emit_contrast_changed(&self, contrast: Contrast) -> zbus::Result<()> {
+        self.contrast_changed(contrast).await
+    }
+
+    async fn emit_accent_color_changed(&self, color: Color) -> zbus::Result<()> {
+        self.accent_color_changed(color).await
+    }
+
+    async fn emit_color_scheme_changed(&self, scheme: ColorScheme) -> zbus::Result<()> {
+        self.color_scheme_changed(scheme).await
+    }
+}
+
 #[zbus::interface(name = "org.freedesktop.impl.portal.Settings")]
 impl SettingsInterface {
     #[zbus(property(emits_changed_signal = "const"), name = "version")]