feat(relay): add site eligibility check for Relay with Remote Settings (#7039)

Adds Remote Settings integration to enable mobile clients to determine
whether to show Firefox Relay UI based on site allowlist/denylist and
user Relay account status.

- Add new `RelayRemoteSettingsClient` in rs.rs module
  - Fetches allowlist/denylist from Remote Settings collections
  - Implements `should_show_relay()` with three-factor decision logic
  - Includes subdomain-aware domain matching (not PSL-aware)

Author: groovecoder

CHANGELOG.md

@@ -5,6 +5,9 @@
 ### Autofill
 - Adds a migration to migrate users to use subregion codes over fully qualified strings. ([bug 1993388](https://bugzilla.mozilla.org/show_bug.cgi?id=1993388))
 
+### Relay
+- Added Remote Settings integration to determine site eligibility for displaying Relay UI. The new `RelayRemoteSettingsClient` fetches allowlist/denylist data, and `should_show_relay()` provides subdomain-aware domain matching to decide when to show Relay email mask suggestions. ([#7039](https://github.com/mozilla/application-services/pull/7039))
+
 ## 🦊 What's Changed 🦊
 
 ### Android

Cargo.lock

@@ -6,6 +6,7 @@ edition = "2021"
 [dependencies]
 error-support = { path = "../support/error", features = ["tracing-logging"] }
 log = "0.4"
+remote_settings = { path = "../remote_settings" }
 serde = { version = "1", features=["derive"] }
 serde_json = "1"
 thiserror = "2"

components/relay/Cargo.toml

@@ -5,6 +5,10 @@ android {
     namespace 'org.mozilla.appservices.relay'
 }
 
+dependencies {
+    api project(":remotesettings")
+}
+
 ext.configureUniFFIBindgen("relay")
 ext.dependsOnTheMegazord()
 ext.configurePublish()

components/relay/android/build.gradle

@@ -4,6 +4,7 @@
 
 pub use error_support::error;
 use error_support::{ErrorHandling, GetErrorHandling};
+use remote_settings::RemoteSettingsError;
 
 pub type Result<T> = std::result::Result<T, Error>;
 pub type ApiResult<T> = std::result::Result<T, RelayApiError>;
@@ -42,6 +43,12 @@ pub enum Error {
     Viaduct(#[from] viaduct::ViaductError),
     #[error("URL parsing error: {0}")]
     UrlParse(#[from] url::ParseError),
+
+    #[error("Error from Remote Settings: {0}")]
+    RemoteSettings(#[from] RemoteSettingsError),
+
+    #[error("Failed to parse Remote Settings record: {0}")]
+    InvalidRemoteSettingsRecord(String),
 }
 
 impl GetErrorHandling for Error {
@@ -73,6 +80,24 @@ impl GetErrorHandling for Error {
                 })
                 .report_error("relay-api-error")
             }
+            // Handle Remote Settings errors
+            // Note: these are just logged/reported but not exposed to consumers
+            Error::RemoteSettings(RemoteSettingsError::Network { reason }) => {
+                ErrorHandling::convert(RelayApiError::Other {
+                    reason: format!("Remote Settings network error: {}", reason),
+                })
+                .log_warning()
+            }
+            Error::RemoteSettings(e) => ErrorHandling::convert(RelayApiError::Other {
+                reason: format!("Remote Settings error: {}", e),
+            })
+            .report_error("relay-rs-error"),
+            Error::InvalidRemoteSettingsRecord(msg) => {
+                ErrorHandling::convert(RelayApiError::Other {
+                    reason: format!("Invalid Remote Settings record: {}", msg),
+                })
+                .report_error("relay-invalid-record")
+            }
             _ => ErrorHandling::convert(RelayApiError::Other {
                 reason: self.to_string(),
             })

components/relay/src/error.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 mod error;
+mod rs;
 
 uniffi::setup_scaffolding!("relay");