Change dependency to intercept at MetricsSystem level

Author: finestructure

Sources/App/Core/AppMetrics.swift

@@ -141,13 +141,13 @@ enum AppMetrics {
 extension AppMetrics {
 
     static func counter<V: Numeric>(_ name: String) -> PromCounter<V>? {
-        @Dependency(\.prometheus) var prometheus
-        return prometheus?.createCounter(forType: V.self, named: name)
+        @Dependency(\.metricsSystem.prometheus) var prometheus
+        return try? prometheus().createCounter(forType: V.self, named: name)
     }
 
     static func gauge<V: DoubleRepresentable>(_ name: String) -> PromGauge<V>? {
-        @Dependency(\.prometheus) var prometheus
-        return prometheus?.createGauge(forType: V.self, named: name)
+        @Dependency(\.metricsSystem.prometheus) var prometheus
+        return try? prometheus().createGauge(forType: V.self, named: name)
     }
 
 }
@@ -162,19 +162,15 @@ extension AppMetrics {
     static func push(client: Client, jobName: String) async throws {
         @Dependency(\.environment) var environment
         @Dependency(\.logger) var logger
-        @Dependency(\.prometheus) var prometheus
-
-        guard let prometheus else {
-            throw AppError.genericError(nil, "Prometheus client unavailable (nil)")
-        }
+        @Dependency(\.metricsSystem.prometheus) var prometheus
 
         guard let pushGatewayUrl = environment.metricsPushGatewayUrl() else {
             throw AppError.envVariableNotSet("METRICS_PUSHGATEWAY_URL")
         }
         let url = URI(string: "\(pushGatewayUrl)/metrics/job/\(jobName)")
 
         do {
-            let metrics: String = await prometheus.collect()
+            let metrics: String = try await prometheus().collect()
             _ = try await client.post(url) { req in
                 // append "\n" to avoid
                 //   text format parsing error in line 4: unexpected end of input stream

Sources/App/Core/Dependencies/AppMetricsClient.swift renamed to Sources/App/Core/Dependencies/MetricsSystemClient.swift

@@ -18,12 +18,17 @@ import Synchronization
 @preconcurrency import Prometheus
 
 
-enum AppMetricsClient {
+struct MetricsSystemClient {
+    var prometheus: @Sendable () throws -> PrometheusClient
+}
+
+
+extension MetricsSystemClient {
     private static let initialized = Mutex(false)
 
-    static func bootstrap() {
-        guard !initialized.withLock({ $0 }) else { return }
-        initialized.withLock {
+    func bootstrap() {
+        guard !Self.initialized.withLock({ $0 }) else { return }
+        Self.initialized.withLock {
             let client = PrometheusClient()
             MetricsSystem.bootstrap(PrometheusMetricsFactory(client: client))
             $0 = true
@@ -32,23 +37,33 @@ enum AppMetricsClient {
 }
 
 
-extension AppMetricsClient: DependencyKey {
-    static var liveValue: PrometheusClient? {
-        try? MetricsSystem.prometheus()
+extension MetricsSystemClient: DependencyKey {
+    static var liveValue: Self {
+        .init(prometheus: { try MetricsSystem.prometheus() })
     }
 }
 
 
-extension AppMetricsClient: TestDependencyKey {
-    static var testValue: PrometheusClient? {
-        unimplemented("testValue"); return nil
+extension MetricsSystemClient: TestDependencyKey {
+    static var testValue: Self {
+        .init(prometheus: { unimplemented("testValue"); return .init() })
     }
 }
 
 
 extension DependencyValues {
-    public var prometheus: PrometheusClient? {
-        get { self[AppMetricsClient.self] }
-        set { self[AppMetricsClient.self] = newValue }
+    var metricsSystem: MetricsSystemClient {
+        get { self[MetricsSystemClient.self] }
+        set { self[MetricsSystemClient.self] = newValue }
+    }
+}
+
+
+#if DEBUG
+extension MetricsSystemClient {
+    static var mock: Self {
+        let prometheus = PrometheusClient()
+        return .init(prometheus: { prometheus })
     }
 }
+#endif

Sources/App/configure.swift

@@ -365,7 +365,8 @@ public func configure(_ app: Application, databasePort: Int? = nil) async throws
     try routes(app)
 
     // bootstrap app metrics
-    AppMetricsClient.bootstrap()
+    @Dependency(\.metricsSystem) var metricsSystem
+    metricsSystem.bootstrap()
 
     return host
 }

Sources/App/routes.swift

@@ -211,8 +211,8 @@ func routes(_ app: Application) throws {
 
     do {  // Metrics
         app.get("metrics") { req -> String in
-            @Dependency(\.prometheus) var prometheus
-            return await prometheus?.collect() ?? ""
+            @Dependency(\.metricsSystem.prometheus) var prometheus
+            return try await prometheus().collect()
         }
     }
 }

Tests/AppTests/AllTests.swift

@@ -12,13 +12,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import Testing
+@testable import App
+
 import Dependencies
+import Testing
 
 
 @Suite(
     .dependency(\.date.now, .t0),
-    .dependency(\.prometheus, .init())
+    .dependency(\.metricsSystem, .mock)
 ) struct AllTests { }