Filter out pixels older than 28 days.

Core/PersistentPixel.swift

@@ -42,13 +42,19 @@ public final class PersistentPixel: PersistentPixelFiring {
 
     enum Constants {
         static let lastProcessingDateKey = "com.duckduckgo.ios.persistent-pixel.last-processing-timestamp"
+
+#if DEBUG
+        static let minimumProcessingInterval: TimeInterval = .minutes(1)
+#else
         static let minimumProcessingInterval: TimeInterval = .hours(1)
+#endif
     }
 
     private let pixelFiring: PixelFiring.Type
     private let dailyPixelFiring: DailyPixelFiring.Type
     private let persistentPixelStorage: PersistentPixelStoring
     private let lastProcessingDateStorage: KeyValueStoring
+    private let calendar: Calendar
     private let dateGenerator: () -> Date
 
     private let pixelProcessingLock = NSLock()
@@ -72,11 +78,13 @@ public final class PersistentPixel: PersistentPixelFiring {
          dailyPixelFiring: DailyPixelFiring.Type,
          persistentPixelStorage: PersistentPixelStoring,
          lastProcessingDateStorage: KeyValueStoring,
+         calendar: Calendar = .current,
          dateGenerator: @escaping () -> Date = { Date() }) {
         self.pixelFiring = pixelFiring
         self.dailyPixelFiring = dailyPixelFiring
         self.persistentPixelStorage = persistentPixelStorage
         self.lastProcessingDateStorage = lastProcessingDateStorage
+        self.calendar = calendar
         self.dateGenerator = dateGenerator
     }
 
@@ -194,7 +202,7 @@ public final class PersistentPixel: PersistentPixelFiring {
 
         if let lastProcessingDate = lastProcessingDateStorage.object(forKey: Constants.lastProcessingDateKey) as? Date {
             let threshold = dateGenerator().addingTimeInterval(-Constants.minimumProcessingInterval)
-            if threshold < lastProcessingDate {
+            if threshold <= lastProcessingDate {
                 pixelProcessingLock.unlock()
                 completion(nil)
                 return
@@ -239,8 +247,20 @@ public final class PersistentPixel: PersistentPixelFiring {
 
         let failedPixelsAccessQueue = DispatchQueue(label: "Failed Pixel Retry Attempt Metadata Queue")
         var failedPixels: [PersistentPixelMetadata] = []
+        let currentDate = dateGenerator()
 
         for pixelMetadata in queuedPixels {
+            if let originalSendDateString = pixelMetadata.timestamp,
+               let originalSendDate = dateFormatter.date(from: originalSendDateString),
+               let date28DaysAgo = calendar.date(byAdding: .day, value: -28, to: currentDate) {
+                if originalSendDate < date28DaysAgo {
+                    continue
+                }
+            } else {
+                // If we don't have a timestamp for some reason, ignore the retry - retries are only useful if they have a timestamp attached
+                continue
+            }
+
             var pixelParameters = pixelMetadata.additionalParameters
             pixelParameters[PixelParameters.retriedPixel] = "1"
 

Core/PersistentPixelStoring.swift

@@ -39,6 +39,10 @@ public struct PersistentPixelMetadata: Codable, Equatable {
         case .regular: return eventName
         }
     }
+
+    var timestamp: String? {
+        return additionalParameters[PixelParameters.originalPixelTimestamp]
+    }
 }
 
 protocol PersistentPixelStoring {

DuckDuckGoTests/PersistentPixelTests.swift

@@ -29,7 +29,9 @@ final class PersistentPixelTests: XCTestCase {
     var currentStorageURL: URL!
     var persistentStorage: DefaultPersistentPixelStorage!
     var timestampStorage: KeyValueStoring!
-    let testDateString = "2024-01-01T12:00:00Z"
+
+    var testDateString: String!
+    var oldDateString: String!
 
     override func setUp() {
         super.setUp()
@@ -40,6 +42,11 @@ final class PersistentPixelTests: XCTestCase {
 
         PixelFiringMock.tearDown()
         DelayedPixelFiringMock.tearDown()
+
+        let formatter = ISO8601DateFormatter()
+        formatter.formatOptions = [.withInternetDateTime]
+        testDateString = formatter.string(from: Date())
+        oldDateString = formatter.string(from: Date().addingTimeInterval(-.days(30)))
     }
 
     override func tearDown() {
@@ -179,7 +186,7 @@ final class PersistentPixelTests: XCTestCase {
         let pixel = PersistentPixelMetadata(
             eventName: "test",
             pixelType: .daily,
-            additionalParameters: ["key": "value"],
+            additionalParameters: ["key": "value", PixelParameters.originalPixelTimestamp: testDateString],
             includedParameters: [.appVersion]
         )
 
@@ -194,7 +201,11 @@ final class PersistentPixelTests: XCTestCase {
         XCTAssert(storedPixels.isEmpty)
 
         XCTAssertEqual(PixelFiringMock.lastPixelName, "test_d")
-        XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.params, ["key": "value", PixelParameters.retriedPixel: "1"])
+        XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.params, [
+            "key": "value",
+            PixelParameters.retriedPixel: "1",
+            PixelParameters.originalPixelTimestamp: testDateString
+        ])
         XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.includedParams, [.appVersion])
     }
 
@@ -205,7 +216,7 @@ final class PersistentPixelTests: XCTestCase {
         let pixel = PersistentPixelMetadata(
             eventName: "test",
             pixelType: .count,
-            additionalParameters: ["key": "value"],
+            additionalParameters: ["key": "value", PixelParameters.originalPixelTimestamp: testDateString],
             includedParameters: [.appVersion]
         )
 
@@ -220,10 +231,39 @@ final class PersistentPixelTests: XCTestCase {
         XCTAssert(storedPixels.isEmpty)
 
         XCTAssertEqual(PixelFiringMock.lastPixelName, "test_c")
-        XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.params, ["key": "value", PixelParameters.retriedPixel: "1"])
+        XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.params, [
+            "key": "value",
+            PixelParameters.retriedPixel: "1",
+            PixelParameters.originalPixelTimestamp: testDateString
+        ])
         XCTAssertEqual(PixelFiringMock.lastDailyPixelInfo?.includedParams, [.appVersion])
     }
 
+    func testWhenPixelIsStored_AndSendQueuedPixelsIsCalled_AndPixelIsOlderThan28Days_ThenPixelIsNotSent_AndPixelIsNoLongerStored() throws {
+        let persistentPixel = createPersistentPixel()
+        let expectation = expectation(description: "sendQueuedPixels")
+
+        let pixel = PersistentPixelMetadata(
+            eventName: "test",
+            pixelType: .daily,
+            additionalParameters: ["key": "value", PixelParameters.originalPixelTimestamp: oldDateString],
+            includedParameters: [.appVersion]
+        )
+
+        try persistentStorage.replaceStoredPixels(with: [pixel])
+        persistentPixel.sendQueuedPixels { _ in
+            expectation.fulfill()
+        }
+
+        wait(for: [expectation], timeout: 3.0)
+
+        let storedPixels = try persistentStorage.storedPixels()
+        XCTAssert(storedPixels.isEmpty)
+
+        XCTAssertNil(PixelFiringMock.lastPixelName)
+        XCTAssertNil(PixelFiringMock.lastDailyPixelInfo)
+    }
+
     func testWhenPixelQueueIsProcessing_AndProcessingSucceeds_AndNewFailedPixelIsReceived_ThenPixelIsNotStoredUntilProcessingIsComplete() throws {
         PixelFiringMock.expectedCountPixelFireError = NSError(domain: "PixelFailure", code: 1)
 
@@ -273,7 +313,13 @@ final class PersistentPixelTests: XCTestCase {
         DelayedPixelFiringMock.completionError = NSError(domain: "PixelFailure", code: 1)
 
         let persistentPixel = createPersistentPixel(pixelFiring: DelayedPixelFiringMock.self)
-        let initialPixel = PersistentPixelMetadata(eventName: "test", pixelType: .count, additionalParameters: [:], includedParameters: [.appVersion])
+        let initialPixel = PersistentPixelMetadata(
+            eventName: "test",
+            pixelType: .count,
+            additionalParameters: [PixelParameters.originalPixelTimestamp: testDateString],
+            includedParameters: [.appVersion]
+        )
+
         try persistentStorage.replaceStoredPixels(with: [initialPixel])
 
         let sendQueuedPixelsExpectation = expectation(description: "sendQueuedPixels")