chore: change event hash code calculation method to sha256 (#33)

Author: zhu-xiaowei

Sources/Clickstream/Dependency/Clickstream/Analytics/AnalyticsClient.swift

@@ -136,8 +136,6 @@ class AnalyticsClient: AnalyticsClientBehaviour {
             }
         }
         event.setUserAttribute(userAttributes)
-        let objId = ObjectIdentifier(event)
-        event.hashCode = objId.hashValue
         try eventRecorder.save(event)
     }
 

Sources/Clickstream/Dependency/Clickstream/Event/ClickstreamEvent.swift

@@ -11,8 +11,7 @@ import Foundation
 private typealias Limit = Event.Limit
 typealias JsonObject = [String: Any]
 
-class ClickstreamEvent: AnalyticsPropertiesModel, Hashable {
-    var hashCode: Int!
+class ClickstreamEvent: AnalyticsPropertiesModel {
     let eventId: String
     let appId: String
     let uniqueId: String
@@ -65,14 +64,9 @@ class ClickstreamEvent: AnalyticsPropertiesModel, Hashable {
         attributes[key]
     }
 
-    func toJson(forHashCode: Bool = false) -> String {
+    func toJson() -> String {
         var event = JsonObject()
-        if !forHashCode {
-            if hashCode == nil {
-                hashCode = hashValue
-            }
-            event["hashCode"] = String(format: "%08X", hashCode)
-        }
+        event["hashCode"] = ""
         event["unique_id"] = uniqueId
         event["event_type"] = eventType
         event["event_id"] = eventId
@@ -100,6 +94,8 @@ class ClickstreamEvent: AnalyticsPropertiesModel, Hashable {
         event["app_title"] = systemInfo.appTitle
         event["user"] = userAttributes
         event["attributes"] = getAttributeObject(from: attributes)
+        let eventJson = getJsonStringFromObject(jsonObject: event)
+        event["hashCode"] = eventJson.hashCode()
         return getJsonStringFromObject(jsonObject: event)
     }
 
@@ -134,10 +130,6 @@ class ClickstreamEvent: AnalyticsPropertiesModel, Hashable {
         return attribute
     }
 
-    func hash(into hasher: inout Hasher) {
-        hasher.combine(toJson(forHashCode: true))
-    }
-
     static func == (lhs: ClickstreamEvent, rhs: ClickstreamEvent) -> Bool {
         lhs.toJson() == rhs.toJson()
     }

Sources/Clickstream/Support/Extension/String+HashCode.swift

@@ -0,0 +1,20 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+import CryptoKit
+import Foundation
+
+extension String {
+    func hashCode() -> String {
+        if let data = data(using: .utf8) {
+            let hashed = SHA256.hash(data: data)
+            let hashString = hashed.compactMap { String(format: "%02x", $0) }.joined()
+            return String(hashString.prefix(8))
+        }
+        return ""
+    }
+}

Tests/ClickstreamTests/Clickstream/ClickstreamEventTest.swift

@@ -64,7 +64,7 @@ class ClickstreamEventTest: XCTestCase {
     }
 
     func testEventEqualsFail() {
-        let event1 = clickstreamEvent
+        let event1 = clickstreamEvent!
         let event2 = ClickstreamEvent(eventType: "testEvent",
                                       appId: testAppId,
                                       uniqueId: UUID().uuidString,

Tests/ClickstreamTests/Clickstream/EventRecorderTest.swift

@@ -412,6 +412,36 @@ class EventRecorderTest: XCTestCase {
         activityTracker.callback?(.runningInBackground)
         XCTAssertTrue(eventRecorder.queue.operationCount > 0)
     }
+
+    func testGetEventHashCodeTwice() {
+        let eventJson = clickstreamEvent.toJson()
+        let hashCode1 = eventJson.hashCode()
+        let hashCode2 = eventJson.hashCode()
+        XCTAssertEqual(hashCode1, hashCode2)
+    }
+
+    func testEventModified() throws {
+        let originJson = clickstreamEvent.toJson()
+        let originJsonData = originJson.data(using: .utf8)!
+        var jsonObject = try JSONSerialization.jsonObject(with: originJsonData, options: []) as! [String: Any]
+        let originHashCode = jsonObject["hashCode"] as! String
+        jsonObject["hashCode"] = ""
+        jsonObject["event_type"] = "testEvent1"
+        let jsonWithoutHashCode = clickstreamEvent.getJsonStringFromObject(jsonObject: jsonObject)
+        let computedHashCode = jsonWithoutHashCode.hashCode()
+        XCTAssertNotEqual(originHashCode, computedHashCode)
+    }
+
+    func testEventNotModified() throws {
+        let originJson = clickstreamEvent.toJson()
+        let originJsonData = originJson.data(using: .utf8)!
+        var jsonObject = try JSONSerialization.jsonObject(with: originJsonData, options: []) as! [String: Any]
+        let originHashCode = jsonObject["hashCode"] as! String
+        jsonObject["hashCode"] = ""
+        let jsonWithoutHashCode = clickstreamEvent.getJsonStringFromObject(jsonObject: jsonObject)
+        let computedHashCode = jsonWithoutHashCode.hashCode()
+        XCTAssertEqual(originHashCode, computedHashCode)
+    }
 }
 
 extension String {