Allow configuration of custom userAgent

Sources/Segment/Configuration.swift

@@ -26,6 +26,7 @@ public class Configuration {
         var requestFactory: ((URLRequest) -> URLRequest)? = nil
         var errorHandler: ((Error) -> Void)? = nil
         var flushPolicies: [FlushPolicy] = [CountBasedFlushPolicy(), IntervalBasedFlushPolicy()]
+        var userAgent: String? = nil
     }
 
     internal var values: Values
@@ -182,6 +183,12 @@ public extension Configuration {
         values.flushPolicies = policies
         return self
     }
+
+    @discardableResult
+    func userAgent(_ userAgent: String) -> Configuration {
+        values.userAgent = userAgent
+        return self
+    }
 }
 
 extension Analytics {

Sources/Segment/Plugins/Context.swift

@@ -148,7 +148,7 @@ public class Context: PlatformPlugin {
         // BKS: This use to be in the static section, however it was discovered that on some platforms
         // there can be a delay in retrieval.  It has to be fetched on the main thread, so we've spun it off
         // async and cache it when it comes back.
-        let userAgent = device.userAgent
+        let userAgent = analytics?.configuration.values.userAgent ?? device.userAgent
         context["userAgent"] = userAgent
 
         // other stuff?? ...

Tests/Segment-Tests/Analytics_Tests.swift

@@ -165,6 +165,53 @@ final class Analytics_Tests: XCTestCase {
 #endif
     }
 
+
+    func testContextWithUserAgent() {
+        let configuration = Configuration(writeKey: "test")
+        configuration.userAgent("testing user agent")
+        let analytics = Analytics(configuration: configuration)
+        let outputReader = OutputReaderPlugin()
+        analytics.add(plugin: outputReader)
+
+#if !os(watchOS) && !os(Linux)
+        // prime the pump for userAgent, since it's retrieved async.
+        let vendorSystem = VendorSystem.current
+        while vendorSystem.userAgent == nil {
+            RunLoop.main.run(until: Date.distantPast)
+        }
+#endif
+
+        waitUntilStarted(analytics: analytics)
+
+        // add a referrer
+        analytics.openURL(URL(string: "https://google.com")!)
+
+        analytics.track(name: "token check")
+
+        let trackEvent: TrackEvent? = outputReader.lastEvent as? TrackEvent
+        let context = trackEvent?.context?.dictionaryValue
+        // Verify that context isn't empty here.
+        // We need to verify the values but will do that in separate platform specific tests.
+        XCTAssertNotNil(context)
+        XCTAssertNotNil(context?["screen"], "screen missing!")
+        XCTAssertNotNil(context?["network"], "network missing!")
+        XCTAssertNotNil(context?["os"], "os missing!")
+        XCTAssertNotNil(context?["timezone"], "timezone missing!")
+        XCTAssertNotNil(context?["library"], "library missing!")
+        XCTAssertNotNil(context?["device"], "device missing!")
+
+        let referrer = context?["referrer"] as! [String: Any]
+        XCTAssertEqual(referrer["url"] as! String, "https://google.com")
+
+        XCTAssertEqual(context?["userAgent"] as! String, "testing user agent")
+
+        // these keys not present on linux
+#if !os(Linux)
+        XCTAssertNotNil(context?["app"], "app missing!")
+        XCTAssertNotNil(context?["locale"], "locale missing!")
+#endif
+    }
+
     func testDeviceToken() {
         let analytics = Analytics(configuration: Configuration(writeKey: "test"))
         let outputReader = OutputReaderPlugin()