useragent override and skipAdvertisingIdDetection (#17)

* Improve unit tests for eidFromURI

* skipAdvertisingIdDetection and useragent override

- OptableSDK constructor now accepts a useragent String argument,
  null by default. When not null, disables WebView based user
  agent detection and overrides with provided value.

- OptableSDK constructor now accepts a skipAdvertisingIdDetection
  Boolean argument, false by default. When true, disables
  AdvertisingIdClient ad info detection which runs in a background
  coroutine. If the caller doesn't use the identify(email: String,
  gaid: Boolean, ppid: String) variant then ad ID detection is
  not needed and can be skipped.

- Document in README

README.md

@@ -108,6 +108,18 @@ MainActivity.OPTABLE = OptableSDK(this, "sandbox.customer.com", "my-app", true)
 
 However, since production sandboxes only listen to TLS traffic, the above is really only useful for developers of `optable-sandbox` running the sandbox locally for testing.
 
+By default, the SDK detects the application user agent by sniffing `settings.userAgentString` from a `WebView`. The resulting user agent string is sent to your sandbox for analytics purposes. To disable this behavior, you can provide an optional fifth string parameter `useragent`, which allows you to set whatever user agent string you would like to send instead. For example, in Kotlin:
+
+```kotlin
+MainActivity.OPTABLE = OptableSDK(this, "sandbox.customer.com", "my-app", false, "custom-ua")
+```
+
+Finally, an optional sixth boolean parameter `skipAdvertisingIdDetection` can be used to skip any ID info detection from `AdvertisingIdClient` which by default runs in a background co-routine. Disabling ad ID detection means that the SDK will not be able to automatically obtain the Google Advertising ID. For example, to disable ad ID detection, in Kotlin:
+
+```kotlin
+MainActivity.OPTABLE = OptableSDK(this, "sandbox.customer.com", "my-app", false, null, true)
+```
+
 ### Identify API
 
 To associate a user device with an authenticated identifier such as an Email address, or with other known IDs such as the Google Advertising ID, or even your own vendor or app level `PPID`, you can call the `identify` API as follows:

android_sdk/src/main/java/co/optable/android_sdk/OptableSDK.kt

@@ -67,9 +67,9 @@ typealias OptableTargetingResponse = HashMap<String, List<String>>
  *  unique to the app across devices.
  */
 
-class OptableSDK @JvmOverloads constructor(context: Context, host: String, app: String, insecure: Boolean = false) {
+class OptableSDK @JvmOverloads constructor(context: Context, host: String, app: String, insecure: Boolean = false, useragent: String? = null, skipAdvertisingIdDetection: Boolean = false) {
     val config = Config(host, app, insecure)
-    val client = Client(config, context)
+    val client = Client(config, context, useragent, skipAdvertisingIdDetection)
 
     /*
      *  OptableSDK.Status lists all of the possible OptableSDK API result statuses.

android_sdk/src/main/java/co/optable/android_sdk/core/Client.kt

@@ -18,13 +18,13 @@ import okhttp3.*
 import retrofit2.Retrofit
 import retrofit2.converter.gson.GsonConverterFactory
 
-class Client(private val config: Config, private val context: Context) {
+class Client(private val config: Config, private val context: Context, private val useragent: String?, private val skipAdvertisingIdDetection: Boolean) {
     var gaid: String? = null
     var gaidLAT: Boolean? = true
 
     private val edgeService: EdgeService?
-    private val userAgent = this.userAgent()
     private val storage = LocalStorage(this.config, this.context)
+    private var userAgent: String? = this.useragent
 
     private class RequestInterceptor(private val userAgent: String, private val storage: LocalStorage): Interceptor {
         override fun intercept(chain: Interceptor.Chain): Response {
@@ -59,10 +59,16 @@ class Client(private val config: Config, private val context: Context) {
     }
 
     init {
-        this.determineAdvertisingInfo()
+        if (!this.skipAdvertisingIdDetection) {
+            this.determineAdvertisingInfo()
+        }
+
+        if (this.userAgent == null) {
+            this.userAgent = this.userAgent()
+        }
 
         val client = OkHttpClient.Builder()
-            .addInterceptor(RequestInterceptor(userAgent, storage))
+            .addInterceptor(RequestInterceptor(this.userAgent!!, storage))
             .addInterceptor(ResponseInterceptor(storage))
             .build()
 
@@ -122,7 +128,7 @@ class Client(private val config: Config, private val context: Context) {
     }
 
     fun GAID(): String? {
-        return gaid!!
+        return gaid
     }
 
     private fun userAgent(): String {

android_sdk/src/test/java/co/optable/android_sdk/OptableSDKUnitTest.kt

@@ -72,13 +72,29 @@ class OptableSDKUnitTest {
     }
 
     @Test
-    fun eidFromURI_returnsEmptyWhenOeidAbsent() {
+    fun eidFromURI_returnsEmptyWhenOeidAbsentFromQuerystr() {
         val url = "http://some.domain.com/some/path?some=query&something=else"
         val expected = ""
 
         assertEquals(expected, OptableSDK.eidFromURI(Uri.parse(url)))
     }
 
+    @Test
+    fun eidFromURI_returnsEmptyWhenQuerystrAbsent() {
+        val url = "http://some.domain.com/some/path"
+        val expected = ""
+
+        assertEquals(expected, OptableSDK.eidFromURI(Uri.parse(url)))
+    }
+
+    @Test
+    fun eidFromURI_returnsEmptyWhenInputEmptyString() {
+        val url = ""
+        val expected = ""
+
+        assertEquals(expected, OptableSDK.eidFromURI(Uri.parse(url)))
+    }
+
     @Test
     fun eidFromURI_expectsSHA256() {
         val url = "http://some.domain.com/some/path?some=query&something=else&oeid=AAAAAAAa665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3&foo=bar&baz"