Add support for enabling/disabling the NetworkObserver.

coil-base/api/coil-base.api

@@ -109,6 +109,7 @@ public final class coil/ImageLoader$Builder {
 	public final fun memoryCache (Lcoil/memory/MemoryCache;)Lcoil/ImageLoader$Builder;
 	public final fun memoryCachePolicy (Lcoil/request/CachePolicy;)Lcoil/ImageLoader$Builder;
 	public final fun networkCachePolicy (Lcoil/request/CachePolicy;)Lcoil/ImageLoader$Builder;
+	public final fun networkObserverEnabled (Z)Lcoil/ImageLoader$Builder;
 	public final fun okHttpClient (Lkotlin/jvm/functions/Function0;)Lcoil/ImageLoader$Builder;
 	public final fun okHttpClient (Lokhttp3/OkHttpClient;)Lcoil/ImageLoader$Builder;
 	public final fun placeholder (I)Lcoil/ImageLoader$Builder;

coil-base/src/androidTest/java/coil/util/SystemCallbacksTest.kt

@@ -33,7 +33,7 @@ class SystemCallbacksTest {
 
     @Test
     fun imageLoaderIsFreedWithoutShutdown() {
-        val systemCallbacks = SystemCallbacks(ImageLoader(context) as RealImageLoader, context)
+        val systemCallbacks = SystemCallbacks(ImageLoader(context) as RealImageLoader, context, true)
 
         val bitmaps = mutableListOf<Bitmap>()
         while (systemCallbacks.imageLoader.get() != null) {
@@ -69,7 +69,7 @@ class SystemCallbacksTest {
             options = ImageLoaderOptions(),
             logger = null
         )
-        val systemCallbacks = SystemCallbacks(imageLoader, context)
+        val systemCallbacks = SystemCallbacks(imageLoader, context, true)
 
         strongMemoryCache.set(
             key = MemoryCache.Key("1"),

coil-base/src/main/java/coil/ImageLoader.kt

@@ -328,6 +328,20 @@ interface ImageLoader {
             this.memoryCache = null
         }
 
+        /**
+         * Enables short circuiting network requests if the device is offline.
+         *
+         * If true, reading from the network will automatically be disabled if the device is offline.
+         * If a cached response is unavailable the request will fail with a '504 Unsatisfiable Request' response.
+         *
+         * If false, the image loader will attempt a network request even if the device is offline.
+         *
+         * Default: true
+         */
+        fun networkObserverEnabled(enable: Boolean) = apply {
+            this.options = this.options.copy(networkObserverEnabled = enable)
+        }
+
         /**
          * Enables weak reference tracking of loaded images.
          *

coil-base/src/main/java/coil/RealImageLoader.kt

@@ -83,7 +83,7 @@ internal class RealImageLoader(
         memoryCache.strongMemoryCache, memoryCache.weakMemoryCache)
     private val requestService = RequestService(logger)
     private val drawableDecoder = DrawableDecoderService(bitmapPool)
-    private val systemCallbacks = SystemCallbacks(this, context)
+    private val systemCallbacks = SystemCallbacks(this, context, options.networkObserverEnabled)
     private val registry = componentRegistry.newBuilder()
         // Mappers
         .add(StringMapper())

coil-base/src/main/java/coil/network/NetworkObserver.kt

@@ -32,7 +32,16 @@ internal interface NetworkObserver {
         private const val TAG = "NetworkObserver"
 
         /** Create a new [NetworkObserver] instance. */
-        operator fun invoke(context: Context, listener: Listener, logger: Logger?): NetworkObserver {
+        operator fun invoke(
+            context: Context,
+            isEnabled: Boolean,
+            listener: Listener,
+            logger: Logger?
+        ): NetworkObserver {
+            if (!isEnabled) {
+                return EmptyNetworkObserver
+            }
+
             val connectivityManager: ConnectivityManager? = context.getSystemService()
             if (connectivityManager == null || !context.isPermissionGranted(ACCESS_NETWORK_STATE)) {
                 logger?.log(TAG, Log.WARN) { "Unable to register network observer." }

coil-base/src/main/java/coil/util/ImageLoaderOptions.kt

@@ -10,5 +10,6 @@ import coil.RealImageLoader
  */
 internal data class ImageLoaderOptions(
     val addLastModifiedToFileCacheKey: Boolean = true,
-    val launchInterceptorChainOnMainThread: Boolean = true
+    val launchInterceptorChainOnMainThread: Boolean = true,
+    val networkObserverEnabled: Boolean = true
 )

coil-base/src/main/java/coil/util/SystemCallbacks.kt

@@ -21,11 +21,12 @@ import java.util.concurrent.atomic.AtomicBoolean
  */
 internal class SystemCallbacks(
     imageLoader: RealImageLoader,
-    private val context: Context
+    private val context: Context,
+    isNetworkObserverEnabled: Boolean
 ) : ComponentCallbacks2, NetworkObserver.Listener {
 
     @VisibleForTesting internal val imageLoader = WeakReference(imageLoader)
-    private val networkObserver = NetworkObserver(context, this, imageLoader.logger)
+    private val networkObserver = NetworkObserver(context, isNetworkObserverEnabled, this, imageLoader.logger)
 
     @Volatile private var _isOnline = networkObserver.isOnline
     private val _isShutdown = AtomicBoolean(false)

coil-base/src/test/java/coil/intercept/EngineInterceptorTest.kt

@@ -70,7 +70,7 @@ class EngineInterceptorTest {
             strongMemoryCache = strongMemoryCache,
             memoryCacheService = MemoryCacheService(referenceCounter, strongMemoryCache, weakMemoryCache),
             requestService = RequestService(null),
-            systemCallbacks = SystemCallbacks(ImageLoader(context) as RealImageLoader, context),
+            systemCallbacks = SystemCallbacks(ImageLoader(context) as RealImageLoader, context, true),
             drawableDecoder = DrawableDecoderService(bitmapPool),
             logger = null
         )