Make Calls more stateful and add deferring factory.

The deferring factory allows you to provide functionality that can change when Call.clone() is being used.

retrofit-mock/src/main/java/retrofit2/mock/Calls.java

@@ -16,82 +16,155 @@
 package retrofit2.mock;
 
 import java.io.IOException;
+import java.util.concurrent.Callable;
+import java.util.concurrent.atomic.AtomicBoolean;
 import okhttp3.Request;
 import retrofit2.Call;
 import retrofit2.Callback;
 import retrofit2.Response;
 
 /** Factory methods for creating {@link Call} instances which immediately respond or fail. */
 public final class Calls {
+  /**
+   * Invokes {@code callable} once for the returned {@link Call} and once for each instance that is
+   * obtained from {@linkplain Call#clone() cloning} the returned {@link Call}.
+   */
+  public static <T> Call<T> defer(Callable<Call<T>> callable) {
+    return new DeferredCall<>(callable);
+  }
+
   public static <T> Call<T> response(T successValue) {
-    return response(Response.success(successValue));
+    return new FakeCall<>(Response.success(successValue), null);
+  }
+
+  public static <T> Call<T> response(Response<T> response) {
+    return new FakeCall<>(response, null);
   }
 
-  public static <T> Call<T> response(final Response<T> response) {
-    return new Call<T>() {
-      @Override public Response<T> execute() throws IOException {
+  public static <T> Call<T> failure(IOException failure) {
+    return new FakeCall<>(null, failure);
+  }
+
+  private Calls() {
+    throw new AssertionError("No instances.");
+  }
+
+  static final class FakeCall<T> implements Call<T> {
+    private final Response<T> response;
+    private final IOException error;
+    private final AtomicBoolean canceled = new AtomicBoolean();
+    private final AtomicBoolean executed = new AtomicBoolean();
+
+    FakeCall(Response<T> response, IOException error) {
+      if ((response == null) == (error == null)) {
+        throw new AssertionError("Only one of response or error can be set.");
+      }
+      this.response = response;
+      this.error = error;
+    }
+
+    @Override public Response<T> execute() throws IOException {
+      if (!executed.compareAndSet(false, true)) {
+        throw new IllegalStateException("Already executed");
+      }
+      if (canceled.get()) {
+        throw new IOException("canceled");
+      }
+      if (response != null) {
         return response;
       }
+      throw error;
+    }
 
-      @Override public void enqueue(Callback<T> callback) {
+    @Override public void enqueue(Callback<T> callback) {
+      if (callback == null) {
+        throw new NullPointerException("callback == null");
+      }
+      if (!executed.compareAndSet(false, true)) {
+        throw new IllegalStateException("Already executed");
+      }
+      if (canceled.get()) {
+        callback.onFailure(this, new IOException("canceled"));
+      } else if (response != null) {
         callback.onResponse(this, response);
+      } else {
+        callback.onFailure(this, error);
       }
+    }
 
-      @Override public boolean isExecuted() {
-        return false;
-      }
+    @Override public boolean isExecuted() {
+      return executed.get();
+    }
 
-      @Override public void cancel() {
-      }
+    @Override public void cancel() {
+      canceled.set(true);
+    }
 
-      @Override public boolean isCanceled() {
-        return false;
-      }
+    @Override public boolean isCanceled() {
+      return canceled.get();
+    }
 
-      @SuppressWarnings("CloneDoesntCallSuperClone") // Immutable object.
-      @Override public Call<T> clone() {
-        return this;
-      }
+    @Override public Call<T> clone() {
+      return new FakeCall<>(response, error);
+    }
 
-      @Override public Request request() {
+    @Override public Request request() {
+      if (response != null) {
         return response.raw().request();
       }
-    };
+      return new Request.Builder().url("http://localhost").build();
+    }
   }
 
-  public static <T> Call<T> failure(final IOException failure) {
-    return new Call<T>() {
-      @Override public Response<T> execute() throws IOException {
-        throw failure;
+  static final class DeferredCall<T> implements Call<T> {
+    private final Callable<Call<T>> callable;
+    private Call<T> delegate;
+
+    DeferredCall(Callable<Call<T>> callable) {
+      this.callable = callable;
+    }
+
+    private synchronized Call<T> getDelegate() {
+      Call<T> delegate = this.delegate;
+      if (delegate == null) {
+        try {
+          delegate = callable.call();
+        } catch (IOException e) {
+          delegate = failure(e);
+        } catch (Exception e) {
+          throw new IllegalStateException("Callable threw unrecoverable exception", e);
+        }
+        this.delegate = delegate;
       }
+      return delegate;
+    }
 
-      @Override public void enqueue(Callback<T> callback) {
-        callback.onFailure(this, failure);
-      }
+    @Override public Response<T> execute() throws IOException {
+      return getDelegate().execute();
+    }
 
-      @Override public boolean isExecuted() {
-        return false;
-      }
+    @Override public void enqueue(Callback<T> callback) {
+      getDelegate().enqueue(callback);
+    }
 
-      @Override public void cancel() {
-      }
+    @Override public boolean isExecuted() {
+      return getDelegate().isExecuted();
+    }
 
-      @Override public boolean isCanceled() {
-        return false;
-      }
+    @Override public void cancel() {
+      getDelegate().cancel();
+    }
 
-      @SuppressWarnings("CloneDoesntCallSuperClone") // Immutable object.
-      @Override public Call<T> clone() {
-        return this;
-      }
+    @Override public boolean isCanceled() {
+      return getDelegate().isCanceled();
+    }
 
-      @Override public Request request() {
-        return new Request.Builder().url("http://localhost").build();
-      }
-    };
-  }
+    @Override public Call<T> clone() {
+      return new DeferredCall<>(callable);
+    }
 
-  private Calls() {
-    throw new AssertionError("No instances.");
+    @Override public Request request() {
+      return getDelegate().request();
+    }
   }
 }