WIP

src/main/java/com/linecorp/armeria/server/http/HttpService.java

@@ -18,12 +18,20 @@
 
 import static java.util.Objects.requireNonNull;
 
+import java.util.concurrent.Executor;
+
+import com.linecorp.armeria.common.ServiceInvocationContext;
 import com.linecorp.armeria.common.SessionProtocol;
 import com.linecorp.armeria.server.ServerPort;
 import com.linecorp.armeria.server.Service;
 import com.linecorp.armeria.server.ServiceCodec;
 import com.linecorp.armeria.server.ServiceInvocationHandler;
 
+import io.netty.handler.codec.http.FullHttpResponse;
+import io.netty.handler.codec.http.HttpResponseStatus;
+import io.netty.util.concurrent.Future;
+import io.netty.util.concurrent.Promise;
+
 /**
  * A {@link Service} that handles an HTTP request. This {@link Service} must run on a {@link ServerPort}
  * whose {@link SessionProtocol} is {@linkplain SessionProtocol#ofHttp() HTTP}.
@@ -69,8 +77,69 @@ public ServiceInvocationHandler handler() {
         return handler;
     }
 
+    public HttpService orElse(HttpService nextService) {
+        return new HttpService(new OrElseHandler(handler(), nextService.handler()));
+    }
+
     @Override
     public String toString() {
         return "HttpService(" + handler().getClass().getSimpleName() + ')';
     }
+
+    private static final class OrElseHandler implements ServiceInvocationHandler {
+
+        private final ServiceInvocationHandler first;
+        private final ServiceInvocationHandler second;
+
+        OrElseHandler(ServiceInvocationHandler first, ServiceInvocationHandler second) {
+            this.first = first;
+            this.second = second;
+        }
+
+        @Override
+        public void invoke(ServiceInvocationContext ctx,
+                           Executor blockingTaskExecutor, Promise<Object> promise) throws Exception {
+
+            invoke0(ctx, blockingTaskExecutor, promise, first, second);
+        }
+
+        private void invoke0(ServiceInvocationContext ctx, Executor blockingTaskExecutor, Promise<Object> promise,
+                             ServiceInvocationHandler subHandler,
+                             ServiceInvocationHandler nextSubHandler) throws Exception {
+
+            Promise<Object> subPromise = ctx.eventLoop().newPromise();
+            subHandler.invoke(ctx, blockingTaskExecutor, subPromise);
+            if (subPromise.isDone()) {
+                handleResponse(ctx, blockingTaskExecutor, promise, subPromise, nextSubHandler);
+            } else {
+                subPromise.addListener(
+                        future -> handleResponse(ctx, blockingTaskExecutor, promise, future, nextSubHandler));
+            }
+        }
+
+        void handleResponse(ServiceInvocationContext ctx, Executor blockingTaskExecutor, Promise<Object> promise,
+                            Future<Object> subFuture, ServiceInvocationHandler nextSubHandler) throws Exception {
+
+            if (!subFuture.isSuccess()) {
+                // sub-handler failed with an exception.
+                promise.tryFailure(subFuture.cause());
+                return;
+            }
+
+            final FullHttpResponse res = (FullHttpResponse) subFuture.getNow();
+            if (nextSubHandler != null && res.status().code() == HttpResponseStatus.NOT_FOUND.code()) {
+                // The current sub-handler returned 404. Try the next sub-handler.
+                res.release();
+                if (!promise.isDone()) {
+                    invoke0(ctx, blockingTaskExecutor, promise, nextSubHandler, null);
+                }
+                return;
+            }
+
+            // The current sub-handler returned non-404 or it is the last resort.
+            if (!promise.trySuccess(res)) {
+                res.release();
+            }
+        }
+    }
 }

src/test/java/com/linecorp/armeria/server/http/file/HttpFileServiceTest.java

@@ -75,9 +75,12 @@ public class HttpFileServiceTest {
                     "/fs/",
                     HttpFileService.forFileSystem(tmpDir.toPath()).decorate(LoggingService::new));
 
+            final String baseResourceDir = HttpFileServiceTest.class.getPackage().getName().replace('.', '/');
             defaultVirtualHost.serviceUnder(
                     "/",
-                    HttpFileService.forClassPath("/http_file_service").decorate(LoggingService::new));
+                    HttpFileService.forClassPath(baseResourceDir + "/foo")
+                                   .orElse(HttpFileService.forClassPath(baseResourceDir + "/bar"))
+                                   .decorate(LoggingService::new));
 
             sb.defaultVirtualHost(defaultVirtualHost.build());
         } catch (Exception e) {
@@ -120,7 +123,7 @@ public void testClassPathGet() throws Exception {
         try (CloseableHttpClient hc = HttpClients.createMinimal()) {
             final String lastModified;
             try (CloseableHttpResponse res = hc.execute(new HttpGet(newUri("/foo.txt")))) {
-                lastModified = assert200Ok(res, "text/plain", "bar");
+                lastModified = assert200Ok(res, "text/plain", "foo");
             }
 
             // Test if the 'If-Modified-Since' header works as expected.
@@ -134,6 +137,16 @@ public void testClassPathGet() throws Exception {
         }
     }
 
+    @Test
+    public void testClassPathOrElseGet() throws Exception {
+        try (CloseableHttpClient hc = HttpClients.createMinimal()) {
+            final String lastModified;
+            try (CloseableHttpResponse res = hc.execute(new HttpGet(newUri("/bar.txt")))) {
+                lastModified = assert200Ok(res, "text/plain", "bar");
+            }
+        }
+    }
+
     @Test
     public void testFileSystemGet() throws Exception {
         final File barFile = new File(tmpDir, "bar.html");

src/test/resources/com/linecorp/armeria/server/http/file/foo/foo.txt

@@ -0,0 +1 @@
+foo