ratpack.exec.Upstream Maven / Gradle / Ivy
/*
* Copyright 2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package ratpack.exec;
/**
* An upstream asynchronous data source.
*
* An upstream can be {@link #connect connected} at any time to a {@link Downstream}, zero or more times.
* Once connected, the upstream will at some time in the future invoke one of the downstream's {@link Downstream#success}, {@link Downstream#error}, {@link Downstream#complete} methods.
* Only one of these methods will be invoked per downstream that is connected, and only invoked once.
*
* An upstream is the producer side of a {@link Promise}.
* Unlike a {@link org.reactivestreams.Publisher}, it only produces one value and does not stream.
*
* Multiple downstreams can connect to a single upstream.
*
* @see Promise#transform(ratpack.func.Function)
* @param the type of item emitted downstream
*/
public interface Upstream {
/**
* Connect the downstream.
*
* @param downstream the downstream to emit data to
* @throws Exception any
*/
void connect(Downstream downstream) throws Exception;
}