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/*
* Copyright 2014 The gRPC 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 org.apache.ratis.thirdparty.io.grpc.stub;
/**
* Receives notifications from an observable stream of messages.
*
* It is used by both the client stubs and service implementations for sending or receiving
* stream messages. It is used for all {@link org.apache.ratis.thirdparty.io.grpc.MethodDescriptor.MethodType}, including
* {@code UNARY} calls. For outgoing messages, a {@code StreamObserver} is provided by the GRPC
* library to the application. For incoming messages, the application implements the
* {@code StreamObserver} and passes it to the GRPC library for receiving.
*
*
Implementations are not required to be thread-safe (but should be
*
* thread-compatible). Separate {@code StreamObserver}s do
* not need to be synchronized together; incoming and outgoing directions are independent.
* Since individual {@code StreamObserver}s are not thread-safe, if multiple threads will be
* writing to a {@code StreamObserver} concurrently, the application must synchronize calls.
*
*
This API is asynchronous, so methods may return before the operation completes. The API
* provides no guarantees for how quickly an operation will complete, so utilizing flow control via
* {@link ClientCallStreamObserver} and {@link ServerCallStreamObserver} to avoid excessive
* buffering is recommended for streaming RPCs. gRPC's implementation of {@code onError()} on
* client-side causes the RPC to be cancelled and discards all messages, so completes quickly.
*
*
gRPC guarantees it does not block on I/O in its implementation, but applications are allowed
* to perform blocking operations in their implementations. However, doing so will delay other
* callbacks because the methods cannot be called concurrently.
*/
public interface StreamObserver {
/**
* Receives a value from the stream.
*
* Can be called many times but is never called after {@link #onError(Throwable)} or {@link
* #onCompleted()} are called.
*
*
Unary calls must invoke onNext at most once. Clients may invoke onNext at most once for
* server streaming calls, but may receive many onNext callbacks. Servers may invoke onNext at
* most once for client streaming calls, but may receive many onNext callbacks.
*
*
If an exception is thrown by an implementation the caller is expected to terminate the
* stream by calling {@link #onError(Throwable)} with the caught exception prior to
* propagating it.
*
* @param value the value passed to the stream
*/
void onNext(V value);
/**
* Receives a terminating error from the stream.
*
*
May only be called once and if called it must be the last method called. In particular if an
* exception is thrown by an implementation of {@code onError} no further calls to any method are
* allowed.
*
*
{@code t} should be a {@link org.apache.ratis.thirdparty.io.grpc.StatusException} or {@link
* org.apache.ratis.thirdparty.io.grpc.StatusRuntimeException}, but other {@code Throwable} types are possible. Callers should
* generally convert from a {@link org.apache.ratis.thirdparty.io.grpc.Status} via {@link org.apache.ratis.thirdparty.io.grpc.Status#asException()} or
* {@link org.apache.ratis.thirdparty.io.grpc.Status#asRuntimeException()}. Implementations should generally convert to a
* {@code Status} via {@link org.apache.ratis.thirdparty.io.grpc.Status#fromThrowable(Throwable)}.
*
* @param t the error occurred on the stream
*/
void onError(Throwable t);
/**
* Receives a notification of successful stream completion.
*
*
May only be called once and if called it must be the last method called. In particular if an
* exception is thrown by an implementation of {@code onCompleted} no further calls to any method
* are allowed.
*/
void onCompleted();
}