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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;

import javax.annotation.Nullable;

/**
 * An instance of a call to a remote method. A call will send zero or more
 * request messages to the server and receive zero or more response messages back.
 *
 * 

Instances are created * by a {@link Channel} and used by stubs to invoke their remote behavior. * *

More advanced usages may consume this interface directly as opposed to using a stub. Common * reasons for doing so would be the need to interact with flow-control or when acting as a generic * proxy for arbitrary operations. * *

{@link #start} must be called prior to calling any other methods, with the exception of * {@link #cancel}. Whereas {@link #cancel} must not be followed by any other methods, * but can be called more than once, while only the first one has effect. * *

No generic method for determining message receipt or providing acknowledgement is provided. * Applications are expected to utilize normal payload messages for such signals, as a response * naturally acknowledges its request. * *

Methods are guaranteed to be non-blocking. Not thread-safe except for {@link #request}, which * may be called from any thread. * *

There is no interaction between the states on the {@link Listener Listener} and {@link * ClientCall}, i.e., if {@link Listener#onClose Listener.onClose()} is called, it has no bearing on * the permitted operations on {@code ClientCall} (but it may impact whether they do anything). * *

There is a race between {@link #cancel} and the completion/failure of the RPC in other ways. * If {@link #cancel} won the race, {@link Listener#onClose Listener.onClose()} is called with * {@link Status#CANCELLED CANCELLED}. Otherwise, {@link Listener#onClose Listener.onClose()} is * called with whatever status the RPC was finished. We ensure that at most one is called. * *

Usage examples

*

Simple Unary (1 request, 1 response) RPC

*
 *   call = channel.newCall(unaryMethod, callOptions);
 *   call.start(listener, headers);
 *   call.sendMessage(message);
 *   call.halfClose();
 *   call.request(1);
 *   // wait for listener.onMessage()
 * 
* *

Flow-control in Streaming RPC

* *

The following snippet demonstrates a bi-directional streaming case, where the client sends * requests produced by a fictional makeNextRequest() in a flow-control-compliant * manner, and notifies gRPC library to receive additional response after one is consumed by * a fictional processResponse(). * *

 *   call = channel.newCall(bidiStreamingMethod, callOptions);
 *   listener = new ClientCall.Listener<FooResponse>() {
 *     @Override
 *     public void onMessage(FooResponse response) {
 *       processResponse(response);
 *       // Notify gRPC to receive one additional response.
 *       call.request(1);
 *     }
 *
 *     @Override
 *     public void onReady() {
 *       while (call.isReady()) {
 *         FooRequest nextRequest = makeNextRequest();
 *         if (nextRequest == null) {  // No more requests to send
 *           call.halfClose();
 *           return;
 *         }
 *         call.sendMessage(nextRequest);
 *       }
 *     }
 *   }
 *   call.start(listener, headers);
 *   // Notify gRPC to receive one response. Without this line, onMessage() would never be called.
 *   call.request(1);
 * 
* *

DO NOT MOCK: Use InProcessServerBuilder and make a test server instead. * * @param type of message sent one or more times to the server. * @param type of message received one or more times from the server. */ public abstract class ClientCall { /** * Callbacks for receiving metadata, response messages and completion status from the server. * *

Implementations are free to block for extended periods of time. Implementations are not * required to be thread-safe, but they must not be thread-hostile. The caller is free to call * an instance from multiple threads, but only one call simultaneously. A single thread may * interleave calls to multiple instances, so implementations using ThreadLocals must be careful * to avoid leaking inappropriate state (e.g., clearing the ThreadLocal before returning). * * @param type of message received. */ public abstract static class Listener { /** * The response headers have been received. Headers always precede messages. * *

Since {@link Metadata} is not thread-safe, the caller must not access (read or write) * {@code headers} after this point. * * @param headers containing metadata sent by the server at the start of the response. */ public void onHeaders(Metadata headers) {} /** * A response message has been received. May be called zero or more times depending on whether * the call response is empty, a single message or a stream of messages. * * @param message returned by the server */ public void onMessage(T message) {} /** * The ClientCall has been closed. Any additional calls to the {@code ClientCall} will not be * processed by the server. No further receiving will occur and no further notifications will be * made. * *

Since {@link Metadata} is not thread-safe, the caller must not access (read or write) * {@code trailers} after this point. * *

If {@code status} returns false for {@link Status#isOk()}, then the call failed. * An additional block of trailer metadata may be received at the end of the call from the * server. An empty {@link Metadata} object is passed if no trailers are received. * *

This method should not throw. If this method throws, there is no way to be notified of the * exception. Implementations should therefore be careful of exceptions which can accidentally * leak resources. * * @param status the result of the remote call. * @param trailers metadata provided at call completion. */ public void onClose(Status status, Metadata trailers) {} /** * This indicates that the ClientCall may now be capable of sending additional messages (via * {@link #sendMessage}) without requiring excessive buffering internally. This event is * just a suggestion and the application is free to ignore it, however doing so may * result in excessive buffering within the ClientCall. * *

Because there is a processing delay to deliver this notification, it is possible for * concurrent writes to cause {@code isReady() == false} within this callback. Handle "spurious" * notifications by checking {@code isReady()}'s current value instead of assuming it is now * {@code true}. If {@code isReady() == false} the normal expectations apply, so there would be * another {@code onReady()} callback. * *

If the type of a call is either {@link MethodDescriptor.MethodType#UNARY} or * {@link MethodDescriptor.MethodType#SERVER_STREAMING}, this callback may not be fired. Calls * that send exactly one message should not await this callback. */ public void onReady() {} } /** * Start a call, using {@code responseListener} for processing response messages. * *

It must be called prior to any other method on this class, except for {@link #cancel} which * may be called at any time. * *

Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code * headers} after this point. * * @param responseListener receives response messages * @param headers which can contain extra call metadata, e.g. authentication credentials. * @throws IllegalStateException if a method (including {@code start()}) on this class has been * called. */ public abstract void start(Listener responseListener, Metadata headers); /** * Requests up to the given number of messages from the call to be delivered to * {@link Listener#onMessage(Object)}. No additional messages will be delivered. * *

Message delivery is guaranteed to be sequential in the order received. In addition, the * listener methods will not be accessed concurrently. While it is not guaranteed that the same * thread will always be used, it is guaranteed that only a single thread will access the listener * at a time. * *

If it is desired to bypass inbound flow control, a very large number of messages can be * specified (e.g. {@link Integer#MAX_VALUE}). * *

If called multiple times, the number of messages able to delivered will be the sum of the * calls. * *

This method is safe to call from multiple threads without external synchronization. * * @param numMessages the requested number of messages to be delivered to the listener. Must be * non-negative. * @throws IllegalStateException if call is not {@code start()}ed * @throws IllegalArgumentException if numMessages is negative */ public abstract void request(int numMessages); /** * Prevent any further processing for this {@code ClientCall}. No further messages may be sent or * will be received. The server is informed of cancellations, but may not stop processing the * call. Cancellation is permitted even if previously {@link #halfClose}d. Cancelling an already * {@code cancel()}ed {@code ClientCall} has no effect. * *

No other methods on this class can be called after this method has been called. * *

It is recommended that at least one of the arguments to be non-{@code null}, to provide * useful debug information. Both argument being null may log warnings and result in suboptimal * performance. Also note that the provided information will not be sent to the server. * * @param message if not {@code null}, will appear as the description of the CANCELLED status * @param cause if not {@code null}, will appear as the cause of the CANCELLED status */ public abstract void cancel(@Nullable String message, @Nullable Throwable cause); /** * Close the call for request message sending. Incoming response messages are unaffected. This * should be called when no more messages will be sent from the client. * * @throws IllegalStateException if call is already {@code halfClose()}d or {@link #cancel}ed */ public abstract void halfClose(); /** * Send a request message to the server. May be called zero or more times depending on how many * messages the server is willing to accept for the operation. * * @param message message to be sent to the server. * @throws IllegalStateException if call is {@link #halfClose}d or explicitly {@link #cancel}ed */ public abstract void sendMessage(ReqT message); /** * If {@code true}, indicates that the call is capable of sending additional messages * without requiring excessive buffering internally. This event is * just a suggestion and the application is free to ignore it, however doing so may * result in excessive buffering within the call. * *

If {@code false}, {@link Listener#onReady()} will be called after {@code isReady()} * transitions to {@code true}. * *

If the type of the call is either {@link MethodDescriptor.MethodType#UNARY} or * {@link MethodDescriptor.MethodType#SERVER_STREAMING}, this method may persistently return * false. Calls that send exactly one message should not check this method. * *

This abstract class's implementation always returns {@code true}. Implementations generally * override the method. */ public boolean isReady() { return true; } /** * Enables per-message compression, if an encoding type has been negotiated. If no message * encoding has been negotiated, this is a no-op. By default per-message compression is enabled, * but may not have any effect if compression is not enabled on the call. */ @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1703") public void setMessageCompression(boolean enabled) { // noop } /** * Returns additional properties of the call. May only be called after {@link Listener#onHeaders} * or {@link Listener#onClose}. If called prematurely, the implementation may throw {@code * IllegalStateException} or return arbitrary {@code Attributes}. * * @return non-{@code null} attributes * @throws IllegalStateException (optional) if called before permitted */ @ExperimentalApi("https://github.com/grpc/grpc-java/issues/2607") @Grpc.TransportAttr public Attributes getAttributes() { return Attributes.EMPTY; } }





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