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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 io.grpc;
import javax.annotation.Nullable;
/**
* Encapsulates a single call received from a remote client. Calls may not simply be unary
* request-response even though this is the most common pattern. Calls may stream any number of
* requests and responses. This API is generally intended for use by generated handlers,
* but applications may use it directly if they need to.
*
* Headers must be sent before any messages, which must be sent before closing.
*
*
No generic method for determining message receipt or providing acknowledgement is provided.
* Applications are expected to utilize normal messages for such signals, as a response
* naturally acknowledges its request.
*
*
Methods are guaranteed to be non-blocking. Implementations are not required to be thread-safe.
*
*
DO NOT MOCK: Use InProcessTransport and make a fake server instead.
*
* @param parsed type of request message.
* @param parsed type of response message.
*/
public abstract class ServerCall {
/**
* Callbacks for consuming incoming RPC messages.
*
* Any contexts are guaranteed to arrive before any messages, which are guaranteed before half
* close, which is guaranteed before completion.
*
*
Implementations are free to block for extended periods of time. Implementations are not
* required to be thread-safe.
*/
// TODO(ejona86): We need to decide what to do in the case of server closing with non-cancellation
// before client half closes. It may be that we treat such a case as an error. If we permit such
// a case then we either get to generate a half close or purposefully omit it.
public abstract static class Listener {
/**
* A request message has been received. For streaming calls, there may be zero or more request
* messages.
*
* @param message a received request message.
*/
public void onMessage(ReqT message) {}
/**
* The client completed all message sending. However, the call may still be cancelled.
*/
public void onHalfClose() {}
/**
* The call was cancelled and the server is encouraged to abort processing to save resources,
* since the client will not process any further messages. Cancellations can be caused by
* timeouts, explicit cancellation by the client, network errors, etc.
*
* There will be no further callbacks for the call.
*/
public void onCancel() {}
/**
* The call is considered complete and {@link #onCancel} is guaranteed not to be called.
* However, the client is not guaranteed to have received all messages.
*
*
There will be no further callbacks for the call.
*/
public void onComplete() {}
/**
* This indicates that the call 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 call.
*
*
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.
*/
public void onReady() {}
}
/**
* Requests up to the given number of messages from the call to be delivered to
* {@link Listener#onMessage(Object)}. Once {@code numMessages} have been delivered
* no further request messages will be delivered until more messages are requested by
* calling this method again.
*
*
Servers use this mechanism to provide back-pressure to the client for flow-control.
*
*
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.
*/
public abstract void request(int numMessages);
/**
* Send response header metadata prior to sending a response message. This method may
* only be called once and cannot be called after calls to {@link #sendMessage} or {@link #close}.
*
*
Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
* headers} after this point.
*
* @param headers metadata to send prior to any response body.
* @throws IllegalStateException if {@code close} has been called, a message has been sent, or
* headers have already been sent
*/
public abstract void sendHeaders(Metadata headers);
/**
* Send a response message. Messages are the primary form of communication associated with
* RPCs. Multiple response messages may exist for streaming calls.
*
* @param message response message.
* @throws IllegalStateException if headers not sent or call is {@link #close}d
*/
public abstract void sendMessage(RespT 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}.
*
*
This abstract class's implementation always returns {@code true}. Implementations generally
* override the method.
*/
public boolean isReady() {
return true;
}
/**
* Close the call with the provided status. No further sending or receiving will occur. If {@link
* Status#isOk} is {@code false}, then the call is said to have failed.
*
*
If no errors or cancellations are known to have occurred, then a {@link Listener#onComplete}
* notification should be expected, independent of {@code status}. Otherwise {@link
* Listener#onCancel} has been or will be called.
*
*
Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
* trailers} after this point.
*
* @throws IllegalStateException if call is already {@code close}d
*/
public abstract void close(Status status, Metadata trailers);
/**
* Returns {@code true} when the call is cancelled and the server is encouraged to abort
* processing to save resources, since the client will not be processing any further methods.
* Cancellations can be caused by timeouts, explicit cancel by client, network errors, and
* similar.
*
*
This method may safely be called concurrently from multiple threads.
*/
public abstract boolean isCancelled();
/**
* 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/1704")
public void setMessageCompression(boolean enabled) {
// noop
}
/**
* Sets the compression algorithm for this call. If the server does not support the compression
* algorithm, the call will fail. This method may only be called before {@link #sendHeaders}.
* The compressor to use will be looked up in the {@link CompressorRegistry}. Default gRPC
* servers support the "gzip" compressor.
*
*
It is safe to call this even if the client does not support the compression format chosen.
* The implementation will handle negotiation with the client and may fall back to no compression.
*
* @param compressor the name of the compressor to use.
* @throws IllegalArgumentException if the compressor name can not be found.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1704")
public void setCompression(String compressor) {
// noop
}
/**
* Returns properties of a single call.
*
*
Attributes originate from the transport and can be altered by {@link ServerTransportFilter}.
*
* @return non-{@code null} Attributes container
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1779")
@Grpc.TransportAttr
public Attributes getAttributes() {
return Attributes.EMPTY;
}
/**
* Gets the authority this call is addressed to.
*
* @return the authority string. {@code null} if not available.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/2924")
@Nullable
public String getAuthority() {
return null;
}
/**
* The {@link MethodDescriptor} for the call.
*/
public abstract MethodDescriptor getMethodDescriptor();
}