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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc.handler;
import com.yahoo.jdisc.Container;
import com.yahoo.jdisc.Request;
import com.yahoo.jdisc.Response;
import java.nio.ByteBuffer;
/**
* This interface defines a callback for asynchronously writing the content of a {@link Request} or a {@link Response}
* to a recipient. It is the returned both by {@link RequestHandler#handleRequest(Request, ResponseHandler)} and {@link
* ResponseHandler#handleResponse(Response)}. Note that methods of this channel only <em>schedule</em> the appropriate
* action - if you need to act on the result you will need submit a {@link CompletionHandler} to the appropriate method.
* <p>
* Because a ContentChannel might have a different lifespan than the originating Request and Response
* objects, all instances of this interface are internally backed by a reference to the {@link Container} that was
* active when the initial Request was created. This ensures that the configured environment of the ContentChannel is
* stable throughout its lifetime. This also means that the {@link #close(CompletionHandler)} method MUST be called in
* order to release that reference. Failure to do so will prevent the Container from ever shutting down. This
* requirement is regardless of any errors that may occur while calling any of its other methods or its derived {@link
* CompletionHandler}s.
*
* @author Simon Thoresen Hult
*/
public interface ContentChannel {
/**
* Schedules the given {@link ByteBuffer} to be written to the content corresponding to this ContentChannel. This
* call <em>transfers ownership</em> of the given ByteBuffer to this ContentChannel, i.e. no further calls can be
* made to the buffer. The execution of writes happen in the same order as this method was invoked.
*
* @param buf The {@link ByteBuffer} to schedule for write. No further calls can be made to this buffer.
* @param handler The {@link CompletionHandler} to call after the write has been executed.
*/
void write(ByteBuffer buf, CompletionHandler handler);
/**
* Closes this ContentChannel. After a channel is closed, any further attempt to invoke {@link #write(ByteBuffer,
* CompletionHandler)} upon it will cause an {@link IllegalStateException} to be thrown. If this channel is already
* closed then invoking this method has no effect, but {@link CompletionHandler#completed()} will still be called.
*
* Notice that you MUST call this method, regardless of any exceptions that might have occurred while writing to this
* ContentChannel. Failure to do so will prevent the {@link Container} from ever shutting down.
*
* @param handler The {@link CompletionHandler} to call after the close has been executed.
*/
void close(CompletionHandler handler);
/**
* Invoked when an error occurs during processing of request content. Signals that the caller was
* unable to write all data to this ContentChannel.
*
* This method can be invoked at any time after the content channel is created, but it's never invoked after {@link #close(CompletionHandler)}.
* {@link #close(CompletionHandler)} will be invoked immediately after this method returning
* (no intermediate calls to #{@link #write(ByteBuffer, CompletionHandler)}).
*/
default void onError(Throwable error) {}
}
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