src/main/java/org/apache/sling/scripting/sightly/compiler/commands/CommandHandler.java

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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
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 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
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package org.apache.sling.scripting.sightly.compiler.commands;

import org.osgi.annotation.versioning.ProviderType;

/**
 * The {@code CommandHandler} is the mechanism through which a {@link CommandStream} can be processed synchronously, as the stream is
 * written.
 */
@ProviderType
public interface CommandHandler {

    /**
     * Allows this handler to process the {@link Command} that was just written into the stream to which this handler was attached.
     *
     * @param command the received command
     */
    void onEmit(Command command);

    /**
     * Allows this handler to process error states.
     *
     * @param errorMessage the error's message
     */
    void onError(String errorMessage);

    /**
     * This method is called when the stream has been closed. The contract is that after this call, no other commands or errors will be
     * emitted.
     */
    void onDone();

}