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Graylog
There is a newer version: 6.0.5
/**
 * This file is part of Graylog.
 *
 * Graylog is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Graylog is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Graylog.  If not, see .
 */
package org.graylog2.rest;

import au.com.bytecode.opencsv.CSVWriter;
import org.graylog2.indexer.results.ResultMessage;
import org.graylog2.indexer.results.ScrollResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.nio.charset.StandardCharsets;
import java.util.List;

@Provider
@Produces(MoreMediaTypes.TEXT_CSV)
public class ScrollChunkWriter implements MessageBodyWriter {
    private static final Logger LOG = LoggerFactory.getLogger(ScrollChunkWriter.class);

    @Override
    public boolean isWriteable(Class type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        return ScrollResult.ScrollChunk.class.equals(type) && MoreMediaTypes.TEXT_CSV_TYPE.isCompatible(mediaType);

    }

    @Override
    public long getSize(ScrollResult.ScrollChunk scrollChunk,
                        Class type,
                        Type genericType,
                        Annotation[] annotations,
                        MediaType mediaType) {
        return -1;
    }

    @Override
    public void writeTo(ScrollResult.ScrollChunk scrollChunk,
                        Class type,
                        Type genericType,
                        Annotation[] annotations,
                        MediaType mediaType,
                        MultivaluedMap httpHeaders,
                        OutputStream entityStream) throws IOException, WebApplicationException {
        if (LOG.isDebugEnabled()) {
            LOG.debug("[{}] Writing chunk {}", Thread.currentThread().getId(), scrollChunk.getChunkNumber());
        }
        final CSVWriter csvWriter = new CSVWriter(new OutputStreamWriter(entityStream, StandardCharsets.UTF_8));

        final List fields = scrollChunk.getFields();
        final int numberOfFields = fields.size();

        if (scrollChunk.isFirstChunk()) {
            // write field headers only on first chunk
            csvWriter.writeNext(fields.toArray(new String[numberOfFields]));
        }
        // write result set in same order as the header row
        final String[] fieldValues = new String[numberOfFields];
        for (ResultMessage message : scrollChunk.getMessages()) {
            int idx = 0;
            // first collect all values from the current message
            for (String fieldName : fields) {
                final Object val = message.getMessage().getField(fieldName);
                if (val == null) {
                    fieldValues[idx] = null;
                } else {
                    String stringVal = val.toString();
                    fieldValues[idx] = stringVal
                            .replaceAll("\n", "\\\\n")
                            .replaceAll("\r", "\\\\r");
                }
                idx++;
            }

            // write the complete line, some fields might not be present in the message, so there might be null values
            csvWriter.writeNext(fieldValues);
        }
        if (csvWriter.checkError()) {
            LOG.error("Encountered unspecified error when writing message result as CSV, result is likely malformed.");
        }
        csvWriter.close();
    }
}