Solr SearchComponent to set limits to start and rows parameters on a SearchRequestHandler

gistfile1.java

package cu.uci.solr;

import org.apache.solr.common.SolrException;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.core.SolrCore;
import org.apache.solr.handler.component.ResponseBuilder;
import org.apache.solr.handler.component.SearchComponent;
import org.apache.solr.util.plugin.SolrCoreAware;
import org.apache.solr.common.util.NamedList;

import java.io.IOException;

/**
 * Block requests with a higher start or rows parameters than the configured in this components, this could be used
 * as some safeguard policy for some use cases
 * <p/>
 * <pre class="prettyprint">
 * <p/>
 * &lt;searchComponent name="max-parameters" class="cu.uci.solr.MaxParamsSearchComponent"/&gt;
 *  &lt;str name="rows"&gt;1000&lt;/str&gt;
 *  &lt;str name="start"&gt;1000&lt;/str&gt;
 *  &lt;str name="overwriteParams"&gt;false&lt;/str&gt;
 * &lt;/searchComponent&gt;</pre>
 *
 * @version 1.0
 */
public class MaxParamsSearchComponent extends SearchComponent implements SolrCoreAware {

    private int maxRowsParam;
    private int maxStartParam;
    private boolean overwriteParams;

    @Override
    public void init(NamedList args) {
        if (null != args) {
            SolrParams params = SolrParams.toSolrParams(args);

            maxRowsParam = params.getInt("rows", -1);
            maxStartParam = params.getInt("start", -1);

            if (maxRowsParam == -1 || maxStartParam == -1) {
                throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
                        "You must set the rows and start parameters in the configuration of this search component");
            }

            overwriteParams = params.getBool("overwriteParams", false);
        }
    }

    @Override
    public void inform(SolrCore core) {

    }

    @Override
    public void prepare(ResponseBuilder rb) throws IOException {
        SolrParams params = rb.req.getParams();

        int rows = params.getInt("rows", -1);
        int start = params.getInt("start", -1);

        if (rows == -1 && start == -1) {
            // nothing to do, there is no rows or start parameter
            return;
        } else {
            if (rows > maxRowsParam || start > maxStartParam) {
                if (overwriteParams) {
                    // overwrite the rows and start parameters
                    NamedList list = params.toNamedList();

                    if (rows > maxRowsParam) {
                        list.removeAll("rows");
                        list.add("rows", maxRowsParam);
                    }

                    if (start > maxStartParam) {
                        list.removeAll("start");
                        list.add("start", maxStartParam);
                    }

                    rb.req.setParams(SolrParams.toSolrParams(list));
                } else {
                    throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
                            "Your start or rows parameter has exceeded the allowed values");
                }
            }
        }
    }

    @Override
    public void process(ResponseBuilder rb) throws IOException {

    }

    @Override
    public String getDescription() {
        return "A component to set max values for start and rows parameters";
    }

    @Override
    public String getSource() {
        return "MaxParamsSearchComponent.java";
    }
}