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A driver for DataStax Enterprise (DSE) and Apache Cassandra 1.2+ clusters that works exclusively with the Cassandra Query Language version 3 (CQL3) and Cassandra's binary protocol, supporting DSE-specific features such as geospatial types, DSE Graph and DSE authentication.

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/*
 * Copyright DataStax, Inc.
 *
 * This software can be used solely with DataStax Enterprise. Please consult the license at
 * http://www.datastax.com/terms/datastax-dse-driver-license-terms
 */
package com.datastax.driver.dse.geometry;

import com.esri.core.geometry.Geometry;
import com.esri.core.geometry.*;
import com.esri.core.geometry.ogc.OGCGeometry;
import com.esri.core.geometry.ogc.OGCLineString;
import com.esri.core.geometry.ogc.OGCPoint;
import com.esri.core.geometry.ogc.OGCPolygon;

import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * Helper class to serialize OGC geometries to Well-Known Binary, forcing the byte order to little endian.
 * 
 * WKB encodes the byte order, so in theory we could send the buffer in any order, even if it is different from the
 * server. However DSE server performs an additional validation step server-side: it deserializes to Java, serializes
 * back to WKB, and then compares the original buffer to the "re-serialized" one. If they don't match, a
 * MarshalException is thrown. So with a client in big-endian and a server in little-endian, we would get:
 * 
 * incoming buffer (big endian) --> Java --> reserialized buffer (little endian)
 * 
 * Since the two buffers have a different endian-ness, they don't match.
 * 
 * The ESRI library defaults to the native byte order and doesn't let us change it. Therefore:
 * 

 * if the native order is little endian (vast majority of cases), this class simply delegates to the appropriate
 * public API method;
 * if the native order is big endian, it re-implements the serialization code, using reflection to get access to a
 * private method. If reflection fails for any reason (updated ESRI library, security manager...), a runtime exception
 * will be thrown.
 * 
 */
class WkbUtil {

    private static final boolean IS_NATIVE_LITTLE_ENDIAN = ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_ENDIAN) &&
            System.getProperty("com.datastax.driver.dse.geometry.FORCE_REFLECTION_WKB") == null; // only for tests

    static ByteBuffer asLittleEndianBinary(OGCGeometry ogcGeometry) {
        if (IS_NATIVE_LITTLE_ENDIAN)
            return ogcGeometry.asBinary(); // the default implementation does what we want
        else {
            int exportFlags;
            if (ogcGeometry instanceof OGCPoint)
                exportFlags = 0;
            else if (ogcGeometry instanceof OGCLineString)
                exportFlags = WkbExportFlags.wkbExportLineString;
            else if (ogcGeometry instanceof OGCPolygon)
                exportFlags = WkbExportFlags.wkbExportPolygon;
            else
                throw new AssertionError("Unsupported type: " + ogcGeometry.getClass());

            // Copy-pasted from OperatorExportToWkbLocal#execute, except for the flags and order
            int size = exportToWKB(exportFlags, ogcGeometry.getEsriGeometry(), null);
            ByteBuffer wkbBuffer = ByteBuffer.allocate(size).order(ByteOrder.LITTLE_ENDIAN);
            exportToWKB(exportFlags, ogcGeometry.getEsriGeometry(), wkbBuffer);
            return wkbBuffer;
        }
    }

    // Provides reflective access to the private static method OperatorExportToWkbLocal#exportToWKB
    private static int exportToWKB(int exportFlags, Geometry geometry,
                                   ByteBuffer wkbBuffer) {
        assert !IS_NATIVE_LITTLE_ENDIAN;
        try {
            return (Integer) exportToWKB.invoke(null, exportFlags, geometry, wkbBuffer);
        } catch (Exception e) {
            throw new RuntimeException("Couldn't invoke private method OperatorExportToWkbLocal#exportToWKB", e);
        }
    }

    private static final Method exportToWKB;

    static {
        if (IS_NATIVE_LITTLE_ENDIAN)
            exportToWKB = null; // won't be used
        else
            try {
                OperatorExportToWkb op = (OperatorExportToWkb) OperatorFactoryLocal
                        .getInstance().getOperator(Operator.Type.ExportToWkb);
                exportToWKB = op.getClass()
                        .getDeclaredMethod("exportToWKB", int.class, Geometry.class, ByteBuffer.class);
                exportToWKB.setAccessible(true);
            } catch (NoSuchMethodException e) {
                throw new RuntimeException("Couldn't get access to private method OperatorExportToWkbLocal#exportToWKB", e);
            }
    }
}