lang/c++/api/Generic.hh

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef avro_Generic_hh__
#define avro_Generic_hh__

#include <boost/utility.hpp>

#include "Config.hh"
#include "Types.hh"
#include "Encoder.hh"
#include "Decoder.hh"
#include "GenericDatum.hh"

namespace avro {
/**
 * A utility class to read generic datum from decoders.
 */
class AVRO_DECL GenericReader : boost::noncopyable {
    const ValidSchema schema_;
    const bool isResolving_;
    const DecoderPtr decoder_;

    static void read(GenericDatum& datum, Decoder& d, bool isResolving);
public:
    /**
     * Constructs a reader for the given schema using the given decoder.
     */
    GenericReader(const ValidSchema& s, const DecoderPtr& decoder);

    /**
     * Constructs a reader for the given reader's schema \c readerSchema
     * using the given
     * decoder which holds data matching writer's schema \c writerSchema.
     */
    GenericReader(const ValidSchema& writerSchema,
        const ValidSchema& readerSchema, const DecoderPtr& decoder);

    /**
     * Reads a value off the decoder.
     */
    void read(GenericDatum& datum) const;

    /**
     * Drains any residual bytes in the input stream (e.g. because
     * reader's schema has no use of them) and return unused bytes
     * back to the underlying input stream.
     */
    void drain() {
        decoder_->drain();
    }
    /**
     * Reads a generic datum from the stream, using the given schema.
     */
    static void read(Decoder& d, GenericDatum& g);

    /**
     * Reads a generic datum from the stream, using the given schema.
     */
    static void read(Decoder& d, GenericDatum& g, const ValidSchema& s);
};


/**
 * A utility class to write generic datum to encoders.
 */
class AVRO_DECL GenericWriter : boost::noncopyable {
    const ValidSchema schema_;
    const EncoderPtr encoder_;

    static void write(const GenericDatum& datum, Encoder& e);
public:
    /**
     * Constructs a writer for the given schema using the given encoder.
     */
    GenericWriter(const ValidSchema& s, const EncoderPtr& encoder);

    /**
     * Writes a value onto the encoder.
     */
    void write(const GenericDatum& datum) const;

    /**
     * Writes a generic datum on to the stream.
     */
    static void write(Encoder& e, const GenericDatum& g);

    /**
     * Writes a generic datum on to the stream, using the given schema.
     * Retained for backward compatibility.
     */
    static void write(Encoder& e, const GenericDatum& g, const ValidSchema&) {
        write(e, g);
    }
};

template <typename T> struct codec_traits;

/**
 * Specialization of codec_traits for Generic datum along with its schema.
 * This is maintained for compatibility with old code. Please use the
 * cleaner codec_traits<GenericDatum> instead.
 */
template <> struct codec_traits<std::pair<ValidSchema, GenericDatum> > {
    /** Encodes */
    static void encode(Encoder& e,
        const std::pair<ValidSchema, GenericDatum>& p) {
        GenericWriter::write(e, p.second, p.first);
    }

    /** Decodes */
    static void decode(Decoder& d, std::pair<ValidSchema, GenericDatum>& p) {
        GenericReader::read(d, p.second, p.first);
    }
};

/**
 * Specialization of codec_traits for GenericDatum.
 */
template <> struct codec_traits<GenericDatum> {
    /** Encodes */
    static void encode(Encoder& e, const GenericDatum& g) {
        GenericWriter::write(e, g);
    }

    /** Decodes */
    static void decode(Decoder& d, GenericDatum& g) {
        GenericReader::read(d, g);
    }
};
    
}   // namespace avro
#endif