SequenceIterator.hpp

/*
(c) Copyright, Real-Time Innovations, 2018.
All rights reserved.

No duplications, whole or partial, manual or electronic, may be made
without express written permission.  Any such copies, or
revisions thereof, must display this notice unaltered.
This code contains trade secrets of Real-Time Innovations, Inc.
*/

#ifndef RTI_DDS_FLAT_SEQUENCEITERATOR_HPP_
#define RTI_DDS_FLAT_SEQUENCEITERATOR_HPP_

#include <iterator>

#include "rti/flat/Offset.hpp"

namespace rti { namespace flat {

template <typename E, typename OffsetKind>
class SequenceIterator {
public:
    typedef std::forward_iterator_tag iterator_category;

    typedef E value_type;

    typedef value_type reference;

    typedef value_type pointer;

    typedef std::ptrdiff_t difference_type;

    SequenceIterator() : sample_(NULL), current_offset_(0), max_offset_(0)
    {
    }

    SequenceIterator(
            rti::flat::SampleBase *sample,  
            offset_t initial_offset,
            offset_t max_offset)
        : sample_(sample), 
          current_offset_(initial_offset), 
          max_offset_(max_offset)
    {
        RTI_FLAT_ASSERT(sample != NULL, return);
    }

    bool is_null() const
    {
        return sample_ == NULL;
    }

    value_type operator*() const 
    {
        return get_impl(OffsetKind());
    }

    value_type operator->() const 
    {
        return get_impl(OffsetKind());
    }

    bool advance()
    {
        // Unlike operator++, advance() allows checking for errors when
        // exceptions are disabled (traditional C++)
        return advance_impl(OffsetKind());
    }

    SequenceIterator& operator++()
    {
        bool can_advance_iter = advance_impl(OffsetKind());
        RTI_FLAT_CHECK_PRECONDITION(can_advance_iter, return *this);
        return *this;
    }

    SequenceIterator operator++(int) 
    {
        SequenceIterator tmp(*this);
        ++(*this);
        return tmp;
    }

    friend bool operator<(
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return s1.get_position() < s2.get_position();
    }

    friend bool operator > (
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return s1.get_position() > s2.get_position();
    }

    friend bool operator <= (
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return s1.get_position() <= s2.get_position();
    }

    friend bool operator >= (
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return s1.get_position() >= s2.get_position();
    }

    friend bool operator == (
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return s1.get_position() == s2.get_position();
    }

    friend bool operator != (
            const SequenceIterator & s1,
            const SequenceIterator & s2) 
    {
        return !(s1 == s2);
    }

    unsigned char * get_position() const
    {
        if (is_null()) {
            return NULL;
        } else {
            return sample_->get_buffer() + current_offset_;
        }
    }    

private:
    E get_impl(variable_size_type_tag_t) const
    {   
        if (is_null()) {
            return E();
        }

        // The iterator points to the end of the previous element. If elements
        // need padding, we have to add it here (required alignment is 4 because
        // mutable types (variable_size_type_tag_t) are always aligned to 4)
        offset_t offset = RTIXCdrAlignment_alignSizeUp(current_offset_, 4);

        if (offset >= max_offset_) {
            return E();
        }

        // Calculate the size of the current element; if E is a struct type,
        // this will be quick (just deserialize the DHeader); if we're itearating
        // over an array of sequences (E is a sequence), this will require
        // skipping over the current sequence.
        offset_t size = E::Helper::calculate_serialized_size(
                sample_, 
                offset,
                max_offset_);
        // size 0 indicates an error; a variable-size type E cannot have size
        // zero because it will always have a header (DHeader for mutable structs,
        // length for sequences)
        if (size == 0) {
            return E();
        }

        return E(sample_, offset, size);
    }

    E get_impl(fixed_size_type_tag_t) const
    {
        if (is_null()) {
            return E();
        }

        // The iterator points to the end of the previous element. If elements
        // need padding, we have to add it here.
        offset_t offset = RTIXCdrAlignment_alignSizeUp(
                current_offset_, 
                E::required_alignment);
        if (offset >= max_offset_) {
            return E();
        }

        return E(sample_, offset);        
    }

    bool advance_impl(variable_size_type_tag_t)
    {
        if (is_null()) {
            return false;
        }

        current_offset_ = RTIXCdrAlignment_alignSizeUp(current_offset_, 4);
        offset_t size = E::Helper::calculate_serialized_size(
                sample_, // beginning of the buffer
                current_offset_, // absolute offset to the current element
                max_offset_); // maximum offset in the list
        if (size == 0) {
            return false;
        }

        current_offset_ += size;

        if (current_offset_ > max_offset_) {
            current_offset_ = max_offset_;
            return false;
        }

        return true;
    }

    bool advance_impl(fixed_size_type_tag_t)
    {
        if (is_null()) {
            return false;
        }

        // The iterator points to the end of the previous element. If elements
        // need padding, we have to add it here. We do that to keep the end()
        // iterator consistent, becuase the last element may not need padding.
        current_offset_ = RTIXCdrAlignment_alignSizeUp(
                current_offset_, 
                E::required_alignment);        
        current_offset_ += E::serialized_size(0);

        if (current_offset_ > max_offset_) {
            current_offset_ = max_offset_;
            return false;
        }

        return true;
    }

    rti::flat::SampleBase *sample_;
    offset_t current_offset_;
    offset_t max_offset_;
};

} }

#endif // RTI_DDS_FLAT_SEQUENCEITERATOR_HPP_