zmq.hpp

/*
    Copyright (c) 2016-2017 ZeroMQ community
    Copyright (c) 2009-2011 250bpm s.r.o.
    Copyright (c) 2011 Botond Ballo
    Copyright (c) 2007-2009 iMatix Corporation

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to
    deal in the Software without restriction, including without limitation the
    rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
    sell copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
    IN THE SOFTWARE.
*/

#ifndef __ZMQ_HPP_INCLUDED__
#define __ZMQ_HPP_INCLUDED__

// macros defined if has a specific standard or greater
#if (defined(__cplusplus) && __cplusplus >= 201103L) || (defined(_MSC_VER) && _MSC_VER >= 1900)
    #define ZMQ_CPP11
#endif
#if (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
    #define ZMQ_CPP14
#endif
#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)
    #define ZMQ_CPP17
#endif

#if defined(ZMQ_CPP14)
#define ZMQ_DEPRECATED(msg) [[deprecated(msg)]]
#elif defined(_MSC_VER)
#define ZMQ_DEPRECATED(msg) __declspec(deprecated(msg))
#elif defined(__GNUC__)
#define ZMQ_DEPRECATED(msg) __attribute__((deprecated(msg)))
#endif

#if defined(ZMQ_CPP17)
#define ZMQ_NODISCARD [[nodiscard]]
#else
#define ZMQ_NODISCARD
#endif

#if defined(ZMQ_CPP11)
#define ZMQ_NOTHROW noexcept
#define ZMQ_EXPLICIT explicit
#define ZMQ_OVERRIDE override
#define ZMQ_NULLPTR nullptr
#define ZMQ_CONSTEXPR_FN constexpr
#define ZMQ_CONSTEXPR_VAR constexpr
#else
#define ZMQ_NOTHROW throw()
#define ZMQ_EXPLICIT
#define ZMQ_OVERRIDE
#define ZMQ_NULLPTR 0
#define ZMQ_CONSTEXPR_FN
#define ZMQ_CONSTEXPR_VAR const
#endif

#include <zmq.h>

#include <cassert>
#include <cstring>

#include <algorithm>
#include <exception>
#include <iomanip>
#include <sstream>
#include <string>
#include <vector>
#ifdef ZMQ_CPP11
#include <array>
#include <chrono>
#include <tuple>
#include <memory>
#endif
#ifdef ZMQ_CPP17
#include <optional>
#endif

/*  Version macros for compile-time API version detection                     */
#define CPPZMQ_VERSION_MAJOR 4
#define CPPZMQ_VERSION_MINOR 3
#define CPPZMQ_VERSION_PATCH 1

#define CPPZMQ_VERSION                                                              \
    ZMQ_MAKE_VERSION(CPPZMQ_VERSION_MAJOR, CPPZMQ_VERSION_MINOR,                    \
                     CPPZMQ_VERSION_PATCH)

//  Detect whether the compiler supports C++11 rvalue references.
#if (defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2))   \
     && defined(__GXX_EXPERIMENTAL_CXX0X__))
#define ZMQ_HAS_RVALUE_REFS
#define ZMQ_DELETED_FUNCTION = delete
#elif defined(__clang__)
#if __has_feature(cxx_rvalue_references)
#define ZMQ_HAS_RVALUE_REFS
#endif

#if __has_feature(cxx_deleted_functions)
#define ZMQ_DELETED_FUNCTION = delete
#else
#define ZMQ_DELETED_FUNCTION
#endif
#elif defined(_MSC_VER) && (_MSC_VER >= 1900)
#define ZMQ_HAS_RVALUE_REFS
#define ZMQ_DELETED_FUNCTION = delete
#elif defined(_MSC_VER) && (_MSC_VER >= 1600)
#define ZMQ_HAS_RVALUE_REFS
#define ZMQ_DELETED_FUNCTION
#else
#define ZMQ_DELETED_FUNCTION
#endif

#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(3, 3, 0)
#define ZMQ_NEW_MONITOR_EVENT_LAYOUT
#endif

#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 1, 0)
#define ZMQ_HAS_PROXY_STEERABLE
/*  Socket event data  */
typedef struct
{
    uint16_t event; // id of the event as bitfield
    int32_t value;  // value is either error code, fd or reconnect interval
} zmq_event_t;
#endif

// Avoid using deprecated message receive function when possible
#if ZMQ_VERSION < ZMQ_MAKE_VERSION(3, 2, 0)
#define zmq_msg_recv(msg, socket, flags) zmq_recvmsg(socket, msg, flags)
#endif


// In order to prevent unused variable warnings when building in non-debug
// mode use this macro to make assertions.
#ifndef NDEBUG
#define ZMQ_ASSERT(expression) assert(expression)
#else
#define ZMQ_ASSERT(expression) (void) (expression)
#endif

namespace zmq
{

#ifdef ZMQ_CPP11
namespace detail
{
namespace ranges
{
using std::begin;
using std::end;
template<class T>
auto begin(T&& r) -> decltype(begin(std::forward<T>(r)))
{
    return begin(std::forward<T>(r));
}
template<class T>
auto end(T&& r) -> decltype(end(std::forward<T>(r)))
{
    return end(std::forward<T>(r));
}
} // namespace ranges

template<class T> using void_t = void;

template<class Iter>
using iter_value_t = typename std::iterator_traits<Iter>::value_type;

template<class Range>
using range_iter_t = decltype(
  ranges::begin(std::declval<typename std::remove_reference<Range>::type &>()));

template<class Range>
using range_value_t = iter_value_t<range_iter_t<Range>>;

template<class T, class = void> struct is_range : std::false_type
{
};

template<class T>
struct is_range<
  T,
  void_t<decltype(
    ranges::begin(std::declval<typename std::remove_reference<T>::type &>())
    == ranges::end(std::declval<typename std::remove_reference<T>::type &>()))>>
    : std::true_type
{
};

} // namespace detail
#endif

typedef zmq_free_fn free_fn;
typedef zmq_pollitem_t pollitem_t;

class error_t : public std::exception
{
  public:
    error_t() : errnum(zmq_errno()) {}
    virtual const char *what() const ZMQ_NOTHROW ZMQ_OVERRIDE { return zmq_strerror(errnum); }
    int num() const { return errnum; }

  private:
    int errnum;
};

inline int poll(zmq_pollitem_t *items_, size_t nitems_, long timeout_ = -1)
{
    int rc = zmq_poll(items_, static_cast<int>(nitems_), timeout_);
    if (rc < 0)
        throw error_t();
    return rc;
}

ZMQ_DEPRECATED("from 4.3.1, use poll taking non-const items")
inline int poll(zmq_pollitem_t const *items_, size_t nitems_, long timeout_ = -1)
{
    return poll(const_cast<zmq_pollitem_t *>(items_), nitems_, timeout_);
}

#ifdef ZMQ_CPP11
ZMQ_DEPRECATED("from 4.3.1, use poll taking non-const items")
inline int
poll(zmq_pollitem_t const *items, size_t nitems, std::chrono::milliseconds timeout)
{
    return poll(const_cast<zmq_pollitem_t *>(items), nitems, static_cast<long>(timeout.count()));
}

ZMQ_DEPRECATED("from 4.3.1, use poll taking non-const items")
inline int poll(std::vector<zmq_pollitem_t> const &items,
                std::chrono::milliseconds timeout)
{
    return poll(const_cast<zmq_pollitem_t *>(items.data()), items.size(), static_cast<long>(timeout.count()));
}

ZMQ_DEPRECATED("from 4.3.1, use poll taking non-const items")
inline int poll(std::vector<zmq_pollitem_t> const &items, long timeout_ = -1)
{
    return poll(const_cast<zmq_pollitem_t *>(items.data()), items.size(), timeout_);
}

inline int
poll(zmq_pollitem_t *items, size_t nitems, std::chrono::milliseconds timeout)
{
    return poll(items, nitems, static_cast<long>(timeout.count()));
}

inline int poll(std::vector<zmq_pollitem_t> &items,
                std::chrono::milliseconds timeout)
{
    return poll(items.data(), items.size(), static_cast<long>(timeout.count()));
}

inline int poll(std::vector<zmq_pollitem_t> &items, long timeout_ = -1)
{
    return poll(items.data(), items.size(), timeout_);
}
#endif


inline void version(int *major_, int *minor_, int *patch_)
{
    zmq_version(major_, minor_, patch_);
}

#ifdef ZMQ_CPP11
inline std::tuple<int, int, int> version()
{
    std::tuple<int, int, int> v;
    zmq_version(&std::get<0>(v), &std::get<1>(v), &std::get<2>(v));
    return v;
}
#endif

class message_t
{
  public:
    message_t() ZMQ_NOTHROW
    {
        int rc = zmq_msg_init(&msg);
        ZMQ_ASSERT(rc == 0);
    }

    explicit message_t(size_t size_)
    {
        int rc = zmq_msg_init_size(&msg, size_);
        if (rc != 0)
            throw error_t();
    }

    template<class ForwardIter> message_t(ForwardIter first, ForwardIter last)
    {
        typedef typename std::iterator_traits<ForwardIter>::value_type value_t;

        assert(std::distance(first, last) >= 0);
        size_t const size_ =
          static_cast<size_t>(std::distance(first, last)) * sizeof(value_t);
        int const rc = zmq_msg_init_size(&msg, size_);
        if (rc != 0)
            throw error_t();
        std::copy(first, last, data<value_t>());
    }

    message_t(const void *data_, size_t size_)
    {
        int rc = zmq_msg_init_size(&msg, size_);
        if (rc != 0)
            throw error_t();
        memcpy(data(), data_, size_);
    }

    message_t(void *data_, size_t size_, free_fn *ffn_, void *hint_ = ZMQ_NULLPTR)
    {
        int rc = zmq_msg_init_data(&msg, data_, size_, ffn_, hint_);
        if (rc != 0)
            throw error_t();
    }

#ifdef ZMQ_CPP11
    template<class Range,
             typename = typename std::enable_if<
               detail::is_range<Range>::value
               && std::is_trivially_copyable<detail::range_value_t<Range>>::value
               && !std::is_same<Range, message_t>::value>::type>
    explicit message_t(const Range &rng) :
        message_t(detail::ranges::begin(rng), detail::ranges::end(rng))
    {
    }
#endif

#ifdef ZMQ_HAS_RVALUE_REFS
    message_t(message_t &&rhs) ZMQ_NOTHROW : msg(rhs.msg)
    {
        int rc = zmq_msg_init(&rhs.msg);
        ZMQ_ASSERT(rc == 0);
    }

    message_t &operator=(message_t &&rhs) ZMQ_NOTHROW
    {
        std::swap(msg, rhs.msg);
        return *this;
    }
#endif

    ~message_t() ZMQ_NOTHROW
    {
        int rc = zmq_msg_close(&msg);
        ZMQ_ASSERT(rc == 0);
    }

    void rebuild()
    {
        int rc = zmq_msg_close(&msg);
        if (rc != 0)
            throw error_t();
        rc = zmq_msg_init(&msg);
        ZMQ_ASSERT(rc == 0);
    }

    void rebuild(size_t size_)
    {
        int rc = zmq_msg_close(&msg);
        if (rc != 0)
            throw error_t();
        rc = zmq_msg_init_size(&msg, size_);
        if (rc != 0)
            throw error_t();
    }

    void rebuild(const void *data_, size_t size_)
    {
        int rc = zmq_msg_close(&msg);
        if (rc != 0)
            throw error_t();
        rc = zmq_msg_init_size(&msg, size_);
        if (rc != 0)
            throw error_t();
        memcpy(data(), data_, size_);
    }

    void rebuild(void *data_, size_t size_, free_fn *ffn_, void *hint_ = ZMQ_NULLPTR)
    {
        int rc = zmq_msg_close(&msg);
        if (rc != 0)
            throw error_t();
        rc = zmq_msg_init_data(&msg, data_, size_, ffn_, hint_);
        if (rc != 0)
            throw error_t();
    }

    ZMQ_DEPRECATED("from 4.3.1, use move taking non-const reference instead")
    void move(message_t const *msg_)
    {
        int rc = zmq_msg_move(&msg, const_cast<zmq_msg_t *>(msg_->handle()));
        if (rc != 0)
            throw error_t();
    }

    void move(message_t &msg_)
    {
        int rc = zmq_msg_move(&msg, msg_.handle());
        if (rc != 0)
            throw error_t();
    }

    ZMQ_DEPRECATED("from 4.3.1, use copy taking non-const reference instead")
    void copy(message_t const *msg_)
    {
        int rc = zmq_msg_copy(&msg, const_cast<zmq_msg_t *>(msg_->handle()));
        if (rc != 0)
            throw error_t();
    }

    void copy(message_t &msg_)
    {
        int rc = zmq_msg_copy(&msg, msg_.handle());
        if (rc != 0)
            throw error_t();
    }

    bool more() const ZMQ_NOTHROW
    {
        int rc = zmq_msg_more(const_cast<zmq_msg_t *>(&msg));
        return rc != 0;
    }

    void *data() ZMQ_NOTHROW { return zmq_msg_data(&msg); }

    const void *data() const ZMQ_NOTHROW
    {
        return zmq_msg_data(const_cast<zmq_msg_t *>(&msg));
    }

    size_t size() const ZMQ_NOTHROW
    {
        return zmq_msg_size(const_cast<zmq_msg_t *>(&msg));
    }

    ZMQ_NODISCARD bool empty() const ZMQ_NOTHROW
    {
        return size() == 0u;
    }

    template<typename T> T *data() ZMQ_NOTHROW { return static_cast<T *>(data()); }

    template<typename T> T const *data() const ZMQ_NOTHROW
    {
        return static_cast<T const *>(data());
    }

    ZMQ_DEPRECATED("from 4.3.0, use operator== instead")
    bool equal(const message_t *other) const ZMQ_NOTHROW
    {
        return *this == *other;
    }

    bool operator==(const message_t &other) const ZMQ_NOTHROW
    {
        const size_t my_size = size();
        return my_size == other.size() && 0 == memcmp(data(), other.data(), my_size);
    }

    bool operator!=(const message_t &other) const ZMQ_NOTHROW
    {
        return !(*this == other);
    }

#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(3, 2, 0)
    int get(int property_)
    {
        int value = zmq_msg_get(&msg, property_);
        if (value == -1)
            throw error_t();
        return value;
    }
#endif

#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 1, 0)
    const char *gets(const char *property_)
    {
        const char *value = zmq_msg_gets(&msg, property_);
        if (value == ZMQ_NULLPTR)
            throw error_t();
        return value;
    }
#endif

#if defined(ZMQ_BUILD_DRAFT_API) && ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 0)
    uint32_t routing_id() const
    {
        return zmq_msg_routing_id(const_cast<zmq_msg_t*>(&msg));
    }

    void set_routing_id(uint32_t routing_id)
    {
        int rc = zmq_msg_set_routing_id(&msg, routing_id);
        if (rc != 0)
            throw error_t();
    }

    const char* group() const
    {
        return zmq_msg_group(const_cast<zmq_msg_t*>(&msg));
    }

    void set_group(const char* group)
    {
        int rc = zmq_msg_set_group(&msg, group);
        if (rc != 0)
            throw error_t();
    }
#endif

    /** Dump content to string. Ascii chars are readable, the rest is printed as hex.
         *  Probably ridiculously slow.
         */
    std::string str() const
    {
        // Partly mutuated from the same method in zmq::multipart_t
        std::stringstream os;

        const unsigned char *msg_data = this->data<unsigned char>();
        unsigned char byte;
        size_t size = this->size();
        int is_ascii[2] = {0, 0};

        os << "zmq::message_t [size " << std::dec << std::setw(3)
           << std::setfill('0') << size << "] (";
        // Totally arbitrary
        if (size >= 1000) {
            os << "... too big to print)";
        } else {
            while (size--) {
                byte = *msg_data++;

                is_ascii[1] = (byte >= 33 && byte < 127);
                if (is_ascii[1] != is_ascii[0])
                    os << " "; // Separate text/non text

                if (is_ascii[1]) {
                    os << byte;
                } else {
                    os << std::hex << std::uppercase << std::setw(2)
                       << std::setfill('0') << static_cast<short>(byte);
                }
                is_ascii[0] = is_ascii[1];
            }
            os << ")";
        }
        return os.str();
    }

    void swap(message_t &other) ZMQ_NOTHROW
    {
        // this assumes zmq::msg_t from libzmq is trivially relocatable
        std::swap(msg, other.msg);
    }

    ZMQ_NODISCARD zmq_msg_t *handle() ZMQ_NOTHROW { return &msg; }
    ZMQ_NODISCARD const zmq_msg_t *handle() const ZMQ_NOTHROW { return &msg; }

  private:
    //  The underlying message
    zmq_msg_t msg;

    //  Disable implicit message copying, so that users won't use shared
    //  messages (less efficient) without being aware of the fact.
    message_t(const message_t &) ZMQ_DELETED_FUNCTION;
    void operator=(const message_t &) ZMQ_DELETED_FUNCTION;
};

inline void swap(message_t &a, message_t &b) ZMQ_NOTHROW
{
    a.swap(b);
}

class context_t
{
  public:
    context_t()
    {
        ptr = zmq_ctx_new();
        if (ptr == ZMQ_NULLPTR)
            throw error_t();
    }


    explicit context_t(int io_threads_,
                              int max_sockets_ = ZMQ_MAX_SOCKETS_DFLT)
    {
        ptr = zmq_ctx_new();
        if (ptr == ZMQ_NULLPTR)
            throw error_t();

        int rc = zmq_ctx_set(ptr, ZMQ_IO_THREADS, io_threads_);
        ZMQ_ASSERT(rc == 0);

        rc = zmq_ctx_set(ptr, ZMQ_MAX_SOCKETS, max_sockets_);
        ZMQ_ASSERT(rc == 0);
    }

#ifdef ZMQ_HAS_RVALUE_REFS
    context_t(context_t &&rhs) ZMQ_NOTHROW : ptr(rhs.ptr) { rhs.ptr = ZMQ_NULLPTR; }
    context_t &operator=(context_t &&rhs) ZMQ_NOTHROW
    {
        std::swap(ptr, rhs.ptr);
        return *this;
    }
#endif

    int setctxopt(int option_, int optval_)
    {
        int rc = zmq_ctx_set(ptr, option_, optval_);
        ZMQ_ASSERT(rc == 0);
        return rc;
    }

    int getctxopt(int option_) { return zmq_ctx_get(ptr, option_); }

    ~context_t() ZMQ_NOTHROW { close(); }

    void close() ZMQ_NOTHROW
    {
        if (ptr == ZMQ_NULLPTR)
            return;

        int rc;
        do {
            rc = zmq_ctx_destroy(ptr);
        } while (rc == -1 && errno == EINTR);

        ZMQ_ASSERT(rc == 0);
        ptr = ZMQ_NULLPTR;
    }

    //  Be careful with this, it's probably only useful for
    //  using the C api together with an existing C++ api.
    //  Normally you should never need to use this.
    ZMQ_EXPLICIT operator void *() ZMQ_NOTHROW { return ptr; }

    ZMQ_EXPLICIT operator void const *() const ZMQ_NOTHROW { return ptr; }

    operator bool() const ZMQ_NOTHROW { return ptr != ZMQ_NULLPTR; }

    void swap(context_t &other) ZMQ_NOTHROW
    {
        std::swap(ptr, other.ptr);
    }

  private:
    void *ptr;

    context_t(const context_t &) ZMQ_DELETED_FUNCTION;
    void operator=(const context_t &) ZMQ_DELETED_FUNCTION;
};

inline void swap(context_t &a, context_t &b) ZMQ_NOTHROW {
    a.swap(b);
}

#ifdef ZMQ_CPP11

struct recv_buffer_size
{
    size_t size;    // number of bytes written to buffer
    size_t untruncated_size;  // untruncated message size in bytes

    ZMQ_NODISCARD bool truncated() const noexcept
    {
        return size != untruncated_size;
    }
};

namespace detail
{

#ifdef ZMQ_CPP17
using send_result_t = std::optional<size_t>;
using recv_result_t = std::optional<size_t>;
using recv_buffer_result_t = std::optional<recv_buffer_size>;
#else
// A C++11 type emulating the most basic
// operations of std::optional for trivial types
template<class T> class trivial_optional
{
  public:
    static_assert(std::is_trivial<T>::value, "T must be trivial");
    using value_type = T;

    trivial_optional() = default;
    trivial_optional(T value) noexcept : _value(value), _has_value(true) {}

    const T *operator->() const noexcept
    {
        assert(_has_value);
        return &_value;
    }
    T *operator->() noexcept
    {
        assert(_has_value);
        return &_value;
    }

    const T &operator*() const noexcept
    {
        assert(_has_value);
        return _value;
    }
    T &operator*() noexcept
    {
        assert(_has_value);
        return _value;
    }

    T &value()
    {
        if (!_has_value)
            throw std::exception();
        return _value;
    }
    const T &value() const
    {
        if (!_has_value)
            throw std::exception();
        return _value;
    }

    explicit operator bool() const noexcept { return _has_value; }
    bool has_value() const noexcept { return _has_value; }

  private:
    T _value{};
    bool _has_value{false};
};

using send_result_t = trivial_optional<size_t>;
using recv_result_t = trivial_optional<size_t>;
using recv_buffer_result_t = trivial_optional<recv_buffer_size>;
#endif

template<class T>
constexpr T enum_bit_or(T a, T b) noexcept
{
    static_assert(std::is_enum<T>::value, "must be enum");
    using U = typename std::underlying_type<T>::type;
    return static_cast<T>(static_cast<U>(a) | static_cast<U>(b));
}
template<class T>
constexpr T enum_bit_and(T a, T b) noexcept
{
    static_assert(std::is_enum<T>::value, "must be enum");
    using U = typename std::underlying_type<T>::type;
    return static_cast<T>(static_cast<U>(a) & static_cast<U>(b));
}
template<class T>
constexpr T enum_bit_xor(T a, T b) noexcept
{
    static_assert(std::is_enum<T>::value, "must be enum");
    using U = typename std::underlying_type<T>::type;
    return static_cast<T>(static_cast<U>(a) ^ static_cast<U>(b));
}
template<class T>
constexpr T enum_bit_not(T a) noexcept
{
    static_assert(std::is_enum<T>::value, "must be enum");
    using U = typename std::underlying_type<T>::type;
    return static_cast<T>(~static_cast<U>(a));
}
} // namespace detail

// partially satisfies named requirement BitmaskType
enum class send_flags : int
{
    none = 0,
    dontwait = ZMQ_DONTWAIT,
    sndmore = ZMQ_SNDMORE
};

constexpr send_flags operator|(send_flags a, send_flags b) noexcept
{
    return detail::enum_bit_or(a, b);
}
constexpr send_flags operator&(send_flags a, send_flags b) noexcept
{
    return detail::enum_bit_and(a, b);
}
constexpr send_flags operator^(send_flags a, send_flags b) noexcept
{
    return detail::enum_bit_xor(a, b);
}
constexpr send_flags operator~(send_flags a) noexcept
{
    return detail::enum_bit_not(a);
}

// partially satisfies named requirement BitmaskType
enum class recv_flags : int
{
    none = 0,
    dontwait = ZMQ_DONTWAIT
};

constexpr recv_flags operator|(recv_flags a, recv_flags b) noexcept
{
    return detail::enum_bit_or(a, b);
}
constexpr recv_flags operator&(recv_flags a, recv_flags b) noexcept
{
    return detail::enum_bit_and(a, b);
}
constexpr recv_flags operator^(recv_flags a, recv_flags b) noexcept
{
    return detail::enum_bit_xor(a, b);
}
constexpr recv_flags operator~(recv_flags a) noexcept
{
    return detail::enum_bit_not(a);
}


// mutable_buffer, const_buffer and buffer are based on
// the Networking TS specification, draft:
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/n4771.pdf

class mutable_buffer
{
  public:
    constexpr mutable_buffer() noexcept : _data(nullptr), _size(0) {}
    constexpr mutable_buffer(void *p, size_t n) noexcept : _data(p), _size(n)
    {
#ifdef ZMQ_CPP14
        assert(p != nullptr || n == 0);
#endif
    }

    constexpr void *data() const noexcept { return _data; }
    constexpr size_t size() const noexcept { return _size; }
    mutable_buffer &operator+=(size_t n) noexcept
    {
        // (std::min) is a workaround for when a min macro is defined
        const auto shift = (std::min)(n, _size);
        _data = static_cast<char *>(_data) + shift;
        _size -= shift;
        return *this;
    }

  private:
    void *_data;
    size_t _size;
};

inline mutable_buffer operator+(const mutable_buffer &mb, size_t n) noexcept
{
    return mutable_buffer(static_cast<char *>(mb.data()) + (std::min)(n, mb.size()),
                          mb.size() - (std::min)(n, mb.size()));
}
inline mutable_buffer operator+(size_t n, const mutable_buffer &mb) noexcept
{
    return mb + n;
}

class const_buffer
{
  public:
    constexpr const_buffer() noexcept : _data(nullptr), _size(0) {}
    constexpr const_buffer(const void *p, size_t n) noexcept : _data(p), _size(n)
    {
#ifdef ZMQ_CPP14
        assert(p != nullptr || n == 0);
#endif
    }
    constexpr const_buffer(const mutable_buffer &mb) noexcept :
        _data(mb.data()),
        _size(mb.size())
    {
    }

    constexpr const void *data() const noexcept { return _data; }
    constexpr size_t size() const noexcept { return _size; }
    const_buffer &operator+=(size_t n) noexcept
    {
        const auto shift = (std::min)(n, _size);
        _data = static_cast<const char *>(_data) + shift;
        _size -= shift;
        return *this;
    }

  private:
    const void *_data;
    size_t _size;
};

inline const_buffer operator+(const const_buffer &cb, size_t n) noexcept
{
    return const_buffer(static_cast<const char *>(cb.data())
                          + (std::min)(n, cb.size()),
                        cb.size() - (std::min)(n, cb.size()));
}
inline const_buffer operator+(size_t n, const const_buffer &cb) noexcept
{
    return cb + n;
}

// buffer creation

constexpr mutable_buffer buffer(void* p, size_t n) noexcept
{
    return mutable_buffer(p, n);
}
constexpr const_buffer buffer(const void* p, size_t n) noexcept
{
    return const_buffer(p, n);
}
constexpr mutable_buffer buffer(const mutable_buffer& mb) noexcept
{
    return mb;
}
inline mutable_buffer buffer(const mutable_buffer& mb, size_t n) noexcept
{
    return mutable_buffer(mb.data(), (std::min)(mb.size(), n));
}
constexpr const_buffer buffer(const const_buffer& cb) noexcept
{
    return cb;
}
inline const_buffer buffer(const const_buffer& cb, size_t n) noexcept
{
    return const_buffer(cb.data(), (std::min)(cb.size(), n));
}

namespace detail
{
template<class T> struct is_pod_like
{
    // NOTE: The networking draft N4771 section 16.11 requires
    // T in the buffer functions below to be
    // trivially copyable OR standard layout.
    // Here we decide to be conservative and require both.
    static constexpr bool value =
      std::is_trivially_copyable<T>::value && std::is_standard_layout<T>::value;
};

template<class C> constexpr auto seq_size(const C &c) noexcept -> decltype(c.size())
{
    return c.size();
}
template<class T, size_t N>
constexpr size_t seq_size(const T (&/*array*/)[N]) noexcept
{
    return N;
}

template<class Seq>
auto buffer_contiguous_sequence(Seq &&seq) noexcept
  -> decltype(buffer(std::addressof(*std::begin(seq)), size_t{}))
{
    using T = typename std::remove_cv<
      typename std::remove_reference<decltype(*std::begin(seq))>::type>::type;
    static_assert(detail::is_pod_like<T>::value, "T must be POD");

    const auto size = seq_size(seq);
    return buffer(size != 0u ? std::addressof(*std::begin(seq)) : nullptr,
                  size * sizeof(T));
}
template<class Seq>
auto buffer_contiguous_sequence(Seq &&seq, size_t n_bytes) noexcept
  -> decltype(buffer_contiguous_sequence(seq))
{
    using T = typename std::remove_cv<
      typename std::remove_reference<decltype(*std::begin(seq))>::type>::type;
    static_assert(detail::is_pod_like<T>::value, "T must be POD");

    const auto size = seq_size(seq);
    return buffer(size != 0u ? std::addressof(*std::begin(seq)) : nullptr,
                  (std::min)(size * sizeof(T), n_bytes));
}

} // namespace detail

// C array
template<class T, size_t N> mutable_buffer buffer(T (&data)[N]) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, size_t N>
mutable_buffer buffer(T (&data)[N], size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
template<class T, size_t N> const_buffer buffer(const T (&data)[N]) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, size_t N>
const_buffer buffer(const T (&data)[N], size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
// std::array
template<class T, size_t N> mutable_buffer buffer(std::array<T, N> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, size_t N>
mutable_buffer buffer(std::array<T, N> &data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
template<class T, size_t N>
const_buffer buffer(std::array<const T, N> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, size_t N>
const_buffer buffer(std::array<const T, N> &data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
template<class T, size_t N>
const_buffer buffer(const std::array<T, N> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, size_t N>
const_buffer buffer(const std::array<T, N> &data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
// std::vector
template<class T, class Allocator>
mutable_buffer buffer(std::vector<T, Allocator> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, class Allocator>
mutable_buffer buffer(std::vector<T, Allocator> &data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
template<class T, class Allocator>
const_buffer buffer(const std::vector<T, Allocator> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, class Allocator>
const_buffer buffer(const std::vector<T, Allocator> &data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
// std::basic_string
template<class T, class Traits, class Allocator>
mutable_buffer buffer(std::basic_string<T, Traits, Allocator> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, class Traits, class Allocator>
mutable_buffer buffer(std::basic_string<T, Traits, Allocator> &data,
                      size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
template<class T, class Traits, class Allocator>
const_buffer buffer(const std::basic_string<T, Traits, Allocator> &data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, class Traits, class Allocator>
const_buffer buffer(const std::basic_string<T, Traits, Allocator> &data,
                    size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}

#ifdef ZMQ_CPP17
// std::basic_string_view
template<class T, class Traits>
const_buffer buffer(std::basic_string_view<T, Traits> data) noexcept
{
    return detail::buffer_contiguous_sequence(data);
}
template<class T, class Traits>
const_buffer buffer(std::basic_string_view<T, Traits> data, size_t n_bytes) noexcept
{
    return detail::buffer_contiguous_sequence(data, n_bytes);
}
#endif

#endif // ZMQ_CPP11

namespace detail
{

class socket_base
{
public:
    socket_base() ZMQ_NOTHROW : _handle(ZMQ_NULLPTR) {}
    ZMQ_EXPLICIT socket_base(void *handle) ZMQ_NOTHROW : _handle(handle) {}

    template<typename T> void setsockopt(int option_, T const &optval)
    {
        setsockopt(option_, &optval, sizeof(T));
    }

    void setsockopt(int option_, const void *optval_, size_t optvallen_)
    {
        int rc = zmq_setsockopt(_handle, option_, optval_, optvallen_);
        if (rc != 0)
            throw error_t();
    }

    void getsockopt(int option_, void *optval_, size_t *optvallen_) const
    {
        int rc = zmq_getsockopt(_handle, option_, optval_, optvallen_);
        if (rc != 0)
            throw error_t();
    }

    template<typename T> T getsockopt(int option_) const
    {
        T optval;
        size_t optlen = sizeof(T);
        getsockopt(option_, &optval, &optlen);
        return optval;
    }

    void bind(std::string const &addr) { bind(addr.c_str()); }

    void bind(const char *addr_)
    {
        int rc = zmq_bind(_handle, addr_);
        if (rc != 0)
            throw error_t();
    }

    void unbind(std::string const &addr) { unbind(addr.c_str()); }

    void unbind(const char *addr_)
    {
        int rc = zmq_unbind(_handle, addr_);
        if (rc != 0)
            throw error_t();
    }

    void connect(std::string const &addr) { connect(addr.c_str()); }

    void connect(const char *addr_)
    {
        int rc = zmq_connect(_handle, addr_);
        if (rc != 0)
            throw error_t();
    }

    void disconnect(std::string const &addr) { disconnect(addr.c_str()); }

    void disconnect(const char *addr_)
    {
        int rc = zmq_disconnect(_handle, addr_);
        if (rc != 0)
            throw error_t();
    }

    bool connected() const ZMQ_NOTHROW { return (_handle != ZMQ_NULLPTR); }

#ifdef ZMQ_CPP11
    ZMQ_DEPRECATED("from 4.3.1, use send taking a const_buffer and send_flags")
#endif
    size_t send(const void *buf_, size_t len_, int flags_ = 0)
    {
        int nbytes = zmq_send(_handle, buf_, len_, flags_);
        if (nbytes >= 0)
            return static_cast<size_t>(nbytes);
        if (zmq_errno() == EAGAIN)
            return 0;
        throw error_t();
    }

#ifdef ZMQ_CPP11
    ZMQ_DEPRECATED("from 4.3.1, use send taking message_t and send_flags")
#endif
    bool send(message_t &msg_,
              int flags_ = 0) // default until removed
    {
        int nbytes = zmq_msg_send(msg_.handle(), _handle, flags_);
        if (nbytes >= 0)
            return true;
        if (zmq_errno() == EAGAIN)
            return false;
        throw error_t();
    }

    template<typename T> bool send(T first, T last, int flags_ = 0)
    {
        zmq::message_t msg(first, last);
        return send(msg, flags_);
    }

#ifdef ZMQ_HAS_RVALUE_REFS
#ifdef ZMQ_CPP11
    ZMQ_DEPRECATED("from 4.3.1, use send taking message_t and send_flags")
#endif
    bool send(message_t &&msg_,
              int flags_ = 0) // default until removed
    {
        #ifdef ZMQ_CPP11
        return send(msg_, static_cast<send_flags>(flags_)).has_value();
        #else
        return send(msg_, flags_);
        #endif
    }
#endif

#ifdef ZMQ_CPP11
    detail::send_result_t send(const_buffer buf, send_flags flags = send_flags::none)
    {
        const int nbytes =
          zmq_send(_handle, buf.data(), buf.size(), static_cast<int>(flags));
        if (nbytes >= 0)
            return static_cast<size_t>(nbytes);
        if (zmq_errno() == EAGAIN)
            return {};
        throw error_t();
    }

    detail::send_result_t send(message_t &msg, send_flags flags)
    {
        int nbytes = zmq_msg_send(msg.handle(), _handle, static_cast<int>(flags));
        if (nbytes >= 0)
            return static_cast<size_t>(nbytes);
        if (zmq_errno() == EAGAIN)
            return {};
        throw error_t();
    }

    detail::send_result_t send(message_t &&msg, send_flags flags)
    {
        return send(msg, flags);
    }
#endif

#ifdef ZMQ_CPP11
    ZMQ_DEPRECATED("from 4.3.1, use recv taking a mutable_buffer and recv_flags")
#endif
    size_t recv(void *buf_, size_t len_, int flags_ = 0)
    {
        int nbytes = zmq_recv(_handle, buf_, len_, flags_);
        if (nbytes >= 0)
            return static_cast<size_t>(nbytes);
        if (zmq_errno() == EAGAIN)
            return 0;
        throw error_t();
    }

#ifdef ZMQ_CPP11
    ZMQ_DEPRECATED("from 4.3.1, use recv taking a reference to message_t and recv_flags")
#endif
    bool recv(message_t *msg_, int flags_
#ifndef ZMQ_CPP11
              = 0
#endif
    )
    {
        int nbytes = zmq_msg_recv(msg_->handle(), _handle, flags_);
        if (nbytes >= 0)
            return true;
        if (zmq_errno() == EAGAIN)
            return false;
        throw error_t();
    }

#ifdef ZMQ_CPP11
    detail::recv_buffer_result_t recv(mutable_buffer buf,
                                      recv_flags flags = recv_flags::none)
    {
        const int nbytes =
          zmq_recv(_handle, buf.data(), buf.size(), static_cast<int>(flags));
        if (nbytes >= 0) {
            return recv_buffer_size{(std::min)(static_cast<size_t>(nbytes), buf.size()),
                                 static_cast<size_t>(nbytes)};
        }
        if (zmq_errno() == EAGAIN)
            return {};
        throw error_t();
    }

    detail::recv_result_t recv(message_t &msg, recv_flags flags = recv_flags::none)
    {
        const int nbytes = zmq_msg_recv(msg.handle(), _handle, static_cast<int>(flags));
        if (nbytes >= 0) {
            assert(msg.size() == static_cast<size_t>(nbytes));
            return static_cast<size_t>(nbytes);
        }
        if (zmq_errno() == EAGAIN)
            return {};
        throw error_t();
    }
#endif

#if defined(ZMQ_BUILD_DRAFT_API) && ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 0)
    void join(const char* group)
    {
        int rc = zmq_join(_handle, group);
        if (rc != 0)
            throw error_t();
    }

    void leave(const char* group)
    {
        int rc = zmq_leave(_handle, group);
        if (rc != 0)
            throw error_t();
    }
#endif

    ZMQ_NODISCARD void *handle() ZMQ_NOTHROW { return _handle; }
    ZMQ_NODISCARD const void *handle() const ZMQ_NOTHROW { return _handle; }

    ZMQ_EXPLICIT operator bool() const ZMQ_NOTHROW { return _handle != ZMQ_NULLPTR; }
    // note: non-const operator bool can be removed once
    // operator void* is removed from socket_t
    ZMQ_EXPLICIT operator bool() ZMQ_NOTHROW { return _handle != ZMQ_NULLPTR; }

protected:
    void *_handle;
};
} // namespace detail

#ifdef ZMQ_CPP11
enum class socket_type : int
{
    req = ZMQ_REQ,
    rep = ZMQ_REP,
    dealer = ZMQ_DEALER,
    router = ZMQ_ROUTER,
    pub = ZMQ_PUB,
    sub = ZMQ_SUB,
    xpub = ZMQ_XPUB,
    xsub = ZMQ_XSUB,
    push = ZMQ_PUSH,
    pull = ZMQ_PULL,
#if defined(ZMQ_BUILD_DRAFT_API) && ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 0)
    server = ZMQ_SERVER,
    client = ZMQ_CLIENT,
    radio = ZMQ_RADIO,
    dish = ZMQ_DISH,
#endif
#if ZMQ_VERSION_MAJOR >= 4
    stream = ZMQ_STREAM,
#endif
    pair = ZMQ_PAIR
};
#endif

struct from_handle_t
{
    struct _private {}; // disabling use other than with from_handle
    ZMQ_CONSTEXPR_FN ZMQ_EXPLICIT from_handle_t(_private /*p*/) ZMQ_NOTHROW {}
};

ZMQ_CONSTEXPR_VAR from_handle_t from_handle = from_handle_t(from_handle_t::_private());

// A non-owning nullable reference to a socket.
// The reference is invalidated on socket close or destruction.
class socket_ref : public detail::socket_base
{
  public:
    socket_ref() ZMQ_NOTHROW : detail::socket_base() {}
#ifdef ZMQ_CPP11
    socket_ref(std::nullptr_t) ZMQ_NOTHROW : detail::socket_base() {}
#endif
    socket_ref(from_handle_t /*fh*/, void *handle) ZMQ_NOTHROW
        : detail::socket_base(handle) {}
};

#ifdef ZMQ_CPP11
inline bool operator==(socket_ref sr, std::nullptr_t /*p*/) ZMQ_NOTHROW
{
    return sr.handle() == nullptr;
}
inline bool operator==(std::nullptr_t /*p*/, socket_ref sr) ZMQ_NOTHROW
{
    return sr.handle() == nullptr;
}
inline bool operator!=(socket_ref sr, std::nullptr_t /*p*/) ZMQ_NOTHROW
{
    return !(sr == nullptr);
}
inline bool operator!=(std::nullptr_t /*p*/, socket_ref sr) ZMQ_NOTHROW
{
    return !(sr == nullptr);
}
#endif

inline bool operator==(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return std::equal_to<void*>()(a.handle(), b.handle());
}
inline bool operator!=(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return !(a == b);
}
inline bool operator<(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return std::less<void*>()(a.handle(), b.handle());
}
inline bool operator>(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return b < a;
}
inline bool operator<=(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return !(a > b);
}
inline bool operator>=(socket_ref a, socket_ref b) ZMQ_NOTHROW
{
    return !(a < b);
}

} // namespace zmq

#ifdef ZMQ_CPP11
namespace std
{
template<>
struct hash<zmq::socket_ref>
{
    size_t operator()(zmq::socket_ref sr) const ZMQ_NOTHROW
    {
        return hash<void*>()(sr.handle());
    }
};
} // namespace std
#endif

namespace zmq
{

class socket_t : public detail::socket_base
{
    friend class monitor_t;

  public:
    socket_t() ZMQ_NOTHROW
      : detail::socket_base(ZMQ_NULLPTR)
      , ctxptr(ZMQ_NULLPTR)
    {
    }

    socket_t(context_t &context_, int type_)
        : detail::socket_base(zmq_socket(static_cast<void*>(context_), type_))
        , ctxptr(static_cast<void*>(context_))
    {
        if (_handle == ZMQ_NULLPTR)
            throw error_t();
    }

#ifdef ZMQ_CPP11
    socket_t(context_t &context_, socket_type type_)
        : socket_t(context_, static_cast<int>(type_))
    {
    }
#endif

#ifdef ZMQ_HAS_RVALUE_REFS
    socket_t(socket_t &&rhs) ZMQ_NOTHROW : detail::socket_base(rhs._handle), ctxptr(rhs.ctxptr)
    {
        rhs._handle = ZMQ_NULLPTR;
        rhs.ctxptr = ZMQ_NULLPTR;
    }
    socket_t &operator=(socket_t &&rhs) ZMQ_NOTHROW
    {
        std::swap(_handle, rhs._handle);
        return *this;
    }
#endif

    ~socket_t() ZMQ_NOTHROW { close(); }

    operator void *() ZMQ_NOTHROW { return _handle; }

    operator void const *() const ZMQ_NOTHROW { return _handle; }

    void close() ZMQ_NOTHROW
    {
        if (_handle == ZMQ_NULLPTR)
            // already closed
            return;
        int rc = zmq_close(_handle);
        ZMQ_ASSERT(rc == 0);
        _handle = ZMQ_NULLPTR;
    }

    void swap(socket_t &other) ZMQ_NOTHROW
    {
        std::swap(_handle, other._handle);
        std::swap(ctxptr, other.ctxptr);
    }

    operator socket_ref() ZMQ_NOTHROW
    {
        return socket_ref(from_handle, _handle);
    }

  private:
    void *ctxptr;

    socket_t(const socket_t &) ZMQ_DELETED_FUNCTION;
    void operator=(const socket_t &) ZMQ_DELETED_FUNCTION;

    // used by monitor_t
    socket_t(void *context_, int type_)
        : detail::socket_base(zmq_socket(context_, type_))
        , ctxptr(context_)
    {
        if (_handle == ZMQ_NULLPTR)
            throw error_t();
    }
};

inline void swap(socket_t &a, socket_t &b) ZMQ_NOTHROW {
    a.swap(b);
}

ZMQ_DEPRECATED("from 4.3.1, use proxy taking socket_t objects")
inline void proxy(void *frontend, void *backend, void *capture)
{
    int rc = zmq_proxy(frontend, backend, capture);
    if (rc != 0)
        throw error_t();
}

inline void
proxy(socket_ref frontend, socket_ref backend, socket_ref capture = socket_ref())
{
    int rc = zmq_proxy(frontend.handle(), backend.handle(), capture.handle());
    if (rc != 0)
        throw error_t();
}

#ifdef ZMQ_HAS_PROXY_STEERABLE
ZMQ_DEPRECATED("from 4.3.1, use proxy_steerable taking socket_t objects")
inline void
proxy_steerable(void *frontend, void *backend, void *capture, void *control)
{
    int rc = zmq_proxy_steerable(frontend, backend, capture, control);
    if (rc != 0)
        throw error_t();
}

inline void proxy_steerable(socket_ref frontend,
                            socket_ref backend,
                            socket_ref capture,
                            socket_ref control)
{
    int rc = zmq_proxy_steerable(frontend.handle(), backend.handle(),
                                 capture.handle(), control.handle());
    if (rc != 0)
        throw error_t();
}
#endif

class monitor_t
{
  public:
    monitor_t() : _socket(), _monitor_socket() {}

    virtual ~monitor_t()
    {
        close();
    }

#ifdef ZMQ_HAS_RVALUE_REFS
    monitor_t(monitor_t &&rhs) ZMQ_NOTHROW : _socket(), _monitor_socket()
    {
        std::swap(_socket, rhs._socket);
        std::swap(_monitor_socket, rhs._monitor_socket);
    }

    monitor_t &operator=(monitor_t &&rhs) ZMQ_NOTHROW
    {
        close();
        _socket = socket_ref();
        std::swap(_socket, rhs._socket);
        std::swap(_monitor_socket, rhs._monitor_socket);
        return *this;
    }
#endif


    void
    monitor(socket_t &socket, std::string const &addr, int events = ZMQ_EVENT_ALL)
    {
        monitor(socket, addr.c_str(), events);
    }

    void monitor(socket_t &socket, const char *addr_, int events = ZMQ_EVENT_ALL)
    {
        init(socket, addr_, events);
        while (true) {
            check_event(-1);
        }
    }

    void init(socket_t &socket, std::string const &addr, int events = ZMQ_EVENT_ALL)
    {
        init(socket, addr.c_str(), events);
    }

    void init(socket_t &socket, const char *addr_, int events = ZMQ_EVENT_ALL)
    {
        int rc = zmq_socket_monitor(socket.handle(), addr_, events);
        if (rc != 0)
            throw error_t();

        _socket = socket;
        _monitor_socket = socket_t(socket.ctxptr, ZMQ_PAIR);
        _monitor_socket.connect(addr_);

        on_monitor_started();
    }

    bool check_event(int timeout = 0)
    {
        assert(_monitor_socket);

        zmq_msg_t eventMsg;
        zmq_msg_init(&eventMsg);

        zmq::pollitem_t items[] = {
          {_monitor_socket.handle(), 0, ZMQ_POLLIN, 0},
        };

        zmq::poll(&items[0], 1, timeout);

        if (items[0].revents & ZMQ_POLLIN) {
            int rc = zmq_msg_recv(&eventMsg, _monitor_socket.handle(), 0);
            if (rc == -1 && zmq_errno() == ETERM)
                return false;
            assert(rc != -1);

        } else {
            zmq_msg_close(&eventMsg);
            return false;
        }

#if ZMQ_VERSION_MAJOR >= 4
        const char *data = static_cast<const char *>(zmq_msg_data(&eventMsg));
        zmq_event_t msgEvent;
        memcpy(&msgEvent.event, data, sizeof(uint16_t));
        data += sizeof(uint16_t);
        memcpy(&msgEvent.value, data, sizeof(int32_t));
        zmq_event_t *event = &msgEvent;
#else
        zmq_event_t *event = static_cast<zmq_event_t *>(zmq_msg_data(&eventMsg));
#endif

#ifdef ZMQ_NEW_MONITOR_EVENT_LAYOUT
        zmq_msg_t addrMsg;
        zmq_msg_init(&addrMsg);
        int rc = zmq_msg_recv(&addrMsg, _monitor_socket.handle(), 0);
        if (rc == -1 && zmq_errno() == ETERM) {
            zmq_msg_close(&eventMsg);
            return false;
        }

        assert(rc != -1);
        const char *str = static_cast<const char *>(zmq_msg_data(&addrMsg));
        std::string address(str, str + zmq_msg_size(&addrMsg));
        zmq_msg_close(&addrMsg);
#else
        // Bit of a hack, but all events in the zmq_event_t union have the same layout so this will work for all event types.
        std::string address = event->data.connected.addr;
#endif

#ifdef ZMQ_EVENT_MONITOR_STOPPED
        if (event->event == ZMQ_EVENT_MONITOR_STOPPED) {
            zmq_msg_close(&eventMsg);
            return false;
        }

#endif

        switch (event->event) {
            case ZMQ_EVENT_CONNECTED:
                on_event_connected(*event, address.c_str());
                break;
            case ZMQ_EVENT_CONNECT_DELAYED:
                on_event_connect_delayed(*event, address.c_str());
                break;
            case ZMQ_EVENT_CONNECT_RETRIED:
                on_event_connect_retried(*event, address.c_str());
                break;
            case ZMQ_EVENT_LISTENING:
                on_event_listening(*event, address.c_str());
                break;
            case ZMQ_EVENT_BIND_FAILED:
                on_event_bind_failed(*event, address.c_str());
                break;
            case ZMQ_EVENT_ACCEPTED:
                on_event_accepted(*event, address.c_str());
                break;
            case ZMQ_EVENT_ACCEPT_FAILED:
                on_event_accept_failed(*event, address.c_str());
                break;
            case ZMQ_EVENT_CLOSED:
                on_event_closed(*event, address.c_str());
                break;
            case ZMQ_EVENT_CLOSE_FAILED:
                on_event_close_failed(*event, address.c_str());
                break;
            case ZMQ_EVENT_DISCONNECTED:
                on_event_disconnected(*event, address.c_str());
                break;
#ifdef ZMQ_BUILD_DRAFT_API
#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 3)
            case ZMQ_EVENT_HANDSHAKE_FAILED_NO_DETAIL:
                on_event_handshake_failed_no_detail(*event, address.c_str());
                break;
            case ZMQ_EVENT_HANDSHAKE_FAILED_PROTOCOL:
                on_event_handshake_failed_protocol(*event, address.c_str());
                break;
            case ZMQ_EVENT_HANDSHAKE_FAILED_AUTH:
                on_event_handshake_failed_auth(*event, address.c_str());
                break;
            case ZMQ_EVENT_HANDSHAKE_SUCCEEDED:
                on_event_handshake_succeeded(*event, address.c_str());
                break;
#elif ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 1)
            case ZMQ_EVENT_HANDSHAKE_FAILED:
                on_event_handshake_failed(*event, address.c_str());
                break;
            case ZMQ_EVENT_HANDSHAKE_SUCCEED:
                on_event_handshake_succeed(*event, address.c_str());
                break;
#endif
#endif
            default:
                on_event_unknown(*event, address.c_str());
                break;
        }
        zmq_msg_close(&eventMsg);

        return true;
    }

#ifdef ZMQ_EVENT_MONITOR_STOPPED
    void abort()
    {
        if (_socket)
            zmq_socket_monitor(_socket.handle(), ZMQ_NULLPTR, 0);

        _socket = socket_ref();
    }
#endif
    virtual void on_monitor_started() {}
    virtual void on_event_connected(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_connect_delayed(const zmq_event_t &event_,
                                          const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_connect_retried(const zmq_event_t &event_,
                                          const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_listening(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_bind_failed(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_accepted(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_accept_failed(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_closed(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_close_failed(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_disconnected(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 3)
    virtual void on_event_handshake_failed_no_detail(const zmq_event_t &event_,
                                                     const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_handshake_failed_protocol(const zmq_event_t &event_,
                                                    const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_handshake_failed_auth(const zmq_event_t &event_,
                                                const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_handshake_succeeded(const zmq_event_t &event_,
                                              const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
#elif ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 1)
    virtual void on_event_handshake_failed(const zmq_event_t &event_,
                                           const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
    virtual void on_event_handshake_succeed(const zmq_event_t &event_,
                                            const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }
#endif
    virtual void on_event_unknown(const zmq_event_t &event_, const char *addr_)
    {
        (void) event_;
        (void) addr_;
    }

  private:
    monitor_t(const monitor_t &) ZMQ_DELETED_FUNCTION;
    void operator=(const monitor_t &) ZMQ_DELETED_FUNCTION;

    socket_ref _socket;
    socket_t _monitor_socket;

    void close() ZMQ_NOTHROW
    {
        if (_socket)
            zmq_socket_monitor(_socket.handle(), ZMQ_NULLPTR, 0);
        _monitor_socket.close();
    }
};

#if defined(ZMQ_BUILD_DRAFT_API) && defined(ZMQ_CPP11) && defined(ZMQ_HAVE_POLLER)

// polling events
enum class event_flags : short
{
    none = 0,
    pollin = ZMQ_POLLIN,
    pollout = ZMQ_POLLOUT,
    pollerr = ZMQ_POLLERR,
    pollpri = ZMQ_POLLPRI
};

constexpr event_flags operator|(event_flags a, event_flags b) noexcept
{
    return detail::enum_bit_or(a, b);
}
constexpr event_flags operator&(event_flags a, event_flags b) noexcept
{
    return detail::enum_bit_and(a, b);
}
constexpr event_flags operator^(event_flags a, event_flags b) noexcept
{
    return detail::enum_bit_xor(a, b);
}
constexpr event_flags operator~(event_flags a) noexcept
{
    return detail::enum_bit_not(a);
}

struct no_user_data;

// layout compatible with zmq_poller_event_t
template<class T = no_user_data>
struct poller_event
{
    socket_ref socket;
#ifdef _WIN32
    SOCKET fd;
#else
    int fd;
#endif
    T *user_data;
    event_flags events;
};

template<typename T = no_user_data> class poller_t
{
  public:
    using event_type = poller_event<T>;

    poller_t() : poller_ptr(zmq_poller_new())
    {
        if (!poller_ptr)
            throw error_t();
    }

    template<
      typename Dummy = void,
      typename =
        typename std::enable_if<!std::is_same<T, no_user_data>::value, Dummy>::type>
    void add(zmq::socket_ref socket, event_flags events, T *user_data)
    {
        add_impl(socket, events, user_data);
    }

    void add(zmq::socket_ref socket, event_flags events)
    {
        add_impl(socket, events, nullptr);
    }

    void remove(zmq::socket_ref socket)
    {
        if (0 != zmq_poller_remove(poller_ptr.get(), socket.handle())) {
            throw error_t();
        }
    }

    void modify(zmq::socket_ref socket, event_flags events)
    {
        if (0
            != zmq_poller_modify(poller_ptr.get(), socket.handle(),
                                 static_cast<short>(events))) {
            throw error_t();
        }
    }

    size_t wait_all(std::vector<event_type> &poller_events,
                    const std::chrono::milliseconds timeout)
    {
        int rc = zmq_poller_wait_all(
          poller_ptr.get(),
          reinterpret_cast<zmq_poller_event_t *>(poller_events.data()),
          static_cast<int>(poller_events.size()),
          static_cast<long>(timeout.count()));
        if (rc > 0)
            return static_cast<size_t>(rc);

#if ZMQ_VERSION >= ZMQ_MAKE_VERSION(4, 2, 3)
        if (zmq_errno() == EAGAIN)
#else
        if (zmq_errno() == ETIMEDOUT)
#endif
            return 0;

        throw error_t();
    }

  private:
    struct destroy_poller_t
    {
        void operator()(void *ptr) noexcept
        {
            int rc = zmq_poller_destroy(&ptr);
            ZMQ_ASSERT(rc == 0);
        }
    };

    std::unique_ptr<void, destroy_poller_t> poller_ptr;

    void add_impl(zmq::socket_ref socket, event_flags events, T *user_data)
    {
        if (0
            != zmq_poller_add(poller_ptr.get(), socket.handle(),
                              user_data, static_cast<short>(events))) {
            throw error_t();
        }
    }
};
#endif //  defined(ZMQ_BUILD_DRAFT_API) && defined(ZMQ_CPP11) && defined(ZMQ_HAVE_POLLER)

inline std::ostream &operator<<(std::ostream &os, const message_t &msg)
{
    return os << msg.str();
}

} // namespace zmq

#endif // __ZMQ_HPP_INCLUDED__