// ossig.h - written and placed in the public domain by Jeffrey Walton
//
//! \file ossig.h
//! \brief Utility class for trapping OS signals.
//! \since Crypto++ 5.6.5

#ifndef CRYPTOPP_OS_SIGNAL_H
#define CRYPTOPP_OS_SIGNAL_H

#include "config.h"

#if defined(UNIX_SIGNALS_AVAILABLE)
# include <signal.h>
#endif

NAMESPACE_BEGIN(CryptoPP)

// ************** Unix and Linux compatibles ***************

#if defined(UNIX_SIGNALS_AVAILABLE) || defined(CRYPTOPP_DOXYGEN_PROCESSING)

//! \brief Signal handler function pointer
//! \details SignalHandlerFn is provided as a stand alone function pointer with external "C" linkage
//! \sa SignalHandler, NullSignalHandler
extern "C" {
    typedef void (*SignalHandlerFn) (int);
};

//! \brief Null signal handler function
//! \param unused the signal number
//! \details NullSignalHandler is provided as a stand alone function with external "C" linkage
//!   and not a static member function due to the the member function's implicit
//!   external "C++" linkage.
//! \sa SignalHandler, SignalHandlerFn
extern "C" {
	inline void NullSignalHandler(int unused) {CRYPTOPP_UNUSED(unused);}
};

//! Signal handler for Linux and Unix compatibles
//! \tparam S Signal number
//! \tparam O Flag indicating exsting handler should be overwriiten
//! \details SignalHandler() can be used to install a signal handler with the signature
//!   <tt>void handler_fn(int)</tt>. If <tt>SignalHandlerFn</tt> is not <tt>NULL</tt>, then
//!   the sigaction is set to the function and the sigaction flags is set to the flags.
//!   If <tt>SignalHandlerFn</tt> is <tt>NULL</tt>, then a default handler is installed
//!   using sigaction flags set to 0. The default handler only returns from the call.
//! \details Upon destruction the previous signal handler is restored if the former signal handler
//!   was replaced.
//! \warning Do not use SignalHandler in a code block that uses <tt>setjmp</tt> or <tt>longjmp</tt>
//!   because the destructor may not run.
//! \since Crypto++ 5.6.5
//! \sa NullSignalHandler, SignalHandlerFn, \ref CRYPTOPP_ASSERT "CRYPTOPP_ASSERT", DebugTrapHandler
template <int S, bool O=false>
struct SignalHandler
{
    //! \brief Construct a signal handler
    //! \param pfn Pointer to a signal handler function
    //! \param flags Flags to use with the signal handler
    //! \details SignalHandler() installs a signal handler with the signature
    //!   <tt>void handler_fn(int)</tt>. If <tt>SignalHandlerFn</tt> is not <tt>NULL</tt>, then
    //!   the sigaction is set to the function and the sigaction flags is set to the flags.
    //!   If <tt>SignalHandlerFn</tt> is <tt>NULL</tt>, then a default handler is installed
    //!   using sigaction flags set to 0. The default handler only returns from the call.
    //! \details Upon destruction the previous signal handler is restored if the former signal handler
    //!   was overwritten.
    //! \warning Do not use SignalHandler in a code block that uses <tt>setjmp</tt> or <tt>longjmp</tt>
    //!   because the destructor may not run. <tt>setjmp</tt> is why cpu.cpp does not use SignalHandler
    //!   during CPU feature testing.
    //! \since Crypto++ 5.6.5
    SignalHandler(SignalHandlerFn pfn = NULL, int flags = 0) : m_installed(false)
    {
        // http://pubs.opengroup.org/onlinepubs/007908799/xsh/sigaction.html
        struct sigaction new_handler;

        do
        {
            int ret = 0;

            ret = sigaction (S, 0, &m_old);
            if (ret != 0) break; // Failed

            // Don't step on another's handler if Overwrite=false
            if (m_old.sa_handler != 0 && !O) break;

#if defined __CYGWIN__
            // http://github.com/weidai11/cryptopp/issues/315
            memset(&new_handler, 0x00, sizeof(new_handler));
#else
            ret = sigemptyset (&new_handler.sa_mask);
            if (ret != 0) break; // Failed
#endif

            new_handler.sa_handler = (pfn ? pfn : &NullSignalHandler);
            new_handler.sa_flags = (pfn ? flags : 0);

            // Install it
            ret = sigaction (S, &new_handler, 0);
            if (ret != 0) break; // Failed

            m_installed = true;

        } while(0);
    }

    ~SignalHandler()
    {
        if (m_installed)
            sigaction (S, &m_old, 0);
    }

private:
    struct sigaction m_old;
    bool m_installed;

private:
    // Not copyable
    SignalHandler(const SignalHandler &);
    void operator=(const SignalHandler &);
};
#endif

NAMESPACE_END

#endif // CRYPTOPP_OS_SIGNAL_H