/*

    mtr  --  a network diagnostic tool

    Copyright (C) 2016  Matt Kimball

    This program is free software; you can redistribute it and/or modify

    it under the terms of the GNU General Public License version 2 as

    published by the Free Software Foundation.

    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License

    along with this program; if not, write to the Free Software

    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#include "command.h"

#include <errno.h>

#include <io.h>

#include <stdio.h>

/*

    A completion routine to be called by Windows when a read from

    the command stream has completed.

*/

static

void CALLBACK finish_read_command(

    DWORD status,

    DWORD size_read,

    OVERLAPPED * overlapped)

{

    struct command_buffer_t *buffer;

    char *read_position;

    /*

       hEvent is unusuaed by ReadFileEx, so we use it to pass

       our command_buffer structure.

     */

    buffer = (struct command_buffer_t *) overlapped->hEvent;

    if (status) {

        /*  When the stream is closed ERROR_BROKEN_PIPE will be the result  */

        if (status == ERROR_BROKEN_PIPE) {

            buffer->platform.pipe_open = false;

            return;

        }

        fprintf(stderr, "ReadFileEx completion failure %d\n", status);

        exit(EXIT_FAILURE);

    }

    /*  Copy from the overlapped I/O buffer to the incoming command buffer  */

    read_position =

        &buffer->incoming_buffer[buffer->incoming_read_position];

    memcpy(read_position, buffer->platform.overlapped_buffer, size_read);

    /*  Account for the newly read data  */

    buffer->incoming_read_position += size_read;

    buffer->platform.read_active = false;

}

/*

    An APC which does nothing, to be used only to wake from the current

    alertable wait.

*/

static

void CALLBACK empty_apc(

    ULONG * param)

{

}

/*  Wake from the next alertable wait without waiting for newly read data  */

static

void queue_empty_apc(

    void)

{

    if (QueueUserAPC((PAPCFUNC) empty_apc, GetCurrentThread(), 0) == 0) {

        fprintf(stderr, "Unexpected QueueUserAPC failure %d\n",

                GetLastError());

        exit(EXIT_FAILURE);

    }

}

/*  Start a new overlapped I/O read from the command stream  */

void start_read_command(

    struct command_buffer_t *buffer)

{

    HANDLE command_stream = (HANDLE) get_osfhandle(buffer->command_stream);

    int space_remaining =

        COMMAND_BUFFER_SIZE - buffer->incoming_read_position - 1;

    int err;

    /*  If a read is already active, or the pipe is closed, do nothing  */

    if (!buffer->platform.pipe_open || buffer->platform.read_active) {

        return;

    }

    memset(&buffer->platform.overlapped, 0, sizeof(OVERLAPPED));

    buffer->platform.overlapped.hEvent = (HANDLE) buffer;

    if (!ReadFileEx

        (command_stream, buffer->platform.overlapped_buffer,

         space_remaining, &buffer->platform.overlapped,

         finish_read_command)) {

        err = GetLastError();

        if (err == ERROR_BROKEN_PIPE) {

            /*  If the command stream has been closed, we need to wake from

               the next altertable wait to exit the main loop  */

            buffer->platform.pipe_open = false;

            queue_empty_apc();

            return;

        } else if (err != WAIT_IO_COMPLETION) {

            fprintf(stderr, "Unexpected ReadFileEx failure %d\n",

                    GetLastError());

            exit(EXIT_FAILURE);

        }

    }

    /*  Remember that we have started an overlapped read already  */

    buffer->platform.read_active = true;

}

/*  Initialize the command buffer, and start the first overlapped read  */

void init_command_buffer(

    struct command_buffer_t *command_buffer,

    int command_stream)

{

    memset(command_buffer, 0, sizeof(struct command_buffer_t));

    command_buffer->command_stream = command_stream;

    command_buffer->platform.pipe_open = true;

}

/*

    Return with errno EPIPE if the command stream has been closed.

    Otherwise, not much to do for Cygwin, since we are using Overlapped I/O

    to read commands.

*/

int read_commands(

    struct command_buffer_t *buffer)

{

    if (!buffer->platform.pipe_open) {

        errno = EPIPE;

        return -1;

    }

    return 0;

}