/***************************************************************************
 * nbase_winunix.h -- Background code that allows checking for input on    *
 * stdin on Windows without blocking.                                      *
 *                                                                         *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *                                                                         *
 * The Nmap Security Scanner is (C) 1996-2017 Insecure.Com LLC ("The Nmap  *
 * Project"). Nmap is also a registered trademark of the Nmap Project.     *
 * This program is free software; you may redistribute and/or modify it    *
 * under the terms of the GNU General Public License as published by the   *
 * Free Software Foundation; Version 2 ("GPL"), BUT ONLY WITH ALL OF THE   *
 * CLARIFICATIONS AND EXCEPTIONS DESCRIBED HEREIN.  This guarantees your   *
 * right to use, modify, and redistribute this software under certain      *
 * conditions.  If you wish to embed Nmap technology into proprietary      *
 * software, we sell alternative licenses (contact sales@nmap.com).        *
 * Dozens of software vendors already license Nmap technology such as      *
 * host discovery, port scanning, OS detection, version detection, and     *
 * the Nmap Scripting Engine.                                              *
 *                                                                         *
 * Note that the GPL places important restrictions on "derivative works",  *
 * yet it does not provide a detailed definition of that term.  To avoid   *
 * misunderstandings, we interpret that term as broadly as copyright law   *
 * allows.  For example, we consider an application to constitute a        *
 * derivative work for the purpose of this license if it does any of the   *
 * following with any software or content covered by this license          *
 * ("Covered Software"):                                                   *
 *                                                                         *
 * o Integrates source code from Covered Software.                         *
 *                                                                         *
 * o Reads or includes copyrighted data files, such as Nmap's nmap-os-db   *
 * or nmap-service-probes.                                                 *
 *                                                                         *
 * o Is designed specifically to execute Covered Software and parse the    *
 * results (as opposed to typical shell or execution-menu apps, which will *
 * execute anything you tell them to).                                     *
 *                                                                         *
 * o Includes Covered Software in a proprietary executable installer.  The *
 * installers produced by InstallShield are an example of this.  Including *
 * Nmap with other software in compressed or archival form does not        *
 * trigger this provision, provided appropriate open source decompression  *
 * or de-archiving software is widely available for no charge.  For the    *
 * purposes of this license, an installer is considered to include Covered *
 * Software even if it actually retrieves a copy of Covered Software from  *
 * another source during runtime (such as by downloading it from the       *
 * Internet).                                                              *
 *                                                                         *
 * o Links (statically or dynamically) to a library which does any of the  *
 * above.                                                                  *
 *                                                                         *
 * o Executes a helper program, module, or script to do any of the above.  *
 *                                                                         *
 * This list is not exclusive, but is meant to clarify our interpretation  *
 * of derived works with some common examples.  Other people may interpret *
 * the plain GPL differently, so we consider this a special exception to   *
 * the GPL that we apply to Covered Software.  Works which meet any of     *
 * these conditions must conform to all of the terms of this license,      *
 * particularly including the GPL Section 3 requirements of providing      *
 * source code and allowing free redistribution of the work as a whole.    *
 *                                                                         *
 * As another special exception to the GPL terms, the Nmap Project grants  *
 * permission to link the code of this program with any version of the     *
 * OpenSSL library which is distributed under a license identical to that  *
 * listed in the included docs/licenses/OpenSSL.txt file, and distribute   *
 * linked combinations including the two.                                  *
 *                                                                         *
 * The Nmap Project has permission to redistribute Npcap, a packet         *
 * capturing driver and library for the Microsoft Windows platform.        *
 * Npcap is a separate work with it's own license rather than this Nmap    *
 * license.  Since the Npcap license does not permit redistribution        *
 * without special permission, our Nmap Windows binary packages which      *
 * contain Npcap may not be redistributed without special permission.      *
 *                                                                         *
 * Any redistribution of Covered Software, including any derived works,    *
 * must obey and carry forward all of the terms of this license, including *
 * obeying all GPL rules and restrictions.  For example, source code of    *
 * the whole work must be provided and free redistribution must be         *
 * allowed.  All GPL references to "this License", are to be treated as    *
 * including the terms and conditions of this license text as well.        *
 *                                                                         *
 * Because this license imposes special exceptions to the GPL, Covered     *
 * Work may not be combined (even as part of a larger work) with plain GPL *
 * software.  The terms, conditions, and exceptions of this license must   *
 * be included as well.  This license is incompatible with some other open *
 * source licenses as well.  In some cases we can relicense portions of    *
 * Nmap or grant special permissions to use it in other open source        *
 * software.  Please contact fyodor@nmap.org with any such requests.       *
 * Similarly, we don't incorporate incompatible open source software into  *
 * Covered Software without special permission from the copyright holders. *
 *                                                                         *
 * If you have any questions about the licensing restrictions on using     *
 * Nmap in other works, are happy to help.  As mentioned above, we also    *
 * offer alternative license to integrate Nmap into proprietary            *
 * applications and appliances.  These contracts have been sold to dozens  *
 * of software vendors, and generally include a perpetual license as well  *
 * as providing for priority support and updates.  They also fund the      *
 * continued development of Nmap.  Please email sales@nmap.com for further *
 * information.                                                            *
 *                                                                         *
 * If you have received a written license agreement or contract for        *
 * Covered Software stating terms other than these, you may choose to use  *
 * and redistribute Covered Software under those terms instead of these.   *
 *                                                                         *
 * Source is provided to this software because we believe users have a     *
 * right to know exactly what a program is going to do before they run it. *
 * This also allows you to audit the software for security holes.          *
 *                                                                         *
 * Source code also allows you to port Nmap to new platforms, fix bugs,    *
 * and add new features.  You are highly encouraged to send your changes   *
 * to the dev@nmap.org mailing list for possible incorporation into the    *
 * main distribution.  By sending these changes to Fyodor or one of the    *
 * Insecure.Org development mailing lists, or checking them into the Nmap  *
 * source code repository, it is understood (unless you specify            *
 * otherwise) that you are offering the Nmap Project the unlimited,        *
 * non-exclusive right to reuse, modify, and relicense the code.  Nmap     *
 * will always be available Open Source, but this is important because     *
 * the inability to relicense code has caused devastating problems for     *
 * other Free Software projects (such as KDE and NASM).  We also           *
 * occasionally relicense the code to third parties as discussed above.    *
 * If you wish to specify special license conditions of your               *
 * contributions, just say so when you send them.                          *
 *                                                                         *
 * 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 Nmap      *
 * license file for more details (it's in a COPYING file included with     *
 * Nmap, and also available from https://svn.nmap.org/nmap/COPYING)        *
 *                                                                         *
 ***************************************************************************/

/* $Id$ */

#include <assert.h>

#include "nbase.h"

#include "nbase_winunix.h"

/*
This code makes it possible to check for input on stdin on Windows without
blocking. There are two obstacles that need to be overcome. The first is that
select on Windows works for sockets only, not stdin. The other is that the
Windows command shell doesn't echo typed characters to the screen unless the
program is actively reading from stdin (which would normally mean blocking).

The strategy is to create a background thread that constantly reads from stdin.
The thread blocks while reading, which lets characters be echoed. The thread
writes each block of data into an anonymous pipe. We juggle file descriptors and
Windows file handles to make the rest of the program think that the other end of
the pipe is stdin. Only the thread keeps a reference to the real stdin. Windows
has a PeekNamedPipe function that we use to check for input in the pipe without
blocking.

Call win_stdin_start_thread to start the thread and win_stdin_ready for the
non-blocking input check. Any other operations on stdin (read, scanf, etc.)
should be transparent, except I noticed that eof(0) returns 1 when there is
nothing in the pipe, but will return 0 again if more is written to the pipe. Any
data buffered but not delivered to the program before starting the background
thread may be lost when the thread is started.
*/

/* The background thread that reads and buffers the true stdin. */
static HANDLE stdin_thread = NULL;

/* This is a copy of the true stdin file handle before any redirection. It is
   read by the thread. */
static HANDLE thread_stdin_handle = NULL;
/* The thread writes to this pipe and standard input is reassigned to be the
   read end of it. */
static HANDLE stdin_pipe_r = NULL, stdin_pipe_w = NULL;

/* This is the thread that reads from the true stdin (thread_stdin_handle) and
   writes to stdin_pipe_w, which is reassigned to be the stdin that the rest of
   the program sees. Once started, it never finishes except in case of error.
   win_stdin_start_thread is responsible for setting up thread_stdin_handle. */
static DWORD WINAPI win_stdin_thread_func(void *data) {
    DWORD n, nwritten;
    char buffer[BUFSIZ];

    for (;;) {
        if (ReadFile(thread_stdin_handle, buffer, sizeof(buffer), &n, NULL) == 0)
            break;
        if (n == -1 || n == 0)
            break;

        if (WriteFile(stdin_pipe_w, buffer, n, &nwritten, NULL) == 0)
            break;
        if (nwritten != n)
            break;
    }
    CloseHandle(thread_stdin_handle);
    CloseHandle(stdin_pipe_w);

    return 0;
}

/* Get the newline translation mode (_O_TEXT or _O_BINARY) of a file
   descriptor. _O_TEXT does CRLF-LF translation and _O_BINARY does none.
   Complementary to _setmode. */
static int _getmode(int fd)
{
    int mode;

    /* There is no standard _getmode function, but _setmode returns the
       previous value. Set it to a dummy value and set it back. */
    mode = _setmode(fd, _O_BINARY);
    _setmode(fd, mode);

    return mode;
}

/* Start the reader thread and do all the file handle/descriptor redirection.
   Returns nonzero on success, zero on error. */
int win_stdin_start_thread(void) {
    int stdin_fd;
    int stdin_fmode;

    assert(stdin_thread == NULL);
    assert(stdin_pipe_r == NULL);
    assert(stdin_pipe_w == NULL);
    assert(thread_stdin_handle == NULL);

    /* Create the pipe that win_stdin_thread_func writes to. We reassign the
       read end to be the new stdin that the rest of the program sees. */
    if (CreatePipe(&stdin_pipe_r, &stdin_pipe_w, NULL, 0) == 0)
        return 0;

    /* Make a copy of the stdin handle to be used by win_stdin_thread_func.  It
       will remain a reference to the the true stdin after we fake stdin to read
       from the pipe instead. */
    if (DuplicateHandle(GetCurrentProcess(), GetStdHandle(STD_INPUT_HANDLE),
                        GetCurrentProcess(), &thread_stdin_handle,
                        0, FALSE, DUPLICATE_SAME_ACCESS) == 0) {
        CloseHandle(stdin_pipe_r);
        CloseHandle(stdin_pipe_w);
        return 0;
    }

    /* Set the stdin handle to read from the pipe. */
    if (SetStdHandle(STD_INPUT_HANDLE, stdin_pipe_r) == 0) {
        CloseHandle(stdin_pipe_r);
        CloseHandle(stdin_pipe_w);
        CloseHandle(thread_stdin_handle);
        return 0;
    }
    /* Need to redirect file descriptor 0 also. _open_osfhandle makes a new file
       descriptor from an existing handle. */
    /* Remember the newline translation mode (_O_TEXT or _O_BINARY), and
       restore it in the new file descriptor. */
    stdin_fmode = _getmode(STDIN_FILENO);
    stdin_fd = _open_osfhandle((intptr_t) GetStdHandle(STD_INPUT_HANDLE), _O_RDONLY | stdin_fmode);
    if (stdin_fd == -1) {
        CloseHandle(stdin_pipe_r);
        CloseHandle(stdin_pipe_w);
        CloseHandle(thread_stdin_handle);
        return 0;
    }
    dup2(stdin_fd, STDIN_FILENO);

    /* Finally, start up the thread. We don't bother keeping a reference to it
       because it runs until program termination. From here on out all reads
       from the stdin handle or file descriptor 0 will be reading from the
       anonymous pipe that is fed by the thread. */
    stdin_thread = CreateThread(NULL, 0, win_stdin_thread_func, NULL, 0, NULL);
    if (stdin_thread == NULL) {
        CloseHandle(stdin_pipe_r);
        CloseHandle(stdin_pipe_w);
        CloseHandle(thread_stdin_handle);
        return 0;
    }

    return 1;
}

/* Check if input is available on stdin, once all the above has taken place. */
int win_stdin_ready(void) {
    DWORD n;

    assert(stdin_pipe_r != NULL);

    if (!PeekNamedPipe(stdin_pipe_r, NULL, 0, NULL, &n, NULL))
        return 1;

    return n > 0;
}
