/*
VLC's libqt4_plugin.dll patcher

This program can patch VLC's libqt4_plugin.dll to solve the volume control problem.

Suggested usage:
cd path_to_VLC's_direcotry\plugins
mv libqt4_plugin.dll libqt4_plugin.dll.backup
path_to_this_program.exe libtq4_plugin.dll.backup libqt4_plugin.dll

Note: strings in this program don't use '\0' as terminate character.

Original python code (http://forum.videolan.org/viewtopic.php?f=14&t=79258&sid=d587667b82edc613b75b6d9e24dbbb13&start=20#p272045):

PATH_SRC = r'c:\program files\videolan\vlc\plugins\libqt4_plugin.dll'
PATH_DST = r'libqt4_plugin.dll'

src = open(PATH_SRC, 'rb')
data = src.read()
src.close()

s = 'unknown APPCOMMAND = %d\x00'
pos = data.index(s) + len(s)
if pos % 4 > 0:
    pos += 4 - pos % 4
t = data[pos + 32 : pos + 36]
data = data[:pos] + t * 3 + data[pos + 12:]

dst = open(PATH_DST, 'wb')
dst.write(data)
dst.close()
*/

#include <fcntl.h>
#include <io.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

/*
function to get a substring's position in a string, where strings have not terminate at \0
returns the substring's position in the string, or -1 if the substring not found
*/
int mystrstr(char *a,int na,char *b,int nb)
{
	int j;

	for(int i=0;i<na;i++)
	{
		for(j=0;j<nb;j++)
		{
			if(a[i+j]!=b[j])
			{
				break;
			}
		}

		if(j==nb)
		{
			return i;
		}
	}

	return -1;
}

int main(int argc,char *argv[])
{
	if(argc!=3)	//check arguments
	{
		printf("Parameters required: source destination\n");
		return 255;
	}
	
	int file=open(argv[1],O_RDONLY|O_BINARY);	//open original file for reading
	if(file==-1)
	{
		printf("Cannot open file for reading: \"%s\"\n",argv[1]);
		return 1;
	}

	struct stat filestat;
	fstat(file,&filestat);	//get filestats including filesize into filestat struct

	char *content=(char *)malloc(filestat.st_size);	//allocate memory to the file's contents
	if(content==NULL)
	{
		printf("Cannot allocate %d bytes of memory.\n",filestat.st_size);
		return 1;
	}

	read(file,content,filestat.st_size);	//read the whole file to content

	close(file);	//close the file
	
	int pos=mystrstr(content,filestat.st_size,"unknown APPCOMMAND = %d\x00",24)+24;	//get "magic string"'s position, 24 is the size of "unknown APPCOMMAND = %d\x00"
	if(pos==-1)
	{
		printf("The \"magic string\" not found.\n");
		return 1;
	}

	if(pos%4>0)	//pos have to be divisible by 4
	{
		pos+=4-(pos%4);
	}

	char *temp=(char *)malloc(4);	//allocate 4 bytes for temp string
	if(temp==NULL)
	{
		printf("Cannot allocate 4 bytes of memory.\n");
		return 1;
	}
	
	memcpy(temp,content+pos+32,4);	//get string into temp
	
	file=open(argv[2],O_WRONLY|O_BINARY|O_CREAT,S_IWRITE);	//open new file for writing
	if(file==-1)
	{
		printf("Cannot open file for writing: \"%s\"\n",argv[2]);
		return 1;
	}
	
	write(file,content,pos);	//writing out the first part
	
	for(int i=0;i<4;i++)	//writing out temp for 4 times
	{
		write(file,temp,4);
	}

	write(file,content+pos+16,filestat.st_size-pos-16);	//writing out the last part

	close(file);	//close file
	
	free(temp);	//freeing variables
	free(content);

	printf("Everything OK, file \"%s\" created from \"%s\" successfully.\n",argv[2],argv[1]);
	return 0;
}