Provide a magic database to libmagic

Question

I've a simple C code that returns the filetype of the given file. I can give it any filename from the command line, and it will return the filetype:

#include <magic.h>
#include <stdio.h>

int main(int argc, char **argv) {
    unsigned modes = (
        MAGIC_MIME | MAGIC_CHECK |
        MAGIC_CONTINUE | MAGIC_SYMLINK
    ) ;

    struct magic_set *magic = magic_open(modes) ;

    // unsigned long value ;
    // magic_getparam(magic, MAGIC_PARAM_REGEX_MAX, &value) ;
    // printf("%ld\n", value) ;

    magic_load(magic, NULL) ;

    if(!argv[1]) return 1 ;

    const char *mm = magic_file(magic, argv[1]) ;

    if(mm < 0) {
        const char *err = magic_error(magic) ;
        puts(err) ;
        return 1 ;
    }

    puts(mm) ;
    magic_close(magic) ;
}

The problem is that I don't want to rely on the package file for this. And if I rename /usr/share/file/misc/magic.mgc to something else, it won't work. The manpage says that it's a compiled file, there could be just non-compiled database as well.

So I want to copy the file magic.mgc to a local directory and want to run the compiled program as it is.

Is it possible to pass a local magic database to the C program so that it doesn't rely on the database provided by the system?

Answer 1

So I can use this:

magic_load(magic, "/tmp/magic.mgc") ;

Assuming the file is in /tmp/ directory. I have seen that the mgc extension is important otherwise the program gets segfault.