path-mapping.c

#define _GNU_SOURCE

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <dlfcn.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdarg.h>
#include <malloc.h>

// List of path pairs. Paths beginning with the first item will be
// translated by replacing the matching part with the second item.
static const char *path_map[][2] = {
    { "/home/runningdroid/.recently-used", "/run/user/1000/recently-used" },
    { "/home/runningdroid/Desktop", "/run/user/1000/Desktop" },
    { "/home/runningdroid/.thumbnails", "/run/user/1000/thumbnails" },
    { "/home/runningdroid/.gstreamer-0.10", "/run/user/1000/gstreamer-0.10" },
    { "/home/runningdroid/.dbus", "/run/user/1000/dbus" },
    { "/home/runningdroid/.java", "/run/user/1000/java" },
    { "/home/runningdroid/.oracle_jre_usage", "/run/user/1000/oracle_jre_usage" },
    { "/home/runningdroid/.QtWebEngineProcess", "/run/user/1000/QtWebEngineProcess" },
    { "/home/runningdroid/.QupZilla", "/run/user/1000/QupZilla" },
    { "/home/runningdroid/.gnome", "/run/user/1000/gnome" },
    { "/home/runningdroid/.texlive", "/run/user/1000/texlive" },
    { "/home/runningdroid/.subversion", "/run/user/1000/subversion" },
};

__thread char *buffer = NULL;
__thread int buffer_size = -1;

typedef FILE* (*orig_fopen_func_type)(const char *path, const char *mode);
typedef int (*orig_open_func_type)(const char *pathname, int flags, ...);

static int starts_with(const char *str, const char *prefix) {
    return (strncmp(prefix, str, strlen(prefix)) == 0);
}

static char *get_buffer(int min_size) {
    int step = 63;
    if (min_size < 1) {
        min_size = 1;
    }
    if (min_size > buffer_size) {
        if (buffer != NULL) {
            free(buffer);
            buffer = NULL;
            buffer_size = -1;
        }
        buffer = malloc(min_size + step);
        if (buffer != NULL) {
            buffer_size = min_size + step;
        }
    }
    return buffer;
}

static const char *fix_path(const char *path)
{
    int count = (sizeof path_map) / (sizeof *path_map); // Array length
    for (int i = 0; i < count; i++) {
        const char *prefix = path_map[i][0];
        const char *replace = path_map[i][1];
        if (starts_with(path, prefix)) {
            const char *rest = path + strlen(prefix);
            char *new_path = get_buffer(strlen(path) + strlen(replace) - strlen(prefix));
            strcpy(new_path, replace);
            strcat(new_path, rest);
            printf("Mapped Path: %s  ==>  %s\n", path, new_path);
            return new_path;
        }
    }
    return path;
}


int open(const char *pathname, int flags, ...)
{
    const char *new_path = fix_path(pathname);

    orig_open_func_type orig_func;
    orig_func = (orig_open_func_type)dlsym(RTLD_NEXT, "open");

    // If O_CREAT is used to create a file, the file access mode must be given.
    if (flags & O_CREAT) {
        va_list args;
        va_start(args, flags);
        int mode = va_arg(args, int);
        va_end(args);
        return orig_func(new_path, flags, mode);
    } else {
        return orig_func(new_path, flags);
    }
}

int open64(const char *pathname, int flags, ...)
{
    const char *new_path = fix_path(pathname);

    orig_open_func_type orig_func;
    orig_func = (orig_open_func_type)dlsym(RTLD_NEXT, "open64");

    // If O_CREAT is used to create a file, the file access mode must be given.
    if (flags & O_CREAT) {
        va_list args;
        va_start(args, flags);
        int mode = va_arg(args, int);
        va_end(args);
        return orig_func(new_path, flags, mode);
    } else {
        return orig_func(new_path, flags);
    }
}