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#define _GNU_SOURCE
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <limits.h>
#include <string.h>
#include <spawn.h>
#define MAX_REDIRECTS 128
static int nrRedirects = 0;
static char * from[MAX_REDIRECTS];
static char * to[MAX_REDIRECTS];
// FIXME: might run too late.
static void init() __attribute__((constructor));
static void init()
{
char * spec = getenv("NIX_REDIRECTS");
if (!spec) return;
unsetenv("NIX_REDIRECTS");
char * spec2 = malloc(strlen(spec) + 1);
strcpy(spec2, spec);
char * pos = spec2, * eq;
while ((eq = strchr(pos, '='))) {
*eq = 0;
from[nrRedirects] = pos;
pos = eq + 1;
to[nrRedirects] = pos;
nrRedirects++;
if (nrRedirects == MAX_REDIRECTS) break;
char * end = strchr(pos, ':');
if (!end) break;
*end = 0;
pos = end + 1;
}
}
static const char * rewrite(const char * path, char * buf)
{
if (path == NULL) return path;
for (int n = 0; n < nrRedirects; ++n) {
int len = strlen(from[n]);
if (strncmp(path, from[n], len) != 0) continue;
if (snprintf(buf, PATH_MAX, "%s%s", to[n], path + len) >= PATH_MAX)
abort();
return buf;
}
return path;
}
/* The following set of Glibc library functions is very incomplete -
it contains only what we needed for programs in Nixpkgs. Just add
more functions as needed. */
int open(const char * path, int flags, ...)
{
int (*open_real) (const char *, int, mode_t) = dlsym(RTLD_NEXT, "open");
mode_t mode = 0;
if (flags & O_CREAT) {
va_list ap;
va_start(ap, flags);
mode = va_arg(ap, mode_t);
va_end(ap);
}
char buf[PATH_MAX];
return open_real(rewrite(path, buf), flags, mode);
}
int open64(const char * path, int flags, ...)
{
int (*open64_real) (const char *, int, mode_t) = dlsym(RTLD_NEXT, "open64");
mode_t mode = 0;
if (flags & O_CREAT) {
va_list ap;
va_start(ap, flags);
mode = va_arg(ap, mode_t);
va_end(ap);
}
char buf[PATH_MAX];
return open64_real(rewrite(path, buf), flags, mode);
}
int openat(int dirfd, const char * path, int flags, ...)
{
int (*openat_real) (int, const char *, int, mode_t) = dlsym(RTLD_NEXT, "openat");
mode_t mode = 0;
if (flags & O_CREAT) {
va_list ap;
va_start(ap, flags);
mode = va_arg(ap, mode_t);
va_end(ap);
}
char buf[PATH_MAX];
return openat_real(dirfd, rewrite(path, buf), flags, mode);
}
FILE * fopen(const char * path, const char * mode)
{
FILE * (*fopen_real) (const char *, const char *) = dlsym(RTLD_NEXT, "fopen");
char buf[PATH_MAX];
return fopen_real(rewrite(path, buf), mode);
}
FILE * fopen64(const char * path, const char * mode)
{
FILE * (*fopen64_real) (const char *, const char *) = dlsym(RTLD_NEXT, "fopen64");
char buf[PATH_MAX];
return fopen64_real(rewrite(path, buf), mode);
}
int __xstat(int ver, const char * path, struct stat * st)
{
int (*__xstat_real) (int ver, const char *, struct stat *) = dlsym(RTLD_NEXT, "__xstat");
char buf[PATH_MAX];
return __xstat_real(ver, rewrite(path, buf), st);
}
int __xstat64(int ver, const char * path, struct stat64 * st)
{
int (*__xstat64_real) (int ver, const char *, struct stat64 *) = dlsym(RTLD_NEXT, "__xstat64");
char buf[PATH_MAX];
return __xstat64_real(ver, rewrite(path, buf), st);
}
int stat(const char * path, struct stat * st)
{
int (*__stat_real) (const char *, struct stat *) = dlsym(RTLD_NEXT, "stat");
char buf[PATH_MAX];
return __stat_real(rewrite(path, buf), st);
}
int * access(const char * path, int mode)
{
int * (*access_real) (const char *, int mode) = dlsym(RTLD_NEXT, "access");
char buf[PATH_MAX];
return access_real(rewrite(path, buf), mode);
}
int posix_spawn(pid_t * pid, const char * path,
const posix_spawn_file_actions_t * file_actions,
const posix_spawnattr_t * attrp,
char * const argv[], char * const envp[])
{
int (*posix_spawn_real) (pid_t *, const char *,
const posix_spawn_file_actions_t *,
const posix_spawnattr_t *,
char * const argv[], char * const envp[]) = dlsym(RTLD_NEXT, "posix_spawn");
char buf[PATH_MAX];
return posix_spawn_real(pid, rewrite(path, buf), file_actions, attrp, argv, envp);
}
int posix_spawnp(pid_t * pid, const char * file,
const posix_spawn_file_actions_t * file_actions,
const posix_spawnattr_t * attrp,
char * const argv[], char * const envp[])
{
int (*posix_spawnp_real) (pid_t *, const char *,
const posix_spawn_file_actions_t *,
const posix_spawnattr_t *,
char * const argv[], char * const envp[]) = dlsym(RTLD_NEXT, "posix_spawnp");
char buf[PATH_MAX];
return posix_spawnp_real(pid, rewrite(file, buf), file_actions, attrp, argv, envp);
}
int execv(const char *path, char *const argv[])
{
int (*execv_real) (const char *path, char *const argv[]) = dlsym(RTLD_NEXT, "execv");
char buf[PATH_MAX];
return execv_real(rewrite(path, buf), argv);
}
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