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/* Brgen4 search for configuration under `/etc/opt/brother/scanner/brscan4`. This
LD_PRELOAD library intercepts execvp(), open and open64 calls to redirect them to
the corresponding location in $out. Also support specifying an alternate
file name for `brsanenetdevice4.cfg` which otherwise is invariable
created at `/etc/opt/brother/scanner/brscan4`*/
#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 <dirent.h>
char origDir [] = "/etc/opt/brother/scanner/brscan4";
char realDir [] = OUT "/opt/brother/scanner/brscan4";
char devCfgFileNameEnvVar [] = "BRSANENETDEVICE4_CFG_FILENAME";
char devCfgFileName [] = "/etc/opt/brother/scanner/brscan4//brsanenetdevice4.cfg";
const char * rewrite(const char * path, char * buf)
{
if (strncmp(path, devCfgFileName, sizeof(devCfgFileName)) == 0) {
const char* newCfgFileName = getenv(devCfgFileNameEnvVar);
if (!newCfgFileName) return path;
if (snprintf(buf, PATH_MAX, "%s", newCfgFileName) >= PATH_MAX)
abort();
return buf;
}
if (strncmp(path, origDir, sizeof(origDir) - 1) != 0) return path;
if (snprintf(buf, PATH_MAX, "%s%s", realDir, path + sizeof(origDir) - 1) >= PATH_MAX)
abort();
return buf;
}
const char* findAndReplaceFirstOccurence(const char* inStr, const char* subStr,
const char* replaceStr,
char* buf, unsigned maxBuf)
{
const char* foundStr = strstr(inStr, subStr);
if (!foundStr)
return inStr;
const unsigned inStrLen = strlen(inStr);
const unsigned subStrLen = strlen(subStr);
const unsigned replaceStrLen = strlen(replaceStr);
const unsigned precedingStrLen = foundStr - inStr;
if (precedingStrLen + 1 > maxBuf)
return NULL;
const unsigned followingStrPos = precedingStrLen + subStrLen;
const unsigned followingStrLen = inStrLen - followingStrPos;
strncpy(buf, inStr, precedingStrLen);
unsigned outLength = precedingStrLen;
if (outLength + replaceStrLen + 1 > maxBuf)
return NULL;
strncpy(buf + outLength, replaceStr, replaceStrLen);
outLength += replaceStrLen;
if (outLength + followingStrLen + 1 > maxBuf)
return NULL;
strncpy(buf + outLength, inStr + followingStrPos, followingStrLen);
outLength += followingStrLen;
buf[outLength] = '\0';
return buf;
}
const char* rewriteSystemCall(const char* command, char* buf, unsigned maxBuf)
{
const char* foundStr = strstr(command, devCfgFileName);
if (!foundStr)
return command;
const char* replaceStr = getenv(devCfgFileNameEnvVar);
if (!replaceStr) return command;
const char* result =
findAndReplaceFirstOccurence(command, devCfgFileName, replaceStr, buf, maxBuf);
if (!result)
abort();
return result;
}
int execvp(const char * path, char * const argv[])
{
int (*_execvp) (const char *, char * const argv[]) = dlsym(RTLD_NEXT, "execvp");
char buf[PATH_MAX];
return _execvp(rewrite(path, buf), argv);
}
int open(const char *path, int flags, ...)
{
char buf[PATH_MAX];
int (*_open) (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);
}
return _open(rewrite(path, buf), flags, mode);
}
int open64(const char *path, int flags, ...)
{
char buf[PATH_MAX];
int (*_open64) (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);
}
return _open64(rewrite(path, buf), flags, mode);
}
FILE* fopen(const char* path, const char* mode)
{
char buf[PATH_MAX];
FILE* (*_fopen) (const char*, const char*) = dlsym(RTLD_NEXT, "fopen");
return _fopen(rewrite(path, buf), mode);
}
FILE *fopen64(const char *path, const char *mode)
{
char buf[PATH_MAX];
FILE* (*_fopen64) (const char*, const char*) = dlsym(RTLD_NEXT, "fopen64");
return _fopen64(rewrite(path, buf), mode);
}
DIR* opendir(const char* path)
{
char buf[PATH_MAX];
DIR* (*_opendir) (const char*) = dlsym(RTLD_NEXT, "opendir");
return _opendir(rewrite(path, buf));
}
#define SYSTEM_CMD_MAX 512
int system(const char *command)
{
char buf[SYSTEM_CMD_MAX];
int (*_system) (const char*) = dlsym(RTLD_NEXT, "system");
const char* newCommand = rewriteSystemCall(command, buf, SYSTEM_CMD_MAX);
return _system(newCommand);
}
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