nativelibc/readlink.c

/*	A part of the Native C Library for Windows NT
	Copyright 2007-2015 PC GO Ld.
	Copyright 2015-2024 Rivoreo

	This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

	This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
*/

#include <windows.h>
#include <nt.h>
#include <errno.h>
#include <pathname.h>
#include <ntstatus.h>
#include <assert.h>

//#include <stdio.h>

int readlink(const char *path, char *buffer, size_t size) {
	//printf("function: readlink(%p<%s>, %p, %lu)\n", path, path, buffer, (long int)size);
	if(!path || !buffer) {
		errno = EFAULT;
		return -1;
	}
	if(!size) {
		errno = EINVAL;
		return -1;
	}
	if(!*path) {
		errno = ENOENT;
		return -1;
	}

	UNICODE_STRING wpath;
	if(!RtlCreateUnicodeStringFromAsciiz(&wpath, path)) {
		errno = ENOMEM;
		return -1;
	}
	PATHNAME_UNIX2NT_UTF16_STRUCT(wpath);
	OBJECT_ATTRIBUTES object_attribute = { sizeof(OBJECT_ATTRIBUTES), NULL, &wpath, 0, NULL, NULL };
	void *handle;
	long int status = NtOpenSymbolicLinkObject(&handle, GENERIC_READ, &object_attribute);
	RtlFreeUnicodeString(&wpath);
	if(status < 0) {
		__set_errno_from_ntstatus(status);
		return -1;
	}
	UNICODE_STRING rpath = { size * sizeof(wchar_t), (size + 1) * sizeof(wchar_t), malloc((size + 1) * sizeof(wchar_t)) };
	if(!rpath.Buffer) {
		NtClose(handle);
		errno = ENOMEM;
		return -1;
	}
	char tmp_buffer[size * 2];
	unsigned long int rsize;		// Size of the wide char string including L'\0' (MaximumLength)
	status = NtQuerySymbolicLinkObject(handle, &rpath, &rsize);
	if(status == STATUS_BUFFER_TOO_SMALL) {
		UNICODE_STRING tpath = { rsize - sizeof(wchar_t), rsize, malloc(rsize) };
		if(!tpath.Buffer) {
			free(rpath.Buffer);
			NtClose(handle);
			errno = ENOMEM;
			return -1;
		}
		status = NtQuerySymbolicLinkObject(handle, &tpath, NULL);
		if(status < 0) goto failed;
		memcpy(rpath.Buffer, tpath.Buffer, rpath.Length);
		rpath.Buffer[rpath.Length / sizeof(wchar_t)] = 0;
		rsize = rpath.MaximumLength;
		free(tpath.Buffer);
	} else if(status < 0) {
failed:
		free(rpath.Buffer);
		NtClose(handle);
		__set_errno_from_ntstatus(status);
		return -1;
	}
	NtClose(handle);
	assert(rsize / 2 - 1 <= size);
	PATHNAME_NT2UNIX_UTF16_STRUCT(rpath);
	int r = wcstombs(tmp_buffer, rpath.Buffer, rsize * 2);
	//printf("nativelibc debug: r = %d\n", r);
	free(rpath.Buffer);
	if(r < 0) r = 0;
	memcpy(buffer, tmp_buffer, r);
	assert(r <= size);
	return r;
}