os: add new function os.loginname(), improve some error messages (#9794)

vlib/builtin/cfns.c.v

@@ -267,7 +267,7 @@ fn C.wcslen(str &u16) int
 
 fn C.WideCharToMultiByte(codePage u32, dwFlags u32, lpWideCharStr &u16, cchWideChar int, lpMultiByteStr &char, cbMultiByte int, lpDefaultChar &char, lpUsedDefaultChar &int) int
 
-fn C._wstat(path &u16, buffer &C._stat)
+fn C._wstat(path &u16, buffer &C._stat) int
 
 fn C._wrename(oldname &u16, newname &u16) int
 

vlib/os/os_c.v

@@ -143,7 +143,7 @@ pub fn truncate(path string, len u64) ? {
 		C.close(fp)
 	}
 	if fp < 0 {
-		return error('open file failed')
+		return error_with_code(posix_get_error_msg(C.errno), C.errno)
 	}
 	$if windows {
 		if C._chsize_s(fp, len) != 0 {
@@ -165,10 +165,18 @@ pub fn file_size(path string) u64 {
 		$if x64 {
 			$if windows {
 				mut swin := C.__stat64{}
-				C._wstat64(&char(path.to_wide()), voidptr(&swin))
+				if C._wstat64(&char(path.to_wide()), voidptr(&swin)) != 0 {
+					eprintln('os.file_size() Cannot determine file-size: ' +
+						posix_get_error_msg(C.errno))
+					return 0
+				}
 				return swin.st_size
 			} $else {
-				C.stat(&char(path.str), &s)
+				if C.stat(&char(path.str), &s) != 0 {
+					eprintln('os.file_size() Cannot determine file-size: ' +
+						posix_get_error_msg(C.errno))
+					return 0
+				}
 				return u64(s.st_size)
 			}
 		}
@@ -177,10 +185,18 @@ pub fn file_size(path string) u64 {
 				println('Using os.file_size() on 32bit systems may not work on big files.')
 			}
 			$if windows {
-				C._wstat(path.to_wide(), voidptr(&s))
+				if C._wstat(path.to_wide(), voidptr(&s)) != 0 {
+					eprintln('os.file_size() Cannot determine file-size: ' +
+						posix_get_error_msg(C.errno))
+					return 0
+				}
 				return u64(s.st_size)
 			} $else {
-				C.stat(&char(path.str), &s)
+				if C.stat(&char(path.str), &s) != 0 {
+					eprintln('os.file_size() Cannot determine file-size: ' +
+						posix_get_error_msg(C.errno))
+					return 0
+				}
 				return u64(s.st_size)
 			}
 		}

vlib/os/os_nix.c.v

@@ -53,6 +53,8 @@ fn C.symlink(&char, &char) int
 
 fn C.gethostname(&char, int) int
 
+fn C.getlogin_r(&char, int) int
+
 pub fn uname() Uname {
 	mut u := Uname{}
 	utsize := sizeof(C.utsname)
@@ -83,6 +85,18 @@ pub fn hostname() string {
 	return ''
 }
 
+pub fn loginname() string {
+	mut lgnname := ''
+	size := 256
+	mut buf := unsafe { &char(malloc(size)) }
+	if C.getlogin_r(buf, size) == 0 {
+		lgnname = unsafe { cstring_to_vstring(buf) }
+		unsafe { free(buf) }
+		return lgnname
+	}
+	return ''
+}
+
 fn init_os_args(argc int, argv &&byte) []string {
 	mut args_ := []string{}
 	// mut args := []string(make(0, argc, sizeof(string)))

vlib/os/os_windows.c.v

@@ -394,6 +394,11 @@ pub fn hostname() string {
 	return execute('cmd /c hostname').output
 }
 
+pub fn loginname() string {
+	// TODO: use C.GetUserName(&char, u32) bool instead
+	return execute('cmd /c echo %USERNAME%').output
+}
+
 // `is_writable_folder` - `folder` exists and is writable to the process
 pub fn is_writable_folder(folder string) ?bool {
 	if !exists(folder) {