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Rework Windows implementation of g_getenv()

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Fixes the following issues:

1. g_getenv didn't properly differentiate between non-exisiting variables
   and variables with empty values. This happened bacause we didn't call
   SetLastError (0) before GetEnvironmentVariable (as with most APIs,
   GetEnvironmentVariable doesn't set the error code to 0 on success).

2. g_getenv called GetEnvironmentVariable, g_free, and GetLastError in sequence;
   the call to g_free could change the last error code.

3. We can use the looping pattern to call APIs that return the required buffer
   size. The looping pattern makes the two phases (get size and retrieve value)
   appear as just one call. It's also important for values that can change at any
   time like environment variables [1].

[1] https://devblogs.microsoft.com/oldnewthing/20220302-00/?p=106303
This commit is contained in:
Luca Bacci
2025-05-12 14:23:10 +02:00
parent 314d63fcf7
commit 01454b823b
1 changed files with 87 additions and 54 deletions
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141
glib/genviron.c
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@@ -448,81 +448,114 @@ g_get_environ (void)
}
/* Win32 implementation {{{1 */
#else /* G_OS_WIN32 */
#else /* G_OS_WIN32 */
static wchar_t *
expand_environment_string (const wchar_t *string_utf16)
{
wchar_t *expanded = NULL;
DWORD previous_wchars_count = 0;
DWORD wchars_count = 0;
do
{
previous_wchars_count = wchars_count;
expanded = g_renew (wchar_t, expanded, wchars_count);
/* Note: ExpandEnvironmentStrings is 1-pass only. In addition, placeholders
* referring to non-existing variables are kept as-is, they aren't removed.
* That differs e.g from CMD. */
wchars_count = ExpandEnvironmentStrings (string_utf16, expanded, wchars_count);
}
while (wchars_count > previous_wchars_count);
if (wchars_count == 0)
{
g_warning ("%s failed with error code %u",
"ExpandEnvironmentStrings", (unsigned int) GetLastError ());
g_clear_pointer (&expanded, g_free);
}
return expanded;
}
const gchar *
g_getenv (const gchar *variable)
{
GQuark quark;
gchar *value;
wchar_t dummy[2], *wname, *wvalue;
DWORD len;
wchar_t *name_utf16 = NULL;
wchar_t *value_utf16 = NULL;
DWORD previous_wchars_count = 0;
DWORD wchars_count = 0;
char *value_utf8 = NULL;
GQuark quark = 0;
g_return_val_if_fail (variable != NULL, NULL);
g_return_val_if_fail (g_utf8_validate (variable, -1, NULL), NULL);
/* On Windows NT, it is relatively typical that environment
* variables contain references to other environment variables. If
* so, use ExpandEnvironmentStrings(). (In an ideal world, such
* environment variables would be stored in the Registry as
* REG_EXPAND_SZ type values, and would then get automatically
* expanded before a program sees them. But there is broken software
* that stores environment variables as REG_SZ values even if they
* contain references to other environment variables.)
*/
name_utf16 = g_utf8_to_utf16 (variable, -1, NULL, NULL, NULL);
g_assert (name_utf16);
wname = g_utf8_to_utf16 (variable, -1, NULL, NULL, NULL);
len = GetEnvironmentVariableW (wname, dummy, 2);
if (len == 0)
do
{
g_free (wname);
if (GetLastError () == ERROR_ENVVAR_NOT_FOUND)
return NULL;
value_utf16 = g_renew (wchar_t, value_utf16, wchars_count);
quark = g_quark_from_static_string ("");
return g_quark_to_string (quark);
previous_wchars_count = wchars_count;
SetLastError (ERROR_SUCCESS);
wchars_count = GetEnvironmentVariable (name_utf16, value_utf16, wchars_count);
}
else if (len == 1)
len = 2;
while (wchars_count > previous_wchars_count);
wvalue = g_new (wchar_t, len);
if (GetEnvironmentVariableW (wname, wvalue, len) != len - 1)
if (wchars_count == 0)
{
g_free (wname);
g_free (wvalue);
return NULL;
}
DWORD code = GetLastError ();
if (wcschr (wvalue, L'%') != NULL)
{
wchar_t *tem = wvalue;
len = ExpandEnvironmentStringsW (wvalue, dummy, 2);
if (len > 0)
if (code == ERROR_SUCCESS)
{
wvalue = g_new (wchar_t, len);
/* Value is an empty string */
quark = g_quark_from_static_string ("");
}
else if (code == ERROR_ENVVAR_NOT_FOUND)
{
/* The variable doesn't exist */
}
else
{
g_warning ("%s failed with error code %u",
"GetEnvironmentVariable", (unsigned int) GetLastError ());
}
}
else
{
g_assert (wchars_count != previous_wchars_count);
g_assert (value_utf16[wchars_count] == L'\0');
if (ExpandEnvironmentStringsW (tem, wvalue, len) != len)
{
g_free (wvalue);
wvalue = tem;
}
/* On Windows NT, it is relatively typical that environment
* variables contain references to other environment variables.
* If so, use ExpandEnvironmentStrings() */
if (wcschr (value_utf16, L'%'))
{
wchar_t *expanded = expand_environment_string (value_utf16);
g_free (value_utf16);
value_utf16 = expanded;
}
if (value_utf16)
{
value_utf8 = g_utf16_to_utf8 (value_utf16, -1, NULL, NULL, NULL);
if (value_utf8 == NULL)
g_warning ("Environment variable `%s' contains invalid UTF-16", variable);
else
g_free (tem);
quark = g_quark_from_string (value_utf8);
}
}
value = g_utf16_to_utf8 (wvalue, -1, NULL, NULL, NULL);
g_free (wname);
g_free (wvalue);
quark = g_quark_from_string (value);
g_free (value);
g_free (name_utf16);
g_free (value_utf16);
g_free (value_utf8);
return g_quark_to_string (quark);
}