From: Viktor Szakats <commit@vsz.me>
Date: Tue, 14 Jul 2026 17:06:37 +0000 (+0200)
Subject: idn: restore `MultiByteToWideChar()` `MB_ERR_INVALID_CHARS` flag
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d52c7e78a3531f975591eb1bb1250185a9fd14c2;p=thirdparty%2Fcurl.git

idn: restore `MultiByteToWideChar()` `MB_ERR_INVALID_CHARS` flag

Also:
- curlx: pass this flag to the actual conversion calls, for consistency
  and robustness. (It's not stricly necessary because the initial call
  to determine size, with this flag passed, fails already on bad input.)
- schannel: unfold `MultiByteToWideChar()` line (formatting).

Ref: https://learn.microsoft.com/windows/win32/api/stringapiset/nf-stringapiset-multibytetowidechar

Follow-up to 6694a42aa0e820a6fe1e59d85ff8597b6d768d8d #19798

Closes #22326
---

diff --git a/lib/curlx/fopen.c b/lib/curlx/fopen.c
index 37ca02671a..976eff9e2b 100644
--- a/lib/curlx/fopen.c
+++ b/lib/curlx/fopen.c
@@ -68,7 +68,7 @@ static wchar_t *fn_convert_UTF8_to_wchar(const char *str_utf8)
     if(str_w_len > 0) {
       str_w = CURLX_MALLOC(str_w_len * sizeof(wchar_t));
       if(str_w) {
-        if(MultiByteToWideChar(CP_UTF8, 0,
+        if(MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
                                str_utf8, -1, str_w, str_w_len) == 0) {
           CURLX_FREE(str_w);
           return NULL;
diff --git a/lib/curlx/multibyte.c b/lib/curlx/multibyte.c
index 715d2b8dc2..4ee39d962a 100644
--- a/lib/curlx/multibyte.c
+++ b/lib/curlx/multibyte.c
@@ -41,8 +41,8 @@ wchar_t *curlx_convert_UTF8_to_wchar(const char *str_utf8)
     if(str_w_len > 0) {
       str_w = curlx_malloc(str_w_len * sizeof(wchar_t));
       if(str_w) {
-        if(MultiByteToWideChar(CP_UTF8, 0, str_utf8, -1, str_w,
-                               str_w_len) == 0) {
+        if(MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+                               str_utf8, -1, str_w, str_w_len) == 0) {
           curlx_free(str_w);
           return NULL;
         }
diff --git a/lib/idn.c b/lib/idn.c
index b26f251d97..943a520eff 100644
--- a/lib/idn.c
+++ b/lib/idn.c
@@ -172,7 +172,8 @@ static CURLcode win32_idn_to_ascii(const char *in, char **out)
   /* Returned in_w_len includes the null-terminator, which then gets
      preserved across the calls that follow, ending up terminating
      the buffer returned to the caller. */
-  in_w_len = MultiByteToWideChar(CP_UTF8, 0, in, -1, in_w, IDN_MAX_LENGTH);
+  in_w_len = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+                                 in, -1, in_w, IDN_MAX_LENGTH);
   if(in_w_len) {
     wchar_t punycode[IDN_MAX_LENGTH];
     int chars = IdnToAscii(0, in_w, in_w_len, punycode, IDN_MAX_LENGTH);
@@ -198,7 +199,8 @@ static CURLcode win32_ascii_to_idn(const char *in, char **out)
   /* Returned in_w_len includes the null-terminator, which then gets
      preserved across the calls that follow, ending up terminating
      the buffer returned to the caller. */
-  in_w_len = MultiByteToWideChar(CP_UTF8, 0, in, -1, in_w, IDN_MAX_LENGTH);
+  in_w_len = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+                                 in, -1, in_w, IDN_MAX_LENGTH);
   if(in_w_len) {
     WCHAR idn[IDN_MAX_LENGTH]; /* stores a UTF-16 string */
     int chars = IdnToUnicode(0, in_w, in_w_len, idn, IDN_MAX_LENGTH);
diff --git a/lib/vtls/schannel.c b/lib/vtls/schannel.c
index d322c755e8..2b8166de12 100644
--- a/lib/vtls/schannel.c
+++ b/lib/vtls/schannel.c
@@ -473,10 +473,8 @@ static CURLcode get_client_cert(struct Curl_cfilter *cf,
       if(pszPassword) {
         int str_w_len = 0;
         if(pwd_len > 0)
-          str_w_len = MultiByteToWideChar(CP_UTF8,
-                                          MB_ERR_INVALID_CHARS,
-                                          sslc->key_passwd,
-                                          (int)pwd_len,
+          str_w_len = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+                                          sslc->key_passwd, (int)pwd_len,
                                           pszPassword, (int)(pwd_len + 1));
 
         if((str_w_len >= 0) && (str_w_len <= (int)pwd_len))