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idn: avoid allocations and wcslen on Windows

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Eliminate a heap buffer in both `win32_idn_to_ascii()` and
`win32_ascii_to_idn()`, by replacing it with stack buffer. The maximum
size is fixed in these cases, and small enough to fit there.

Also reuse length returned by the UTF-8 to wchar conversion, allowing
to drop `wcslen()` call in both functions, and allowing to call
the wchar to UTF-8 conversion API `WideCharToMultiByte()` with the known
length, saving length calculations within that API too.

Ref: https://github.com/curl/curl/pull/19748#issuecomment-3592015200

Closes #19798
This commit is contained in:
Viktor Szakats 2025-12-01 22:18:41 +01:00
parent c3b030b860
commit 6694a42aa0
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GPG key ID: B5ABD165E2AEF201
1 changed files with 24 additions and 48 deletions
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72
lib/idn.c
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@ -162,42 +162,18 @@ WINBASEAPI int WINAPI IdnToUnicode(DWORD dwFlags,
#define IDN_MAX_LENGTH 255
static wchar_t *idn_curlx_convert_UTF8_to_wchar(const char *str_utf8)
{
wchar_t *str_w = NULL;
if(str_utf8) {
int str_w_len = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
str_utf8, -1, NULL, 0);
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) {
curlx_free(str_w);
return NULL;
}
}
}
}
return str_w;
}
static char *idn_curlx_convert_wchar_to_UTF8(const wchar_t *str_w)
static char *idn_curlx_convert_wchar_to_UTF8(const wchar_t *str_w, int chars)
{
char *str_utf8 = NULL;
if(str_w) {
int bytes = WideCharToMultiByte(CP_UTF8, 0, str_w, -1,
NULL, 0, NULL, NULL);
if(bytes > 0) {
str_utf8 = curlx_malloc(bytes);
if(str_utf8) {
if(WideCharToMultiByte(CP_UTF8, 0, str_w, -1, str_utf8, bytes,
NULL, NULL) == 0) {
curlx_free(str_utf8);
return NULL;
}
int bytes = WideCharToMultiByte(CP_UTF8, 0, str_w, chars, NULL, 0,
NULL, NULL);
if(bytes > 0) {
str_utf8 = curlx_malloc(bytes);
if(str_utf8) {
if(WideCharToMultiByte(CP_UTF8, 0, str_w, chars, str_utf8, bytes,
NULL, NULL) == 0) {
curlx_free(str_utf8);
return NULL;
}
}
}
@ -206,15 +182,15 @@ static char *idn_curlx_convert_wchar_to_UTF8(const wchar_t *str_w)
static CURLcode win32_idn_to_ascii(const char *in, char **out)
{
wchar_t *in_w = idn_curlx_convert_UTF8_to_wchar(in);
wchar_t in_w[IDN_MAX_LENGTH];
int in_w_len;
*out = NULL;
if(in_w) {
in_w_len = MultiByteToWideChar(CP_UTF8, 0, in, -1, in_w, IDN_MAX_LENGTH);
if(in_w_len) {
wchar_t punycode[IDN_MAX_LENGTH];
int chars = IdnToAscii(0, in_w, (int)(wcslen(in_w) + 1), punycode,
IDN_MAX_LENGTH);
curlx_free(in_w);
if(chars) {
*out = idn_curlx_convert_wchar_to_UTF8(punycode);
int chars = IdnToAscii(0, in_w, in_w_len, punycode, IDN_MAX_LENGTH);
if(chars > 0) {
*out = idn_curlx_convert_wchar_to_UTF8(punycode, chars);
if(!*out)
return CURLE_OUT_OF_MEMORY;
}
@ -229,15 +205,15 @@ static CURLcode win32_idn_to_ascii(const char *in, char **out)
static CURLcode win32_ascii_to_idn(const char *in, char **out)
{
wchar_t *in_w = idn_curlx_convert_UTF8_to_wchar(in);
wchar_t in_w[IDN_MAX_LENGTH];
int in_w_len;
*out = NULL;
if(in_w) {
in_w_len = MultiByteToWideChar(CP_UTF8, 0, 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, (int)(wcslen(in_w) + 1), idn,
IDN_MAX_LENGTH);
curlx_free(in_w);
if(chars) { /* 'chars' is "the number of characters retrieved" */
*out = idn_curlx_convert_wchar_to_UTF8(idn);
int chars = IdnToUnicode(0, in_w, in_w_len, idn, IDN_MAX_LENGTH);
if(chars > 0) { /* 'chars' is "the number of characters retrieved" */
*out = idn_curlx_convert_wchar_to_UTF8(idn, chars);
if(!*out)
return CURLE_OUT_OF_MEMORY;
}