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Improve Fl_Cairo_Graphics_Driver::clean_utf8() (#1569)

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Avoid re-encoding valid UTF-8 characters. Only *invalid* characters
need to be encoded, valid characters are moved.

Increase size of intermediate UTF-8 character buffer from 4 to 6 bytes
to prevent potential overflow.

Benign: make `use_priv_buffer` bool.

Some of these changes were suggested by AI.

Backported from master.
This commit is contained in:
Albrecht Schlosser
2026-08-12 22:40:36 +02:00
parent 5ac0b37d96
commit 70c921aa82
1 changed files with 12 additions and 6 deletions
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src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
+12 -6
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@@ -1311,19 +1311,20 @@ const char *Fl_Cairo_Graphics_Driver::clean_utf8(const char* str, int &n) {
const char *p = str;
int len, len2;
const char *end = str + n;
char buf4[4];
int use_priv_buffer = 0;
char buf6[6];
bool use_priv_buffer = false;
while (p < end) {
unsigned codepoint = fl_utf8decode(p, end, &len);
bool invalid = (len == 1 && *(uchar*)p >= 0x80);
// Switch to using utf8_buffer if needed
if (!use_priv_buffer && (len == 1 && *(uchar*)p >= 0x80)) {
if (!use_priv_buffer && invalid) {
// Make room if needed
if (utf8_buffer_len < p - str) {
utf8_buffer_len = (p - str) + 1000;
utf8_buffer = (char *)realloc(utf8_buffer, utf8_buffer_len);
}
use_priv_buffer = 1;
use_priv_buffer = true;
// Fill private buffer with data so far
if (p > str) {
memcpy(utf8_buffer, str, p - str);
@@ -1332,7 +1333,12 @@ const char *Fl_Cairo_Graphics_Driver::clean_utf8(const char* str, int &n) {
}
if (use_priv_buffer) {
len2 = fl_utf8encode(codepoint, buf4);
if (invalid) {
len2 = fl_utf8encode(codepoint, buf6);
} else {
memcpy(buf6, p, len);
len2 = len;
}
// Increase buffer if needed
if (utf8_buffer_len < q + len2) {
@@ -1341,7 +1347,7 @@ const char *Fl_Cairo_Graphics_Driver::clean_utf8(const char* str, int &n) {
}
// Copy decoded codepoint
memcpy(utf8_buffer + q, buf4, len2);
memcpy(utf8_buffer + q, buf6, len2);
q += len2;
}
p += len;