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Prevent undefined behavior in Windows vasprintf #2630

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Prevent undefined behavior in Windows vasprintf #2630

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25 changes: 21 additions & 4 deletions folly/portability/Stdio.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -65,17 +65,34 @@ void setbuffer(FILE* f, char* buf, size_t size) {
}

int vasprintf(char** dest, const char* format, va_list ap) {
int len = vsnprintf(nullptr, 0, format, ap);
va_list ap1;
va_copy(ap1, ap);
int len = vsnprintf(nullptr, 0, format, ap1);
va_end(ap1);

if (len <= 0) {
return -1;
}
char* buf = *dest = (char*)malloc(size_t(len + 1));
if (vsnprintf(buf, size_t(len + 1), format, ap) == len) {

char* buf = (char*)malloc(size_t(len + 1));
if (!buf) {
return -1;
}

va_list ap2;
va_copy(ap2, ap);
int const rc = vsnprintf(buf, size_t(len + 1), format, ap2);
va_end(ap2);

if (rc == len) {
*dest = buf;
return len;
}

free(buf);
*dest = nullptr;
return -1;
}
}

#endif
#endif