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time: Make std::string version of strftime() avoid runaway memory allocations (#5348)

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Kevin P. Fleming 2023-09-11 16:02:07 -04:00 committed by GitHub
parent 892d2ce34f
commit deb34c9473
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2 changed files with 9 additions and 0 deletions
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5
esphome/core/time.cpp
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@ -49,6 +49,11 @@ std::string ESPTime::strftime(const std::string &format) {
struct tm c_tm = this->to_c_tm();
size_t len = ::strftime(&timestr[0], timestr.size(), format.c_str(), &c_tm);
while (len == 0) {
if (timestr.size() >= 128) {
// strftime has failed for reasons unrelated to the size of the buffer
// so return a formatting error
return "ERROR";
}
timestr.resize(timestr.size() * 2);
len = ::strftime(&timestr[0], timestr.size(), format.c_str(), &c_tm);
}

4
esphome/core/time.h
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@ -45,6 +45,10 @@ struct ESPTime {
*
* @warning This method uses dynamically allocated strings which can cause heap fragmentation with some
* microcontrollers.
*
* @warning This method can return "ERROR" when the underlying strftime() call fails, e.g. when the
* format string contains unsupported specifiers or when the format string doesn't produce any
* output.
*/
std::string strftime(const std::string &format);