StreamString SSO bug

[mongozmaki]

With SSO implementation in String, StreamString::write generates wrong strings under some circumstances.
Reason is that String::len() returns strlen(sso_buf) if SSO=true but with newly written data (in StreamString::write) the null-termination missing at the time len() is called.
Furthermore, len() is called twice which is inefficient if SSO=true.

Testcode:

StreamString s;
s.print('{');
s.print('\"');
s.print(String("message"));
s.print('\"');
Serial.println(s);

Expected: '{"message"'
Actual: '{"message��"'

[earlephilhower]

This is great. Thanks! Would you be able to add a test to the host tests that catches the error (you already have the code, just need to encapsulate it).

This also needs to apply to the ESP32 core. Do you want to submit a patch there or would you like me to?

[mongozmaki]

Hi!
I added a pull request for the test case.
I was not sure where to put it so I put it in host/core/test_string.cpp. I could not test the test case but it should work.

I will submit the same to the ESP32