intelligently avoiding a fatal stack overflow crash?

[societyofrobots]

I have a file, X, that logs events and is stored in SPIFFS.

Once every few months, X fills up SPIFFS. When that happens, my software prunes older data from the log.

To do this, I:
- create String S
- copy only the newer half of file X into string S
- dump S into a new file, Y
- then I delete X, using Y as the new log

This code is working great for me, but...

I am concerned that one day for unforeseen reasons my available memory (stack?) could be less than the size of S. Boom, overflow.

Is there a way to ensure S won't overflow the stack? Could I check for free memory, thereby limiting data into S?

I could just appendFile(), byte by byte, from X to Y, without using S. But...

I also serve S in a webpage for users to view the log:

Code: Select all

server.send(200, "text/html", S);

Any advice? I'm not the most skilled of programmers, so dumb it down for me!

[WiFive]

Is there a way to ensure S won't overflow the stack?

Yes, don't put S in the stack. Put it in the heap and make sure you don't write more than its size.

I also serve S in a webpage for users to view the log:

Plenty of web server examples that can serve files from spiffs.

[societyofrobots]

don't put S in the stack. Put it in the heap and make sure you don't write more than its size.

How do I control whether S is put in the stack or heap?

Plenty of web server examples that can serve files from spiffs.

Thanks I'll look into it.

Some code I figured out which should be 'good enough' to make sure S will be smaller than the available heap...

Code: Select all

if(file.size() > ESP.getMaxAllocHeap()-10000)
   prune();