Bizarre SPIFFS readBytes crash - only when exactly 52 bytes read

[philbowles]

Basic Infos

Hardware

Hardware: Wemos D1 Mini
Core Version: 2.3.0

Description

readBytes on a SPIFFS file causes reboot (with no error messages) - but only when exactly 52 bytes are read. The file is the same in all case (a "config" file named "/conf").

Dozens of other (shorter AND longer) strings work perfectly and have done for weeks.

The only thing I can think of is that my SPIFFS memory area has become corrupted somehow and that some historic "footprint" of a bad 52-byte file is lying around and keeps getting re-used when the same length string is written again.

Settings in IDE

Module: WeMos D1 R2 & Mini
Flash Size: 4MB (1M SPIFFS)
CPU Frequency: 80Mhz
Upload Using: SERIAL

Sketch

String ICACHE_FLASH_ATTR ESPArto::readSPIFFS(const char* fn){
	String rv;
	File f=SPIFFS.open(fn, "r");
	if(f) {
		int n=f.size();
		Serial.printf("readSPIFFS size=%d\n",n);
		char* buff=(char *) malloc(n);
		f.readBytes(buff,n);
		rv=buff;
		free(buff);
	}
	f.close();
	return rv;	
}

Debug Messages

Here's a working Example:

readSPIFFS size=53
CFG data=Middle EarthX,Righthander,0,30000,30000,300000,300000

09826c6d
uptime=0d 0h 0m 2s H=27496 W=0 WiFi Connected SSID=ToiioT-Etage

Here's another:

readSPIFFS size=51
CFG data=MiddleEarth,Righthander,0,30000,30000,300000,300000

09826c6d
uptime=0d 0h 0m 1s H=27680 W=0 asyncp: event/5/4 [1]
uptime=0d 0h 0m 1s H=27856 W=0 asyncp: sound [1]
uptime=0d 0h 0m 2s H=27320 W=0 WiFi Connected SSID=ToiioT-Etage

And a 3rd:

readSPIFFS size=59
CFG data=Middle Earth,Much longer string,0,30000,30000,300000,300000

09826c6d
uptime=0d 0h 0m 2s H=27488 W=0 WiFi Connected SSID=ToiioT-Etage

But as soon as the same file containing exactly 52 bytes is read:

readSPIFFS size=52
"B΃K���⸮⸮	⸮%⸮⸮u⸮�⸮)S
!⸮o�XÈ

There are no other messages: no boot reason code, nothing but the gibberish and then my setup() routine running again.

I'm convinved it's a SPIFFS corruption as the same code running on a NodeMCU v0.9 shows:

uptime=0d 0h 0m 0s H=36832 W=0 Alive as esparto6
readSPIFFS size=52
CFG data=Middle Earth,Righthander,0,30000,30000,300000,300000

09826c6d
uptime=0d 0h 0m 2s H=27504 W=0 WiFi Connected SSID=ToiioT-Etage

How to further diagnose or fix? I have reuploaded my SPIFFS image (which does NOT include the /conf file) many times using the IDE (1.8.3) tool, as well as automatically on boot via ESPhttpUpdate. After each such re-upload, I then use my config web page to write the file, which appears to be written fine. Upon next reboot, the problem of the 52-byte read appears.

I'm going to try one more thing and that is to change the SPIFFS size and try the whole process again, unless someone has any other ideas?

[devyte]

@philbowles You are mallocing 53 bytes for your buff, and I count 53 chars in your printout. Aren't you forgetting the null term? You should allocate n+1, and probably also do buff[n] = 0; after reading (index right after your read data).
Also, why are you reading into an alloced char * only to assign to a String, when you can call f.readString() directly?
Closing due to usage error (see #3655 ). If after you fix the errors you still see an issue, please revisit or open a new issue, and also please provide a MCVE.

[philbowles]

I changed the SPIFFS size to 4M (3M SPIFFS) uploaded SPIFFS image using IDE ...same problem. Will now look into reformatting the SPIFFS area and starting again...

[philbowles]

DOH! Schoolboy error - just spotted it myself and working to fix...I feel such an idiot! Sorry to have wasted your time (and tons of mine!) :(