Buffer overflow error in ESP8266_SoftwareSerial library

Question

I am running into buffer issues when running the Firmware.ino example here.

The output from my Arduino serial log on baudrate 115200 (I put the ESP on baudrate 9600):

Begin
01:17:15.538 -> Baudrate set success
01:17:15.585 -> Station + softAP - OK
01:17:18.631 -> Joining AP successful, IP: 192.168 r⸮+@⸮
01:17:18.991 -> Single Mode OK
01:17:18.991 -> Sending Request to www.google.com
01:17:19.084 -> create tcp - OK
01:17:19.710 -> not sentbuffer is full!
01:17:20.022 -> HZiw93GUFmVJYFz-yRmahGURP_UBbRb4EF0Ahwzx8MJ1GOyC5Z0dns8UD41G8kUqnL0oxNPxa6xF9nAqNF3X3B_hKW11zoyaBPn8trvUNt-69qbFCNOZwNjgoaloKbOQs7NN-B3tpmwFKpHfKsfKyZfiMdhulN3SgZMhewYBg9c; expires=Wed, 05-Feb-2020 05:17:18 GMT; path=/; domain=.google.com; HttpOnly
01:17:20.162 -> Accept-Ranges: none
01:17:20.162 -> Vary: Accept-Encoding
01:17:20.209 -> ConnecS,
01:17:24.179 -> Sending Request to www.google.com
01:17:24.774 -> create tcp - ERROR
01:17:28.759 -> Sending Request to www.google.com
01:17:29.432 -> create tcp - ERROR
01:17:33.402 -> Sending Request to www.google.com
01:17:34.021 -> create tcp - ERROR
01:17:38.028 -> Sending Request to www.google.com
01:17:38.669 -> create tcp - ERROR
01:17:42.681 -> Sending Request to www.google.com
01:17:43.294 -> create tcp - ERROR
01:17:47.298 -> Sending Request to www.google.com
01:17:47.954 -> create tcp - ERROR
01:17:51.925 -> Sending Request to www.google.com
01:17:52.595 -> create tcp - ERROR
01:17:56.563 -> Sending Request to www.google.com
01:17:57.204 -> create tcp - ERROR
01:18:01.222 -> Sending Request to www.google.com
01:18:01.871 -> create tcp - ERROR
01:18:05.839 -> Sending Request to www.google.com
01:18:06.460 -> create tcp - ERROR
01:18:10.456 -> Sending Request to www.google.com
01:18:10.596 -> create tcp - OK
01:18:11.049 -> buffer is full!
01:18:11.049 -> 
01:18:11.049 -> 
01:18:11.049 -> +IPD,1430:HTTP/1.1 200 OK
01:18:11.096 -> Date: Tue, 06 Aug 2019 05:18:09 GMT
01:18:11.096 -> Expires: -1
01:18:11.096 -> Cache-Control: private, max-age=0
01:18:11.143 -> Content-Type: text/ht
l; charset=ISO-8859-1
01:18:11.143 -> P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."
01:18:11.190 -> Server: gws
01:18:11.190 -> X-XSS-Protection: 0
01:18:11.190 -> X-Frame-Options: SAMEORIGIN
01:18:11.224 -> Set-CooS,
01:18:15.192 -> Sending Request to www.google.com
01:18:15.822 -> create tcp - ERROR
01:18:19.849 -> Sending Request to www.google.com
01:18:20.473 -> create tcp - ERROR

As you can see, at first it starts ok, gives a buffer error, runs in error for a while, then runs OK again. This happens a couple times, then it runs only in error. I imagine this is some issue with the buffer of the ESP or the Arduino, but I'm not sure how to diagnose it further.

Things I have tried to fix the error: - As mentioned in the Firmware.ino example comments, I uncommented #define ESP8266_USE_SOFTWARE_SERIAL - Also as mentioned in the comment, I changed line 42 from 64 to 256. It didn't work either time. - There is a MAX_BUFFER_SIZE in the included ESP8266.h library that I also changed, from 300 to 256, because I thought that might help, but the error persisted.

Answer 1

There's some heavy String usage in that library, would not recommend it for anything you want to be stable, especially with an Uno.

The library seems to create a connection by first clearing the SoftwareSerial buffer and then issuing the right AT command. It waits for 500ms for a response before giving up. I suspect the wait interval is sometimes not long enough for the module to receive, parse and handle the command before responding. So you should try increasing it to 2000 ms at line 773.

The buffer is full message just refers to the library's own buffer for holding received data, which is 300 bytes by default. The buffer's getting filled so quickly (and the SoftwareSerial internal buffer likely overrun too) because you're loading a webpage like Google's which has more than 300 bytes in the response header alone. It's even possible that by the time the next request commences with another AT command, the ESP8266 is still dumping the response from the previous request, and so the command's response is still way down the queue and so doesn't get read before the timeout.

Instead, try loading a simple webpage like httpbin.org/ip. That is, at lines 952, 954:

char* request =  "GET /ip HTTP/1.1\r\nHost: www.httpbin.org\r\nConnection: close\r\n\r\n";

if (createTCP("www.httpbin.org", 80))