ESP32 string length overflow bug in xdrv_12_home_assistant.ino

[vic42]

PROBLEM DESCRIPTION

A clear and concise description of what the problem is.

ESP32 string length overflow bug in xdrv_12_home_assistant.ino

REQUESTED INFORMATION

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• [ ] Device used (e.g., Sonoff Basic): _____
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TO REPRODUCE

Steps to reproduce the behavior:

Here's the invalid JSON that tasmota was sending (extra comma after last null): 2021-03-13 11:10:21 WARNING (MainThread) [hatasmota.discovery] Invalid discovery message 3C6105**:

'{"ip":"192.168.1.220","dn":"Tasmota-Heltec","fn":["Tasmota1",null,null,null,null,null,null,null],"hn":"HeltecTopic-0724","mac":"3C6105******","md":"Heltec WiFi Kit 32","ty":0,"if":0,"ofln":"Offline","onln":"Online","state":["OFF","ON","TOGGLE","HOLD"],"sw":"9.3.1","t":"HeltecTopic","ft":"%prefix%/%topic%/","tp":["cmnd","stat","tele"],"rl":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"swc":[-1,1,1,1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1],"swn":[null,"Switch2","Switch3","Switch4",null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,],"btn":[0,0,0,0,0,0,0,0],"so":{"4":0,"11":0,"13":0,"17":0,"20":0,"30":0,"68":0,"73":0,"82":0,"114":1,"117":0},"lk":1,"lt_st":0,"sho":[0,0,0,0],"ver":1}'

Note the ostensibly stray comma before the bracket at the end of the "swn" value: null,null,],

EXPECTED BEHAVIOUR

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A valid and complete JSON string

SCREENSHOTS

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ADDITIONAL CONTEXT

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I am only reporting this as a proxy from Tasmota Discord chat. See thread here: https://discord.com/channels/479389167382691863/790185752855052288/820353710185906219 There is a good description of what is actually going wrong. I checked the code and found the cause of the problem. The issue was introduced when increasing the number of possible switches in tasmota32.

stemp4 is only TOPSZ (151 Bytes) long. The resulting JSON string in this code becomes longer than that on a regular basis and gets truncated: https://github.com/arendst/Tasmota/blob/development/tasmota/xdrv_12_home_assistant.ino#L302-L308

(Please, remember to close the issue when the problem has been addressed)

[scottcopus]

@vic42 Thanks for opening this bug. I finally had some time to submit this bug report when I saw you beat me to the punch. 👍

[arendst]

Thx for documented reporting.