CJSON decode limited to 250 characters

[Jonathan411]

A json string with 250 characters or less decodes correctly, but if the string of json data is 251 characters or more in length then an error is raised: LUA interpreter error detected!

The following code works:

jstr='{"aa":"1","bb":"2","cc":"3","dd":"4","ee":"5","ff":"6","gg":"7","hh":"8","ii":"9","jj":"10","kk":"11","ll":"12","mm":"13","nn":"14","oo":"15","pp":"16","qq":"17","rr":"18","ss":"19","tt":"20","uu":"21","vv":"22","w":"23","x":"24","y":"25","z":"26"}'
for k,v in pairs(cjson.decode(jstr)) do print(k,v) end

The following code generates an error (one additional "w" character):

jstr='{"aa":"1","bb":"2","cc":"3","dd":"4","ee":"5","ff":"6","gg":"7","hh":"8","ii":"9","jj":"10","kk":"11","ll":"12","mm":"13","nn":"14","oo":"15","pp":"16","qq":"17","rr":"18","ss":"19","tt":"20","uu":"21","vv":"22","ww":"23","x":"24","y":"25","z":"26"}'
for k,v in pairs(cjson.decode(jstr)) do print(k,v) end

I also tested a json string that contained a single key/value pair. If the combined length of the key/value pair exceeds 250 characters the same error is raised.

I am using the following:

NodeMCU custom build by frightanic.com
branch: dev
commit: 3109497
SSL: true
modules: cjson,file,gpio,http,net,node,tmr,uart,wifi
build built on: 2016-09-06 13:26
powered by Lua 5.1.4 on SDK 1.5.4.1(39cb9a32)

Is the 250 character limit a feature or a bug? I couldn't find any documentation which mentions a limit on the size of the json input string.

[luismfonseca]

This doesn't seem to be a limitation of the cjson module, but rather the max length that Lua String can be declared (without concatenation).

The following code works:

jstr = '"aa":"1","bb":"2","cc":"3","dd":"4","ee":"5","ff":"6","gg":"7","hh":"8","ii":"9","jj":"10","kk":"11","ll":"12","mm":"13","nn":"14","oo":"15","pp":"16","qq":"17","rr":"18","ss":"19","tt":"20","uu":"21","vv":"22","w":"23","x":"24","y":"25","z":"26"'

jstr = '{'..jstr..',"xyz":"1231231231231"}'

print(string.len(jstr) .. '\n') -- 270

for k,v in pairs(cjson.decode(jstr)) do print(k,v) end

[Jonathan411]

Not a NodeMCU issue then. Thanks.

[luismfonseca]

Well, I think it sorta is, in the sense that the 250 is the limit configured in NodeMCU...

If you run Lua on a computer, it doesn't have this limitation. Well, at least not 250. So I suppose that this was mostly a decision based on memory constraints.