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Entry  08 Sep 2020, Zaher Salman, Forum, json parser error 
    Reply  08 Sep 2020, Konstantin Olchanski, Forum, json parser error 
Message ID: 1994     Entry time: 08 Sep 2020     In reply to: 1993
Author: Konstantin Olchanski 
Topic: Forum 
Subject: json parser error 
> I am getting the following error alert in a custom page whenever a run starts
> json parser exception: SyntaxError: Unexpected token < in JSON at position 985, batch request: method: "db_get_values", params: [object Object], id: 1598691925697 method: "get_alarms", params: null, id: 1598691925697 method: "cm_msg_retrieve", params: [object Object], id: 1598691925697 method: "cm_msg_retrieve", params: [object Object], id: 1598691925697
> Does anyone know why and what causes this? This does not affect anything and things seem to continue running fine.

this is bug #242,

we read stuff from midas.log and push it to the web browser. we have seen this stuff
contain arbitrary binary data (both intentionally written into midas.log by cm_msg() and
file content corruption/truncation from computer crashes), the json decoder in the web browser
does not like that stuff - it is invalid utf-8 unicode - and throws an exception.

since we cannot ensure content of midas.log (and other files on disk) are always valid utf-8,
we have to sanitize it before sending it to the browser.

right now I am not sure of the best way to do this sanitizing. we do have a function to check
for valid utf-8 unicode, perhaps it should be extended to replace invalid unicode with spaces
or Xes or "?" or whatever, I am open to suggestions and ideas.

BTW, this is a new recent change to how strings generally work. C NUL-terminated strings are
permitted to contain arbitrary binary data (except for NUL char, of course). C++ std::string
are permitted to contain arbitrary binary data. but javascript strings are only permitted
to contain valid unicode, and the json standard was recently amended to require that json
strings are valid utf-8 unicode. So there is a disconnect between C/C++ code written in the
last 50 years where strings can contain binary data and the javascript world requiring
valid utf-8 unicode pretty much everywhere.

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