LStream JSON Deserializer crashes PLC

Refer to the documentation, appendix, and the support link(s).

Use that link to ask these types of questions and report these types of bugs.

If there is a newer version available for V17/V18/V19, you might consider updating your project and gain access to a newer - perhaps less buggy version.

And, now that you know, you need to edit check your incoming data to ensure it meets the expectations before calling LSTREAM library blocks. 

dnajda

Hi,

I'm having trouble with the LStream JSON Deserializer in TIAP v16 (version 1.6.0). It seems quite unsafe:

• If the input buffer is empty, a crash occurs - "first null" is idx `0`, "last char" is idx `-1` and the code checks if there is a whitespace one before at idx `-2`, thus dying to bad memory access.
• Another happens if the input buffer is not a valid JSON (I'm scanning QR/bar codes, so just a regular numeric string) - from what I've found, it tries to check previous nesting in the tree array, but there is no previous entry, so again it dies due to accessing index `-1`.

Is there another version, or another library, or a function which would perform all the necessary safety checks?

Also, it seems not to get activated by a single tick for some reason (which is outputted by my QR-scanner wrapper FB).

After reviewing the library documentation, the input buffer being empty violates one of the requirements for calling the JSON deserializer.  The JSON structure must exist and be valid - and in a compressed JSON format.

You need to write your own JSON validation logic, with at least verification of the buffer not being empty, and starting and stopping with the correct delimiters.

If you feel this should be provided as part of the library, you are welcome to share that with Siemens Support as noted in the documentation at this link: https://www.siemens.com/SupportRequest

dnajda

Hi,

I'm having trouble with the LStream JSON Deserializer in TIAP v16 (version 1.6.0). It seems quite unsafe:

• If the input buffer is empty, a crash occurs - "first null" is idx `0`, "last char" is idx `-1` and the code checks if there is a whitespace one before at idx `-2`, thus dying to bad memory access.
• Another happens if the input buffer is not a valid JSON (I'm scanning QR/bar codes, so just a regular numeric string) - from what I've found, it tries to check previous nesting in the tree array, but there is no previous entry, so again it dies due to accessing index `-1`.

Is there another version, or another library, or a function which would perform all the necessary safety checks?

Also, it seems not to get activated by a single tick for some reason (which is outputted by my QR-scanner wrapper FB).