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Simple and lightweight JSON decoder for TwinCAT and CODESYS

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Twinson

Simple and lightweight JSON decoder for TwinCAT and CODESYS.

State of the implementation

  • Continuous integration
  • Parser
    • Strings
    • Numbers
    • Boolean
    • Null
    • Objects (including nested objects)
    • Arrays (including mixed array and nested arrays)
  • Basic element access
  • Monadic element access
  • Unittests
  • Performance improvements for accessing elements, use tree to store data instead of array
  • Performance tuning
  • Node access for "cached" element access

Comparison to Tc3_Json

Twinson is lightweight alternative to Beckhoff's Tc3_Json.FB_JsonDomParser. When comparing Twinson with the Tc3_Json (TC 3.1.4024.25), I discovered issues with Tc3_Json that might be addressed by Beckhoff in the future.

  • null, as specified by the JSON format, is not parsed correctly.
  • Parsing nested arrays is cumbersome, because there is no way (at least I didn't find any documented) to access an array element directly.

Benchmark

Twinson includes a seperate PLC for benchmarking the library against Tc3_Json. The benchmark uses several examples with increasing JSON complexity (In terms of how many "levels" the JSON objects have). We measure the duration it takes for parsing a JSON document and assigning all members of the JSON document to TwinCAT variables with direct element access.

  • Example 1: Object with 3 key/value pairs
  • Example 2: Object with 10 key/value pairs
  • Example 3: Object with 3 arrays, each containing 10 strings
  • Example 4: Object with 3 arrays, each containing 3 objects and each object has 10 key/value pairs
  • Example 5: Nested object with 10 levels object1.object2.(...).object9.string1...string10)
benchmark

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Simple and lightweight JSON decoder for TwinCAT and CODESYS

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