Re: Publish JSON structure as PVA

["Veseli, Sinisa via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Ralph,

The attached example (converter plus input file used for testing) probably isn't perfect, but it might be useful as a start.

When I run it in my environment it serves object on the 'jsonObject' channel and produces something like this:

$ python jsonToPva.py

structure

...

    structure codec

        string name 

        string parameters 

    long compressedSize 60000

    long uncompressedSize 60000

    structure[] dimension

        structure 

            long size 300

            long offset 0

            long fullSize 300

            long binning 1

            boolean reverse false

        structure 

            long size 200

            long offset 0

            long fullSize 200

            long binning 1

            boolean reverse false

    long uniqueId 246

    structure dataTimeStamp

        long secondsPastEpoch 1712765362

        long nanoseconds 566374540

        long userTag 0

 ...

$ pvget -r dataTimeStamp jsonObject

jsonObject structure 

    structure dataTimeStamp

        long secondsPastEpoch 1712765362

        long nanoseconds 566374540

        long userTag 0

Sinisa

import json

import pvaccess as pva

class JsonToPvaConverter:

    PVA_DATA_TYPE_MAP = {

        bool  : pva.BOOLEAN,

        int   : pva.LONG,

        float : pva.DOUBLE,

        str   : pva.STRING,

        type(None) : pva.STRING,

    }

    @classmethod

    def getPvaType(cls, value):

        if isinstance(value, dict):

            typeDict = {}

            for k,v in value.items():

                typeDict[k] = cls.getPvaType(v)

            return typeDict

        elif isinstance(value, list):

            if value:

                return [cls.getPvaType(value[0])]

            else:

                return [cls.getPvaType(None)]

        return cls.PVA_DATA_TYPE_MAP[type(value)]

    @classmethod

    def scrubValueDict(cls, valueDict):

        for k, v in list(valueDict.items()):

            if v is None:

                del valueDict[k]

            elif isinstance(v, dict):

               cls. scrubValueDict(v)

        return valueDict

    @classmethod

    def toPvObject(cls, s):

        valueDict = json.loads(s)

        typeDict = cls.getPvaType(valueDict)

        valueDict = cls.scrubValueDict(valueDict)

        pvObject = pva.PvObject(typeDict,valueDict)

        return pvObject

if __name__ == '__main__':

    s = open('t.json').read()

    pvObject = JsonToPvaConverter.toPvObject(s)

    print(pvObject)

    s = pva.PvaServer('jsonObject', pvObject)

    import time

    time.sleep(100)

--

Siniša Veseli

Scientific Software Engineering & Data Management

Advanced Photon Source

Argonne National Laboratory

sveseli at anl.gov

(630)252-9182

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Ralph Lange via Tech-talk <tech-talk at aps.anl.gov>
Sent: Wednesday, April 10, 2024 8:27 AM
To: EPICS Tech Talk <tech-talk at aps.anl.gov>
Subject: Publish JSON structure as PVA

 

Dear all,

Does anyone have an application / PVA server that reads a JSON structure (e.g., from file) and publishes it as pvAccess?

Cheers,
~Ralph

Attachment: t.json.gz
Description: t.json.gz

Attachment: jsonToPva.py.gz
Description: jsonToPva.py.gz