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Re: Static JSON parser for embedded

Cross-posted to 2 groups.

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Il 07/06/2019 01:11, Clifford Heath ha scritto:
> On 6/6/19 7:12 pm, pozz wrote:
>> Il 19/05/2019 01:12, Clifford Heath ha scritto:
>>> On 19/5/19 12:03 am, pozz wrote:
>>>> Il 18/05/2019 09:14, Clifford Heath ha scritto:
>>>>> On 17/5/19 5:20 pm, pozz wrote:
>>>>>> I'd like to use JSON documents in my embedded project. I don't 
>>>>>> need full parsing capabilities, because JSON could be very complex 
>>>>>> in general.
>>>>>>
>>>>>> Do you know of something code generator?
>>>>>
>>>>> Ok. Latecomer, but I read most of the thread. Introduction: I've 
>>>>> been writing C since 1979 and have a million lines of my code in 
>>>>> production in mission-critical software on tens of millions of 
>>>>> enterprise computers. Although these days my C is mostly C++, I use 
>>>>> C++ mostly for the features that make it "a better C".
>>>>>
>>>>> Neither JSON nor C has a very strong type system. Neither is a good 
>>>>> specification language. You should choose a specification language 
>>>>> that does a good job of specifying your intent, and a compiler for 
>>>>> it that emits C that handles one or more packing syntaxes such as 
>>>>> JSON (if you must!)
>>>>>
>>>>> The European Space Agency has followed the lead of the ISO 
>>>>> networking standards and built a compiler for ASN.1, which emits C 
>>>>> code targeted at static-memory embedded systems. The downside: I 
>>>>> don't think it has a JSON packing rule (the ASN.1 name for a 
>>>>> transfer syntax). Other ASN.1 compilers do support JSON, but I 
>>>>> don't know whether they target static-memory or embedded systems.
>>>>>
>>>>> The ESA-funded ASN1CC is here: <https://github.com/ttsiodras/asn1scc>.
>>>>>
>>>>> It supports BER (Basic encoding rules, a compact & fast binary 
>>>>> format), PER (Packed Encoding Rules, a bit-packed binary format 
>>>>> that will be slower but tighter), XER (XML Encoding Rules, you can 
>>>>> imagine!), and ACN, where you get to define the encoding yourself.
>>>>>
>>>>> If you wish to serve the community as well as yourself, write JER, 
>>>>> JSON Encoding Rules and submit it.
>>>>>
>>>>> A quick search finds a proposed standard: 
>>>>> <https://www.obj-sys.com/docs/JSONEncodingRules.pdf> and a tool 
>>>>> that analyses a JSON fragment and produces a proposed ASN.1 
>>>>> definition for the shape of the fragment <https://asn1.io/json2asn/>
>>>>>
>>>>> So there is existing work, and no doubt community support for more.
>>>>> You could do a lot worse than start with ASN1CC.
>>>>
>>>> ASN.1 is interested. I will look at it more deeply.
>>>>
>>>> Just a simple question. Are optional fields possible in a message?
>>>
>>> Yes. And pretty-much everything else you might need in a static type 
>>> system; sets of alternates with a discriminator (discriminated 
>>> unions), arbitrary nesting of arrays of structures of arrays of 
>>> structures, strings of many and various character sets and encodings, 
>>> enumerations, numbers limited by range not storage size, etc.
>>>
>>> Not all ASN.1 implementations are equal. This one is targeted at 
>>> systems that use no dynamic memory allocation, which is truly an 
>>> excellent thing - but you probably can't do JSON like that. It's used 
>>> for the majority of inter-module communications on ESA space 
>>> missions, so it's pretty well tested and reliable too.
>>>
>>> The point is that the ASN.1 definitions are focussed on defining the 
>>> values that can be meaningfully transferred, not the possible values 
>>> of a set of representations. It's not fully powerful, but it's a lot 
>>> better than most programming languages.
>>>
>>> I plan to emit ASN.1 from my Constellation Query Language tools at 
>>> some stage this year, see 
>>> <http://dataconstellation.com/ActiveFacts/>. CQL has a complete 
>>> first-order logic constraint language, so it is even more powerful 
>>> than ASN.1; and every feature (definition, constraint) is also 
>>> expressible in controlled natural language and *compilable* from that 
>>> language.
>>
>> Incredibly, it seems there isn't any ASN.1 PER codec for 
>> javascript/typescript (web-oriented) world. This limits the use to BER 
>> only :-(
> 
> ASN1CC has support for two languages, so I assume that it is set up for 
> multi-language support. If that has been done well (and I haven't 
> checked but I'd be surprised if it hasn't) it should be a fairly 
> straight-forward matter to add support for a third language. Probably 
> easier than implementing a fixed JS/TS processor for your desired 
> message schema. I daresay you'd make many people grateful for that.

Yes, but I haven't the know-how and time to add a third language to 
asn1scc. I need to find an off-the-shelf solution.

It seems there isn't a *proprietary* ASN1 PER Javascript implementation 
too (I found only JAVA support).

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Re: Static JSON parser for embedded Clifford Heath <no.spam@please.net> - 2019-05-19 09:12 +1000
  Re: Static JSON parser for embedded Niklas Holsti <niklas.holsti@tidorum.invalid> - 2019-05-19 17:13 +0300
    Re: Static JSON parser for embedded Clifford Heath <no.spam@please.net> - 2019-05-20 09:25 +1000
  Re: Static JSON parser for embedded pozz <pozzugno@gmail.com> - 2019-06-06 11:12 +0200
    Re: Static JSON parser for embedded Clifford Heath <no.spam@please.net> - 2019-06-07 09:11 +1000
      Re: Static JSON parser for embedded pozz <pozzugno@gmail.com> - 2019-06-07 08:59 +0200
        Re: Static JSON parser for embedded Clifford Heath <no.spam@please.net> - 2019-06-12 09:41 +1000

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