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Re: Static JSON parser for embedded

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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 :-(

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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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