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What even is a JSON number?

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Re: What even is a JSON number?

#111

Post by wruza »

jillesvangurp wrote: post #97
yawaramin wrote: post #76

Long story short: don't use JSON numbers to represent money or monetary rates. Always use decimals encoded as string. It's surprising how many APIs fall short of this basic bar.

Depends on the language. On the JVM you are fine. With Javascript, doing math on big numbers is probably going to end in tears unless you know what you are doing. Either way, have some tests for this and make sure your code is doing what you expect. Encoding numbers as string because you are using a language and parser that can't deal with numbers properly (even 64 bit doubles), is a bit of a hack. Basically the rest…

Accounting for the lowest common denominator that has a huge share in it is always a great plan. Every trading platform out there uses "+-ddd.ddd" format, even binary-born protocols completely unrelated to js used it since forever.

Re: What even is a JSON number?

#113

Post by Cloudef »

First thing that I check before using a JSON parser library is that if it lets me to get the number as a string and let me do my own conversion. Libraries that try to treat the number as double or bring in a large bigint/decimal library gets usually pass from me.

Re: What even is a JSON number?

#114

Post by magicalhippo »

yawaramin wrote: post #76

Long story short: don't use JSON numbers to represent money or monetary rates. Always use decimals encoded as string. It's surprising how many APIs fall short of this basic bar.

We've used XML for interchange of order-like data. Customers have started demanding JSON, so I built a tool to generate XML JSON converters, along with JSON Schema file, based on an XSD, so we could continue to use our existing XML infrastructure on the inside.

I must admit I totally forgot about the JSON number issue. Our files include fields for various monetary amounts and similar, and in XML we just used "xs:decimal".

Most will be less than a million and requires less than four decimal digits. But I guess someone might decide to use it for the equivalent of a space station or similar, ya never know...

Re: What even is a JSON number?

#115

Post by speedgoose »

Cloudef wrote: post #113

First thing that I check before using a JSON parser library is that if it lets me to get the number as a string and let me do my own conversion. Libraries that try to treat the number as double or bring in a large bigint/decimal library gets usually pass from me.

If you need a specific exotic JSON parser to parse the numbers you have correctly, I would argue that you should serialise them as strings and not as numbers.

That's what prometheus is doing for example. https://prometheus.io/docs/prometheus/latest/querying/api/

Re: What even is a JSON number?

#116

Post by Cloudef »

speedgoose wrote: post #115
Cloudef wrote: post #113

First thing that I check before using a JSON parser library is that if it lets me to get the number as a string and let me do my own conversion. Libraries that try to treat the number as double or bring in a large bigint/decimal library gets usually pass from me.

If you need a specific exotic JSON parser to parse the numbers you have correctly, I would argue that you should serialise them as strings and not as numbers. That's what prometheus is doing for example. https://prometheus.io/docs/prometheus/latest/querying/api/

That only works if you are the one who serializes the json in the first place.

Re: What even is a JSON number?

#118

Post by im3w1l »

akubera wrote: post #54
kccqzy wrote: post #28

I'll add that for Haskell, the library everyone uses for JSON parses numbers into Scientific types with almost unlimited size and precision. I say almost unlimited because they use a decimal coefficient-and-exponent representation where the exponent is a 64-bit integer. The documentation is quite paranoid that if you are dealing with untrusted inputs, you could parse two JSON numbers from the untrusted source fine an…

I was attempting to solve this very problem in the Rust BigDecimal crate this weekend. Is it better to just let it crash with an out of memory error, or have a compile-time constant limit (I was thinking ~8 billion digits) and panic if any operation would exceed that limit with a more specific error-message (does that mean it's no longer arbitrary-precision?). Or keep some kind of overflow-state/nan, but then the com…

If I understand the situation correctly, in Haskell an unbounded number is the default that you get if you do something similar to JSON.parse(mystr). That means you can have issues basically anywhere. Whereas in Rust with Serde you would only get an unbounded number if you explicitly ask for one. That's a pretty major difference. Only a small number of places will explicitly ask for BigDecimal, and in those cases they probably want an actual unbounded number. And they should be prepared to deal with the consequences of that.

My 2cent anyway.

Re: What even is a JSON number?

#120

Post by p0w3n3d »

I think that good decision regarding numbers in API (as it was made in my project) is to put meaningful decimal numbers into string and let them be handled by exact decimal calculation framework, e.g. BigDecimal in Java etc.
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