JSON encoding with records and 'null'/'undefined' mapping

This is a wrapper around jsx to handle encoding and decoding of Erlang records.

JSON null handling

To ease the interop between Erlang and JSON the 'null' handling is changed:

Erlang    ->    JSON     ->     Erlang

undefined       null            undefined
null            null            undefined

How to use

Before records can be encoded or decoded the record definitions need to be loaded.

After the definitions are loaded then all encoding/decoding is done transparently.

Loading record definitions

The record definitions are loaded from modules and compiled into a runtime loaded module containing all field names and default values.

To add record definitions from mymodule

ok = jsxrecord:load_records( [ mymodule ]).

To see the current record definitions:

jsxrecord:record_defs()

This returns a map with all known record definitions.

Encoding/decoding records

Let's assume the following record definition has been loaded:

-record(test, { a = 1, b = 2, c }).

This can now be encoded with:

jsxrecord:encode( #test{} ).

The resulting JSON is:

{"_record":"test","a":1,"b":2,"c":null}

Decoding returns the #test{}:

#test{} = jsxrecord:decode(<<"{\"_record\":\"test\",\"a\":1,\"b\":2,\"c\":null}">>).

Defaults are automatically added for fields missing in the JSON:

#test{ a = 1, b = 2, c = undefined } = jsxrecord:decode(<<"{\"_record\":\"test\"}">>).

Encoding and decoding datetime and timestamp tuples

Datetime tuples are assumed to be in UTC, and are converted into an ISO8601 string:

<<"\"2008-12-10T13:30:00Z\"">> = jsxrecord:encode({{2008, 12, 10}, {13, 30, 0}})

They are converted back into a datetime tuple:

{{2008, 12, 10}, {13, 30, 0}} = jsxrecord:decode(<<"\"2008-12-10T13:30:00Z\"">>)

Erlang timestamp tuples are also converted into an ISO8601 string, but with added precision:

<<"\"2020-06-12T14:00:11.571Z\"">> = jsxrecord:encode({1591,970411,571321})

A little bit of precision is lost when converting it back to a timestamp tuple:

{1591,970411,571000} = jsxrecord:decode(<<"\"2020-06-12T14:00:11.571Z\"">>)

Configuration

Set the application env jsxrecord.record_modules to a list of modules whose records need to be loaded on first use of the encoder or decoder.

Performance

The input of encode and the output of decode are parsed and expanded. This makes the encoder and decoder slower than pure jsx. Though the difference shouldn't be too bad in normal usage.