/json_eval

Primary LanguageC++

JSON processor (deserialize and query) written in C++

One pass, no tokenization.

Building

git clone https://github.com/k4lizen/json_eval.git
cd json_eval
make

Usage

Example json file tests/data/simple.json:

{
  "arr": [
    1, 2,
    "a", "b",
    {
      "c": [true, false, null]
    }
  ],
  "some string": "something\u000A\u0041bb\uAAAA\uD801\uDD01nya",
  "two": 2
}

Commands:

~> ./json_eval
usage: ./json_eval <json file> <query>

~> ./json_eval tests/data/simple.json "arr[two - 3]"
{
  "c": [
    true,
    false,
    null
  ]
}
~> ./json_eval tests/data/simple.json "arr[(two+6)/(2*size(arr[2]))]['c'][2]"
null

Testing

make test

Specification

Parsing of the input json file follows the latest RFC specification https://www.rfc-editor.org/rfc/rfc8259 .

Parsing of the query is a subset of https://www.rfc-editor.org/rfc/rfc9535 with certain extensions. The most notable restriction from the specification is that filter selectors are not supported.

Extensions

The root identifier ($) can be ommited, "abc.efg" can be used as shorthand for "$.abc.efg".

Everything is an expression. An expression can also be used as a selector "arr[7 - 3]" or even "arr[arr[0]]".

Functions aren't selectors, they can be used freely in expressions "min(4, size(arr))". The currently supported functions are min, max, size and nchildren. The first three do what you'd expect, nchildren calculates the total number of (possibly duplicate) Jsons compromising its arguments, recursively. For example, "nchildren(arr)" is 5,"nchildren($, two)" is 14.

Binary operators are allowed in expressions e.g. size(arr) + 3, there are +, -, * and /. You can also use brackets ( and ) to enforce an order of operations other than left->right (important for expected behaviour of * and /!).

Trivia

Bugs that came out of this project: