vcpe/srcs/libs/docs/json_schema

json-c d'accord library (libjsoncdac)

jsonc-daccord is a lightweight JSON Schema validation library written in C, and is taking advantage of the libjson-c library.

Design Goals

The goal is to have a lightweight JSON Schema validation implementation in C using json-c. json-c is popular in OpenWRT communities. Initially I just wanted it to support a small subset of JSON Schema to suit a need to validate simple json files. See the minimum build supports below. However to suit a broader audience, supporting more JSON Schema is important.

Currently the footprint of libjsoncdac.so is 8KB. The keep the footprint from bloating out, new features should be selectable using CMake options.

Minimal build supports:

• all: type, enum, required, properties, const.
• objects:
• strings: minLength, maxLength.
• integers and doubles: minimum, maximum.
• arrays: minItems, maxItems, uniqeItems, items.

Example Use

Public headers:

See jsoncdaccord.h

    int jdac_validate_file(const char *jsonfile, const char *jsonschemafile);
    int jdac_validate(json_object *jobj, json_object *jschema);
    int jdac_ref_set_localpath(const char *_localpath);

    const char* jdac_errorstr(unsigned int jdac_errors);

Link your binary to: -ljsoncdac -ljson-c

Use the #include header: #include <jsoncdaccord.h>

Example C code:

#include <stdio.h>
#include <json-c/json.h>
#include <jsoncdaccord.h>

int main(int argc, char *argv[])
{
    char *json_file = "test.json";
    char *schema_file = "schema.json";

    // optional: load referenced schema files from filesystem
    char *localpath = "/my/path/to_json_files/";
    jdac_ref_set_localpath(localpath);

    printf("validating %s with %s\n", json_file, schema_file);
    int err = jdac_validate_file(json_file, schema_file);
    if (err==JDAC_ERR_VALID) {
        printf("validation ok\n");
    } else {
        printf("validate failed %d: %s\n", err, jdac_errorstr(err));
    }
    return err;
}

See jdac-cli.c as well.

Install

Building from source:

Install json-c and libcmocka-dev (used in the debug builds).

• Release version:

git clone --branch libjsoncdac-0.2 https://github.com/domoslabs/jsonc-daccord &&\
cd jsonc-daccord && mkdir build && cd build &&\
cmake .. -DCMAKE_BUILD_TYPE=Release && make && sudo make install

• Debug version:

git clone --branch libjsoncdac-0.2 https://github.com/domoslabs/jsonc-daccord &&\
cd jsonc-daccord && mkdir build && cd build &&\
cmake .. -DCMAKE_BUILD_TYPE=Debug && make && sudo make install

Note: After install you might need to run sudo ldconfig.

CMake Options

build options:

option	description
CMAKE_BUILD_TYPE	Build as Release or Debug. Default: Release.
RUN_TEST_SUITE	Run JSON Schema test suite (CMAKE_BUILD_TYPE=Debug Only)
BUILD_PATTERN	Support pattern.
BUILD_PATTERNPROPERTIES	Support patternProperties
BUILD_ADDITIONALPROPERTIES	Support additionalProperties
BUILD_PROPERTYNAMES	Support propertyNames
BUILD_SUBSCHEMALOGIC	Support allOf, anyOf, oneOf, not, if-then-else
BUILD_CONTAINS	Support contains, minContains, and maxContains
BUILD_DOWNLOAD	Support downloading referenced schema files
BUILD_STORE	Support build a list of schema uri, id, and anchors
BUILD_REF	Support $ref keyword. load schemas by file.

Note: All BUILD_* options are selected by default

Run tests

For debug builds:

ctest
ctest -V # to see output of tests

Running test suites are currently optional, and are select with RUN_TEST_SUITE=ON in the cmake options.

Command Line Interface

You can try the library with the jdac-cli command.

jdac-cli -h

To do

• prevent infinite recursion

Related links

• https://json-schema.org/specification.html
• https://github.com/json-schema-org/JSON-Schema-Test-Suite
• https://github.com/json-c/json-c