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ivjson - input validating JSON parser for C

-- At the moment ivjson is just a stub, an unfinished project --

A common cause of problems with JSON is caused by its dynamic nature,
which gives extensibility and flexibility. However, when a field that
was assumed to be there, is not there, or the field contains a value
of an unexpected type, the software could crash.

Normally these cases can be handled individually by painstaking error
handling, but often error handling is not done, or there are gaps in
the completeness of error handling, leading to crashes or even
vulnerabilities.

The ivjson parser solves this problem by

 1) making sure error handling is always done;
 2) localizes error handling to just one place.

The ivjson parser will not care about the data that was not asked for,
even though such data would be in the file, i.e. it is totally fine to
add fields to JSON. As a bonus, in theory ivjson performs better than
some other parsers, because it needs to concern itself only with the
data that is asked for.

The ivjson parser does not use the JSON schema standard because in
author's opinion that fights with the KISS principle i.e. effort vs
benefit balance is not good.

Example
=======

struct ivjson_spec	 spec = { 0 };
ivjson_array_t		 h_users;
ivjson_number_t		 h_id;
ivjson_string_t		 h_name;
static const char	*json = "{ \"users\" : ["
			 	"{ \"id\" : 3, \"name\" : \"foo\" }"
			 	"{ \"id\" : 4, \"name\" : \"bar\" }"
			 	"] }";
int			 ret, i;
int			 id;
char			 name[40 + 1];

/*
 * These can fail, but if they do, it is not a runtime error,
 * but a programmer error -- i.e. assert will fail.
 */
h_users = ivjson_add_array(&spec, "/users", 1, -1);
h_id = ivjson_add_number_to_array(&spec, h_users, "id", 0, 1000);
h_name = ivjson_add_string_to_array(&spec, h_users, "name", 1, 40);

/*
 * This can fail because of many reasons. Error code is given,
 * which can be translated to text by ivjson_error().
 */
if ((ret = ivjson_parse(json, &spec)) != 0)
	errx(1, "ivjson_parse: %s", ivjson_error(ret));

/*
 * These cannot fail.
 */
while ((i = ivjson_array(h_users)) != 0) {
	id = ivjson_number_from_array(h_users, i, h_id);
	strcpy(name, ivjson_string_from_array(h_users, i, h_name));
	printf("id=%d name: %s\n", id, name);
}

Configure & Install
===================

./configure ~
make install

See also
========

https://github.com/tleino/jsonkv/
https://github.com/tleino/dhdb/