Haketilo

/**

 * part of Hachette

 * Powerful, full-blown format enforcer for externally-obtained JSON

 *

 * Copyright (C) 2021 Wojtek Kosior

 * Redistribution terms are gathered in the `copyright' file.

 */

var error_path;

var invalid_schema;

function parse_json_with_schema(schema, json_string)

{

    error_path = [];

    invalid_schema = false;

    try {

	return sanitize_unknown(schema, JSON.parse(json_string));

    } catch (e) {

	throw `Invalid JSON${invalid_schema ? " schema" : ""}: ${e}.`;

    } finally {

	/* Allow garbage collection. */

	error_path = undefined;

    }

}

function error_message(cause)

{

    return `object${error_path.join("")} ${cause}`;

}

function sanitize_unknown(schema, item)

{

    let error_msg = undefined;

    let schema_options = [];

    let has_default = false;

    let _default = undefined;

    if (!Array.isArray(schema) || schema[1] === "matchentry" ||

	schema.length < 2 || !["ordefault", "or"].includes(schema))

	return sanitize_unknown_no_alternatives(schema, item);

    if ((schema.length & 1) !== 1) {

	invalid_schema = true;

	throw error_message("was not understood");

    }

    for (let i = 0; i < schema.length; i++) {

	if ((i & 1) !== 1) {

	    schema_options.push(schema[i]);

	    continue;

	}

	if (schema[i] === "or")

	    continue;

	if (schema[i] === "ordefault" && schema.length === i + 2) {

	    has_default = true;

	    _default = schema[i + 1];

	    break;

	}

	invalid_schema = true;

	throw error_message("was not understood");

    }

    for (const schema_option of schema_options) {

	try {

	    return sanitize_unknown_no_alternatives(schema_option, item);

	} catch (e) {

	    if (invalid_schema)

		throw e;

	    if (has_default)

		continue;

	    if (error_msg === undefined)

		error_msg = e;

	    else

		error_msg = `${error_msg}, or ${e}`;

	}

    }

    if (has_default)

	return _default;

    throw error_msg;

}

function sanitize_unknown_no_alternatives(schema, item)

{

    for (const [schema_check, item_check, sanitizer, type_name] of checks) {

	if (schema_check(schema)) {

	    if (item_check(item))

		return sanitizer(schema, item);

	    throw error_message(`should be ${type_name} but is not`);

	}

    }

    invalid_schema = true;

    throw error_message("was not understood");

}

function key_error_path_segment(key)

{

    return /^[a-zA-Z_][a-zA-Z_0-9]*$/.exec(key) ?

	`.${key}` : `[${JSON.stringify(key)}]`;

}

/*

 * Generic object - one that can contain arbitrary keys (in addition to ones

 * specified explicitly in the schema).

 */

function sanitize_genobj(schema, object)

{

    let max_matched_entries = Infinity;

    let min_matched_entries = 0;

    let matched_entries = 0;

    const entry_schemas = [];

    schema = [...schema];

    if (schema[2] === "minentries") {

	if (schema.length < 4) {

	    invalid_schema = true;

	    throw error_message("was not understood");

	}

	min_matched_entries = schema[3];

	schema.splice(2, 2);

    }

    if (min_matched_entries < 0) {

	invalid_schema = true;

	throw error_message('specifies invalid "minentries" (should be a non-negative number)');

    }

    if (schema[2] === "maxentries") {

	if (schema.length < 4) {

	    invalid_schema = true;

	    throw error_message("was not understood");

	}

	max_matched_entries = schema[3];

	schema.splice(2, 2);

    }

    if (max_matched_entries < 0) {

	invalid_schema = true;

	throw error_message('specifies invalid "maxentries" (should be a non-negative number)');

    }

    while (schema.length > 2) {

	let regex = /.+/;

	if (schema.length > 3) {

	    regex = schema[2];

	    schema.splice(2, 1);

	}

	if (typeof regex === "string")

	    regex = new RegExp(regex);

	entry_schemas.push([regex, schema[2]]);

	schema.splice(2, 1);

    }

    const result = sanitize_object(schema[0], object);

    for (const [key, entry] of Object.entries(object)) {

	if (result.hasOwnProperty(key))

	    continue;

	matched_entries += 1;

	if (matched_entries > max_matched_entries)

	    throw error_message(`has more than ${max_matched_entries} matched entr${max_matched_entries === 1 ? "y" : "ies"}`);

	error_path.push(key_error_path_segment(key));

	let match = false;

	for (const [key_regex, entry_schema] of entry_schemas) {

	    if (!key_regex.exec(key))

		continue;

	    match = true;

	    sanitize_object_entry(result, key, entry_schema, object);

	    break;

	}

	if (!match) {

	    const regex_list = entry_schemas.map(i => i[0]).join(", ");

	    throw error_message(`does not match any of key regexes: [${regex_list}]`);

	}

	error_path.pop();

    }

    if (matched_entries < min_matched_entries)

	throw error_message(`has less than ${min_matched_entries} matched entr${min_matched_entries === 1 ? "y" : "ies"}`);

    return result;

}

function sanitize_array(schema, array)

{

    let min_length = 0;

    let max_length = Infinity;

    let repeat_length = 1;

    let i = 0;

    const result = [];

    schema = [...schema];

    if (schema[schema.length - 2] === "maxlen") {

	max_length = schema[schema.length - 1];

	schema.splice(schema.length - 2);

    }

    if (schema[schema.length - 2] === "minlen") {

	min_length = schema[schema.length - 1];

	schema.splice(schema.length - 2);

    }

    if (["repeat", "repeatfull"].includes(schema[schema.length - 2]))

	repeat_length = schema.pop();

    if (repeat_length < 1) {

	invalid_schema = true;

	throw error_message('specifies invalid "${schema[schema.length - 2]}" (should be number greater than 1)');

    }

    if (["repeat", "repeatfull"].includes(schema[schema.length - 1])) {

	var repeat_directive = schema.pop();

	var repeat = schema.splice(schema.length - repeat_length);

    } else if (schema.length !== array.length) {

	throw error_message(`does not have exactly ${schema.length} items`);

    }

    if (repeat_directive === "repeatfull" &&

	(array.length - schema.length) % repeat_length !== 0)

	throw error_message(`does not contain a full number of item group repetitions`);

    if (array.length < min_length)

	throw error_message(`has less than ${min_length} element${min_length === 1 ? "" : "s"}`);

    if (array.length > max_length)

	throw error_message(`has more than ${max_length} element${max_length === 1 ? "" : "s"}`);

    for (const item of array) {

	if (i >= schema.length) {

	    i = 0;

	    schema = repeat;

	}

	error_path.push(`[${i}]`);

	const sanitized = sanitize_unknown(schema[i], item);

	if (sanitized !== discard)

	    result.push(sanitized);

	error_path.pop();

	i++;

    }

    return result;

}

function sanitize_regex(schema, string)

{

    if (schema.test(string))

	return string;

    throw error_message(`does not match regex ${schema}`);

}

const string_spec_regex = /^string(:(.*))?$/;

function sanitize_string(schema, string)

{

    const regex = string_spec_regex.exec(schema)[2];

    if (regex === undefined)

	return string;

    return sanitize_regex(new RegExp(regex), string);

}

function sanitize_object(schema, object)

{

    const result = {};

    for (let [key, entry_schema] of Object.entries(schema)) {

	error_path.push(key_error_path_segment(key));

	sanitize_object_entry(result, key, entry_schema, object);

	error_path.pop();

    }

    return result;

}

function sanitize_object_entry(result, key, entry_schema, object)

{

    let optional = false;

    let has_default = false;

    let _default = undefined;

    if (Array.isArray(entry_schema) && entry_schema.length > 1) {

	if (entry_schema[0] === "optional") {

	    optional = true;

	    entry_schema = [...entry_schema].splice(1);

	    const idx_def = entry_schema.length - (entry_schema.length & 1) - 1;

	    if (entry_schema[idx_def] === "default") {

		has_default = true;

		_default = entry_schema[idx_def + 1];

		entry_schema.splice(idx_def);

	    } else if ((entry_schema.length & 1) !== 1) {

		invalid_schema = true;

		throw error_message("was not understood");

	    }

	    if (entry_schema.length < 2)

		entry_schema = entry_schema[0];

	}

    }

    let unsanitized_value = object[key];

    if (unsanitized_value === undefined) {

	if (!optional)

	    throw error_message("is missing");

	if (has_default)

	    result[key] = _default;

	return;

    }

    const sanitized = sanitize_unknown(entry_schema, unsanitized_value);

    if (sanitized !== discard)

	result[key] = sanitized;

}

function take_literal(schema, item)

{

    return item;

}

/*

 * This function is used like a symbol. Other parts of code do sth like

 * `item === discard` to check if item was returned by this function.

 */

function discard(schema, item)

{

    return discard;

}

/*

 * The following are some helper functions to categorize various

 * schema item specifiers (used in the array below).

 */

function is_genobj_spec(item)

{

    return Array.isArray(item) && item[1] === "matchentry";

}

function is_regex(item)

{

    return typeof item === "object" && typeof item.test === "function";

}

function is_string_spec(item)

{

    return typeof item === "string" && string_spec_regex.test(item);

}

function is_object(item)

{

    return typeof item === "object";

}

function eq(what)

{

    return i => i === what;

}

/* Array and null checks must go before object check. */

const checks = [

    [is_genobj_spec, is_object,                   sanitize_genobj, "an object"],

    [Array.isArray,  Array.isArray,               sanitize_array,  "an array"],

    [eq(null),       i => i === null,             take_literal,    "null"],

    [is_regex,       i => typeof i === "string",  sanitize_regex,  "a string"],

    [is_string_spec, i => typeof i === "string",  sanitize_string, "a string"],

    [is_object,      is_object,                   sanitize_object, "an object"],

    [eq("number"),   i => typeof i === "number",  take_literal,    "a number"],

    [eq("boolean"),  i => typeof i === "boolean", take_literal,    "a boolean"],

    [eq("anything"), i => true,                   take_literal,    "dummy"],

    [eq("discard"),  i => true,                   discard,         "dummy"]

];

/*

 * EXPORTS_START

 * EXPORT parse_json_with_schema

 * EXPORTS_END

 */