70 lines
1.9 KiB
JavaScript
70 lines
1.9 KiB
JavaScript
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/** This module defines a express.Router() instance
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* - supporting offset=<number> and limit=<number>*
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* - calls next with error if a impossible offset and/or limit value is given
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*
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* Note: it expects to be called BEFORE any data fetched from DB
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* Note: it sets an object { limit: 0, skip: 0 } with the proper number values in req.locals.limitskip
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* Note: it sets an Error-Object to next with error.status set to HTTP status code 400
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*
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* @author Johannes Konert
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* @licence CC BY-SA 4.0
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*
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* @module restapi/limitoffset-middleware-mongo
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* @type {Router}
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*/
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// remember: in modules you have 3 variables given by CommonJS
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// 1.) require() function
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// 2.) module.exports
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// 3.) exports (which is module.exports)
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"use strict";
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const router = require('express').Router();
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const logger = require('debug')('middleware:offsetlimit');
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// the exported router with handler
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router.use((req, res, next) => {
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let offset = undefined;
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let limit = undefined;
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const offsetString = req.query.offset;
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const limitString = req.query.limit;
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let err = null;
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if (offsetString) {
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if (!isNaN(offsetString)) {
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offset = parseInt(offsetString);
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if (offset < 0) {
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err = new Error('offset is negative')
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}
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}
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else {
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err = new Error('given offset is not a valid number ' + offsetString);
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}
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}
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if (limitString) {
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if (!isNaN(limitString)) {
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limit = parseInt(limitString);
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if (limit < 1) {
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err = new Error('limit is zero or negative')
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}
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}
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else {
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err = new Error('given limit is not a valid number ' + limitString);
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}
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}
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if (err) {
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logger('problem occurred with limit/offset values');
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err.status = 400;
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next(err)
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} else {
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res.locals.limitskip = {}; // mongoDB uses parameter object for skip/limit
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if (limit) res.locals.limitskip.limit = limit;
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if (offset) res.locals.limitskip.skip = offset;
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next()
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}
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});
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module.exports = router;
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