content-negotiation.js
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// Copyright IBM Corp. 2016. All Rights Reserved.
// Node module: strong-error-handler
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT
'use strict';
var accepts = require('accepts');
var debug = require('debug')('strong-error-handler:http-response');
var sendJson = require('./send-json');
var sendHtml = require('./send-html');
var sendXml = require('./send-xml');
var util = require('util');
module.exports = negotiateContentProducer;
/**
* Handles req.accepts and req.query._format and options.defaultType
* to resolve the correct operation
*
* @param req request object
* @param {Function} logWarning a logger function for reporting warnings
* @param {Object} options options of strong-error-handler
* @returns {Function} Operation function with signature `fn(res, data)`
*/
function negotiateContentProducer(req, logWarning, options) {
var SUPPORTED_TYPES = [
'application/json', 'json',
'text/html', 'html',
'text/xml', 'xml',
];
options = options || {};
var defaultType = 'json';
// checking if user provided defaultType is supported
if (options.defaultType) {
if (SUPPORTED_TYPES.indexOf(options.defaultType) > -1) {
debug('Accepting options.defaultType `%s`', options.defaultType);
defaultType = options.defaultType;
} else {
debug('defaultType: `%s` is not supported, ' +
'falling back to defaultType: `%s`', options.defaultType, defaultType);
}
}
// decide to use resolvedType or defaultType
// Please note that accepts assumes the order of content-type is provided
// in the priority returned
// example
// Accepts: text/html, */*, application/json ---> will resolve as text/html
// Accepts: application/json, */*, text/html ---> will resolve as application/json
// Accepts: */*, application/json, text/html ---> will resolve as application/json
// eg. Chrome accepts defaults to `text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*`
// In this case `resolvedContentType` will result as: `text/html` due to the order given
var resolvedContentType = accepts(req).types(SUPPORTED_TYPES);
debug('Resolved content-type', resolvedContentType);
var contentType = resolvedContentType || defaultType;
// to receive _format from user's url param to overide the content type
// req.query (eg /api/Users/1?_format=json will overide content negotiation
// https://github.com/strongloop/strong-remoting/blob/ac3093dcfbb787977ca0229b0f672703859e52e1/lib/http-context.js#L643-L645
var query = req.query || {};
if (query._format) {
if (SUPPORTED_TYPES.indexOf(query._format) > -1) {
contentType = query._format;
} else {
// format passed through query but not supported
var msg = util.format('Response _format "%s" is not supported' +
'used "%s" instead"', query._format, defaultType);
logWarning(msg);
}
}
debug('Content-negotiation: req.headers.accept: `%s` Resolved as: `%s`',
req.headers.accept, contentType);
return resolveOperation(contentType);
}
function resolveOperation(contentType) {
switch (contentType) {
case 'application/json':
case 'json':
return sendJson;
case 'text/html':
case 'html':
return sendHtml;
case 'text/xml':
case 'xml':
return sendXml;
}
}