Subclassing, extending or wrapping Node.js 'request' module to enhance response - node.js

I'm trying to extend request in order to hijack and enhance its response and other 'body' params. In the end, I want to add some convenience methods for my API:
var myRequest = require('./myRequest');
myRequest.get(function(err, hijackedResponse, rows) {
console.log(hijackedResponse.metadata)
console.log(rows)
console.log(rows.first)
});
According to the Node docs on inherits, I thought I could make it work (and using the EventEmitter example in the docs works OK). I tried getting it to work using #Trott's suggestion but realized that for my use case it's probably not going to work:
// myRequest.js
var inherits = require('util').inherits;
var Request = require("request").Request;
function MyRequest(options) {
Request.call(this, options);
}
inherits(MyRequest, Request);
MyRequest.prototype.pet = function() {
console.log('purr')
}
module.exports = MyRequest;
I've been toying with extend as well, hoping that I could find a way to intercept request's onRequestResponse prototype method, but I'm drawing blanks:
var extend = require('extend'),
request = require("request")
function myResponse() {}
extend(myResponse, request)
// maybe some magic happens here?
module.exports = myResponse
Ended up with:
var extend = require('extend'),
Ok = require('objectkit').Ok
function MyResponse(response) {
var rows = Ok(response.body).getIfExists('rows');
extend(response, {
metadata: extend({}, response.body),
rows: rows
});
response.first = (function() {
return rows[0]
})();
response.last = (function() {
return rows[rows.length - 1] || rows[0]
})();
delete response.metadata.rows
return response;
}
module.exports = MyResponse
Keep in mind in this example, I cheated and wrote it all inside the .get() method. In my final wrapper module, I'm actually taking method as a parameter.

UPDATED to answer the edited question:
Here's a rough template for the contents of your myResponse.js. It only implements get(). But as a bare bones, this-is-how-this-sort-of-thing-can-be-done demo, I hope it gets you going.
var request = require('request');
var myRequest = {};
myRequest.get = function (callback) {
// hardcoding url for demo purposes only
// could easily get it as a function argument, config option, whatever...
request.get('http://www.google.com/', function (error, response, body) {
var rows = [];
// only checking error here but you might want to check the response code as well
if (!error) {
// mess with response here to add metadata. For example...
response.metadata = 'I am awesome';
// convert body to rows however you process that. I'm just hardcoding.
// maybe you'll use JSON.parse() or something.
rows = ['a', 'b', 'c'];
// You can add properties to the array if you want.
rows.first = 'I am first! a a a a';
}
// now fire the callback that the user sent you...
callback(error, response, rows);
});
};
module.exports = myRequest;
ORIGINAL answer:
Looking at the source code for the Request constructor, it requires an options object that in turn requires a uri property.
So you need to specify such an object as the second parameter in your call():
Request.call(this, {uri: 'http://localhost/'});
You likely don't want to hard code uri like that inside the constructor. You probably want the code to look something more like this:
function MyRequest(options) {
Request.call(this, options);
}
...
var myRequest = new MyRequest({uri: 'http://localhost/'});
For your code to work, you will also need to move util.inherits() above the declaration for MyRequest.prototype.pat(). It appears that util.inherits() clobbers any existing prototype methods of the first argument.

Related

Cannot modify variable inside couchbase callback when using node js

I don't know if this is normal or not but when I try to access a variable inside a callback ( Couchbase callback ) in node.js it doesn't work properly.
var obj = new Object();
bucket.get(key, function(error, count) {
bucket.get(key2, function(error, prop) {
obj.entry = prop.value.value;
obj[entry+"_date"] = new Date(prop.value.created_at).toString();
})
})
Am I missing something ?
Also: I can't declare the Object var inside the callback because I'm accessing it later on.
Ok, I would try this:
var obj = {};
bucket.get(key, function(error, count) {
bucket.get(key2, function(error, prop) {
obj[entry] = prop.value.value;
var extraKey = entry+"_date"; // ensure this is an string
obj[extraKey] = new Date(prop.value.created_at).toString();
console.log(obj);
// obj[entry] exists here
})
})
// but obj would be empty here :(
Also please keep in mind that if you use obj after the context of the callbacks, in fact you may not have the property set, simply because the callback has not executed yet. Callbacks are async. Anything you want to do with that obj new props should happen in the same context of where those are set. The other option is to refactor this code with promises, so you can have the desired order of execution.

How to use promise bluebird in nested for loop?

I need to use bluebird in my code and I have no idea how to use it. My code contains nested loops. When the user logs in, my code will run. It will begin to look for any files under the user, and if there are files then, it will loop through to get the name of the files, since the name is stored in a dictionary. Once it got the name, it will store the name in an array. Once all the names are stored, it will be passed along in res.render().
Here is my code:
router.post('/login', function(req, res){
var username = req.body.username;
var password = req.body.password;
Parse.User.logIn(username, password, {
success: function(user){
var Files = Parse.Object.extend("File");
var object = [];
var query = new Parse.Query(Files);
query.equalTo("user", Parse.User.current());
var temp;
query.find({
success:function(results){
for(var i=0; i< results.length; i++){
var file = results[i].toJSON();
for(var k in file){
if (k ==="javaFile"){
for(var t in file[k]){
if (t === "name"){
temp = file[k][t];
var getname = temp.split("-").pop();
object[i] = getname;
}
}
}
}
}
}
});
console.log(object);
res.render('filename', {title: 'File Name', FIles: object});
console.log(object);
},
error: function(user, error) {
console.log("Invalid username/password");
res.render('logins');
}
})
});
EDIT:The code doesn't work, because on the first and second console.log(object), I get an empty array. I am suppose to get one item in that array, because I have one file saved
JavaScript code is all parsed from top to bottom, but it doesn't necessarily execute in that order with asynchronous code. The problem is that you have the log statements inside of the success callback of your login function, but it's NOT inside of the query's success callback.
You have a few options:
Move the console.log statements inside of the inner success callback so that while they may be parsed at load time, they do not execute until both callbacks have been invoked.
Promisify functions that traditionally rely on and invoke callback functions, and hang then handlers off of the returned value to chain the promises together.
The first option is not using promises at all, but relying solely on callbacks. To flatten your code you will want to promisify the functions and then chain them.
I'm not familiar with the syntax you're using there with the success and error callbacks, nor am I familiar with Parse. Typically you would do something like:
query.find(someArgsHere, function(success, err) {
});
But then you would have to nest another callback inside of that, and another callback inside of that. To "flatten" the pyramid, we make the function return a promise instead, and then we can chain the promises. Assuming that Parse.User.logIn is a callback-style function (as is Parse.Query.find), you might do something like:
var Promise = require('bluebird');
var login = Promise.promisify(Parse.User.logIn);
var find = Promise.promisify(Parse.Query.find);
var outerOutput = [];
return login(yourArgsHere)
.then(function(user) {
return find(user.someValue);
})
.then(function(results) {
var innerOutput = [];
// do something with innerOutput or outerOutput and render it
});
This should look familiar to synchronous code that you might be used to, except instead of saving the returned value into a variable and then passing that variable to your next function call, you use "then" handlers to chain the promises together. You could either create the entire output variable inside of the second then handler, or you can declare the variable output prior to even starting this promise chain, and then it will be in scope for all of those functions. I have shown you both options above, but obviously you don't need to define both of those variables and assign them values. Just pick the option that suits your needs.
You can also use Bluebird's promisifyAll() function to wrap an entire library with equivalent promise-returning functions. They will all have the same name of the functions in the library suffixed with Async. So assuming the Parse library contains callback-style functions named someFunctionName() and someOtherFunc() you could do this:
var Parse = Promise.promisifyAll(require("Parse"));
var promiseyFunction = function() {
return Parse.someFunctionNameAsync()
.then(function(result) {
return Parse.someOtherFuncAsync(result.someProperty);
})
.then(function(otherFuncResult) {
var something;
// do stuff to assign a value to something
return something;
});
}
I have a few pointers. ... Btw tho, are you trying to use Parse's Promises?
You can get rid of those inner nested loops and a few other changes:
Use some syntax like this to be more elegant:
/// You could use a map function like this to get the files into an array of just thier names
var fileNames = matchedFiles.map(function _getJavaFile(item) {
return item && item.javaFile && item.javaFile.name // NOT NULL
&& item.javaFile.name.split('-')[0]; // RETURN first part of name
});
// Example to filter/retrieve only valid file objs (with dashes in name)
var matchedFiles = results.filter(function _hasJavaFile(item) {
return item && item.javaFile && item.javaFile.name // NOT NULL
&& item.javaFile.name.indexOf('-') > -1; // and has a dash
});
And here is an example on using Parse's native promises (add code above to line 4/5 below, note the 'then()' function, that's effectively now your 'callback' handler):
var GameScore = Parse.Object.extend("GameScore");
var query = new Parse.Query(GameScore);
query.select("score", "playerName");
query.find().then(function(results) {
// each of results will only have the selected fields available.
});

How to "subclass" a node.js module

I've been primarily a Perl coder for years, but also have a background in C++, so I'm coming from a "classical" OO background, and now learning node.js. I just read through The Principles of Object-Oriented JavaScript, which did a good job of explaining the JS concept of OO to classically-minded people like me. But I'm left with a question, specifically related to node.js and inheritance. Pardon me if I'm still using "classical" vocabulary to explain my problem.
Lets suppose I have a module lib/foo.js:
function foo() {
console.log('Foo was called');
}
module.exports.foo = foo;
And I want to "subclass" this in another module lib/bar.js:
var foo = require('foo.js');
// Do some magic here with *.prototype, maybe?
function bar() {
console.log('Bar was called');
}
module.exports.bar = bar;
Such that my main script can do this:
var bar = require('lib/bar.js');
bar.foo(); // Output "Foo was called"
bar.bar(); // Output "Bar was called"
Is this even possible? If so, what am I missing?
Or is this an anti-pattern? Or plain impossible? What should I do instead?
Here's how I did it, to override one method in the request module. Warning: many node modules are poorly designed for extension, including request, as they do way too much stuff in the constructor. Not just a gazillion argument options, but starting up IO, connections, etc. For example, request does the http connection (eventually) as part of the constructor. There is no explicit .call() or .goDoIt() method.
In my example, I wanted to use querystring instead of qs to format forms. My module is cleverly named "MyRequest". In a separate file named myrequest.js you have:
var Request = require('request/request.js');
var querystring = require('querystring');
MyRequest.prototype = Object.create(Request.prototype);
MyRequest.prototype.constructor = MyRequest;
// jury rig the constructor to do "just enough". Don't parse all the gazillion options
// In my case, all I wanted to patch was for a POST request
function MyRequest(options, callbackfn) {
"use strict";
if (callbackfn)
options.callback = callbackfn;
options.method = options.method || 'POST'; // used currently only for posts
Request.prototype.constructor.call(this, options);
// ^^^ this will trigger everything, including the actual http request (icky)
// so at this point you can't change anything more
}
// override form method to use querystring to do the stringify
MyRequest.prototype.form = function (form) {
"use strict";
if (form) {
this.setHeader('content-type', 'application/x-www-form-urlencoded; charset=utf-8');
this.body = querystring.stringify(form).toString('utf8');
// note that this.body and this.setHeader are fields/methods inherited from Request, not added in MyRequest.
return this;
}
else
return Request.prototype.form.apply(this, arguments);
};
Then, in your application, instead of
var Request = require("request");
Request(url, function(err, resp, body)
{
// do something here
});
you go
var MyRequest = require("lib/myrequest");
MyRequest(url, function(err, resp, body)
{
// do that same something here
});
I'm not a JavaScript guru so there may be better ways...
For reference, the specific solution I came up with to my sample code problem follows:
In lib/foo.js:
var Foo = function() {}
Foo.prototype.foo = function() {
console.log('Foo was called!');
};
module.exports = new Foo;
In lib/bar.js:
var foo = require('./foo.js');
var Bar = function() {}
Bar.prototype = Object.create(foo.__proto__);
Bar.prototype.constructor = Foo;
Bar.prototype.bar = function() {
console.log('Bar was called!');
};
module.exports = new Bar;
Then in my test script:
var bar = require('lib/bar.js');
bar.foo(); // Output "Foo was called"
bar.bar(); // Output "Bar was called"

node js restler result "get" not complete when trying to return result

I'm trying to get the HTML of a website using restler. But when I try to get the relevant part of result, I always get the error,
"TypeError: Cannot read property 'rawEncoded' of undefined".
'rawEncoded' sometimes is 'res'. I think it changes based on processing time.
I'm trying to get result.request.res.rawEncode from restler get result.
My function:
var rest = require('restler');
var loadHtmlUrl = function(weburl) {
var resultstr = rest.get(weburl).on('complete', function(result) {
var string = result.request.res.rawEncode;
return string;
});
return resultstr;
};
Then:
var htmlstring = loadHtmlUrl('http://google.com');
Maybe restler is the entirely wrong way to go. Maybe I don't understand it completely. But I'm definitely stuck...
Thanks!
Would your return resultstr; not run before the on('complete' callback gets called because it is asynchronous, therefore resulting in your htmlstring being null? I think you need to have a callback as a parameter to your loadHtmlUrl like so:
var rest = require('restler');
var loadHtmlUrl = function(weburl, callback) {
var resultstr = rest.get(weburl).on('complete', function(result) {
callback(result.request.res.rawEncode);
});
};
And then call it like so:
var htmlstring = null;
loadHtmlUrl('http://google.com', function(rawEncode) {
htmlstring = rawEncode;
//Do your stuff here...
});
I think that will resolve future problems you will have. However, I think the real problem you're facing is that result.request does not have the property of res. I'm thinking that my change above may fix this problem (not quite sure how). If not, then I would recommend looking at what properties result.request has as a debugging starter...

http.Clientrequest.abort() ends program

I'm having some issues using Node.js as a http client against an existing long polling server. I'm using 'http' and 'events' as requires.
I've created a wrapper object that contains the logic for handling the http.clientrequest. Here's a simplified version of the code. It works exactly as expected. When I call EndMe it aborts the request as anticipated.
var http = require('http');
var events = require('events');
function lpTest(urlHost,urlPath){
this.options = {
host: urlHost,
port: 80,
path: urlPath,
method: 'GET'
};
var req = {};
events.EventEmitter.call(this);
}
lpTest.super_ = events.EventEmitter;
lpTest.prototype = Object.create(events.EventEmitter.prototype, {
constructor: {
value: lpTest,
enumerable: false
}
});
lpTest.prototype.getData = function getData(){
this.req = http.request(this.options, function(res){
var httpData = "";
res.on('data', function(chunk){
httpData += chunk;
});
res.on('end', function(){
this.emit('res_complete', httpData);
}
};
}
lpTest.prototype.EndMe = function EndMe(){
this.req.abort();
}
module.exports = lpTest;
Now I want to create a bunch of these objects and use them to long poll a bunch of URL's. So I create an object to contain them all, generate each object individually, initiate it, then store it in my containing object. This works a treat, all of the stored long-polling objects fire events and return the data as expected.
var lpObject = require('./lpTest.js');
var objWatchers = {};
function DoSomething(hostURL, hostPath){
var tempLP = new lpObject(hostURL,hostPath);
tempLP.on('res_complete', function(httpData){
console.log(httpData);
this.getData();
});
objWatchers[hosturl + hostPath] = tempLP;
}
DoSomething('firsturl.com','firstpath');
DoSomething('secondurl.com','secondpath);
objWatchers['firsturl.com' + 'firstpath'].getData();
objWatchers['secondurl.com' + 'secondpath'].getData();
Now here's where it fails... I want to be able to stop a long-polling object while leaving the rest going. So naturally I try adding:
objWatchers['firsturl.com' + 'firstpath'].EndMe();
But this causes the entire node execution to cease and return me to the command line. All of the remaining long-polling objects, that are happily doing what they're supposed to do, suddenly stop.
Any ideas?
Could it have something to do with the fact that you are only calling getData() when the data is being returned?
Fixed code:
function DoSomething(hostURL, hostPath){
var tempLP = new lpObject(hostURL,hostPath);
tempLP.on('res_complete', function(httpData){
console.log(httpData);
});
tempLP.getData();
objWatchers[hosturl + hostPath] = tempLP;
}
I have seemingly solved this, although I'm note entirely happy with how it works:
var timeout = setTimeout(function(){
objWatchers['firsturl.com' + 'firstpath'].EndMe();
}, 100);
By calling the closing function on the object after a delay I seem to be able to preserve the program execution. Not exactly ideal, but I'll take it! If anyone can offer a better method please feel free to let me know :)

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