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• iOS chat application design, sending/relaying the message over to the end user

  - by AyBayBay

  I have a design question. Let us say you were tasked with building a chat application, specifically for iOS (iOS Chat Application). For simplicity let us say you can only chat with one person at a time (no group chat functionality). How then can you achieve sending a message directly to an end user from phone A to phone B? Obviously there is a web service layer with some API calls. One of the API calls available will be startChat(). After starting a chat, when you send a message, you make another async call, let us call it sendMessage() and pass in a string with your message. Once it goes to the web service layer, the message gets stored in a database. Here is where I am currently stuck. After the message gets sent to the web service layer, how do we then achieve sending/relaying the message over to the end user? Should the web server send out a message to the end user and notify them, or should each client call a receiveMessage() method periodically, and if the server side has some info for them it can then respond with that info? Finally, how can we handle the case in which the user you are trying to send a message to is offline? How can we make sure the end user gets the packet when he moves back to an area with signal?

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• From a DDD perspective is a report generating service a domain service or an infrastructure service?

  - by Songo

  Let assume we have the following service whose responsibility is to generate Excel reports: class ExcelReportService{ public String generateReport(String fileFormatFilePath, ResultSet data){ ReportFormat reportFormat = new ReportFormat(fileFormatFilePath); ExcelDataFormatterService excelDataFormatterService = new ExcelDataFormatterService(); FormattedData formattedData = excelDataFormatterService.format(data); ExcelFileService excelFileService = new ExcelFileService(); String reportPath= excelFileService.generateReport(reportFormat,formattedData); return reportPath; } } This is pseudo code for the service I want to design where: fileFormatFilePath: path to a configuration file where I'll keep the format of my excel file (headers, column widths, number of columns,..etc) data: the actual records returned from the database. This data can't be used directly coz I might need to make further calculations to the data before inserting them to the excel file. ReportFormat: Value object to hold the report format, has methods like getHeaders(), getColumnWidth(),...etc. ExcelDataFormatterService: a service to hold any logic that need to be applied to the data returned from the database before inserting it to the file. FormattedData: Value object the represents the formatted data to be inserted. ExcelFileService: a wrapper top the 3rd party library that generates the excel file. Now how do you determine whether a service is an infrastructure or domain service? I have the following 3 services here: ExcelReportService, ExcelDataFormatterService and ExcelFileService?

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• How can I gather client's data on Google App Engine without using Datastore/Backend Instances too much?

  - by ruslan

  One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting?

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• MQTT, GWT, ActiveMQ stack to bring jms to the browser

  - by scphantm

  I am in the preliminary stages of architecting a legacy replacement project. They already have sub half second performance on their green screens and they want the same on their web app. We have a 390 mainframe that can handle anything we throw at it but they don't have a good jvm for it, so we have two tiers of websphere servers between the mainframe and the browser, The ui server, and the bl server. For the ui, I'm leaning towards GWT. But one thing that I think would seal the deal is to add messaging capabilities to the browser. The idea is say you click on a link that displays a second panel of information, instead of the classic GWT where it triggers a GWT-RPC call to the ui server, the ui server routs it to the bl server, the bl sends it to the mainframe and back out, it drops an MQTT message directly to the bl server or directly to the mainframe. Say writes go to the bl, reads go to the mainframe. This is an easy enough thing in classic jms because you can issue a message that has an expected response. Then have your callback ready to get the resonse. But from what I'm reading so far. It looks like mqtt doesn't have that. It looks like it's strictly fire and forget, which would make it really tough to come up with a way to get a response back to the workstation that called it. Am I right here? Has anyone tried this stack before with gwt.

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• Best approach to designing multi-client applications

  - by Tomh

  Hi, I was wondering how you guys start out if you need to design a multi-client project where multiple clients can interact with a server. In specific how do you go about dealing with different states and message handling, how do you start designing and considering all these cases? For example a video webchat application where it is possible that you call another client, while that client is already in a call, or is stuck in a modal dialog such that the calling dialog does not come through.

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• How to prevent system to generate log file

  - by shantanu

  My Question is little bit surprising, but i need it. I am using a slow processor laptop, now i found that HDD has some bad sectors and HDD response becomes slow. But disk health is ok(according to smart tools). I can not change my HDD right now. So decide to reduce disk operation. How do i prevent system to generate log file or any other file which are used to keep history? I know LOG file is very important but i don't care it right now. Please help.

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• Leveraging Code Across Platforms in Ever Bigger Games

  - by ashes999

  Summary: The same way that I continually build complex engines and libraries within a single platform and technology to allow me to build increasingly bigger and better games, how to continue this when development crosses into different platforms? If I switch platforms, how do I leverage past code and experiences? Games are hard to build. Big games are even harder to build. I've decided that to be able to make big games, I need to start building smaller games, and building up an asset base of code, assets (graphics, sounds), tools, and most importantly, game engines, so that I can eventually get there. One game at a time. Let me give an analogy. To build an MMO 3D RPG, I would approach this by building and releasing small games with increasingly more features. This could entail, for example: A simple 2D game A tile-based game A game with RPG elements (items, equipment, monsters, battle) A full-fledged RPG A 3D RPG The problem now is if I have to change platforms or tools, I don't know how to leverage past code-bases (and experience) to start with a mature product. Right now, I'm writing Silverlight (FlatRedBall) games. Let's say I stick with this for ten years, and then suddenly decide to write a PS6 game, which is in a different programming language entirely. Granted, I have ten years of game-development experience (and correspondingly ten years of professional software development experience from my day job) to back me up. But I would still like some way to transplant that 2D RPG engine into the new programming language, or else leverage it somehow. Is this even possible? What are my options?

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• Decorator not calling the decorated instance - alternative design needed

  - by Daniel Hilgarth

  Assume I have a simple interface for translating text (sample code in C#): public interface ITranslationService { string GetTranslation(string key, CultureInfo targetLanguage); // some other methods... } A first simple implementation of this interface already exists and simply goes to the database for every method call. Assuming a UI that is being translated at start up this results in one database call per control. To improve this, I want to add the following behavior: As soon as a request for one language comes in, fetch all translations from this language and cache them. All translation requests are served from the cache. I thought about implementing this new behavior as a decorator, because all other methods of that interface implemented by the decorater would simple delegate to the decorated instance. However, the implementation of GetTranslation wouldn't use GetTranslation of the decorated instance at all to get all translations of a certain language. It would fire its own query against the database. This breaks the decorator pattern, because every functionality provided by the decorated instance is simply skipped. This becomes a real problem if there are other decorators involved. My understanding is that a Decorator should be additive. In this case however, the decorator is replacing the behavior of the decorated instance. I can't really think of a nice solution for this - how would you solve it? Everything is allowed, even a complete re-design of ITranslationService itself.

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• Repairing or recreating a bootloader on a multi-booting EFI GPT system

  - by Emre

  Reinstalling Ubuntu messed up my boot loader so I I tried to fix it with boot repair. It detected my OSX installation and asked about removing the "separate boot/EFI". It also said my partition was full despite the fact that it wasn't and asked me to remove stuff. I declined both and proceeded. It's been stuck at the "purge and reinstall the GRUB" stage for half an hour. Is this typical, bearing in mind I have a fast SSD and CPU? Is there a better way to re-install grub on a multi-booting UEFI system? Does my pastebin provide any insight?

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• Techniques for separating game model from presentation

  - by liortal

  I am creating a simple 2D game using XNA. The elements that make up the game world are what i refer to as the "model". For instance, in a board game, i would have a GameBoard class that stores information about the board. This information could be things such as: Location Size Details about cells on the board (occupied/not occupied) etc This object should either know how to draw itself, or describe how to draw itself to some other entity (renderer) in order to be displayed. I believe that since the board only contains the data+logic for things regarding it or cells on it, it should not provide the logic of how to draw things (separation of concerns). How can i achieve a good partitioning and easily allow some other entity to draw it properly? My motivations for doing so are: Allow multiple "implementations" of presentation for a single game entity Easier porting to other environments where the presentation code is not available (for example - porting my code to Unity or other game technology that does not rely on XNA).

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• Service Layer - how broad should it be, and should it be used also on the local application?

  - by BornToCode

  Background: I need to build a main application with some operations (CRUD and more) (-in winforms), I need to make another application which will re-use some of the functions of the main application (-in webforms). I understood that using service layer is the best approach here. If I understood correctly the service should be calling the function on the BL layer (correct me if I'm wrong) The dilemma: In my main winform UI - should I call the functions from the BL, or from the service? (please explain why) Should I create a service for every single function on the BL even if I need some of the functions only in one UI? for example - should I create services for all the CRUD operations, even though I need to re-use only update operation in the webform? YOUR HELP IS MUCH APPRECIATED

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• Develop for Desktop and mobile use?

  - by ran2

  I am in the very beginning of developing an app / desktop program. I want it to be cross-platform and possibly also as a tablet version (preferably Android Icecream sandwich). Note that I need to run it offline. I thought about the following approaches: ADOBE Air, since I do not need much performance. Plus I did some web programming in the past which might be of some use. Afaik it would run on OS X and Windows and should run on mobile OSes, too. Qt. Found some nice Qt based desktop recently and read it also works on android. Plus I like the SDK. HTML5 / JS. Again my web background should help me here. I wont need no sever side scripts, thus it should work without installing anything but a browser. How easy could this be converted into an Android app? There might be a plethora of other (better) ways to do it, but I haven't thought of them yet. Can you help out? How would you create such an application. Would it be better to do some pure desktop client and then create tablet versions? Would you rather start to create a website and worry later on how to turn into an app?

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• Document Management System

  - by rjayavrp

  Is there any Document Management System in Ubuntu? I tried Alfresco, RavenDB, Owl, Document Manager. Alfresco, RavenDB are heavy. More than my requirements. Owl having source issues. Document Manager im trying to install. Should keep data on the same machine as I am looking for more of internal purpose. Should allow to upload Zip files as well. If it extracts Zip it will be a great + Should allow to send email to preconfigured email addresses Should allow to upload data of size around 100MB at one go Should maintain history of documents also deleted documents Should allow role based document access. Should be Free :) It should not do any spoofing on data. Documents are confidential. Please share your knowledge. Thanks.

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• Designing a "Grid" like object that contains game objects

  - by liortal

  I am working on a 2D game, where there's a game "board" on which other game objects are placed. This this is 2D, my starting point was to design a class that will internally use a 2d array for the actual stored game objects. This class could be simply accessed by 2 indices: (i, j) to get game objects on it. My problem is that i have no idea how to make the game "board" "propagate" its data onto its children. Design questions i ran into are: Should the children placed on the board have display properties such as size, screen position? Should the board itself dictate this information? How to update children in case the board changes some of its properties? (position, etc). Should the board be aware of the types of objects stored in it ? I have no idea how similar things such as WPF or other UI frameworks go about organizing a "container like" object that can arrange or apply certain UI properties to its children.

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• About shared (static) Members and its behavior

  - by Allende

  I just realized that I can access shared members from instances of classes (probably this is not correct, but compile and run), and also learn/discover that, I can modify shared members, then create a new instance and access the new value of the shared member. My question is, what happens to the shared members, when it comes back to the "default" value (class declaration), how dangerous is it do this ? is it totally bad ? is it valid in some cases ?. If you want to test my point here is the code (console project vb.net) that I used to test shared members, as you can see/compile/run, the shared member "x" of the class "Hello" has default value string "Default", but at runtime it changes it, and after creating a new object of that class, this object has the new value of the shared member. Module Module1 Public Class hello Public Shared x As String = "Default" Public Sub New() End Sub End Class Sub Main() Console.WriteLine("hello.x=" & hello.x) Dim obj As New hello() Console.WriteLine("obj.x=" & obj.x) obj.x = "Default shared memeber, modified in object" Console.WriteLine("obj.x=" & obj.x) hello.x = "Defaul shared member, modified in class" Console.WriteLine("hello.x=" & hello.x) Dim obj2 As New hello() Console.WriteLine("obj2.x=" & obj2.x) Console.ReadLine() End Sub End Module UPDATE: First at all, thanks to everyone, each answer give feedback, I suppose, by respect I should choose one as "the answer", I don't want to be offensive to anyone, so please don't take it so bad if I didn't choose you answer.

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• Structure of a correctly implemented JTable with TableModel and Listeners?

  - by bamboocha

  I am pretty new to Java and its JTables and this is where I am struggling at the moment. I need to create a GUI which shows me results of a sql query like SELECT * FROM tblPeople WHERE name='Doe'. My idea was to create a a JFrame which displays a JTable with all found records. Besides this, I need to also implement some code to handle when a user is double clicking a record or selecting it by using his arrow keys (additional feature: pressing 12(e.g.) should select the 12th record). What is the best way to structure my program (what classes do I need and especially where do I store my logic)? I came up with structuring it the following way: Main.java ("view") SQLConnection.java PeopleTableModel.java (only stores and returns data given by the passed ResultSet, "model" inherits from DefaultTableModel) PeopleTable.java (stores basically all my logic including KeyListener and MouseListener, "controller", inherits from JTable) Are there better ways to achieve my goals? If so, what are they?

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• How do I design a game framework for fast reaction to user input?

  - by Miro

  I've played some games at cca 30 fps and some of them had low reaction time - cca 0.1sec. I hadn't knew why. Now when I'm designing my framework for crossplatform game, I know why. Probably they've been preparing new frame during rendering the previous. RENDER 1 | RENDER 2 | RENDER 3 | RENDER 4 PREPARE 2 | PREPARE 3 | PREPARE 4 | PREPARE 5 I see first frame when second frame is being rendered and third frame being prepared. If I react in that time to 1st frame it will result in forth frame. So it takes 3/FPS seconds to appear results. In 30 fps it would be 100ms, what is quite bad. So i'm wondering what should I design my framework to response to user interaction quickly?

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• "The system is running in low graphics mode", unable to connect to the Internet

  - by Blah

  When I try to log onto Ubuntu, I get a notice that reads: The system is running in low graphics mode. I searched for a solution and there are a slew of answers. However, many of them seem to suggest reinstalling different things. After pressing Ctrl+Alt+F1 and getting to a terminal, I attempt commands like sudo apt-get install example. Upon doing so I get notices that say things such as could not resolve host which I am assuming means I'm not connected to the Internet. Since I can not connect to the Internet, none of these responses are helpful to me. What can I do?

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• How should I load level data in java?

  - by Matthew G.

  I'm setting up my engine for a certain action/arcade game to have a set of commands that would look something like this. Set landscape to grass Create rocks at ... Create player at X, Y Set goal to "Get to point X Y" Spawn enemy at X, Y I'd then have each object knowing what it has to do, and acting on its own. I've been thinking about how to store this data. External data files could be parsed by a level class, and certain objects can be spawned through that. I could also create a base level class and extend it for each level, but that'd create a large amount of classes. Another idea is to have one level parser class, but have a case for each level. This would be extremely silly and bulky, but I mention it because I found that I did this at 2 AM last night. I'm finally getting why I have to plan out my inheritances, though. RIP project. I might be completely missing another option.

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• Where to implement storable items

  - by James Hay

  I'm creating a multiplayer online trading game. The things that are traded range from raw items to complex products. For example Steel is a raw item. Mechanical Assembly is a more complex item that requires 2x Steel and maybe 1x Rubber. Then Hydraulics is an item that contains 2x Mechanical Assemblies and 1x Electronics (which is another complex item). So and so forth. These items will be created by me, players can't create their own items, so it doesn't need to be able to handle arbitrary layers of complexity for items. If my example isn't clear, think Minecraft. You have wooden planks, which can be made into sticks. From there the sticks - combined with metals - can be made into tools. My game is nothing to do with minecraft or any sandbox building game, but it uses a similar progressive complexity to creating items that I want to have in my game. My question is basically, how do you store something like this assuming that I will want to add more items in the future? Do you store it in a database or in a seperate library that the game uses? EDIT None of the items actually "do" anything, they are simply there to either sell, purchase, or combine with other items to make a more complex item, which can then be sold, purchased or combined... you get the idea. The items themselves would not have any properties, but the instances of the items would. For example an item that one player has would have a certain "quality" and if they were selling it a certain "price". An instance of that same item that a different player had would need to have a different "quality" and "price" if they were selling it. I think the price part will not be required on an individual item because instead I would have a "sale" object which was for a price and contained certain items.

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• How to keep a generic process unique?

  - by Steve Van Opstal

  I'm currently working on a project that makes connection between different banks which send us information on which that project replies. A part of that project configures the different protocols that are used (not every bank uses the same protocol), this runs on a separate server. These processes all have unique id's which are stored in a database. But to save time and money on configurations and new processes, we want to make a generic protocol that banks can use. Because of PCI requirements we have to make a separate process for every bank we connect to. But the generic process has only 1 unique identifier and therefor we cannot keep them apart. Giving every copy of that process a different identifier is as I see it impossible because they run entirely separate. So how do I keep my generic process unique?

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• How would you represent an object that can be of multiple types, when storing it as a document in MongoDB?

  - by blueberryfields

  Somewhat related to this question, say that I have an object category which, depending on which type of object I have, has different restrictions on what it contains. (if you can reword the previous sentence to make more sense I'd appreciate it) For example var SomeSchema = new Schema({ _id: ObjectID, [... large number of common fields ...] type: //Restricted somehow to members of a fixed array data: //depending on type, this might be restricted - sometimes an integer, sometimes array, etc... }); What's the idiosyncratic method for defining this type of schema? Is it appropriate to define a single schema, and handle the types inside of it's members, or am I better off with separate schema for each type?

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• Digital "Post It" notes for organizing content of sites/pages

  - by Alex

  We're restructuring our old intranet into a new one and are going through each site to find content and use our new standard structure/look-and-feel. Do you recommend a tool where you can do "digital Post-It" notes? It would provide a way to type some items on a "card" and be able to move it around and organize it quickly. Also, if you know of tools in general for this kind of task, please advise. Thank you.

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• prism and multiple screens

  - by Avi

  OK - I am studying Prism a little because of a "free weekend" offer on Pluralsight. As this is proving too complex for me, I went to the Prism book and looked at the forward, and this is what it said: What comes after “Hello, World?” WPF and Silverlight developers are blessed with an abundance of excellent books... There’s no lack of tutorials on Model-View-ViewModel ... But they stop short of the guidance you need to deliver a non-trivial application in full. Your first screen goes well. You add a second screen and a third. Because you started your solution with the built-in “Navigation Application Template,” adding new screens feels like hanging shirts on a closet rod. You are on a roll. Until the harsh reality of real application requirements sets in. As it happens, your application has 30 screens not three. There’s no room on that closet rod for 30 screens. Some screens are modal pop-ups; you don’t navigate to a pop-up. Screens become interdependent such that user activity in one screen triggers changes that propagate throughout the UI. Some screens are optional; others are visible only to authorized users. Some screens are permanent, while other screens can be opened and closed at will. You discover that navigating back to a previously displayed screen creates a new instance. That’s not what you expected and, to your horror, the prior instance is gone along with the user’s unsaved changes. Now the issue is, I don't relate to this description. I've never been a UI programmer, but same as everyone else I'm using Windows apps such as MS-Office, and web sites such as Amazon, Facebook and StackExchange. And I look at these and I don't see many "so many screens" issues! Indeed, the only applications having many windows I can think of is Visual Studio. Maybe also Visio, a little. But take Word - You have a ribbon and a main window. Or take Facebook: You have those lists on the left (Favorites, Lists, Groups etc.), the status middle, the adds and then the Contacts sidebar. But it's only one page. Of course, I understand that in enterprise scenarios there are dashboad applications where multiple segments of the screen are updated from multiple non-related services. This I dig. But other scenarios? So - What am I missing? What is the "multiple screens" monster Pirsm is supposed to be the silver bullet solution for? Shoud I invest in studying Prism in addition to learning WPF or ASP.NET MVC?

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• Why make the login page to a single page application a separate page?

  - by ryanzec

  I am wondering why it seems to be popular to have the login page of a SPA be a separate page that is not page of the SPA (as in loaded and send data through ajax requests)? I only thing I can think of is security but I can't think a specific security reason. I mean the only thing that come to mind is that if your login page in part of the SPA, it sends the username/password through ajax which can be seen by such tools like firebug or web inspector however even if you send it as a normal POST request, there are other tools that can easily capture this data (like fiddler, httpscoop, etc...). Is there something I am missing?

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