Hey,
first of all this is a conceptional question and I do not know if StackOverflow is the appropriate place - so my apologies if I am wrong.
Nowadays the web is not only used for passing raw informations. Many and especially complex web applications are in use. These web application seem to be so complex that it seems irrational to use the HTTP protocol, which is based on so simple data exchange, plus it is stateless.
Would it not be more convincing to use remote invocations for this web applications? The big advantage to my mind is a unified GUI by using HTML. But there are applications, which have no need for a graphical interfaces and then it comes to a point where the HTTP protocol is really cumbersome.
Short answer: HTTP is allowed through firewalls where other protocols would be blocked.
A short partial answer is: first, for historical reasons - HTTP was used since the dawn of the web as protocol for requesting documents, and has since been used for some different purposes. One reason to keep using it is that it is generally served on port 80 which you can be sure won't be blocked by firewalls between your client and the server. The statelessness of the protocol may not always be what you want, but it has at least the advantage of protecting the server side from very trivial overloading problems.
OS independence
firewall passing
the web server is already a well understood and mostly "solved" problem in terms of load balancing, server fall over, etc.
don't have to reinvent the wheel
Other protocols are being used more and more now, including remote invocations and (the one I am particularly familiar with) WCF (which allows binary TCP/IP data transfer).
This allows data to travel faster for applications which require more bandwidth. For example an n-tier application may use WCF binary transfer between application and presentation tiers. Also public web services allow multiple protocols, including binary.
For data transfer protocols, firewalls should be configured (ie. expose a port specifically for your application), not worked around, I would not recommend using a protocol because firewalls do not block it.
The protocol used really depends on who will consume it and what control you have over the consumption - eg external third parties may need a plain-text version with a commonly agrreed data interface. On the other hand, two tiers in a single web application may be able to utilise binary data transfer for performance and security.
Related
I want to create a program for my desktop and an app for my android. Both of them will do the same, just on those different devices. They will be something like personal assistants, so I want to put a lot of data into them ( for example contacts, notes and a huge lot of other stuff). All of this data should be saved on a server (at least for the beginning I will use my own Ubuntu server at home).
For the android app I will obviously use java and the database on the server will be a MySQL database, because that's the database I have used for everything. The Windows program will most likely be written in of these languages: Java, C#c C++, as these are the languages I am able to use quite well.
Now to the problem/question: The server should have a good backend which will be communicating with the apps/programs and read/write data in the database, manage the users and all that stuff. But I am not sure how I should approach programming the backend and the "network communication" itself. I would really like to have some relatively easy way to send secured messages between server and clients, but I have no experience in that matter. I do have programming experience in general, but not with backend and network programming.
side notes:
I would like to "scale big". At first this system will only be used by me, but it may be opened to more people or even sold.
Also I would really like to a (partly) self programmed backend on the server, because I could very well use this for a lot of other stuff, like some automation features in my house, which will be implemented.
EDIT: I would like to be able to scale big. I don't need support for hundreds of people at the beginning ;)
You need to research Socket programming. They provide relatively easy, secured network communication. Essentially, you will create some sort of connection or socket listener on your server. The clients will create Sockets, initialize them to connect to a certain IP address and port number, and then connect. Once the server receives these connections, the server creates a Socket for that specific connection, and the two sockets can communicate back and forth.
If you want your server to be able to handle multiple clients, I suggest creating a new Thread every time the server receives a connection, and that Thread will be dedicated to that specific client connection. Having a multi-threaded server where each client has its own dedicated Thread is a good starting point for an efficient server.
Here are some good C# examples of Socket clients and servers: https://msdn.microsoft.com/en-us/library/w89fhyex(v=vs.110).aspx
As a side note, you can also write Android apps in C# with Xamarin. If you did your desktop program and Android app both in C#, you'd be able to write most of the code once and share it between the two apps easily.
I suggest you start learning socket programming by creating very simple client and server applications in order to grasp how they will be communicating in your larger project. Once you can grasp the communication procedures well enough, start designing your larger project.
But I am not sure how I should approach programming the backend and
the "network communication" itself.
Traditionally, a server for your case would be a web server exposing REST API (JSON). All clients need to do http requests and render/parse JSON. REST API is mapped to database calls and exposes some data model. If it was in Java, it would be Jetty web server, Jackson Json parser.
I would really like to have some relatively easy way to send secured
messages between server and clients,
Sending HTTP requests probably the easiest way to communicate with a service. Having it secured is a matter of enabling HTTPS on the server side and implementing some user access authentication and action authorization. Enabling HTTPS with Jetty for Java will require few lines of code. Authentication is usually done via OAuth2 technique, and authorization could be based on ACL. You may go beyond of this and enable encryption of data at rest and employ other practices.
I would like to "scale big". At first this system will only be used by
me, but it may be opened to more people or even sold.
I would like to be able to scale big. I don't need support for
hundreds of people at the beginning
I anticipate scalability can become the main challenge. Depending on how far you want to scale, you may need to go to distributed (Big Data) databases and distributed serving and messaging layers.
Also I would really like to a (partly) self programmed backend on the
server, because I could very well use this for a lot of other stuff,
like some automation features in my house, which will be implemented.
I am not sure what you mean self-programmed. Usually a backend encapsulates some application specific business logic.
It could be a piece of logic between your database and http transport layer.
In more complicated scenario your logic can be put into asynchronous service behind the backend, so the service can do it's job without blocking clients' requests.
And in the most (probably) complicated scenario your backend may do machine learning (for example, if you would like you software stack to learn your home-being habits and automate house accordingly to your expectations without actually coding this automation)
but I have no experience in that matter. I do have programming
experience in general, but not with backend and network programming.
If you can code, writing a backend is not very hard problem. There are a lot of resources. However, you would need time (or money) to learn and to do it, what may distract you from the development of your applications or you may enjoy it.
The alternative to in-house developed of a backend could be a Backend-as-a-Service (BaaS) in cloud or on premises. There are number of product in this market. BaaS will allow you to eliminate the development of the backend entirely (or close to this). At minimum it should do:
REST API to data storage with configurable data model,
security,
scalability,
custom business-logic
Disclaimer: I am a member of webintrinsics.io team, which is a Backend-as-a-Service. Check our website and contact if you need to, we will be able to work with you and help you either with BaaS or with guiding you towards some useful resources.
Good luck with your work!
I am new to SignalR and I try to understand the difference between consistent connection and long polling,Is there different use in methods ? is one better than the other? are there any diffrenet functions need to polling and other functions to use consistent connection?, I googled but didn't find a simple answer to this question, can someone help? need an explanation.
SignalR is a framework that allows us to build real-time web applications. Ideally, we would use web sockets for this. However, web sockets is a new protocol and requires support from both the browser and the server. Thus, web sockets are not generally available and SignalR tries to provide an abstract connection similar to web sockets but built upon existing technologies and techniques. This abstraction is called a Persistent Connection.
Persistent connection is the term used to describe SignalR's abstract connections.
Long polling is one of several techniques used to implement SignalR's persistent connections (the others are Forever Frame, Server-Sent Events and Web Sockets).
I am searching for a good method to transfer data over internet, and I work in C++/windows environment. The data is binary, a compressed blob of an extracted image. Input and requirements are as follows:
6kB/packet # 10 packets/sec (60kBytes per second)
Reliable data transfer
I am new to network programming and so far I could figure out that one of the following methods will be suitable.
Sockets
MSMQ (MS Message Queuing)
The Client runs on a browser (Shows realtime images on browser). While server runs native C++ code. Please let me know if there are any other methods for achieving the same? Which one should I go for and why?
If the server determines the pace at which images are sent, which is what it looks like, a server push style solution would make sense. What most browsers (and even non-browsers) are settling for these days are WebSockets.
The main advantage WebSockets have over most proprietary protocols, apart from becoming a widely adopted standard, is that they run on top of HTTP and can thus permeate (most) proxies and firewalls etc.
On the server side, you could potentially integrate node.js, which allows you to easily implement WebSockets, and comes with a lot of other libraries. It's written in C++, and extensible via C++ and JavaScript, which node.js hosts a VM for. node.js's main feature is being asynchronous at every level, making that style of programming the default.
But of course there are other ways to implement WebSockets on the server side, maybe node.js is more than you need. I have implemented a C++ extension for node.js on Windows and use socket.io to do WebSockets and non-WebSocket transports for older browsers, and that has worked out fine for me.
But that was textual data. In your binary data case, socket.io wouldn't do it, so you could check out other libraries that do binary over WebSockets.
Is there any specific reason why you cannot run a server on your windows machine? 60kb/seconds, looks like some kind of an embedded device?
Based on our description, you ned to show image information, in realtime on a browser. You can possibly use HTTP. but its stateless, meaning once the information is transferred, you lose the connection. You client needs to poll the C++/Windows machine. If you are prety confident the information generated is periodic, you can use this approach. This requires a server, so only if a yes to my first question
A chat protocol. Something like a Jabber client running on your client, and a Jabber server on your C++/Windows machine. Chat protocols allow almost realtime
While it may seem to make sense, I wouldn't use MSMQ in this scenario. You may not run into a problem now, but MSMQ messages are limited in size and you may eventually hit a wall because of this.
I would use TCP for this application, TCP is built with reliability in mind and you can simply feed data through a socket. You may have to figure out a very simple protocol yourself but it should be the best choice.
Unless you are using an embedded device that understands MSMQ out of the box, your best bet to use MSMQ would be to use a proxy and you are then still forced to play with TCP and possibly HTTP.
I do home automation that includes security cameras on my personal time and I use the .net micro framework and even if it did have MSMQ capabilities I still wouldn't use it.
I recommend that you look into MJPEG (Motion JPEG) which sounds exactly like what you would like to do.
http://www.codeproject.com/Articles/371955/Motion-JPEG-Streaming-Server
I am having a Web application sitting on IIS, and talking with [remote]Service-Machine.
I am not sure whether to choose TCP or Http, as the main protocol.
more details:
i will have more than one service\endpoint
some of them will be one-way
the other will be two-ways
the web pages will work infront of the services
we are talking about hi-scale web-site
I know the difference pretty well, but I am looking for a good benchmark, that shows how much faster is the TCP?
HTTP is a layer built ontop of the TCP layer to some what standardize data transmission. So naturally using TCP sockets will be less heavy than using HTTP. If performance is the only thing you care about then plain TCP is the best solution for you.
You may want to consider HTTP because of its ease of use and simplicity which ultimately reduces development time. If you are doing something that might be directly consumed by a browser (through an AJAX call) then you should use HTTP. For a non-modern browser to directly consume TCP connections without HTTP you would have to use Flash or Silverlight and this normally happens for rich content such as video and/or audio. However, many modern browsers now (as of 2013) support API's to access network, audio, and video resources directly via JavaScript. The only thing to consider is the usage rate of modern web browsers among your users; see caniuse.com for the latest info regarding browser compatibility.
As for benchmarks, this is the only thing I found. See page 5, it has the performance graph. Note that it doesn't really compare apples to apples since it compares the TCP/Binary data option with the HTTP/XML data option. Which begs the question: what kind of data are your services outputting? binary (video, audio, files) or text (JSON, XML, HTML)?
In general performance oriented system like those in the military or financial sectors will probably use plain TCP connections. Where as general web focused companies will opt to use HTTP and use IIS or Apache to host their services.
The question you really need an answer for is "will TCP or HTTP be faster for my application". The answer is that it depends on the nature of your application, and on the way that you use TCP and/or HTTP in your application. A generic HTTP vs TCP benchmark won't answer your question, because the chances are that the benchmark won't match your application behaviour.
In theory, an optimally designed / implemented solution using TCP will be faster than one that uses HTTP. But it may also be considerably more work to implement ... depending on the details of your application.
There are other issues that might affect your choice. For example, you are less likely to run into firewall issues if you use HTTP than if you use TCP on some random port. Another is that HTTP would make it easier to implement a load balancer between the IIS server and the backend systems.
Finally, at the end of the day it is probably more important that your system is secure, reliable, maintainable and (maybe) scalable than it is fast. A sensible strategy is to implement the simple version first, but have plans in your head for how to make it faster ... if the simple solution is too slow.
You could always benchmark it.
In general, if what you want to accomplish can be easily done over HTTP (i.e. the only reason you would otherwise think about using raw TCP is for a possible performance boost) you should probably just use HTTP. Sure, you can do socket programming, but why bother? Lots of people have spent a lot of time and effort building HTTP client libraries and servers, and they have spent waaaaaay more time optimizing and testing that code than you will ever be able to possibly spend on your TCP sockets. There are simply so many possible errors that you would have to handle, edge cases, and optimizations that can be done, that it is usually easier and safer to use a library function for HTTP.
Plus, the HTTP specs define all kinds of features (and clients/servers implement, which you get to use "for free", i.e. no extra implementation work) which makes any third-party interoperability that much easier. "Here is my URL, here are the rules for what you send, here are the rules for what I return..."
I have a Self Hosted Windows native C++ server application that I use the Casablanca C++ REST SDK code in. I can use any client C#, JavaScript, C++, cURL, basically anything that can send a POST, GET, PUT, DEL message can be used to send request messages to this self hosted windows app. Also I can use a plain browser address bar to do GET related requests using various parameters. Currently I only run this system on a private intranet so it is very fast - I haven't benchmark it against just doing raw TCP, but on a private intranet I doubt there would be even a few microseconds difference? For the convenience and ease of development and ability to expand to full blown internet app it's a dream come true. It is a dedicated system with a private protocol using small JSON packets so not certain if that fits your application needs or not? Another nice thing is this Windows application native C++ code could be ported fairly easily to run on Linux/MacOS as the Casablanca REST SDK is portable to those OSes.
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If I have a separate system with its own concept of users and presence, what is the most appropriate architecture for creating a bridge to an XMPP server network? As far as I can tell there are three primary ways:
Act as a server. This creates one touchpoint, but I fear it has implications for compatibility, and potentially creates complexity in my system for emulating a server.
Act as a clients. This seems to imply that I need one connection per user in my system, which just isn't going to scale well.
I've heard of an XMPP gateway protocol, but it's unclear if this is any better than the client solution. I also can't tell if this is standard or not.
Any suggestions or tradeoffs would be appreciated. For example, would any of these solutions require running code inside the target XMPP server (not likely something I can do).
The XMPP gateway protocol you've heard of is most likely to do with transports. A transport is a server that connects to both a XMPP server and a non-XMPP server. By running a transport, I can use my Jabber client to talk to someone using, say, MSN Messenger.
A transport typically connects once to the remote network for each JID that it sees as online. That is, it's your option 2 in reverse. This is because there is no special relationship between the transport and the non-XMPP network; the transport is simply acting as a bunch of regular clients. For this to work, XMPP clients must first register with the transport, giving login credentials for the remote network, and allowing the transport to view their presence.
The only reason this has a chance of scaling better is that there can be many transports for the same remote network. For example, my Jabber server could run a transport to MSN, another Jabber server could run another one, and so on, each one providing connections for a different subset of XMPP users. While this spreads out the load on the Jabber side, and load balancing on your system may spread out the load as well, it still requires many connections between the two systems.
In your case, because (I assume) the non-XMPP side of things is cooperating, putting a XMPP server interface on the non-XMPP server is likely your best bet. That server interface is best suited for managing the mapping between XMPP JIDs and how that JID will appear on its own network, rather than forcing XMPP users to register and so on.
In case you haven't seen these, you might find them useful:
http://www.jabber.org/jabber-for-geeks/technology-overview
http://www.xmpp.org/protocols/
http://www.xmpp.org/extensions/
Hope that helps.
I too am working on a similar system.
I am going with the gateway/component route. I have looked at several options and settled with this one.
The gateway is basically a component with the specific purpose of bridging Jabber/XMPP with another network. You will have to build most of the things you take for granted when using XMPP as a client. Stuff like roster control.
There is very little help online on the actual design and building of a component. Like the above answer I found that the xmpp protocols/extensions to be of help. The main ones being:
Basic Client 2008
Basic Server 2008
Intermediate Client 2008
Intermediate Server 2008
Reading through these will show you what XEPs you will be expected to be able to handle. Ignore the stuff that will be handled by the server that your component will be attched to.
It's a shame that Djabberd has such poor documentation as their system of "everything is a module" gave the possibility of backend of the server could interface directly to the other network. I made no headway on this.
There are basically two types of server to server (s2s) connections. The first is either called a gateway or a transport, but they're the same thing. This is probably the kind you're looking for. I couldn't find specific documentation for the non-XMPP side, but how XMPP thinks about doing translations to legacy servers is at http://xmpp.org/extensions/xep-0100.html. The second kind really isn't explained in any additional XEPs -- it's regular XMPP s2s connections. Look for "Server-to-Server Communication" in RFC 3920 or RFC 3920bis for the latest draft update.
Since you have your own users and presence on your server, and it's not XMPP, the concepts aren't going to map completely to the XMPP model. This is where the work of the transport comes in. You have to do the translation from your model to the XMPP model. While this is some work, you do get to make all the decisions.
Which brings us right to one of the key design choices -- you need to really decide which things you are going to map to XMPP from your service and what you aren't. These feature and use case descriptions will drive the overall structure. For example, is this like a transport to talk to AOL or MSN chat services? Then you'll need a way to map their equivalent of rosters, presence, and keep session information along with logins and passwords from your local users to the remote server. This is because your transport will need to pretend to be those users and will need to login for them.
Or, maybe you're just an s2s bridge to someone else's XMPP based chess game, so you don't need a login on the remote server, and can just act similarly to an email server and pass the information back and forth. (With normal s2s connections the only session that would be stored would be SASL authentication used with the remote server, but at the user level s2s just maintains the connection, and not the login session.)
Other factors are scalability and modularity on your end. You nailed some of the scalability concerns. Take a look at putting in multiple transports to balance the load. For modularity, see where you want to make decisions about what to do with each packet or action. For example, how do you handle and keep track of subscription data? You can put it on your transport, but then that makes using multiple transports harder. Or if you make that decision closer to your core server you can have simpler transports and use some common code if you need to talk to services other than XMPP. The trade off is a more complex core server with more vulnerability potential.
What architecture you should use depends on the non-XMPP system.
Do you operate the non-XMPP system? If yes, you should find a way to add an XMPP-S2S interface to that system, in other words, make it act as an XMPP server. AOL is using this approach for AIM. Unfortunately, they have restricted their gateway to GoogleTalk.
You don't operate the non-XMPP system but it has a federation interface that you can use - i. e. your gateway can talk to the other system as a server and has a namespace of its own. In this case, you can build a gateway that acts as a federated server on both sides. For I don't know of any example of a gateway that uses this approach but you could use it if you want to build a public XMPP-to-SIP bridge.
If the non-XMPP system doesn't give you a federation interface, then you have no other option but acting as a bunch of clients. In the XMPP world, this is called a "transport". The differences between a transport and a normal server are basically:
the JIDs of the transport are mapped from another system (e.g. john.doe\40example.net#msngateway.example.org - really ugly!)
XMPP users who want to use the transport need to create an account on the non-XMPP system and give the login credentials of that account to the transport service. The XMPP protocol even has a protocol extension that allows XMPP users to do transport registrations in-band.
One other approach is to work with your XMPP server vendor. Most have internal APIs that make injecting presence possible from third party applications. For example, Jabber XCP provides an API for this that's really easy to use.
(Disclosure: I work for Jabber, Inc, the company behind Jabber XCP)