I am currently working on a project that is very new to me, and I feel a bit over my head as far as knowledge base is concerned. My request is for references and information to help me expand my knowledge base, as well as recommendations for technologies and methods.
I have experience primarily with Java, so all this Windows service stuff is new to me. I am not really asking for a how-to (but if someone has time....I wouldn't object :-P)
The project is as follows:
I am to develop an application in ASP.NET that runs as a process from start-up to shutdown. It will be checking some things in a folder, encrypting some files from that folder, and then check if internet connectivity is available. If it is available, it will be sending those files to a server (via a web service on that server, I believe). If it is not available, it will check every 'insert time interval here' to see if connectivity has become available, at which time it will send the files. Once the files are received by the service, the application will need to recieve some kind of confirmation from the server that the file associated with 'xxxxxxxxxxxxx' uniqueidentifier has been received.
Any explanation of the way that web services work or how to implement file encryption in a desktop app (resource load optimization is a very substantial requirement of this app).
Thanks!
badPanda
There are a couple of things going on here. First off it sounds like you are trying to write a service. Assuming you are writing code for Windows, and that code needs to run regularly and perform some tasks, and you want it to start and stop automatically when the computer is starting or shutting down, a service is ideal for this kind of task. Writing a service isn't too different from writing a normal application except that it has a few extra parts to allow the operating system to control it, and it typically has no user interface.
As far as interacting with a web service goes, typically a web service has a published WSDL (Web Services Description Language) which is just a fancy XML file that contains a description of the service. Most moden programming tools have a feature that loads a WSDL file and creates an object that communicates with the service for you. Then its as simple as creating an instance of that client object and calling the appropriate method. Typically using this created object is as simple as calling normal code, and the object does all the work of converting your parameters to a message, sending them over the network, waiting for the response, and converting the response from the web service back into a return value your client can read.
Encryption methods are going to vary based on operating system and programming language. To get any serious kind of answer you are going to have to add more details.
Really all of this is stuff you should be able to find with google, but one of the ironies of search is sometimes you can't find what you are looking for unless you already know what it is called. Try matching up terms like 'Windows Service' with your programming tools and throw in the word tutorial and you should find lots of good stuff to read. So if you are using Visual Studio and C#, a search like 'Windows Service Visual Studio C# Tutorial' should get you exactly what you need.
Related
I'm using Python and QT (PySide) in a local application (which connect to a database on cloud Azure).
Now, my objective is moving this app on the web, in particular on Azure (I have an Azure subscription), simply transfering it on Azure, it's possible in some manner? I have not found examples on the web.
The important question is: is Python QT (app web) compatible with Azure?
Thanks
UPDATED ANSWER!
Yes, now you can. Well sort of. The mad mads at Digia have created something called "QT for Web Assembly" that can compile your whole app into something that runs embedded into a web page.
https://doc.qt.io/qtcreator/creator-setup-webassembly.html
You might have to rethink connecting directly to the database however, as thats simply not gonna fly with web-sockets (And honestly direct app to remote RDBMS has never been a smart move. Theres a LOT of things that can go wrong letting the internet connnect to your databaes). But you could at least keep the UI and rewrite the databaes layer to interogate something like a GraphQL (or whatever) front end to the data.
OLD ANSWER
I'm afraid your up for a nearly complete rewrite. QT is a desktop/mobile platform. It doesn't go anywhere near HTML/CSS except perhaps for displaying them in a webview component. Azure or AWS won't magically make it into a web application for you.
Your code as it stands needd to be rewritten in a web-first transactional manner. That is it takes a request, processes it, produces a result. To some extent websockets has changed this dynamic for a limited subset of use cases where interaction needs to be non transactional, and modern web app design hides much of the transactionality behind a web-services model, but 90% of web work is still very much transactional.
Database <---> Web server/Web app stack <--- Internet! --> Web browser
My suggestion is to pick up Django (or one of the other systems. If its just simple, Flask is another good alternative. Flask for simple apps, Django for the big stuff. Or use something else, you have choices here!, and start from scratch. Analyse your products function and start mapping out how to make this work as a database driven transactional system.
Theres no shortcuts here, I'm afraid.
I've recently created two C# console applications. The first transforms a bunch of command outputs into an XML, and the second transforms the XML into a Word document using a template.
I'd like to know how I could get this onto the web, i.e having a web page where the command output can be uploaded, the two step conversion executed, and finally the Word document made available for download.
Should the web page be created in ASP.NET or are there other (better) options? Do I need to rewrite the console applications in some other format?
This question is fairly broad, with plenty of room for novel sized explanations, but here's a brief highlevel walk through of what likely needs to happen to achieve the proposed results (language agnostic):
Get a hosting provider that allows users to spin up their own machine (i.e. AWS).
Spin up a machine that is compatible with the "console" programs in question.
Install "console" programs on machine.
Install a programming language (i.e. Node.js, PHP, ASP.NET, even C# could do) on the machine.
Install a web server (i.e. NGINX, Apache) on machine, configure it to serve public requests and run with chosen language.
On server request, execute appropriate commands from within the chosen language. Languages typically come with a exec method (i.e. in node.js: require('child_process').exec(command,options,callback))
Get the results of said commands and send it back to the client. Alternatively (for downloads), write the result to a path on the system that is publicly available to the internet and redirect the user to that url (additional configuration might be required to make sure the browser downloads the file as oppose to just serving it).
The steps above should get you pretty close to that you want. As for your questions:
Should the web page be created in ASP.NET or are there other (better)
options?
The "better" options is whatever you feel most comfortable with at the moment, you could always change it later with reasonable effort (assuming that your "console" apps are not unsuspecting unicorns).
Do I need to rewrite the console applications in some other format?
No, unless you have strong reasons to do so (i.e. multi environment compatibility). You could also rewrite to significantly simplify (i.e. bypass working with a CLI and do everything in C#).
Try thinking through these high level steps, begin working on a implementation, and post more specific questions here on StackOverflow when you get stuck.
I hope that helps!
We are referencing a 3rd party proprietary CLI DLL in our .net project. This DLL is only an interface to their proprietary C++ library. Our project is an asp.net (MVC4/Web API) web application.
The C++ unmanaged library is rather unstable. Sometimes it crashes with e.g. dangling pointers. We have no way of solving it, and using this library is a first-class customer requirement.
When the application crashes, the application pool in IIS doesn't respond anymore. We have to restart it, and doing so takes a couple minutes (yes, that long!).
We would like to keep this unstable DLL from crashing our application. What's the best way of doing it? Can we keep the CLI DLL in a separate AppDomain? How?
Thanks in advance.
I think every answer to this question will be some kind of work around.
My workaround would be to not interact directly with the DLL from your web application.
Instead write your requests from the web application to either a Message Queue or a SQL table. You can then have another application such as a Windows Service which reads the requests, interacts with the DLL and then writes the results back for your web application to read.
I'm not saying that SQL / Message Queues are the right way, I'm more thinking of the general process flow.
I had this exact problem with a third party library that accessed protected memory for purposes of interacting with a hardware copy protection dongle. It worked fine in a console or winforms app, but crashed like crazy when called from an IIS application.
We tried several different things, some of which are mentioned in other answers on this page. But ultimately, the best solution for us was to us a very old technology - .Net Remoting. I know - it's somewhat frowned on these days. But it fit this particular need quite well.
The unstable code was placed in a Windows Service application. The web application made remoting calls to this service, which relayed the commands to the third-party library.
Now I'm sure you could do the same thing with WCF, sockets, etc. But remoting was quick and easy to setup, and since we only talk to the same server it works without opening any ports. It just talks on a named pipe.
It does mean a second service to install besides the web application, but that was acceptable in my particular use case.
If you did something similar, and the third-party code actually crashed the service, you could probably write some code in your main application to bring it back up.
So perhaps a process boundary is more useful than an App Domain when you have unstable code to wrangle.
I would first increase the IIS process recyling rate, maybe the the DLL code fails after a certain number of calls, or after the process reaches a certain amount of memory usage.
You can find information on the configuration of IIS 7.0 recycling options here: http://technet.microsoft.com/en-us/library/cc753179(v=ws.10).aspx
In your case I would recycle the process at a specific time, when you know there is less load on the application. And after a certain number of requests (lower than the default) to try and have "fresh" process most of the time.
The recycling process is graceful in the sense that the the old process is not terminated until the one that will replace it is ready, so there should be no noticeable downtime.
More information about the recycling mechanism here: http://technet.microsoft.com/en-us/library/cc745955.aspx
If the above does not solve the problem I would wrap the calls in my own code that manages the unstable DLL execution.
This code should recover from the failures for example by repeating the failing calls until a result is obtained and failing with a graceful error if it is not possible after a number of attempts.
Internally the calls to the unstable DLL could be made in a spawned thread or even the code could be in an new external executable that you could launch with Process.Start.
This last option has more overhead but it might be your only option. See this SO question for more information on this: How do you handle a thread that has a hung call?
I suggest following solution.
Wrap this dll with another web application. Can be one of the following ones. Since you already use web api, it is most suitable for you.
Simple ASMX Web Service
WCF Service
Asp.Net MVC - WEB Api Service
Control your p-invoke code so that you do not have any bug? See following articles.
The Black Art of P/Invoke and Marshaling in .NET
P/Invoke Revisited
Publish this application to IIS with different application pool.
Use standard techniques suggested before like. I suggest configure recycling IIS for both memory and scheduled times.
IIS process recycling rate
How to limit the memory used by an application in IIS?
I'm working on a UI for a simple inventory system. The users will use a USB barcode scanner to retrieve an ID and then either retrieve information from the database about the scanned object or enter the new information. This will only be used within our corporate environment. I can't decide which is the best way to go with this. I would like to use this opportunity to take a crack at WPF.
I like the idea of having the users interact with a webpage but I don't like the idea of using the USB scanner as a keyboard wedge. I would rather use the service object so that I can capture the event. I thought about writing it as an XBAP running from our server but wasn't sure if it'd be able to interact with the scanner.
I want the flexibility to run this on any computer in the shop without having to install software locally and worry about different versions floating around. I would greatly appreciate some advice on this.
I would use ClickOnce Deployment.
I know you said you don't want to install anything locally, but it does take care of automatically updating the clients from a central location such as web server or file share. You can easily publish new builds right from Visual Studio. Each time the user starts the program locally it checks for updates and installs them, fairly transparently.
This would just be the UI and barcode interface, you could create a WCF service on the server for the actual work, i.e. database querying, business logic, etc.
We were in an almost identical situation in our shop, except it was a time-tracking application. We came up with a Windows Form application deployed via ClickOnce using a WCF service on the server. Its been working well and we don't need to go to each workstation to perform updates.
We have a web application that uses AJAX to talk to an ASP.NET web service. We would like to write another version that can be used offline. We need to be able to re-use our existing code as much as possible. What approaches should we consider?
The app is currently using XmlHttpRequest to get dynamic data from the server. Obviously the offline version will not be able to talk to the server, but it does need to talk to something! I'm sure installing IIS or Cassini on the client would work, but I was hoping for a simpler solution. Is there no other way for JavaScript to talk to some external code?
There are plenty offline web apps nowaday. It simply evolve from AJAX.
For example:
WoaS (wiki on a stick / stickwiki), Tiddly Wiki,
Google doc and Gmail is going to be offline.
You don't need a webserver to run these webapps in offline mode. Just store the required data, scripts on the client side (usually as XML).
One of the possibilities would be to use Cassini. This is a web server that acts as a host for the ASP.Net runtime. You can host Cassini in a Windows application or a Windows Service. In this scenario you do not have to rewrite the web app and the web service.
Most other solutions do require a rewrite of both your web app and your web service. Depending on the way you have written the existing app you can reuse more or less code.
Have you considered HTML5 with application cache and offline storage?
If you hope to create an "offline" version of your package your biggest issue by far will be the need to install your site into a local copy of IIS (registering a virtual directory, etc.). I pursued this briefly a few years ago and gave up in frustration. It can be done: a number of software vendors such as DevExpress do this so you have local copies of their demonstration projects. Indeed, I was able to do this. The problem was the classic "it works on my computer" syndrome. There was simply no way to guarantee that most of my end-users had anywhere near the technical proficiency to make this work.
Thus, I would strongly recommend that you not pursue this path unless you have very technically proficient users and a huge support staff.
But there is one more very important question: did you abstract all data access code to a DAL? If not, then you have a lot of work to do in managing data access as well.
Update: user "Rine" has recommended Cassini. I just wanted to let you know that I pursued Cassini and another 3rd-party web server as well. I think that there are licensing issues with Cassini but may be wrong - it has been awhile. However, I do distinctly remember running into barrier after barrier with this approach and very little documentation to help me out.
if you want a web application run offline, you need a webserver (IIS for ASP) bound to the localhost (127.0.0.1) address. After this so can access your web application by typing http://127.0.0.1/ in your web browser the same way as you do online.
If your AJAX relies on XMLHttpRequest's, you can:
Make the static versions of XML's you get over XMLHttpRequest and put then into a folder on disk.
Rewrite your XMLHttpRequest URL's so that they point to files on disk.
Rewrite your XMLHttpRequest's so that they don't check status (it's always 0 for the file:// protocol.
All JScript works on file:// pages as well as on http:// ones.
Of course it's not the best way to develop static pages, but it may save you some time on rewriting.
I havent come across any framework specifically built for asp.net like the ones available for PHP or RoR.
Here is a good article by Steven to get you started with HTML 5 and ASP.Net Creating HTML 5 Offline application
Obviously the offline version will not be able to talk to the server, but it does need to talk to something!
Enter HTML5 LocalStorage. It works like a database and enables you to put data on your client. Indeed you have to rework parts of your code in javascript and transmit it to the client, but then it would work offline.
Local Storage works like this:
- Setter: window.localStorage.setItem(KEY, VALUE)
- Getter: window.localStorage.getItem(KEY)
- Remove: window.localStorage.removeItem(KEY)
To get the main page working offline you need to create a manifest. This is used to store complete sites on the client. Please refer to this for more information about manifests:
http://diveintohtml5.info/offline.html
You want to build a web application to work offline?? It can't be done.
You could split the interface code from the rest (in diferent dlls) and create a windows application to mimic the behaviour of your web application. This way you have 2 distinct user interfaces but the same code for business rules and data access.
I don't really see any other way...