I have developed a Flask app and GUI in electronJS. I can package it for windows and want to distribute it. I thought a good practice would be for Flask to first check for a free port when being launched and then export the value of that port to a json file. Electron waits for that file to be available and then connects to Flask via the correct port. The intention is to avoid bugs with users whose localhost and port would be already used if my port was set to a fix value (say 5000 for instance).
Is my method the best way to deal with the risk that Flask would run on a busy port if distributed to some users? Is there a smarter way to go around this issue?
Many thanks,
Nick
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Background: I've got an C++/Qt-based application that communicates with servers on the user's LAN. It uses non-blocking TCP and UDP sockets, and the networking is implemented via calls to the BSD sockets API (i.e. socket()/send()/recv()/select()/etc). It all works well.
The other day, just for fun, I decided to recompile the application using emscripten, so that it could run as a WebAssembly app inside a web browser.
This worked surprisingly well -- within an hour or two, I had my app up and running inside Google Chrome. However, the app's usefulness in this configuration is severely limited by the fact that it isn't able to connect to any servers -- presumably this is because it is running in a restricted/sandboxed environment.
If I wanted to pursue this line of development beyond the clever-hack-demo stage and try to make it useful, I would need to find a way for my program to discover and connect to servers on the user's LAN.
My question is: is that functionality at all possible for a Emscripten/WebAssembly-based app to perform? If so, what steps would I need to take? (i.e. would it require upgrading the LAN's servers to handle WebSocket-based connections? Would it require adding some sort of proxy server to run on the web server that the web page was served from? Is UDP even a thing in a web-app context? Are there other hoops that would also have to be jumped through?)
I have two applications. One is the server app and the other is the client app. The server app listens for connections and then feeds messages to all connected clients.
So far all my testing has been done by running both applications on the same machine, and this is working fine. Now though I am trying to test the server running on one machine and the client running on a different machine.
Each of these machines are within my own home network. That network is behind a router with a firewall. From what I have read, my problem might have to do with port forwarding not setup on my router. Does that sound likely?
Is this something I can fix with just my code? Do I really have to require all my users to manually open the port on their firewalls? I have used plenty of other commercial applications that connect to servers and don't require me to open ports on my firewall. What is different about those applications and mine?
Then again, maybe I am barking up the wrong tree here. Maybe there is some other problem preventing my code from working in this situation?
I can provide any code snippets that might help, but I am unsure as to where to start looking and I don't want to just post my entire solution :)
Thank you in advance
You need to bind to 0.0.0.0 (simplified version) in order to accept connections not coming from the local machine. Have you checked that you don't bind to 127.0.0.1?
When you bind to 0.0.0.0 you actually bind to all current and future addresses of the current host and so will be able to accept connections from everywhere, you can also bind to just the address of one of the network interfaces.
I'm building an app which upon login will connect you to certain ip addresses of which will also be running the same app.
The method of which i believe i should be using is direct tunnelling but as i say im a little new to c++, i have general coding skills, and i have sifted through a lot of forums and sites yet im still very unclear on what the best way forward is to achieve the requirement.
The reason for the connection will be to enable a secure chat, file transfer, and update software auto when connected to the program admin.
All those that have the app installed will once authorised, will be connected to admin client, then from that client all available ip's to connect to will become available to slave clients, this will increase the network size avilable to all users.
so the app needs to be able to handle ports but not via a server, instead it would be direct.
The connections also must ideally be encrypted.
Im kind of looking for what the application RetroShare does, but in text app.
(This is using C++ within Dev C++)
so just to recap, What method should i use to achieve the above?
I would take a look at SDL net to start with, its really simple to learn if you have never done any socket programming before.
for a secure connection you will probably want to start with TCP and then once you get the hang of network programming, start looking at other protocols.
Hope this helped! and good luck.
I got everything I wanted to do with django-celery working on my development machine. More specifically, the app accepts photo urls which are then turned into tasks that the same machine downloads.
Now what I want to do is put the django code on heroku and the celery tasks on a dedicated computer that will be kept in the office.
I don't know what the next step is though. How do I tell the django app to connect to the office computer? What is the process for setting up the office computer to accepts tasks from the django app? How do I give the local computer login credentials to the django app so that it can connect to the database to update the models?
Ideally, I am looking to put something like this in my setting.py file:
remote_worker = '123.2.4.23:1234'
and on the office computer
tasks = 'photos/tasks.py'
remote_app = 'herokuapp123.com/myapp'
username = 'me'
password = 'pw'
I know there are a lot of questions. Any help or pointers would be appreciated!
This largely depends on what AMQP backend you are using for celery. If you are using the default (RabbitMQ) you will need do one of the following:
Install RabbitMQ on heroku server, expose its port to your business IP through firewall and configure your office computer to connect to it
Install RabbitMQ locally on your business computer and configure celery on Heroku to connect to it
Install RabbitMQ on both sides and bridge them.
Alternatively you can integrate the heroku server in your own business network using a VPN solution and have them directly talk to each other (because after all you probably don't want to transmit AMQP packets bare over the interwebz).
Scenario 1 is probably the easiest to set up as Heroku already provides you the plugin infrastructure to do so. Scenario 2 is probably not what you want as you will have to punch a hole in your business firewall for that. Both scenarios 1 and 2 will have latency and reliability issues as routing AMQP traffic over the internet is not going to be expedient or reliable. You will have dropped messages and celery will keep retrying until it succeeds or reaches the max number of failures. However AMQP was designed to handle network issues, they just may inadvertently affect your performance if that is critical. But then again in that case you should reconsider putting the celery workers on a business desktop.
Scenario C is probably best in terms of reliability but also more difficult to set up. Choose based on your needs.
In most web (PHP) apps, there is mysql_connect and some DB actions which means that if 1000 users is connected, 1000 connections are opened?
But with C++ app it is incredibly slow...what is the main difference?
Thanks
PHP will automatically close the DB connections when the script terminates (unless you use persistent connections or have closed the connection yourself before the script terminates of course). In your C++ app, this will depend on how you actually handle connections. But I can imagine you will want to keep your connections open for a longer stretch of time in the C++ app, and thus you could hit the maximum number of concurrent users sooner.
You could also tweak some of the MySQL settings if you have performance issues.
But how are you accessing MySQL from your C++ app? Not using ODBC are you?