I am using Rabbit single board computer. I would like to save the data I/O which is connected to another Rabbit single board computer through a wireless connection. Is it able to save the data inside the PC in a .txt file for example?
If you can establish a connection to a PC, and the PC is running some server to log data, yes, you could save to a PC. For example, the PC could run a TFTP server or FTP server on the same wireless network, and you could connect to it from the rabbit SBC and save whatever data you need to.
Yes, this is possible.
There are two parts to this scenario. Your embedded app needs to know how to connect to a server application running on the PC or network, and you must, of course, have said server application running on the target machine.
If you're sending entire files, FTP, as bdonlan suggested, is a good way to go. The protocol is well-understood and you can probably find a library to wrap it for you.
If you need to log data real-time, you'll need to have some sort of application which can receive messages or accept a socket connection, and a protocol to get the text across the wire(less). A web server may be a good way to do this, because you can POST chunks of data to the server with a simple HTTP request, and the server app can decide how to organize and store the information. Once you have a web server running, you may find it beneficial to build some pages that provide basic reporting functionality, so you can see the logged data from any web browser.
This could be less restrictive than FTP, but will require some web development expertise on your part.
Any reasonable solution is going to require that you already have a connection to the wireless network with a correctly-configured and functioning IP stack. Without that, you're probably out of luck connecting to any networked resources.
Related
I am trying to find the location of the database where a particular website is saving to.
The website is saving to some local database in our system, but I am unable to discover where.
I have tried using WireShark to find the IP of the machine where the website sends data to (i.e. the machine which has the database) but currently the only packets showing up are those from the website to my machine and vice versa.
Any ideas?
Thanks
I would start by tracking through the code & website config. If you have sufficient access to run Wireshartk on the host can you not search for config files, find the serverside code, etc?
If you can't see packets on the network interface and you know you've found all network interfaces then it would appear possible the DB has to be on the same machine. Check for recently changed files with you favourite tool (Windows explorer/search, find on Unix, etc).
Is it caching so you haven't yet caused it to read/write to a remote DB while watching? Try watching Wireshark at boot up.
Depending on the nature of the data it could be an in memory DB or something that reads from a disk file into memory at boot up.
I am currently building a chat server (meebo style).
The architecture is something like this.
Bitlbee over libpurple is on host B. Its a trivial server on data center.
User communicates with bitlbee via web server (just like meebo) on Host A. The backend of this web server maintains chat session. It just translates the user commands to proper bitlbee comamnd and sends back to host A.
The most important part here is that host A will be deployed in embedded Linux.
I have 2 questions.
To keep the chat session persistent I am thinking of using node.js. As its much more easier to create a real time application with persistent connection. But I doubt if its supported in such platform.
If I use C instead of node.js (I am not using any web server) I can talk to the irc server at host A by libirc. But how do I implement all the web server features in C (like session, url/cookie/post data parsing etc) ?
Also if you think my approach is wrong or there is a better approach please tell me how can I improve this architecture?
Note: This is NOT a high volume chat server.
If building V8/Node.js is prohibitive on the embedded platform, the next best thing would be to take the event loop and platform layer (libuv) and HTTP parser (http-parser) of Node, both written in C and use those as a starting point. These are the same libraries used to build Node.js so they are battle tested and will give you the performance characteristics you seek.
Ryan Dahl, author of Node.js, demonstrates exactly how to use libuv and http-parser to build an asynchronous web server in C.
Put a ZNC server between Bitlbee and the web-based IRC client. Bitlbee will think that the user has never logged out and ZNC can maintain a backlog of messages until the user connects again with the web client.
I would try to go with node.js if that is your choice, also what embedded system is it? As knowing that would help more. Also, another plus for node.js is that it does have session handling built it, but if you wanted to do it in C try and see if you can get a sqlite wrapper running on the embedded device to store the session information.
But, if possible stick to something with less work on embedded devices, feels bad to reinvent a lot of stuff or have to fiddle with compile issues for your device.
Is it possible to make bittorrent client within silverlight, which will run in browser?
this would be unusual bittorrent client, he will download data from the server and will seed it. is it possible to do?
Is it possible to do within different, web tech, such as e.g. JavaFX?
Yes, completely possible. You can't receiving incoming connections, but that's no requirement for Bittorrent. The only thing that makes it difficult is that the peers you are connecting to need to serve a socketpolicy file on port 80 or 943, and almost none of them do. Without this policy, the Siverlight BT client will only work in the trusted 'Out of browser'-mode, which make it less usefull.
It's like a chicken-egg problem: as long as their is no large userbase for a Silverlight BT client, 'normal' nodes will not open port 943, and without that port, there never will be a large userbase for such an client.
Adobe solved this smartly by introducing Cirrus, their hosted rendezvous routing service which makes P2P possible from Flash without torrents.
No. You don't have access to the client's file system outside sandbox access.
http://betaforums.silverlight.net/forums/p/9351/29437.aspx
I would like to create a wireless network from a laptop. If laptops come within range, I would like it to send them a welcome message and send them a goodbye message when they leave the wifi range. Is it possible to do this in C?
Please help me out with this.
It is possible, but it is a very complex task and I don't think that programming language choice is the first thing to look into.
As a start, you can read up on Wikipedia on Wireless ad-hoc networks.
How should your messages be received and displayed on the remote side? If you want to use some existing protocol over TCP/IP, or create your own (deploying custom applications on the remote machines), you will need to mess with networks and this is not always possible as one machine can be a part of only one network. So the machines need to be not connected to anything and somehow allow you to connect to them, it involves changing network settings on all that machines (for example, setting them to join the ad-hoc network with predefined name).
If all machines automatically join the existing network, this question has nothing to do with wireless (physical layer) but with Avahi, Netbios or whatever other services allowing you to get notifications and/or enumerate devices in the network.
I need to detect the presence/absence of internet connection. More precisely, let us suppose that the application is broken up into 2 parts - A and B.
A is responsible for checking whether or not the system is connected to the internet. If it finds that there is no connection, it starts up part B. And as soon as it detects that there is a network connection, it kills B and continues its own work.
What would be the best way to do the A part of the application? Continual pings sounds hideous. There has to be a better way of doing this (preferably in C).
With sufficient privilege you can test the various network interfaces and examine their state. This would tell you if any of the interfaces was connected to a network and operating. However, this won't tell you if the connection is actually usable, i.e., connected to the internet (or your local net if that's all you need). I don't know of anyway to do that short of actually using it.
Using ICMP (ping) can be useful at a low level, but presumably what you need is a connection to an actual endpoint via TCP/IP to do real work. I would say that you should change the design of your application so that B is responsible for indicating when it is unable to continue due to the absence of resources that it relies on -- network or otherwise. A and B should communicate so that A is aware of the situation and is able to either kill B or respond to B terminating itself and thus continuing its work.
A lot of companies have measures in place to prevent outgoing ICMP requests, TCP connections to ports other than 80/443 for example, or even to prevent you from reaching the internet directly by (transparently) proxying your traffic.
Under an internet connection I would understand any way to contact the outside, be it UDP, TCP or ICMP. Depending on what your application needs to contact the internet for, I would suggest to check over the same protocol, as that is the only thing that matters to your app.
If your application uses HTTP to communicate to an external source, try to connect to a few sites you would suspect to not be blacklisted and that have a reliable uptime. Like google.com, microsoft.com, apple.com, and so on...
Edit:
I am unsure what the specifics are, so let me give you an example with a hypothetical situation.
Application A collects data on the system it is running on and forwards it to a Web Service listening on yourserverhost.yourcompany.com:80
Application B would basically take over the job of the Web Service when it is down and log everything so no data is lost.
When all is well, App A will be sending the data to your web service
Once this connection drops, you immediatly launch App B (the obvious remark here would be, why not keep App B running as a failsafe)
App A connects to App B and forwards what it had been buffering
App A continues to try to reestablish the connection to your Web Service and once it is back up will request App B to stop
If the problem you are facing is nothing like this, please provide a more concrete description of what App A and App B are supposed to be doing. I will be more than happy to help.
In your code, you have to check whether the internet connection exists by using a socket to open a connection to a website.
Firstrun: Ask user to input the network parameters, like proxy settings. Save this info.
Next runs: Use these settings to check for the Internet connection. You may simply do a DNS search.
If results are negative, ask user to check settings.
Check whether the cable is connected , if so ping your internet connection to any host as google.com.
ping google.com