I am trying to create a client in C that will talk with a BACnet server. This BACnet server is stored on an industrial device (CAN2GO) and I am not sure how I could talk with this device.
I spent quite some time reading documentation for BACnet and I never found a clear example for a BACnet client. I already did some server and clients using TCP and UDP but I don't know how to start this BACnet client and I must say I am getting quite desperate.
I found a library which seems to correspond to what I want which is called BACnet protocol stack but when I tried the whois exemple no device was found (I expected to found the bacnet server but maybe I shouldn't ?).
So my question is : could you give me an exemple in C, or another language but C would be better, that would communicate with a BACnet server (nothing complicated just a question and analysing response). This example could be using the library I just wrote about or if you prefer another library I am of course open to everything.
Thank you very much for your time and answers.
I have used that stack and it is the best open source one you are going to find. If you cannot see anything using the demo\whois\bacwi example from that library, then there is something wrong with your setup. In particular, are you using IP? Are your BACnet client and BACnet server on different machines (they cannot be on the same without some serious tweaking)? Are the two machines on the same IP subnet? (They must be, once again, unless you do some serious tweaking (in this case, setting up BBMDs (BACnet Broadcast Management Devices))).
You will also want to try the "Read Property" example (demo\readprop\bacrp.exe) to actually read a value from the server.
If you are still stuck, then post your detailed problem at the link on Sourceforge, Steve, the author, is very responsive to questions.
I am currently using the stack - just started. I had a little trouble at first, not sure if my problem is the same but.. I basically am using some BAC components made from Schneider Electric (UNC-500) and an old un-supported platform (Niagara R2). On my laptop I created a host server and addressed it to a private LAN network between it and the UNC. My laptop was also using wifi, which was utilizing DHCP, so I had two separate interfaces going. This was my problem. I couldn't read or get 'I-AM' responses back from the UNC. As soon as I turned the WIFI off, I got the 'I-AM' broadcasts. Make sure that you are on the same network as your device, and that there are not other interfaces active. Maybe there is a way to assign the interface to use, IDK. I just started using it.
Related
How can a C socket program be made to communicate online on a Wide Area Network (WAN)? For example, having a server program (in C socket) running on a friend's computer in UK that could be accessed on a computer running a client program(in C socket) located in Russia. I tried my client/server online but it did not work. It only worked on my local machine.
A connection between two computers looks very similar to a phone call, but actually there are lots of details that may turn it into a difficult thing.
Unfortunately, you haven't provided these details. So, let me ask them to you:
Are you connected directly to a telco, using 3G, for instance ? Or are you connected to another device that is connected to the Internet ? For instance, a 3G modem, that offers Wi-Fi connectivity ?
The same questions should be answered by your friend.
These two questions will provide a 1st step to understand and solve your problem.
Good luck, and a fine week for you and family.
This may not be in the right location, so tell me and I'll move it.
I am a recent EE grad and I was hired to build a system that exists on a SoC with a simple 32-bit processor. The system basically monitors several external devices and performs some DSP on it, and then is supposed to send the results using a WiFi device (in my case I have the ESP8266 using UDP) to an email server for logging/notification.
I have been trying to find a library that I can use, but my uC can only program in C and I have it set up for UDP, and everything is in C++ using some other protocol, or something else completely.
I am great at DSP, decent at SoC's and uC's, but when it come to this email server communication thing I am at a loss.
I have successfully configured everything for the sensors, the datapath, the DSP, and connected the system to my WiFi via UDP, but I have yet to figure out how to send data to any servers.
Could someone help me understand how I should go about this?
I have looked into some simple SMTP commands such as HELO, MAIL, RCPT, DATA, etc. but I cannot understand how I actually should implement them in my code.
When I send out the WiFi data via UDP what type of data do I send and how do I format it? Do I need to send any other kind of flags? How should I expect the response? I also know the data has to be transformed into base 64 which is confusing me further.
I am also not super familiar with UDP to begin with, I have been using libraries that are part of the SoC's default library to connect to my WiFi.
I know these may either seem like obvious or stupid questions but it is were I no longer have any knowledge, and everything I find online doesn't make sense, or doesn't attempt to explain it, just gives a pre-made solution
I have found the RFC2821 but it doesn't get any clearer.
I know that's a lot but any help at all would be a lifesaver!
Since you are asking this question, I'm assuming that you are not booting and running an OS suitable for micro-controllers such as an embedded variant of Linux or such. If you were, you would simply be able to take advantage of possibly built in applications or other existing code.
But you don't mention having written an Ethernet stack, so are you using some other library or operating environment which might have some of the functionality needed for an implementation of SMTP?
If you don't and really do need to write your own SMTP client to run directly on the processor you are using, then you should be able to find plenty of examples of source code for this. A quick google search of How To Write an SMTP client showed a few articles with some example code. One article seems to be an exact hit, but you need to look at it further.
However, I would highly suggest just sitting down with a telnet client and connect to an SMTP server you are allowed to use and try the commands you need to just send a message. If you only need to send text, you don't need to get involved in MIME encoding or anything like that.
I am looking to develop a C implementation of a 9p file server on a Linux machine. There isn't enough documentation in the internet about 9p and I am not very experienced with implementing servers. My general design is as follows:
Use UNIX sockets to listen to incoming 9p messages.
Decode the 9p message and spawn a new thread to perform the required task.
Reply to the client with the appropriate 9p reply message.
The server would just live in the user space and it will translate the 9p messages into a UNIX call.
Do you see any problems or have any recommendations regarding the proposed design? Are there any documentations that you can refer me to that will help me? How do you think I should debug my server and make sure it is working correctly.
Consider libixp (MIT license).
I've played around with wmii and use it in everyday work. libixp was part of wmii (in the earliest releases) and now it is an independent project. Check wmii's early versions to get a good starting point or dive directly into libixp.
To debug your server just mount it with 9PFUSE(4) with parameter −D to print each FUSE and 9P message.
I am working on a project involving a microcontroller communicating to a PC via Modbus over TCP. My platform is an STM32F4 chip, programming in C with no RTOS. I looked around and found LwIP and Freemodbus and have had pretty good success getting them both to work. Unfortunately, I'm now running into some issues which I'm not sure how to handle.
I've noticed that if I establish connection, then lose connection (by unplugging the Ethernet cable) I will not be able to reconnect (once I've plugged back in, of course). Freemodbus only allows one client and still has the first client registered. Any new clients trying to connect are ignored. It won't drop the first client until after a specific timeout period which, as far as I can tell, is a TCP/IP standard.
My thoughts are...
I need a Modbus module that will handle multiple clients. The new client request after communication loss will be accepted and the first client will eventually be dropped due to the timeout.
How do I modify Freemodbus to handle this? Are there examples out there? I've looked into doing it myself and it appears to be a decently sized project.
Are there any good Modbus packages out there that handle multiple clients, are not too expensive, and easy to use? I've seen several threads about various options, but I'm not sure any of them meet exactly what I need. I've had a hard time finding any on my own. Most don't support TCP and the ones that do only support one client. Is it generally a bad idea to support multiple clients?
Is something wrong with how I connect to the microcontroller from my PC?
Why is the PC changing ports every time it tries to reconnect? If it kept the same port it used before, this wouldn't be a problem
Should I drop the client from Freemodbus as soon as I stop communicating?
This seems to go against standards but might work.
I'm leaning towards 1. Especially since I'm going to need to support multiple connections eventually anyways. Any help would be appreciated.
Thanks.
If you have a limit on the number of modbus clients then dropping old connections when a new one arrives is actually suggested in the modbus implementation guide (https://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf)
Nevertheless a mechanism must be implemented in case of exceeding the number of
authorized connection. In such a case we recommend to close the oldest unused
connection.
It has its own problems but everything is a compromise.
Regarding supporting multiple clients...if you think about modbus/rs server - it could only ever have one master at a time. Then replace the serial cable with TCP and you see why it's not uncommon to only support one client (and of course it's easier to program). It is annoying though.
Depending on what you are doing you wont need the whole modbus protocol and implementing the parts you do need is pretty easy. Of course if you have to support absolutely everything its a different prospect. I haven't used freemodbus, or any other library appropriate to your setup, so I can't help with suggestions there.
Regarding the PC using different TCP source port each time - that is how TCP is supposed to work and no fault on your side. If it did reuse the same source port then it wouldn't help you because e.g. sequence numbers would be wrong.
Regarding dropping clients. You are allowed to drop clients though its better not to. Some clients will send a modbus command, notice the connection has failed, reconnect, but not reissue the command. That may be their problem but still nicer to not see it that often where possible. Of course things like battery life might make the calculation different.
TL;DR available at the bottom
I've been trying to figure out a way to get two laptops (both running Ubuntu) to be able to pass basic messages back and forth without the need for them to be connected via a wireless network,either by an AP or ad-hoc. I want to reiterate here that ad-hoc networking is not what I'm looking for, I've seen many similar questions here with that as the answer.
I guess what I'm asking is: how do I achieve this? All I really need is for one computer to be able to send a packet, and then for another to pick it up via a packet sniffer of some kind.
Currently: I have both laptops in monitor mode (via a mon0 interface created from aircrack-ng's airmon-ng)so that they can sniff nearby traffic (with Wireshark, tcpdump,tcpcump.org's sample libpcap code, and opening a raw socket and just printing out all the packets. I tried each just because I thought one could be doing something differently/leaving something out). I also have a very basic program that consists of opening a raw socket to send crafted ethernet frames out to the air, but I can't get my two machines to see the other's packets. The sniffer running on each machine can only see the packets going out of that machine (in addition to nearby beacons/control traffic from wifi in the area).
Some things to note that might be important are:
-the packets I'm sending out appear in Wireshark (only on the sending machine) as malformed 802.11 packets (probably because I'm just filling them with junk data for now). I was under the impression that my other laptop would also see them as malformed packets, but it gets nothing
-the sockets I'm using are from a call to socket(PF_PACKET,SOCK_RAW,ETH_P_ALL). Raw sockets are something I just recently was aware of, so I could be misunderstanding how they work, but my impression is that I can craft a layer 2 packet by hand and ship out straight out to the wire/air.
If you're curious as to why I want to do something like this, it's part curiosity, part research for a project I'm working on. I want to streamline / automate the process of setting up an ad-hoc network, and what I'm trying to do here is for the laptops to do a small exchange to figure out the specifics of the adhoc network they are about to create and then make/join that network automatically, instead of either one person explicitly setting up the network OR having both people pre-decide the name, etc of the network and have both computers constantly trying to connect to that specific one.
I'm more interested if I'm going about this process in the right way rather than if my code works or not, if someone thinks me posting my (very basic, taken from another post on Stack Overflow) raw socket code will help, I can.
Edit: I am more than happy to post a complete set of code with instructions if I can get this working. I couldn't find much helpful info on this topic on the internet, and I'd love to put it up for future people trying to do the same thing.
TL;DR I want to send out a packet from one laptop and pick it up on another via a packent sniffer of some sort. No wifi network or ad-hoc network involved. Something akin to spoofing an AP's beacon frame (or similar) for the purpose of sending small amounts of data.
Edit 2:After some thought, perhaps what I'm looking for is some kind of raw 802.11 use? Having direct control of the wifi radio? Is such a thing possible?
I found out I was able to send packets out through my monitor mode interface as long as I had correct 802.11 with radiotap headers. I think the problem I was originally experiencing (not being able to sniff the packets) was because they were malformed and thus not actually getting sent out.
I was able to accomplish this by adapting the example code found here, courtesy of someone named Evan Jones, except I did not need to use an Atheros based card or Madwifi drivers, everything worked fine with the mon0 interface created with aircrack-ng.
I am certain that Apple Mac do this. Apple call it 'bonjour'. There may well be a proper IETF spec for it. This is an Article on Bonjour this is Wikipedia on an open component of bonjour which might help get you moving.