Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 4 years ago.
Improve this question
Program which I am trying to make like this
There are three GO Porgram, they are Go program 1, Go Program 2 , Go Program 3
Go Program 1
Which get data from serial port and sent to Go Program 2
GO Program 2
Recv. the data from Go program 1 and sent it to MQTT
GO Program 3
It should be web framework as I need Web UI to control and manage these GO program 1 & Go Program 2
The Go Program 3 task are:
To start stop the GO Program 1 & 2
To change or set the COM port of Go Program 1 and publish topics
To change the broker address ,username & Password of Go Program 2
How to make communicate or Pipes between all the the three GO Programs.
Looking at the discussion in comments I think you make an assumption that Go has some special way for IPC that Python doesn't; that's not exactly true. Channels are useful for communication within a single process. If you want these programs to be truly separate (processes) you'll need all the usual IPC - you can use pipes, or sockets, or shared memory, or what have you.
Personally I'd recommend using sockets, because Go is really well suited for network programming and writing socket servers and clients. Also, once your application uses sockets it's much easier to port these different processes to run on multiple machines, across the internet, etc. In addition you can then leverage higher-level protocol levels and use things like RPCs.
To create a socket server, use net.Listen, and call Accept in a loop on the returned object. Each connection returned by Accept is a remote client you can communicate with - I'd recommend a goroutine here if you want concurrency between multiple clients.
For a first cut in a project like yours, however, I'd go for the net/rpc package which is very simple to use and gives a much higher level API to sending remote commands to other processes.
Related
I have search high and low for this answer. Can one code up a Named Pipes server where the connection that a client makes is persistent until you close the applications? This would be in C/C++. Not asking any one to actually do this, as I am capable. To explain in a little more detail if my question is not clear, I want to be able to have the client connect to the server and then be able to pass data back and forth without having to kill the connection at the end of each data transaction and then start a new one again for the next. It seams that in every example I have seen or read, the transaction only lasted for that one data exchange. That seems wasteful and extremely time consuming. Then I want to thread it so I can have up to 8 clients on the same named pipe. If you know of example code that does this, that would be great also. Already read the Microsoft examples, and they seem to be single data exchanges with new connections every time.
My confusion lies with the readfile() and writefile() functions. They need the pipe handle and pointers to the data structures just like a file R/W on the hard drive. Those files can be opened at program start, used, and then finally closed just before you exit your application. There are risks to doing this, but sometimes necessary. So I want my server application to be in control not the clients.
Thanks in advance. I will answer any questions if this is not clear to you.
I am not surprised at your answers. I was really wanting a way to keep the connection open per instance, but since this is not how pipes work, I get it. I have devised a better way to make my applications talk to each other. I originally had one server and many clients, so I turned that around and now have one client and many servers each with a different pipe name. Since my client, that was the server, did most of the initiating of the messages, I can now manage better they way I send and request the data via messages/pipes. The only draw back is not giving the data to all of them at once, but what is a few microseconds amount friends. Please let me know if this will not work as I expect it will, before I spend a lot of time on the code. Thanks. Any suggestions are welcomed.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 4 years ago.
Improve this question
How should a Golang app handle missing external dependencies ?
When a app starts and it doesn't find the database it is supposed to persist the data on, knowing the app is useless in that state, should I panic the app ?
I can otherwise log infinitely something, print to stderr, or use another method to notify, but I'm not sure when to choose each method.
An application that has no access to the external network service should not panic. This should be expected as networks tend to fail. I would wrap the error and pass it further.
Consider the following scenario. You have multiple application servers connected to two database servers. You are upgrading the database servers one at a time. When one is turned off half of your application servers panicked and crashed. You upgrade the second database server and every application server is gone now. Instead, when the database is not available just report an error for instance by sending HTTP status 500. If you have a load balancer it will pass the request to the working applications servers. When the database server is back, the application servers reconnect and continue to work.
Another scenario, you are running an interactive application that processes a database to create a report. The connection is not available. The application panicked and crashed. From the user perspective, it looks like a bug. I would expect a message that connection cannot be established.
In the standard library it is accepted to panic when an internal resource is not available. See template.Must. This means something is wrong with the application itself.
Here's an example from the Go standard library.
Package crypto
import "crypto"
func (Hash) New
func (h Hash) New() hash.Hash
New returns a new hash.Hash calculating the given hash function. New
panics if the hash function is not linked into the binary.
Is this possible?
Right now I have one wt server being launcher per application instance, but I've been told they would like there to be one wt server per machine (not matter how many application instances are launched).
There will only be a maximum of 3 applications per machine, but this requires 3 different ports to be opened for communication (one per application).
How can this be done?
My boss said something about using JSON to send data...??
Not sure how I should understand your question - do you want to deploy three applications, all listening at port 80, in three different URLs, or do you want to have one process listening on three different ports?
The former can be done by invoking WServer::addEntryPoint() multiple times. See examples/simplechat/simpleChat.C, but then with multiple calls to addEntryPoint() for type Wt::Application.
The latter can be done by instantiating multiple WServer objects, each with their own configuration. See examples/feature/multiple_servers.
Is it possible (for example with C++, but it does not really matter) to create a bridge/proxy application to get the data requested by another application? To be more detailed, I'm talking about a Adobe Air based game. (I want to create a report with stats based on the data acquired, but that is not actually part of this question.)
Rather than simple "boolean" answer please provide some link to example/documentation. Thanks
It would always be possible, and depending on the your target operating system, may require a fair amount of effort, which begs the question - is there a reason you cannot use Fiddler or some packet sniffing software for your target OS?
You can write a proxy by hand, in python can be quite easy. All you have to do is to set localhost as proxy, then forward the request and pass it back to the calling socket.
I've started writing something like this some times ago. The idea was to write a simple replacement for dansguardian.
I've uploaded it on github so you can give it a look if it can help.
I do not remember well (I've started writing it the last year) but maybe with some modification can fit well your requests.
Conceptually, this is your configuration:
app_client -> [app_channel] -> proxy -> [server_channel] -> app_server
Your proxy starts a server socket, the app_client connects to it. This is our app_channel. Now your proxy creates a connection to the app_server. This is your server_channel.
Now start 2 threads, one which reads from the app_channel and writes to the server_channel, the other reads from the server_channel and writes to the app_channel.
This will create a transparent connection to the app_server via your proxy. You can extract the data as you wish. If the data is encrypted though, there's very little you can actually do by way of analysis.
If,for example,The socket in my compiled application is designed to connect to 123.456.789.0.
How do I check if its connected to 123.456.789.0? Is there a way to do this?
The idea is this:I want to prevent other people editing my program and changing the address to,for example, 127.0.0.1 and make it connect through a proxy.
Is there any function/way/trick to check the address after the socket is connected?
Use the getpeername function to retrieve the address of the remote host.
If someone edits your program like you mention, they'll probably alter such a check as well though.
nos's comment about the insecurity of this approach is correct, but incomplete. You wouldn't even need to change the program's code to circumvent your proposed mechanism.
The easiest way around it would be to add an IP alias to one of the machine's network interfaces. Then a program can bind to that interface on the port your program connects to, and the OS's network stack will happily send connections to the attacker's local program, not your remote one.
So, now you say you want to know how to list the computer's interfaces so you can detect this sort of subversion. Your opponent counterattacks, launching your program as a sub-process of theirs after installing a Winsock hook that routes Winsock calls back through the parent process.
We then expect to find you asking how to read the executable code section of a particular DLL loaded into your process space, so you can check that the code is what you expect. Now your opponent drops the Winsock shim, switching to an NDIS layer filter, rewriting packets from your program right before they hit the NIC.
Next we find you looking for someone to tell how to list the drivers installed on a Windows system, so you can check that one of these filters isn't present. Your opponent thinks for about 6 seconds and decides to start screwing with packet routing, selecting one of at least three different attacks I can think of off the top of my head. (No, wait, four.)
I'm not a security expert. Yet, I've spent five minutes on this and already have your security beat seven different ways.
Are you doomed? Maybe, maybe not.
Instead of you coming up with fixes to the risks you can see, better to post a new question saying what it is you're trying to protect, and have the experts comment on risks and possible fixes. (Don't add it here. Your question is already answered, correctly, by nos. This is a different question.)
Security is hard. Expertise counts for far more in that discipline than in most other areas of computer science.