Okay, I just started learning golang and I like it so far. However I don't find their documentation good for go starters, Here is my problem.
I wanted to write little server program that accepts connections and writes something to the client. No problem doing that so far.
However as soon as the thing get a real functionality, I need to be able to handle multiple clients, which I though would also be a good exercise for goroutines.
listener, error := net.Listen("tcp", remote)
con, error := listener.Accept()
go handleClient(&con);
func handleClient(con *net.Conn) {
I've cut most of the code out. The problem is, no matter what I try, I can't pass con.
con.RemoteAddr undefined (type *net.Conn has no field or method RemoteAddr)
(found that in this example: http://raycompstuff.blogspot.com/2009/12/simpler-chat-server-and-client-in.html).
So i tried looking at the documentation, but it just gave me the source of the net package.
Read trough the source, and figured it should be
undefined: TCPConn
How can I pass the connection of a client to a goroutine, so i can handle multiple clients at once?
Ok, figured it out.
There is some guy who actually already wrote what I wanted to write in go.
https://github.com/dustin/gomemcached/blob/master/mc_conn_handler.go
go handleClient(con);
func handleClient(con net.Conn) {
Related
I'm trying to send messages using ZeroMQ from a program written in Go to another program written in Rust. The Rust side seems to be running fine, but the Go side does not send messages when the socket is called from inside a function.
I'm using the Pebbe zmq4 library and defining the sockets in a function that instantiates an object (not technically the constructor, but I may be wrong). Here is some of the code. The relevant parts are very spread out, so I'll only include the most important stuff.
import (
...
zmq "github.com/pebbe/zmq4"
)
func NewPod(...) *Pod {
...
_derSock, err := zmq.NewSocket(zmq.PUSH)
...
myPod := &Pod{
...
derSock: *derSock,
}
myPod.derSock.Connect("ipc:///tmp/router")
_, err = myPod.derSock.Send("hi :)", 0)
}
If I send a message from inside that function, it works fine, but when I use the send function from inside a class method of MyPod, I get the error "socket operation on non-socket" I've seen that other people have similar problems, both with ZeroMQ and with normal sockets, but their problems are mostly in lower-level languages and the problems tend to be logic errors in the send call. However, the syntax that I use inside the class function is exactly the same as the call shown.
Creating sockets has worked fine before in the same part of this program, created the same way, when I used Unix domain sockets, but for some reason the switch to ZeroMQ isn't going as easily. I'm new to both of these languages and network programming, and this has stumped me for hours. Thanks in advance.
I am trying to write unit test for this project
It appears that i need to refactor a lot and currently working on it. In order to test functions in project/api/handlers.go i was trying to write some unit test code however always taking error related with DB initializing. DB is from Psql Docker container. Error says given hostname is not valid, however without testing it works as no problem. Also, for Dockerized postgresql, container name is being used as hostname and this shouldn't be a problem.
The error is:
DB connection error: failed to connect to host=postgresdbT user=postgres database=worth2watchdb: hostname resolving error (lookup postgresdbT: no such host)
Process finished with the exit code 1
Anyway, i did a couple refactor and managed abstracting functions from DB query functions however this error still occurs and i cannot perform the test. So finally i decided to perform a totally blank test within same package simply checks with bcrypt package.
func TestCheckPasswordHash(t *testing.T) {
ret, err := HashPassword("password")
assert.Nil(t, err)
ok := CheckPasswordHash("password", ret)
if !ok {
t.Fail()
}
}
//HashPassword function hashes password with bcrypt algorithm as Cost value and return hashed string value with an error
func HashPassword(password string) (string, error) {
bytes, err := bcrypt.GenerateFromPassword([]byte(password), 4)
return string(bytes), err
}
//CheckPasswordHash function checks two inputs and returns TRUE if matches
func CheckPasswordHash(password, hash string) bool {
err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
return err == nil
}
However when I've tried to perform test for only TestCheckPasswordHash function with command of go test -run TestCheckPasswordHash ./api, it still gives same error. Btw, File is handlers_test.go, functions are at handlers.go file, package name is api for both .
There is no contact with any kind of DB related functions however i am having same error again and again. When i run this TestCheckPasswordHash code in another project or at project/util/util_test.go, it checks and passes as expected.
I don't know what to do, it seems that i cannot perform any test in this package unless figure this out.
Thanks in advance. Best wishes.
Was checking your repo, nice implementation, neat an simple good job!
I think your issue is in the init function, please try commenting it out and see if it work for that single test.
Is a bit complex to explain how the init function works without a graph of files as example but you can check the official documentation:
https://go.dev/doc/effective_go#init
PD: if this doesn't work please write me back
I've found the reason why this error occured and now it's solved.
This is partially related with Docker's working principle of how DB_Hostname must be declared but we can do nothing about it. So we need a better approach to overcome.
When go test command executed for (even) a function, Go testing logic checks whole package(not whole project) as per execution order, such as firstly variable declarations and init() function later. In case of calling an external package item, runtime detours that package for the item also.
Even if you are testing only an irrelevant function, you should consider that, before performing the test, Go runtime will evaluate whole package.
In order to prevent this, i wrapped the package level variables(even though they are in another package) that directly calls DB and cache. On initial stage, these can be allocated as a new variable. However, their connection will be ensured by main or main.init()
And now, prior to testing, all relevant variables (in same package or via external) are checked. Let's say if DB agent (redis.client or pgxpool.Pool) is needed, we are creating a new agent, compiler doesn't complain and testing begins. Agent will be operational only by a function call from main or somewhere we want to.
This is a better(may be not best) practice for a more maintainable code. Initialization of dependants should be able to be handled cautiously and in context with the functional needs. At least, with a simple refactoring, problem should be solvable.
I found some example code online that I'm trying to use to do a CNAME record lookup (notice that I pass a callback block that I want to be run):
DNSServiceQueryRecord(serviceRef, 0, 0, domainName, UInt16(kDNSServiceType_CNAME), UInt16(kDNSServiceClass_IN), callback, &mutableCompletionHandler);
DNSServiceProcessResult(serviceRef.pointee)
The problem is that this code is getting blocked at DNSServiceProcessResult(serviceRef.pointee) and the callback is never called. According to Apple's documentation for DNSServiceProcessResult, I need to
Use DNSServiceRefSockFD in conjunction with a run loop or select() to determine the presence of a response from the server before calling this function to process the reply without blocking.
So I looked at DNSServiceRefSockFD and found that I could create a dnssd_sock_t with DNSServiceRefSockFD(serviceRef.pointee). But now that I have the socket, I'm not sure how to "use it in conjunction with a run loop" as an event source for the run loop (according to the DNSServiceRefSockFD documentation).
I'm just not understanding how this works. I don't understand how to use the dnsssd_sock_t as an event source to a run loop so that I can call DNSServiceProcessResult at the right time without blocking so that my callback will actually run.
If it's better to use the socket as a kqueue event source or in a select() loop (as the documentation mentions), I'm fine with that, but I don't know how to do that either.
CoreFoundation can be quite cryptic, so any help is much appreciated!
And if there's a better way to do a CNAME record lookup then, by all means, please share!
See my (ethan-gerardot) comments on https://gist.github.com/fikeminkel/a9c4bc4d0348527e8df3690e242038d3
The first paragraph answers how to get the callback to be called without blocking.
I've recently become interested in trying to adapt my Rock-Paper-Scissors game into a multiplayer-friendly program, so today I decided I'd look up a tutorial on servers. It seems I'm following it precisely (aside from using a different IDE). However, something is going wrong and I'm not sure exactly what it is, and it works fine for the tutorial maker. I've looked up EOFException but it didn't exactly help me out.
The tutorial on Youtube
My screenshot of the issue.
[Documentation on EOFException](I had a link here, but I need at least 10 reputation to post more than two links)
"Signals that an end of file or end of stream has been reached unexpectedly during input.
This exception is mainly used by data input streams to signal end of stream. Note that many other input operations return a special value on end of stream rather than throwing an exception."
[A similar but apparently unresolved question asked here](I had a link here too]
By the way, if you look up exactly what I've posted here, you'll also find that I've asked it at DaniWeb. I'm just posting in multiple places in case it isn't resolved at one or the other. If it is, well... the more knowledge, the better.
EOFException during readUTF() just means it's reached the end of the stream, like it says on the tin. Note that this method doesn't return null at end of stream, unlike readLine() (but like all other readXXX() methods).
It can also mean that your sending and receiving is out of sync, e.g. you are trying to read some ridiculously large number of bytes because you left out a readInt() or similar, or you wrote something extra at the peer that you shouldn't have, so you're trying to read the next bytes in the stream as the result of writeUTF() when it isn't. This is an application protocol error.
How this happened in the code you posted is another question, but your code doesn't close the sockets, which doesn't help. Add an out.close() to your server code, and in.close() to the client code. However I cannot reproduce your problem with or without these closes. Are you sure this is the real code?
I´ve read that it´s possible to share sockets between processes. Is this also possible in Node.js?
I saw the cluster api in node.js, but that´s not what I´m looking for. I want to be able to accept a connection in one process, maybe send & read a bit, and after a while pass this socket to another fully independent node.js process.
I could already do this with piping, but I don´t want to do this, since it´s not as fast as directly reading/writing to the socket itself.
Any ideas?
Update
I found the following entry in the node.js documentation:
new net.Socket([options]) #
Construct a new socket object.
options is an object with the following defaults:
{ fd: null
type: null
allowHalfOpen: false
}
fd allows you to specify the existing file descriptor of socket. type specified underlying protocol. It can be 'tcp4', 'tcp6', or 'unix'. About allowHalfOpen, refer to createServer() and 'end' event.
I think it would be possible to set the "fd" property to the filedescriptor of the socket and then open the socket with that. But... How can I get the filedescriptor of the socket and pass it to the process that needs it?
Thanks for any help!
This is not possible at the moment, but I've added it as a feature request to the node issues page.
Update
In the mean time, I've written a module for this. You can find it here: https://github.com/VanCoding/node-ancillary
You probably want to take a look at hook.io
hook.io is a distributed EventEmitter built on node.js. In addition to providing a minimalistic event framework, hook.io also provides a rich network of hook libraries for managing all sorts of input and output.