I am trying to build a BitTorrent client in go. I need to make UDP requests to connect to the various trackers. For this I use the net package and do this:
net.Dial("udp", "udp://hostname:1337/announce")
I get a "too many colons in address" error.
If I try this:
net.Dial("udp", "hostname:1337/announce")
I get a "nodename nor servname provided, or not known" error.
How do I fix this?
So you'll need to send it to the IP address and port as provided by the .torrent metafile (announce field).
And once you open the net.Conn you can conn.Write() to the socket and similarly conn.Read()
So you've just about gotten i:
conn, err := net.Dial("udp", announceAddr:Port)
When connecting with HTTP, yeah you use the /announce endpoint, but not with UDP
The specs explain how many bytes to read and write (it is fixed at first, but later dynamic when it comes to reading the peer list). I've found this link, rather, the most useful: https://github.com/naim94a/udpt/wiki/The-BitTorrent-UDP-tracker-protocol
Related
I am trying to build a bittorrent client. I wrote this function to verify that I can establish connection to send messages to other peers but its not working.
func handShake(torrent *gotorrentparser.Torrent, peer Peer, peedId []byte) {
conn,err := net.Dial("tcp", peer.ip + ":" + strconv.Itoa(int(peer.port)))
if err != nil {
panic(err)
}
defer conn.Close()
}
Here peer is a struct of string ip and uint16 port.
Getting the following error:
panic: dial tcp 152.57.73.47:27569: connectex: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Couldn't find any similar issues. I tried to fix my local port address to be same as what I used to send the announce request but that didn't work either.
Edit: I tried with a different torrent, it is failing for some peers, but now it is working for some other peers. Is the issue only when the peer is using utorrent as bittorrent clients?
If you're developing a bittorrent client you should start with a more reproducable setup such as running an existing client with a known infohash on your local machine and then connecting to that (without using a tracker). Once you got that to work you can work on a tracker client implementation and then put those pieces together.
The internet is unreliable and bittorrent consists of many moving parts, so a single connection failure won't tell you much, you'll have to ensure that each part works properly and try with torrents that you have tested in an existing client to narrow down the cause of problems.
After few days here is the problem that I found.
Not all peers are able to accept an inbound request as they are behind a NAT.
Even when I hosted a torrent from one of my computer and tried to download through another system, I couldn't download as there was no reply from the peer for the SYN message being sent.
I was only able to download, when both the clients were on the same network and local peer discovery was enabled, and the TCP connection was also build with the local IP address.
I am working on an application that tries to send some data to a remote server. Once I get the hostname, I get a connection by resolving the hostname using net.Dialer.DialContext. Once, I resolve the hostname, I keep on using conn.Write method to write data to the connection.
conn, err := d.DialContext(ctx, string(transport), addr)
_, err := client.conn.Write([]byte(msg))
Error faced: I observed that due to some issues, I was not able to ping my server. Surprisingly, conn obtained from DialContext did not complain while doing conn.Write and it kept writing to the same connection.
Can someone help me in how to modify my writing methods in order to get an error in case the destination server is not reachable?
From this UDP connection example
the best a "connected" UDP socket can do to simulate a send failure is to save the ICMP response, and return it as an error on the next write.
So try and (for testing) make a second conn.Write, to confirm that you would indeed get an error this time.
I'm attempting to write a script to connect to a DLNA audio renderer.
There are a few articles on the web giving information on how to do this using UDP and curl, however in my particular scenario I'm having some difficulties.
The first step is to send a UDP multicast announcement over the network to discover DLNA devices on the network.
The message sent to discover devices is:
M-SEARCH * HTTP/1.1
HOST: 239.255.255.250:1900
MX: 5
Man: "ssdp:discover"
ST: urn:schemas-upnp-org:device:MediaRenderer:1
All lines in this message sent over UDP should have crlf line endings and the last line should have an extra crlf according to this article
That all seems fine. And if the message above is in a file devicediscovery.txt supposedly it's possible to use netcat to send out this message:
cat devicediscovery.txt | nc -u -4 239.255.255.250 1900
239.255.255.250:1900 is the multicast address and port over which DLNA devices communicate.
This all seems fine too, however, as is pointed out in the linked article netcat ignores the response from the dlna media renderer because there is a mismatch in IP addresses the message is sent out over the dlna multicast address, though the response comes from the router. The article suggests using tcpdump to capture the response, however I'm on Windows and using Bash on Windows WSL so tcpdump is not available and such a technique would possibly be complicated when developing a script to automate the dlna connection.
Would it be possible to use two seperate instances of netcat? One instance sending the message over the dlna multicast address and the other listening for the response from the router?
I have tried to get this working, however I'm unsure which port netcat should be listening on to hear the incomming response. Is there a standard port that netcat should listen on?
I've tried commands such as: nc -luv 192.168.0.1, however I get an error Servname not supported for ai_socktype. I've tried to remedy this by playing around with /etc/services but had no luck.
What command can I use and how must I configure the system to listen for the response from the search for dlna devices? I'd like to parse the response in a script so that the dlna connection can be automated.
Although you mention issues with DLNA it looks that you are really asking for how to best troubleshoot this.
Network cards don't allow access to incoming traffic unless set in promiscuous mode. Netcat won't be able to do what you need because of this. But, you can use Wireshark to read the traffic on the interface. TCPdump and Wireshark have close ties and almost interchangeable.
https://www.wireshark.org/
I would recommend to use it to troubleshoot further. Ppost the capture (not just a picture) and show where it failed.
I'm studying Go for network programming. The problem is Go documentation is too simple. For example， I don't know when to use net.DialTCP, and when to use TCPListener object to AcceptTCP, what's the difference? How about client communicate with another client? Not client to server.
Connecting
In Go, you use the Dial function from net to connect to a remote machine.
net.Dial("tcp","google.com:80")
net.Dial("udp","tracker.thepiratebay.org:6969")
net.Dial("ip","kremvax.su")
net.Dial("unix","/dev/log")
This gives you an abstract Conn object that represents the connection you just established. Conn implements the ReadWriteCloser interface from io and a couple of other functions. You can use this object to send and receive data.
Listening
To listen, i.e. open a port, you use the Listen function from net. Calling Listen gives you a Listener object. Use Accept to accept incoming connections. Accept returns another Conn object that can be used as above.
ls, err := net.Listen("tcp",":1337")
if err != nil {
// port probably blocked, insert error handling here
}
conn, err := ls.Accept()
if err != nil {
// error handling
}
conn.Write("Hello, world!")
DialTCP and ListenTCP
These functions give you more control over TCP connections. I suggest you to only use them if they are definitly needed for your program as Dial and Listen are simpler, more generic and easily allow you to adapt your program to other types of network connections.
net.DialTCP is used on the client side to create a connection to remote server.
net.TCPListener.AcceptTCP is used on the server side to accept new connection (possibly initiated by net.DialTCP if client is written in Go). Note that listener may accept multiple connections, one by one, thus serving multiple clients at once (e.g. each in different goroutine).
Depending on whether you are writing client or server, you use net.DialTCP or net.TCPListener
Maybe you should learn about network programming in general first? Then these would make more sense I think.
I'm using zeromq to develop a dynamic application which operate like upnp protocol( autoconfiguration and auto-discovery of equipment on a living room).
To do it so, i use zeromq to distribute messages, my problem is that when i create a socket and binding on a adress "169.254.1.0 through 169.254.254.255", I receive a error messages like this: ZMQError: Cannot assign requested address.
I've tried to figure out why by changing the address by local adress (127.0.0.1),and it's works !!.
The problem is that i'm implementing autoip, it's means that i'm oblliged to use the adresse on range 169.254.1.0 through 169.254.254.255.
Thanks in advance for your help!
I got this error, too... and I realized I had the wrong idea of who was connecting to whom in the PUB/SUB model.
This was working: Host A as the ZMQ PUB, and could easily connect with Host A as the ZMQ SUB.
Then I tried to set up Host B as the SUB, and have Host A "send" to that... and I kept getting this error. After all don't you need to tell the PUB where to send the data?
No! Host A as the PUB should still bind to IP_ANY (0.0.0.0); it is Host B as the SUB who has to be configured with the address of Host A.
Once I got that straight in my code (and in my head), I was up and running.
After you bring the interface up, you need to get its IP address and then bind on that. Alternatively you may be able to bind on "*", meaning all interfaces.