How can I write a byte to a socket in ruby? I specifically mean how can I write something like 0x02 to a socket. Thanks.
One way of sending integer byte values would be to use array.pack.
socket.write [0x02].pack("C")
Something like this ?
require 'socket' # Get sockets from stdlib
server = TCPServer.open(2000) # Socket to listen on port 2000
loop { # Servers run forever
client = server.accept # Wait for a client to connect
client.write("\x02")
client.close # Disconnect from the client
}
Related
While running a TCPServer in ruby 2.7.0, I want to see when my client has closed the connection (or is unable to continue reading). However, when I check on the server, I never see that the connection has closed.
I've tried using a bunch of the different ruby socket primitives but nothing seems to work here. I've tried writing to the socket as well in hopes of forcing an error but that doesn't seem to help.
I'm including an example here:
# main.rb
require_relative 'server'
PORT = 9000
server_thread = Server.thread
socket = TCPSocket.open("localhost", PORT)
socket.puts '5'
server_thread.join(1)
socket.close
puts socket.closed?
server_thread.join(2)
# server.rb
require 'socket'
class Server
def self.thread
Thread.new do
server = TCPServer.open(PORT)
while true
server.accept do |socket|
while true
socket.puts '1'
# why doesn't this ever happen?
puts 'closed' if socket.closed?
end
end
end
end
end
end
When running ruby main.rb, this code outputs
true
Whereas I expect it to output:
true
closed
The block that you pass to server.accept is ignored because Socket#accept does not accept a block argument.
When you call socket.close in main.rb, you close the client side of the connection. The server side of the connection will remain open.
You could call IO#read to wait until the client closes the connection.
Thread.new do
server = TCPServer.open(PORT)
loop do
socket = server.accept
socket.read
puts 'client closed connection'
socket.eof? #=> true
socket.close
end
end
The only response provided did not work. Attempting to read from the closed socket did not error like I expected it to.
I have come to the conclusion that what I was asking is simply not possible. You must either:
Send a keep-alive from the client and close when you do not receive it or
Face the consequences of not knowing whether or not your writes have
succeeded.
Personally, I was able to live with 2 since this was for a prototype.
I've read some things suggesting that because of the design of TCP this might not be possible (such as: Java socket API: How to tell if a connection has been closed?), but I'm trying to find explicit confirmation. I have a basic TCP server that accepts connections, and a client that initiates a connection, sends a message, and then closes the connection. Is there a way for the server to know that the client closed the connection?
I found some suggestions to look into checking the file descriptors for the sockets (source: How to check if a given file descriptor stored in a variable is still valid?), using the kernel select command (source: https://bytes.com/topic/c/answers/866296-detecting-if-file-descriptor-closed) as well as using recv to check if the client returns 0 (source: http://man7.org/linux/man-pages/man2/recv.2.html#RETURN_VALUE), but these do not seem to work, at least not when called by Ruby. To test this, I wrote a basic server and client:
test_server.rb
require 'socket'
require 'fcntl'
TIMEOUT = 5
server = TCPServer.new('localhost', 8080)
puts "Starting server"
loop do
client = server.accept
puts "New client: #{client}"
puts "** before closed #{Time.now.to_i} closed=#{client.closed?}"
result = IO.select([client], nil, nil, TIMEOUT)
puts "select result=#{result}"
fd = client.fcntl(Fcntl::F_GETFD, 0)
puts "client fd=#{fd}"
stuff = client.recv(30)
puts "received '#{stuff}'"
begin
r = client.recv(1)
rescue => e
end
puts "received #{r} nil?=#{r.nil?}"
sleep 3
puts "** after closed #{Time.now.to_i} closed=#{client.closed?}"
result = IO.select([client], nil, nil, TIMEOUT)
puts "select result=#{result}"
fd = client.fcntl(Fcntl::F_GETFD, 0)
puts "client fd=#{fd}"
begin
r = client.recv(1)
rescue => e
end
puts "received #{r} nil?=#{r.nil?}"
puts "done!"
end
test_client.rb
require 'socket'
class Client
def initialize
#socket = tcp_socket
end
def tcp_socket
Thread.current[:socket] = TCPSocket.new("localhost", 8080)
end
def send(s, args={})
puts "sending str '#{s}'"
nbytes = #socket.send(s, 0)
puts "received #{nbytes} bytes"
sleep 1
#socket.close
puts "done at #{Time.now.to_i}: #{#socket.closed?}"
end
end
msg = 'hello world this is my message'
server = Client.new
server.send(msg)
The client sends a 30-byte message, waits 1s, then closes the connection.
The server accepts the connection, calls select and fcntl on it to check its status, receives the message, tries to read 1 more byte, sleeps for 3 seconds, then calls select and fcntl and again tries to read 1 byte. The intent here is to check if anything changes that the server can see before and after the client closed the connection (hence the 3-second sleep). The result I get from running the server and then the client code is:
Starting server
New client: #<TCPSocket:0x00007fa0930f0880>
** before closed 1578005539 closed=false
select result=[[#<TCPSocket:fd 10>], [], []]
client fd=1
received 'hello world this is my message'
received nil?=false
** after closed 1578005543 closed=false
select result=[[#<TCPSocket:fd 10>], [], []]
client fd=1
received nil?=false
done!
Before and after the client closed the connection, select still sees the socket as readable, the underlying file descriptor does not change, and recv returns empty string (It's possible the kernel call is returning 0 as specified in the man-page but Ruby is capturing that, and if so I don't know how to see it.). Thus none of these seem to be a reliable indicator of whether the connection was closed from the other side. Is there something I'm missing?
I have seen some other suggestions to incorporate a regular heartbeat back to the client, but I'm wondering if there's a way to avoid that. Reason is that I'm trying to accommodate a case where the client may be sending a message in several pieces separated by a delay (e.g. 100 bytes at 1 second each byte). If the server sends a heartbeat message in the middle of that operation and listens for an OK, I presume the client has to be listening for the heartbeat as well and send its OK back, separate from the ongoing message send, and in my test case, I can't change the client to do that.
I have seen some other suggestions to incorporate a regular heartbeat back to the client, but I'm wondering if there's a way to avoid that.
A heartbeat (ping) is the only viable solution.
There is no way to reliably know if the connection is live except by trying to send data over the wire.
Since TCP/IP doesn't require any traffic when data isn't being sent (or received), there's no way for the TCP stack (not even in the OS kernel) to know if the connection is "live" without attempting to exchange data over the wire.
Some connections will close gracefully, allowing the TCP stack to recognize that the connection was closed - but this isn't always true (you can read more about "half-open" or "half-closed" connections).
For this reason, all servers implement a timeout / ping mechanism to test for lost connectivity.
I'm trying to accommodate a case where the client may be sending a message in several pieces separated by a delay (e.g. 100 bytes at 1 second each byte)...
Remember that TCP/IP is a stream based protocol, not a message based protocol.
This means that your 100 bytes might arrive fragmented or they might be combined with a previous message.
If you're sending messages (rather than streaming data), you need - by design - to mark message boundaries.
Since these message boundaries must be marked, it becomes relatively easy to add a message type marker (to mark ping/pong messages).
You can observer the WebSocket protocol message format to learn more about message based protocol design using a TCP/IP (streamed) connection.
I'm trying to write my own implementation of UDP in ruby for educational purposes using raw sockets.
Here's what I have so far:
require 'socket'
addr = Socket.pack_sockaddr_in(4567, '127.0.0.1')
socket = Socket.new(
Socket::PF_INET,
Socket::SOCK_RAW,
Socket::IPPROTO_RAW
)
socket.bind(addr)
socket.recvfrom(1024)
I am testing it like so:
require 'socket'
udp = UDPSocket.new
udp.send "Hello World", 0, "127.0.0.1", 4567
But the call to recvfrom is blocking indefinitely.
If I change it to this:
socket = Socket.new(
Socket::PF_INET,
Socket::SOCK_DGRAM,
Socket::IPPROTO_UDP
)
It of course works because this is the system-level way to accept UDP packets.
How can I receive UDP packets on a raw socket?
To be clear: I want to handle the actual UDP protocol (decoding the datagram & doing a checksum) myself!
Raw sockets work at IP level. You cannot bind a raw socket to a port. You can bind to a local address with bind or to an interface by setting the proper socket options (I don't know how to do it in Ruby, in C you call setsockopt. Instead of IPPROTO_RAW you should use IPPROTO_UDP in protocol.You will receive all UDP datagrams received on that IP address or that interface if the socket is bound to it.
I'm trying to see the exact request incl. potential headers like IP, mac address etc.
Server side code:
require 'socket'
server = TCPServer.new 2000
loop do
client = server.accept
puts client.inspect # This should show IP and all transmitted information
client.close
end
Output is #<TCPSocket:fd 8>, but should show the exact request
You can read what client send to the server like this:
require 'socket'
server = TCPServer.new 2000
loop do
client = server.accept
# Print whatever client sends to server
while line = client.gets
puts line
end
client.close
end
The request header is not stored inside client, it works slightly differently: when your TCP server gets client request, you must accept it and then read whatever client is sending to server.
I want to implement a while-loop that runs as long as a Client is connected at my socket.
It's gonna be Thread based so i want to make shure that the Thread gets closed once the Client disconnected.
question: How do I check if the Client is still connected to my socket?
question: Is the Thread already getting closed when connection closes if I startet it like this: Thread.start(socket.accept) do |client| ...
Check this out,
require 'socket'
th=[]
server = TCPServer.open(2000)
loop do
Thread.start(server.accept) do |client|
client.puts "server started.."
# Something
th = Thread.list
th.each do |t|
if t.status == "sleep" # checks all client status
f = t.kill # kills thread if client is disconnected
end
end
end
end
You may kill the thread or you can store the IP addres of clients using that thread in an array and make a compare with that for exact client.(like, t.addr)
I don't have experience programming ruby. If it was .Net, what you pretend is not possible without some kind of keep-alive protocol. If the server does not get data from client after x seconds it assumes the client disconnected. The client must have a timer to send something to the server when not communicating.
server = TCPServer.open 12345
loop {
Thread.start(server.accept) do |client|
...
puts "client is offline!" if client.closed?
...
client.close
end
}
You may check "closed?" in "client".