Is there a way to find out how many bytes of data is available on an TCPSocket in Ruby? I.e. how many bytes can be ready without blocking?
问题:
回答1:
The standard library io/wait
might be useful here. Requring it gives stream-based I/O (sockets and pipes) some new methods, among which is ready?
. According to the documentation, ready? returns non-nil if there are bytes available without blocking. It just so happens that the non-nil value it returns it the number of bytes that are available in MRI.
Here's an example which creates a dumb little socket server, and then connects to it with a client. The server just sends "foo" and then closes the connection. The client waits a little bit to give the server time to send, and then prints how many bytes are avaiable for reading. The interesting stuff for you is in the client:
require 'socket'
require 'io/wait'
# Server
server_socket = TCPServer.new('localhost', 0)
port = server_socket.addr[1]
Thread.new do
session = server_socket.accept
sleep 0.5
session.puts "foo"
session.close
end
# Client
client_socket = TCPSocket.new('localhost', port)
puts client_socket.ready? # => nil
sleep 1
puts client_socket.ready? # => 4
Don't use that server code in anything real. It's deliberately retarded in order to keep the example simple.
Note: According to the Pickaxe book, io/wait is only available if "FIONREAD feature in ioctl(2)". Which it is in Linux. I don't know about Windows & others.