Socket.read() won't block in Ruby - ruby

Question

I have the following code for a simple TCP server in Ruby:
# server.rb
require 'socket'
class Server
def initialize(port)
#port = port
end
def run
Socket.tcp_server_loop(#port) do |connection|
Thread.new do
loop do
puts "IO: #{IO.select([connection]).inspect} - data: #{connection.read}"
end
end
end
end
end
server = Server.new(16451)
server.run
As well as this trivial TCP client code:
# client.rb
require 'socket'
client = TCPSocket.new('localhost', 16451)
client.write('stuff')
It is my understanding that connection.read in server.rb should block if no data is present on the socket. However, when I run this on my macbook (OS X 10.12.5), it keeps spitting out the following output:
IO: [[#<Socket:fd 12>], [], []] - data: stuff
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
IO: [[#<Socket:fd 12>], [], []] - data:
...
It seems that IO.select thinks there is data available to read on the socket, while no such data has been sent.
How can I achieve a blocking read when working with sockets in Ruby? Am I overlooking something?
Matt's answer pointed me in the right direction. For future readers, here's my new code.
# server.rb
require 'socket'
class Server
BYTESIZE_OF_PACKED_INTEGER = [1].pack('i').bytesize
def initialize(port)
#port = port
end
def run
Socket.tcp_server_loop(#port) do |connection|
Thread.new do
while packed_msg_bytesize = connection.read(BYTESIZE_OF_PACKED_INTEGER)
msg_bytesize = packed_msg_bytesize.unpack('i').first
msg = connection.read(msg_bytesize)
puts msg
end
end
end
end
end
server = Server.new(16451)
server.run
And the client code.
# client.rb
require 'socket'
msg = 'stuff'
msg_bytesize = msg.bytesize
packed_msg_bytesize = [msg_bytesize].pack('i')
client = TCPSocket.new('localhost', 16451)
client.write(packed_msg_bytesize)
client.write(msg)

Answer 1

read will block if there is no data, but not at EOF. The IO#read docs say:
When this method is called at end of file, it returns nil or "", depending on length: read, read(nil), and read(0) return "", read(positive_integer) returns nil.
Since calling read on EOF doesn’t block, select will return the IO as readable straight away.
In your code the first call to read will block until all the data is read from the connection (i.e. the other end has closed it). From then it will be at EOF, so select will return it as ready, and read will return an empty string immediately.