用Socket作异步编程时，检验对端是否已经关闭不能用Socket#eof？，因为这样会造成Ruby将此Socket的IO对象转换成Buffered IO，从而导致recv，recvfrom系列函数读取失败，出现“recv for buffered IO (IOError)”错误。在Buffered IO上只能调用可能会阻塞的read，readline，gets系列函数，严重影响了异步通信服务器的性能。
我也被这个问题困扰了好几天，直到在ruby新闻组中看到一篇很好的解决方案，用异常代替eof？检查，我已经在ruby1.8.2 windows one-click版本上测试通过，特此引用。原帖可在http://groups.google.com/group/comp.lang.ruby/msg/3fabd75cf9a38c1c上找到。
顺便补一句，几乎所有的教学资料上都使用Socket#eof？这个方法，而很少谈到这个错误，真是很奇怪。
Socket programming: recv(bytes) throwing a buffered IO error
Frank Swarbrick <info...@earthlink.net>
Eric Haase wrote:
> Hello everyone,
> I just started learning Ruby and I decided to mess around with
> socket programming. However, I've encountered a problem and was
> wondering if someone could help me out. I wrote a server and a client
> program and the server is behaving strange when I invoke the
> recv(bytes) method in the TCPSocket class. Here is my server code with
> the error I'm receiving:
> require 'socket'
> abort "usage: #{__FILE__} [port]" if ARGV.size > 1
> port = (ARGV[0] || 3434).to_i
> server = TCPServer.new(port)
> sockets = [server]
> puts "listening on port ##{port}"
> loop do
> socketsReady = select(sockets)
> next if socketsReady == nil
> socketsReady[0].each do |socket|
> if socket == server
> client = socket.accept
> sockets.push(client)
> puts "established connection
> (#{client.addr[-1]}:#{client.addr[1]})"
> else
> if socket.eof?
> address = socket.addr
> sockets.delete(socket)
> socket.close
> puts "closed connection (#{address[-1]}:#{address[1]})"
> else
> string = socket.recv(1024)
> puts "received \"#{string}\"
> (#{socket.addr[-1]}:#{socket.addr[1]})"
> socket.puts(" server received your \"#{string}\"")
> end
> end
> end
> end
> ./server_bad.rb:27:in `recv': recv for buffered IO (IOError)
> from ./server_bad.rb:27
> from ./server_bad.rb:15
> from ./server_bad.rb:12
I'm not sure about all of the issues, but I think it may have to do with
you attempting to test socket.eof? prior to reading from socket. I
don't think it can know about it's eof status until it does the read.
I'm just a Ruby beginner, but I know socket programming pretty well.
Try replacing the inside of the socketsReady[0].each loop as follows:
if socket == server
client = socket.accept
sockets.push(client)
puts "established connection" +
"(#{client.addr[-1]}:#{client.addr[1]})"
else
begin
string = socket.recv(1024)
puts "received \"#{string}\""+
"(#{socket.addr[-1]}:#{socket.addr[1]})"
socket.write(" server received your \"#{string}\"")
rescue
address = socket.addr
sockets.delete(socket)
socket.close
puts "closed connection (#{address[-1]}:#{address[1]})"
end
end
Seems to work. Now you need to figure out how to abort from the loop,
such as when the user enters a key (on the server process). I can't
figure it out...
Frank