From: Matt Armstrong <matt@...>
Date: 2002-03-07T07:20:33+09:00
Subject: Re: exception-safety and opening sockets

Paul Brannan <paul@atdesk.com> writes:

> When I open a file and want to make sure a file gets closed, even when I
> get an exception, I do:
>
>   File.open("filename") do |io|
>     puts io.gets
>     raise RuntimeError
>   end
>
> I tried doing the same thing with a socket:

[...]

> but I get no output.  The closest I can get is:
>
>   socket = TCPSocket.new("hostname", "portname")
>   begin
>     puts "here"
>     puts socket.gets
>     raise RuntimeError
>   ensure
>     socket.shutdown
>   end

You can also do this to avoid putting "socket" in the outer scope.

    begin
        socket = TCPSocket.new(...)
        puts socket.gets
    ensure
        socket.shutdown if socket
    end

If TCPSocket.new throws an exception, socket will just be nil.  And if
you're doing the socket operation in a method, this works too:

    def do_something_with_socket
        # you can put a bunch of code here
        socket = TCPSocket.new(...)
        # use the socket here
    ensure
        socket.shutdown if socket
    end


> However, socket is still in scope, but is already closed, which is
> not desirable.  Is there a method in Ruby that does something
> similar to:
>
>   def safe_socket_open(host, port)
>     socket = TCPSocket.new(host, port)
>     begin
>       yield socket
>     ensure
>       socket.shutdown
>     end
>   end

You just wrote it.  :-)

-- 
matt