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Server Sockets in JRuby
JRuby uses classes from the Java platform for sockets, so our API differs slightly when it comes to the lowest-level "Socket" class.
Creating a Server Socket
In JRuby, the Ruby
Socket class can only be used for client-side connections. As a result, only
connect works, not
accept. We provide a separate class called
ServerSocket with mostly the same API as
Socket, but it handles
accept and not
Here's a simple example of a server:
require "socket" socket = ServerSocket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0) sockaddr = ServerSocket.pack_sockaddr_in(12345, "127.0.0.1") socket.bind(sockaddr) socket.accept
The API works basically like
Socket, but with
ServerSocket in its place. You can also include the following code to make server sockets that work on JRuby and other impls with both server and client support in
if RUBY_ENGINE != 'jruby' ServerSocket = Socket end
Bind and Listen and Backlogs
The normal sequence for listening for connections on a Ruby Socket is to call
new for a new Socket,
bind to bind to an address and port,
listen to express intent to listen for connections with the specified connection backlog, and finally
accept to accept incoming connections.
On JRuby's ServerSocket,
listen are combined into
bind, which accepts an optional backlog argument.
Here's an example:
socket = ServerSocket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0) sockaddr = ServerSocket.pack_sockaddr_in(12345, "127.0.0.1") socket.bind(sockaddr, 5) # no call to listen... # socket.listen(5) socket.accept
For non-JRuby impls, the following simple monkey-patch makes their
bind work like ours, for API-compatibility:
if RUBY_ENGINE != 'jruby' ServerSocket = Socket # as shown above class Socket alias :_old_bind, :bind def bind(addr, backlog) _old_bind(addr) listen(backlog) end end end
Details of Sockets and ServerSockets
Because JRuby is built atop the Java Development Kit and uses its classes to implement the Ruby IO subsystem, we must choose at construction time whether a socket will be used for client or server operations. Specifically, we must construct a
Socket or a
ServerSocket to back up the Ruby object.
This means that it's impossible for us to construct a Ruby
Socket object and support both
accept on that same object; we have to choose which of those operations will work right away.
Because connecting to remote servers is more common,
Socket in JRuby is client-only, and therefore will only support the
connect operation (not
accept). We define an additional class,
ServerSocket that has the same basic operations as
Socket but supports
accept instead of
A simple example is at the top of this page, along with code you can include to make it work on non-JRuby versions of Ruby.
Details of Bind and Listen
The JDK ServerSocket class provides no
listen method, instead allowing users to specify backlog at construction time (while simultaneously binding a port) or at bind time (combining the POSIX
listen operations). Because of this, we have no way to separate the two phases of "binding" and "listening" in the API we expose to Ruby.
For this reason,
ServerSocket#bind in JRuby does both
listen at the same time, and accepts an optional backlog argument.
See above for an example, along with code you can use to make the API work in non-JRuby versions of Ruby.