[plt-scheme] IPv6?

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Thu Nov 3 16:41:24 EST 2005

At Sat, 23 Jul 2005 10:35:20 +0200, Johan Liseborn wrote:
> Are there any plans on adding IPv6 support to PLT Scheme?

MzScheme in the SVN respository trunk supports IPv6.

I'm not certain about some of the design decision noted below --- I'm
especially concerned about "localhost" --- so I welcome feedback from
those with more experience on this topic.


 * By default, `tcp-listen' and `udp-open-socket' create sockets that
   work with IPv4, only. For `tcp-connect', etc., the hostname
   determines the protocol family.

 * If you system supports IPv6, beware that "localhost" is probably
   mapped to an IPv6 address by default. In that case, if you're trying
   to contact an IPv4 server, it probably won't work; use ""

 * Depending on your system's capabilities, you might supply "::" as
   the local hostname for `tcp-listen' to get a listener that accepts
   both IPv4 and IPv6 connections. This works under Mac OS X and
   Linux, for example, but under Windows it creates an IPv6-only

 * The `udp-open-socket' function now accepts optional hostname and
   port arguments. If they're supplied, then the new socket's protocol
   family is the one implied by the address and port. For example,
   `(udp-open-socket "::")' creates an IPv6 socket if the system
   supports it. On some systems (e.g., Linux), the resulting IPv6
   socket can also send and receive IPv4; on some systems (e.g., Mac OS
   X), it can only receive IPv4; on some systems (e.g., Windows), it
   doesn't support IPv4 at all.

   Arguments to `udp-open-socket' merely determine the socket's
   protocol family; `udp-open-socket' doesn't bind the socket. If the
   socket is going to be used to communicate with a specific host, then
   supplying the host to `udp-open-socket' is a good way to ensure that
   the socket's protocol family is consistent with the target host.
   Similarly, if the socket is going to be bound to a particular host
   and port, supplying those values to `udp-open-socket' ensures that
   the binding will work.


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