Rob, I don't know if this contributes to answering your question but,
(1) you can get the OS FD:s out of the Gambit TCP server and client ports,
(2) note that (at least the client) ports' FD:s are set up in asynchronous mode at the level of OS FD so your reads & writes will be nonblocking unless you change that setting and supposedly you don't want to do that, and
(3) you can have Gambit do typical select() work for you on port objects using the ##wait-for-input! & -output! procedures i.e. your Gambit and C code can cooperate this way i.e. Gambit code waits for FD readiness and then your C code does the IO. Last,
(4) there's some procedure in Gambit to import an OS FD and make a port object out of it.
Mikael



2014-07-07 23:32 GMT+02:00 Rob Kellock <sales@creditscore.co.nz>:
Hi,

Quite some time ago I managed to successfully interface with a C library
using FFI.  Now I'm having another go, but this time I want to connect
to it using native Scheme code.  The C library is the interface to a
select based TCP socket server, so I figure I should be able to connect
to it directly using open-tcp-client and forgo the whole FFI thing.

The way the C library works is that a C struct is sent to the receiving
socket first so that it knows the length of the message buffer that will
follow and some other information specific to the socket server's
operation. This is immediately followed up by the message buffer which
is in binary format.

So far... I think I've managed to work out that I should be using
u8vector data structure for both the C struct and the message buffer,
although I don't yet understand what kind of encoding is going on in
there. That will come after I've looked at some examples.

My plan is to extend the existing web-server.scm example to produce a
web app that talks to it's relational database using native Scheme. I'm
going down this route because I want to extend web-server.scm using the
GSI.  If I use the FFI I'm restricted to the GSC which prevents the
whole interactive development scenario I want where I can keep the
browser running, the database running and just stop and start the GSI as
I hack code.

What I want to know first though is if I use open-tcp-client inside
Gambit's threads will the native Scheme calls out to the external socket
server block?  If they don't then am I on the right track to use u8vector?

Thanks,

Rob.
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