Hi all,
I have investigated a bit what it would take to support git protocol
(smart transport) over HTTP POST transactions.
The current proxy system is broken, for a very simple reason: it doesn't
convey information about when the channel should be turned around.
HTTP POST -- or, for that matter, any RPC-style transport, is a half
duplex transport: only one direction can be active at a time, after
which the channel has to be explicitly turned around. The "turning
around" consists of posting the queued transaction and listening for the
reply.
Ultimately, it comes down to the following: the transactor needs to be
given explicit information when the git protocol goes from writing to
reading (the opposite direction information is obvious.) I was hoping
that it would be possible to get this information from snooping the
protocol, but it doesn't seem to be so lucky.
I started to hack on a variant which would embed a VFS-style interface
in git itself, looking something like:
struct transactor;
struct transact_ops {
ssize_t (*read)(struct transactor *, void *, size_t);
ssize_t (*write)(struct transactor *, const void *, size_t);
int (*close)(struct transactor *);
};
struct transactor {
union {
void *p;
intptr_t i;
} u;
const struct transact_ops *ops;
};
Replacing the usual fd operations with this interface would allow a
different transactor to see the phase changes explicitly; the
replacement to use xread() and xwrite() is obvious.
Of course, I started hacking on it and found myself with zero time to
continue, but I thought I'd post what I had come up with.
-hpa
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