[Spice-devel] [PATCH spice-common] RFC: spice.proto: add webdav channel

[Marc-André Lureau]

Hey,

ping! still looking for review/ack,

I would like this webdav channel to be part of the specified protocol.
I could do without, and just name a port channel with my own data, but
I prefer to have a proper registered channel, so it is documented
officially as part of Spice.

Although some channels are optionnal, some are mandatory, some must be
unique, there is something that we haven't exploited so far. We could
deprecate channels and replace them with newer versions or different
channels (while keeping same protocol version). Example, if we come to
the conclusion that multiplexing requests in one channel isn't a good
idea, we could deprecate WebDAVChannel and make WebDAVChannel2 appears
(instead or both available for compatibility). In the same vein,
WebDAV could be replaced by SFTP or anything else. Even more, they
could coexist, so a client could be free to choose (this is very much
hypothetical, I don't think that should ever happen).

This is all to say that adding a channel, such as webdav, shouldn't
limit our future development, if somehow it doesn't work as expected
or other reasons.

cheers


On Sun, Jan 12, 2014 at 6:29 PM, Marc-André Lureau
<marcandre.lureau at gmail.com> wrote:
> This channel provides a webdav server (rfc4918). This allows various
> guest or remote system that support webdav to access a folder shared by
> the client (some agent can be used to proxy the requests on a local port
> for example). The webdav server may also be accessed by an hypervisor as
> a remote filesystem interface, which can then be accessed by the guest
> via other means (fs/fat emulation, mtp device, etc)
>
> Due to the usage of a single channel stream and the need for concurrent
> requests, webdav clients streams are multiplexed. Each client stream is
> framed within 64k max messages (in little-endian)
>
>  int64    client_id
>  uint16   size
>  char     data[size]
>
> A new client_id indicates a new connection. A new communication stream
> with the webdav server should be started. A client stream message of
> size 0 indicates a disconnection of client_id. This multiplexed
> communication happens over the channel "data" message.
>
> Only when the port is opened may the communication be started.
> A closed port event should close all currently known multiplexed
> connections.
>
> Why WebDAV?
>
> webdav is supported natively by various OS for a long time (circa
> Windows XP). It has several open-source implementations and a variety of
> tools exist. A webdav implementation can be tested and used without a
> Spice server or any virtualization (this also permit sharing the
> implementation with other projects in the future, such as GNOME). It is
> an IETF open standard and thus thoroughly specified.
>
> The basic requirements for an efficient remote filesystem are provided
> by the standard (pipelining, concurrency, caching, copy/move, partial
> io, compression, locking ...) While other features are easily possible
> via extensions to the protocol (common ones are executable attributes,
> or searching for example).
>
> Given the requirements, and the popularity of http/webdav, I believe it
> is the best candidate for Spice remote filesystem support.
>
> Other alternatives (adhoc, p9, smb2, sftp) have been studied and
> discarded so far since they do not match in term of features or
> requirements.
> ---
>  spice.proto | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/spice.proto b/spice.proto
> index 67b3803..316d287 100644
> --- a/spice.proto
> +++ b/spice.proto
> @@ -1352,6 +1352,9 @@ channel PortChannel : SpicevmcChannel {
>      } event;
>  };
>
> +channel WebDAVChannel : PortChannel {
> +};
> +
>  protocol Spice {
>      MainChannel main = 1;
>      DisplayChannel display;
> @@ -1363,4 +1366,5 @@ protocol Spice {
>      SmartcardChannel smartcard;
>      UsbredirChannel usbredir;
>      PortChannel port;
> +    WebDAVChannel webdav;
>  };
> --
> 1.8.4.2
>



-- 
Marc-André Lureau