[PATCH wayland] client: Use a 0 version to mean indeterminate proxy version

[Jason Ekstrand]

On Nov 26, 2015 1:23 PM, "Derek Foreman" <derekf at osg.samsung.com> wrote:
>
> This sets wl_display's version (for proxy version query purposes)
> to 0.  Any proxy created with unversioned API (this happens when
> a client compiled with old headers links against new wayland)
> will inherit this 0.
>
> This gives us a way for new libraries linked by old clients to
> realize they can't know a proxy's version.
>
> wl_display's version being unqueryable (always returning 0) is
> an acceptable side effect, since it's a special object you can't
> bind specific versions of anyway.
>
> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

> ---
>
> This follows on Jason's proxy version patch that I rebased
> and reposted a little while ago.
>
>  src/wayland-client.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/src/wayland-client.c b/src/wayland-client.c
> index f2df0b9..5ba6edc 100644
> --- a/src/wayland-client.c
> +++ b/src/wayland-client.c
> @@ -928,7 +928,25 @@ wl_display_connect_to_fd(int fd)
>         display->proxy.queue = &display->default_queue;
>         display->proxy.flags = 0;
>         display->proxy.refcount = 1;
> -       display->proxy.version = 1;
> +
> +       /* We set this version to 0 for backwards compatibility.
> +        *
> +        * If a client is using old versions of protocol headers,
> +        * it will use unversioned API to create proxies.  Those
> +        * proxies will inherit this 0.
> +        *
> +        * A client could be passing these proxies into library
> +        * code newer than the headers that checks proxy
> +        * versions.  When the proxy version is reported as 0
> +        * the library will know that it can't reliably determine
> +        * the proxy version, and should do whatever fallback is
> +        * required.
> +        *
> +        * This trick forces wl_display to always report 0, but
> +        * since it's a special object that we can't bind
> +        * specific versions of anyway, this should be fine.
> +        */
> +       display->proxy.version = 0;
>
>         display->connection = wl_connection_create(display->fd);
>         if (display->connection == NULL)
> @@ -1923,7 +1941,18 @@ wl_proxy_get_user_data(struct wl_proxy *proxy)
>  /** Get the protocol object version of a proxy object
>   *
>   * \param proxy The proxy object
> - * \return The protocol object version of the proxy
> + * \return The protocol object version of the proxy or 0
> + *
> + * Gets the protocol object version of a proxy object, or 0
> + * if the proxy was created with unversioned API.
> + *
> + * A returned value of 0 means that no version information is
> + * available, so the caller must make safe assumptions about
> + * the object's real version.
> + *
> + * wl_display's version will always return 0.
> + *
> + * \note This should not normally be used by non-generated code.
>   *
>   * \memberof wl_proxy
>   */
> --
> 2.6.2
>
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