Re: [pve-devel] [PATCH widget-toolkit] fix #4421: ui: guard setProxy against races of slow vs fast requests

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Am 06/03/2023 um 15:03 schrieb Friedrich Weber:
> Some UI components use `Ext.data.Store.setProxy` to change their
> associated API endpoint URL in reaction to user input. One example is
> `BackupView`, which calls `setProxy` when the user switches from
> listing backups on storage A to listing backups on storage B. However,
> if A is slow, the UI may receive the response for A *after* the
> response for B. It will then display the contents of A as if they were
> the contents of B, resulting in a UI inconsistency.
> 
> The reason is that `Ext.data.Store` still processes the slow response
> for A, even though it is obsolete. This patch overrides the
> responsible callback of `Ext.data.Store` to only process responses
> belonging to the currently active proxy object. This should rule out
> similar race conditions in all components that use the `setProxy` API.
> In the above example, the patch results in the response for A being
> ignored.
> 
> Ignored responses are logged to the browser console.
> 
> Note that this patch only concerns components that use `setProxy` for
> changing API endpoints. Other components (e.g. those using
> `proxy.setURL` for the same purpose) may be open to similar race
> conditions.
> 
> Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
> ---
>  The original report only concerns the backup view [1], where the race
>  condition is easy to trigger. While ruling out this particular race is
>  simple, I thought it would be worthwhile to rule out race condition of
>  this category for all components. Hence this patch. However, most of the
>  other races are much harder to trigger, so it may be questionable
>  whether a general fix is needed. So if wanted, I can alternatively
>  submit a patch that only fixes the backup view.

IMO a general fix/future proofing can be OK, so besides a small nit inline:
LGTM, but did not checked/tested this too closely - @Dominik, what do you
think on this?

> 
>  Also, there are several occurrences of the `proxy.setURL` or `proxy.url = ...`
>  patterns (see [1]) which are also susceptible to race conditions, and which
>  are not fixed by this patch. However, for those, I have not found a nice
>  solution that does not involve changing a lot of call sites. If wanted, I can
>  give it another try, or alternatively only submit patches for components for
>  which triggering the race conditions seems realistic.
> 
>  [1] https://bugzilla.proxmox.com/show_bug.cgi?id=4421
> 
>  src/Utils.js | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/src/Utils.js b/src/Utils.js
> index f55b9a5..8a97487 100644
> --- a/src/Utils.js
> +++ b/src/Utils.js
> @@ -1451,3 +1451,18 @@ Ext.define('Proxmox.Async', {
>  	return new Promise((resolve, _reject) => setTimeout(resolve, millis));
>      },
>  });
> +
> +Ext.override(Ext.data.Store, {
> +    // If the store's proxy is changed while it is waiting for an AJAX
> +    // response, `onProxyLoad` will still be called for the outdated response.
> +    // To avoid displaying inconsistent information, only process responses
> +    // belonging to the current proxy.
> +    onProxyLoad: function(operation) {
> +	let me = this;
> +	if (operation.getProxy() === me.getProxy()) {
> +	    me.callParent(arguments);
> +	} else {
> +	    console.log(`ignored outdated response: ${operation.getRequest().getUrl()}`);

maybe warn? also, no need to interpolate text on the console helpers, just add as
it's own param, which often gives a much better dev experience (as object can then
be inspected in full) - here it's just an URL (maybe dump the full thing?), so YNNV.

console.warn('ignored outdated response:', operation.getRequest().getUrl());

> +	}
> +    },
> +});