[Engine-devel] UI Plugins configuration
Vojtech Szocs
vszocs at redhat.com
Mon Aug 27 14:48:44 UTC 2012
Hi Chris,
> Your assumption about the structure of the pluginDefinitions object is correct. It’s no longer a String->String mapping , but a String to Object mapping.
Yes :) but maybe we could also formalize some terms, for example:
Plugin descriptor is the JSON file that contains important plugin meta-data (including the plugin source page URL), e.g. /usr/share/ovirt-engine/ui-plugins/test.json
Plugin definition is the JavaScript object representing plugin descriptor meta-data suitable for use on client (GWT WebAdmin). Plugin definition is embedded into WebAdmin host page within pluginDefinitions object, and read by PluginManager during WebAdmin startup.
Plugin configuration is the JSON file that contains optional plugin configuration, e.g. /etc/ovirt-engine/ui-plugins/test-config.json
I think we can combine two things here:
1) allow plugin authors to define standard (fallback) configuration directly inside plugin descriptor
2) allow plugin users to override standard configuration by modifying dedicated plugin configuration file
Finally, plugin source page is the HTML page used to invoke actual plugin code (this page is referenced by plugin descriptor's "url" attribute). Plugin source page can also load external resources required by the plugin, e.g. 3rd party JavaScript libraries, CSS, images, etc.
> I liked the original IIFE approach, except that it seemed that having additional static resources (jquery, images, html templates, etc) was going to be more cumbersome. I don’t think having the plugin author write a basic start.html is that big of a burden :).
You're right, for such additional plugin resources, even more configuration/parsing/logic would be required. Even though plugin authors need to write the plugin source page themselves, they have full control over it, which is a good thing in general.
> I agree that the plugin configuration was always going to be a resource (probably a local file) that the end user could customize. I’m not sure it I really needs to be separate from the plugin definition file (/usr/share/ovirt-engine/ui-plugins/test.json). I suppose it depends on how complex the configuration is going to be and on some of the implementation details surrounding the plugin definition file.
Yeah, let's make the concept of the plugin configuration file optional for now (standard plugin configuration can be part of plugin descriptor).
> In my patch, I simply used Jackson to parse the file into a tree of JsonNodes. Should the plugin definition be a java object of some sort? (please please please don’t make me learn about java beans…). I stuck with the JsonNodes because Jackson makes them easy to work with and they’re really easy to re-serialize back to json to give to the webadmin.
I think using Jackson's JSON representation in Java (JsonNode) is perfectly suitable in this situation. No need to have separate Java bean for that :)
> We should probably turn on JsonParser.Feature.ALLOW_COMMENTS. The definition and config files will difficult for end-users (or even developers) to understand without comments.
Agreed.
> We need to formalize the structure of the plugin definition and decide which fields are mandatory and which are optional
Sounds good, but I'd skip some attributes for now (enabled, apiVersion, author, license) for the sake of simplicity.
As you wrote, when loading plugin descriptor, we should enforce mandatory attributes (name, version, url) .
As for plugin configuration, there could be two different attributes:
- "config" for standard (fallback) plugin configuration (JSON object)
- "configFile" for external plugin configuration file (path to file, relative to /etc/ovirt-engine/ui-plugins/ ) , that overrides the standard configuration
Note that when loading plugin descriptor, the loader should also "merge" the configuration together (custom config on top of standard config).
> I can work on the plugin Definition loader some more and make it enforce mandatory/optional fields. I’ll also investigate the directory climbing issue I mentioned in my previous mail.
Sounds good! I was planning to incorporate your original patch in next PoC revision, but of course, you can work on the loader some more and send another patch :)
For the directory climbing issue, see <OVIRT_ROOT>/backend/manager/modules/root/src/main/java/org/ovirt/engine/core/FileServlet.java (there's a method called isSane for dealing with such issue).
> Also, I’m curious how things are going to work when the “url” points to a foreign resource as the plugin start page. I don’t think the plugin’s iframe is going to be able to access parent.pluginApi. Perhaps there is some aspect of CORS that I don’t understand?
When the plugin iframe references a resource on different origin (protocol, domain, port) than WebAdmin main page origin, JavaScript code running inside that iframe will not be able to access parent (top-level) pluginApi object. You're right, the statement "parent.pluginApi" will not work, because of Same-Origin Policy enforced by the browser.
CORS is just one alternative, see http://stackoverflow.com/questions/3076414/ways-to-circumvent-the-same-origin-policy for more. However, CORS needs to be supported by the browser (a special HTTP response header is used to tell that the iframe is allowed to access resources from another - WebAdmin main page - origin). We need to investigate this a bit more I guess.
Regards,
Vojtech
----- Original Message -----
From: "Chris Frantz" <Chris.Frantz at hp.com>
To: "Vojtech Szocs" <vszocs at redhat.com>
Cc: "engine-devel" <engine-devel at ovirt.org>
Sent: Thursday, August 23, 2012 5:12:02 PM
Subject: RE: UI Plugins configuration
Vojtech,
Your assumption about the structure of the pluginDefinitions object is correct. It’s no longer a String->String mapping , but a String to Object mapping.
I liked the original IIFE approach, except that it seemed that having additional static resources (jquery, images, html templates, etc) was going to be more cumbersome. I don’t think having the plugin author write a basic start.html is that big of a burden :).
I agree that the plugin configuration was always going to be a resource (probably a local file) that the end user could customize. I’m not sure it I really needs to be separate from the plugin definition file (/usr/share/ovirt-engine/ui-plugins/test.json). I suppose it depends on how complex the configuration is going to be and on some of the implementation details surrounding the plugin definition file.
In my patch, I simply used Jackson to parse the file into a tree of JsonNodes. Should the plugin definition be a java object of some sort? (please please please don’t make me learn about java beans…). I stuck with the JsonNodes because Jackson makes them easy to work with and they’re really easy to re-serialize back to json to give to the webadmin.
We should probably turn on JsonParser.Feature.ALLOW_COMMENTS. The definition and config files will difficult for end-users (or even developers) to understand without comments.
We need to formalize the structure of the plugin definition and decide which fields are mandatory and which are optional:
{
# Mandatory fields: name, enabled, version, url, apiversion, author, license
# Name of the plugin
"name": "test",
# Whether or not plugin is enabed
"enabled": true,
# version of the plugin
"version": "1.0",
# How to load the plugin
"url": "/webadmin/webadmin/plugin/test/start.html",
# Which version of engine plugin is meant to work with
"apiversion": "3.1.0",
# Who wrote the plugin and how is it licensed?
"author": "SuperBig Corporation",
"license": "Proprietary",
# Optional fields path, config
# Where to locate plugin (if loaded by webadmin/plugin)
"path": "/tmp",
# Plugin configuration information (if any)
"config": "test-config.json",
}
I can work on the plugin Definition loader some more and make it enforce mandatory/optional fields. I’ll also investigate the directory climbing issue I mentioned in my previous mail.
Also, I’m curious how things are going to work when the “url” points to a foreign resource as the plugin start page. I don’t think the plugin’s iframe is going to be able to access parent.pluginApi. Perhaps there is some aspect of CORS that I don’t understand?
Thanks,
--Chris
From: Vojtech Szocs [mailto:vszocs at redhat.com]
Sent: Thursday, August 23, 2012 7:14 AM
To: Frantz, Chris
Cc: engine-devel
Subject: Re: UI Plugins configuration
Hi Chris,
thanks for taking the time to make this patch, these are some excellent ideas! (CC'ing engine-devel so that we can discuss this with other guys as well)
First of all, I really like the way you designed plugin source page URLs (going through PluginSourcePageServlet ), e.g. "/webadmin/webadmin/plugin/<pluginName>/<pluginSourcePage>.html", plus the concept of "path" JSON attribute.
WebadminDynamicHostingServlet loads and caches all plugin definitions ( *.json files), and directly embeds them into WebAdmin host page as pluginDefinitions JavaScript object. I'm assuming that pluginDefinitions object will now look like this:
var pluginDefinitions = {
"test": {
"name": "test",
"version": "1.0",
"url": "/webadmin/webadmin/plugin/test/foo.html",
"path": "/tmp",
"config": {"a":1, "b":2, "c":3}
}
}
Originally, the pluginDefinitions object looked like this:
var pluginDefinitions = {
"test": "/webadmin/webadmin/plugin/test/foo.html" // Simple pluginName -> pluginSourcePageUrl mappings
}
This is because PluginManager (WebAdmin) only needs pluginName ("name") and pluginSourcePageUrl ("url") during startup, when creating plugin iframe. But this can be changed :)
Plugin "version" makes sense, plus the plugin configuration object ("config") can be useful directly on the client. Let me explain:
Originally, plugin configuration was supposed to be passed to actual plugin code (through immediately-invoked-function-expression, or IIFE), just like this:
(function (pluginApi, pluginConfig) { // JavaScript IIFE
// ... actual plugin code ...
})(
parent.pluginApi, /* reference to global pluginApi object */
{"a":1, "b":2, "c":3} /* embedded plugin configuration as JavaScript object */
);
The whole purpose of PluginSourcePageServlet was to "wrap" actual plugin code into HTML, so that users don't need to write HTML pages for their plugins manually. PluginSourcePageServlet would handle any plugin dependencies (placed into HTML head), with actual plugin code being wrapped into IIFE, as shown above. Plugin configuration was meant to be stored in a separate file, e.g. <pluginName>-config.json , so that users could change the default plugin configuration to suit their needs.
Inspired by your patch, rather than reading/embedding plugin configuration when serving plugin HTML page ( PluginSourcePageServlet ), it's even better to have the plugin configuration embedded directly into WebAdmin host page, along with introducing new pluginApi function to retrieve the plugin configuration object.
Based on this, I suggest following modifications to the original concept:
- modify original pluginDefinitions structure, from pluginName -> pluginSourcePageUrl , to pluginName -> pluginDefObject
- pluginDefObject is basically a subset of physical plugin definition ( test.json , see below), suitable for use on the client
- add following attributes to pluginDefObject : version , url , config
* note #1: name is not needed, since it's already the key of pluginName -> pluginDefObject mapping
* note #2: path is not needed on the client (more on this below)
- introduce pluginApi.config(pluginName) function for plugins to retrieve their configuration object, and remove pluginConfig parameter from main IIFE (as shown above)
[a] Physical plugin definition file (JSON) might be located at oVirt "DataDir", e.g. /usr/share/ovirt-engine/ui-plugins/test.json , for example:
{
"name": "test",
"version": "1.0",
"url": "/webadmin/webadmin/plugin/test/start.html",
"path": "/tmp",
"config": "test-config.json"
}
[b] Plugin configuration file (JSON) might be located at oVirt "ConfigDir", e.g. /etc/ovirt-engine/ui-plugins/test-config.json , for example:
{
"a":1, "b":2, "c":3
}
[c] Finally, plugin static resources (plugin source page, actual plugin code, plugin dependencies, CSS/images, etc.) would be located at /tmp (as shown in [a]), for example:
/tmp/start.html -> plugin source page, used to load actual plugin code
/tmp/test.js -> actual plugin code
/tmp/deps/jquery-min.js -> simulate 3rd party plugin dependency
For example:
"/webadmin/webadmin/plugin/test/start.html" will be mapped to /tmp/start.html
"/webadmin/webadmin/plugin/test/deps/jquery-min.js" will be mapped to /tmp/deps/jquery-min.js
This approach has some pros and cons:
(+) plugin static resources can be served through PluginSourcePageServlet (pretty much like oVirt documentation resources, served through oVirt Engine root war's FileServlet )
(+) plugin author has complete control over plugin source page
(-) plugin author actually needs to write plugin source page
Overall, I think this approach is better than the previous one (where PluginSourcePageServlet took care of rendering plugin source page, but sacrificed some flexibility).
By the way, here's what would happen behind the scenes:
1. user requests WebAdmin host page, WebadminDynamicHostingServlet loads and caches all plugin definitions [a] + plugin configurations [b] and constructs/embeds appropriate pluginDefinitions JavaScript object
2. during WebAdmin startup, PluginManager registers the plugin (name/version/url/config), and creates/attaches the iframe to fetch plugin source page ansynchronously
3. PluginSourcePageServlet handles plugin source page request, resolves the correct path [c] and just streams the file content back to client
> 1. The plugin configuration files should probably have an "enabled" field and an "apiVersion" field that should be examined to determine whether or not to use the plugin.
Sounds good, we can implement these later on :)
> 2. I suspect the way I've modified PluginSourcePage makes it vulnerable to directory climbing attacks.
Yes, but we can defend against these, restricting access only to plugin's "path" and its sub-directories.
> 3. Is /usr/share/ovirt-engine the right place for the plugin config files?
I suppose you mean plugin definition files [a], cannot tell for sure, but we can change this anytime :)
Chris, please let me know what you think, and again - many thanks for sending the patch!
Regards,
Vojtech
----- Original Message -----
From: "Chris Frantz" < Chris.Frantz at hp.com >
To: vszocs at redhat.com
Sent: Wednesday, August 22, 2012 7:56:45 PM
Subject: UI Plugins configuration
Vojtech,
I decided to work on making the plugin patch a bit more configurable, following some of the ideas expressed by Itamar and others in the meeting yesterday. The attached patch is a simple first-attempt.
Plugin configurations are stored in /usr/share/ovirt-engine/ui-plugins/*.json.
Example:
{
"name": "test",
"version": "1.0",
"url": "/webadmin/webadmin/plugin/test/foo.html",
"path": "/tmp",
"config": {"a":1, "b":2, "c": 3}
}
The engine reads all of the *.json files in that directory to build the list of known plugins and gives that list to the webadmin.
When webadmin loads a plugin, it requests the URL given in the plugin config file. The "plugin" URL is mapped to PluginSourcePage, which will translate the first part of the path ("test") into whatever path is stored in pluginConfig ("/tmp") in this case, and then serve the static file (e.g. "/tmp/foo.html").
I didn't use the renderPluginSourcePage() method in favor of just serving a static file, but I have no strong opinion on the matter. However, a plugin may want to store static resources at "path" and have the engine serve those resources. By just serving files through PluginSourcePage, we don't need any other servlets to provide those resources.
There is still a bit of work to do:
1. The plugin configuration files should probably have an "enabled" field and an "apiVersion" field that should be examined to determine whether or not to use the plugin.
2. I suspect the way I've modified PluginSourcePage makes it vulnerable to directory climbing attacks.
3. Is /usr/share/ovirt-engine the right place for the plugin config files?
Let me know what you think,
--Chris
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