Jaap Vossers' SharePoint Blog

Just another WordPress.com site

Archive for the ‘SharePoint’ Category

SharePoint Asynchronous Event Receivers and the powershell.exe process

with 5 comments

We recently had a very strange problem with one of our custom Event Receivers in our production SharePoint environment. The Event Receiver implemented the Asynchronous ItemUpdated event. It was used to generate and set a value on one of our fields on the document being updated. The code in the Event Receiver appeared to work most of the times, but would fail at seemingly random occasions and would leave the updated document without the generated field set.

We were struggling to isolate the combination of factors that made it fail. The weirdest thing was that there were no errors to be found in the ULS logs or the Event Log. We added lots of logging and try/catch blocks, but for some reason when the Event Receiver failed it would never enter the catch block, so there was no exception to log.

One key point that helped us with the troubleshooting was that we had noticed that the Event Receiver ALWAYS worked when the document was being updated through the SharePoint web UI. We also had a PowerShell script which was used for bulk updating of documents. This script was scheduled to run at regular intervals using Windows Task Scheduler. It appeared that the issue only occurred when the Updated event was triggered via this scheduled PowerShell script, but even then it still seemed intermittent as it would often work just fine.

We were unable to reproduce the issue at all when calling the ps1 file directly from the PowerShell console. So what was different when the script was run from the Task Scheduler vs directly from the PowerShell console? Well, the Task Scheduler actually calls a BATCH script which in turn invokes the PowerShell script which fires up a new PowerShell process. This process dies when it finishes execution of the ps1 file!

Remember, our Event Receiver is an Asynchronous one, so it would not block the execution of the PowerShell script. The Event Receiver is actually executed on a thread inside the PowerShell process since the ps1 script triggered the Updated event. So, when the PowerShell.exe process dies, it does not seem to wait for any background threads to complete, which in our case causes our Event Receiver to suffer from a sudden death. I was a bit surprised to see this to be honest!

Anyway, I guess one of the reasons why in our case the problem seemed to be appearing randomly is that only the last document in a batch would be affected, which sometimes meant 1 in a couple thousand documents. Only recently users had started feeding the script with “batches” consisting of just one document, which is what highlighted the problem to us and lead to this investigation. We were wondering what had changed recently (we had not touched this part of the code for a while!), since it was all working fine before (we thought), but in reality the bug had always been there but it had never occurred to us!

So everyone please beware when invoking PowerShell scripts from BATCH scripts when you have Asynchronous Event Receivers in your SharePoint environment!

What did we do to work around our problem? We just put a little Sleep at the end of our PowerShell script… 🙂

Written by jvossers

February 3, 2014 at 10:10 pm

Using jQuery to submit forms on remote SharePoint admin pages

with one comment

Imagine you need to develop a piece of functionality to extend SharePoint, but the available APIs do not directly allow you to do this for any of the following reasons:

  1. You are not allowed to deploy any server side code
  2. The server side code you can deploy has limited access to the server object model (e.g. Sandbox Solutions in SharePoint 2010).
  3. The API you need to access is private or internal

Consider the following scenario.

For our SharePoint Online site, we want to implement a Web Part that allows us to save the current site as a WSP in the solution gallery. As it’s SharePoint Online, we can’t deploy Farm Solutions, so we will have to deploy it as a Sandbox Solution. Unfortunately, we have limited access to the Object Model on the server, and there is nothing available in the Client Object Model which we can use to save the current site as a template.

Now, if there is an existing administration page that does what we want to do (in our case /_layouts/savetmpl.aspx does what we want to do), then technically all we need to do is a submit an HTTP POST request to that page with the right HTTP headers and form parameters and the server will happily process the request, as it has no way of telling whether the request was triggered by a user submitting the form, or by something else.

Welcome to the world of stateless protocols.

So we need to find out what the request should look like so that we can use jQuery to build it and issue it as an AJAX request from our own code.

image

Let’s open up Fiddler. With Fiddler open, in the browser we press the button that submits the form on /_layouts/savetmpl.aspx,. After that, we can inspect the form parameters of the HTTP POST request that the browser then makes. We are not really interested in the HTTP headers as the browser will take care of passing any headers related to the current browser session (including the authorization header) to the server when we issue an AJAX request.

image

We have three main categories of form parameters.

The first category is made up of parameters that directly map to user input fields.

  • ctl00$PlaceHolderMain$ctl00$ctl00$TxtSaveAsTemplateName
  • ctl00$PlaceHolderMain$ctl01$ctl00$TxtSaveAsTemplateTitle
  • ctl00$PlaceHolderMain$ctl01$ctl01$TxtSaveAsTemplateDescription
  • ctl00$PlaceHolderMain$ctl03$CbSaveData

The second category consists of a set of hidden fields which are used by ASP.NET & SharePoint to do its postback magic, including validation of the form post.

  • __REQUESTDIGEST
  • __VIEWSTATE
  • __EVENTVALIDATION

The third category is “the rest”. This is stuff we are not really interested in, but we still need to send it to the server.

  • MSOWebPartPage_PostbackSource
  • MSOTlPn_SelectedWpId
  • MSOTlPn_View
  • MSOTlPn_ShowSettings
  • MSOGallery_SelectedLibrary
  • MSOGallery_FilterString
  • MSOTlPn_Button
  • MSOSPWebPartManager_DisplayModeName
  • MSOSPWebPartManager_ExitingDesignMode
  • MSOWebPartPage_Shared
  • MSOLayout_LayoutChanges
  • MSOLayout_InDesignMode
  • MSOSPWebPartManager_OldDisplayModeName
  • MSOSPWebPartManager_StartWebPartEditingName
  • MSOSPWebPartManager_EndWebPartEditing
  • _maintainWorkspaceScrollPosition
  • __spText1
  • __spText2

It’s easy to determine what we want to submit as values for the first category. We either capture these values in our custom UI, or we have some logic in our code that determines these values for us.

The second category is a bit more difficult. Essentially, the server is expecting us to post back these values, which were provided by the server and rendered on the page as hidden input fields at the time of requesting the page which has the form on it. This means we need to make an initial GET request using jQuery so we can extract the values from the form, before we can submit them in our post.

The third category is easy, as we can copy the values from the request we captured with fiddler.

The script

Following the instruction above, we can write a bit of javascript like this to allow us to submit forms on “remote” pages.

function CreateWSP(callback) {

    var sitePrefix = "/";

    if (_spPageContextInfo.siteServerRelativeUrl != "/") {
        sitePrefix = _spPageContextInfo.siteServerRelativeUrl + "/";
    }

    var url = sitePrefix + "_layouts/savetmpl.aspx";

    $.get(url, function (data, textStatus, XMLHttpRequest) {

        var ctx = $(data);

        var rd = ctx.find("[name='__REQUESTDIGEST']").val();
        var vs = ctx.find("[name='__VIEWSTATE']").val();
        var ev = ctx.find("[name='__EVENTVALIDATION']").val();

        var postParams = {
            "MSOWebPartPage_PostbackSource": "",
            "MSOTlPn_SelectedWpId": "",
            "MSOTlPn_View": "0",
            "MSOTlPn_ShowSettings": "False",
            "MSOGallery_SelectedLibrary": "",
            "MSOGallery_FilterString": "",
            "MSOTlPn_Button": "none",
            "MSOSPWebPartManager_DisplayModeName": "Browse",
            "MSOSPWebPartManager_ExitingDesignMode": "false",
            "__EVENTTARGET": "ctl00$PlaceHolderMain$ctl02$RptControls$BtnSaveAsTemplate",
            "__EVENTARGUMENT": "",
            "MSOWebPartPage_Shared": "",
            "MSOLayout_LayoutChanges": "",
            "MSOLayout_InDesignMode": "",
            "MSOSPWebPartManager_OldDisplayModeName": "Browse",
            "MSOSPWebPartManager_StartWebPartEditingName": "false",
            "MSOSPWebPartManager_EndWebPartEditing": "false",
            "_maintainWorkspaceScrollPosition": "0",
            "__REQUESTDIGEST": rd,
            "__VIEWSTATE": vs,
            "__SCROLLPOSITIONX": "0",
            "__SCROLLPOSITIONY": "0",
            "__EVENTVALIDATION": ev,
            "ctl00$PlaceHolderMain$ctl00$ctl00$TxtSaveAsTemplateName": "VossersTeamSite.wsp",
            "ctl00$PlaceHolderMain$ctl01$ctl00$TxtSaveAsTemplateTitle": "Vossers Team Site",
            "ctl00$PlaceHolderMain$ctl01$ctl01$TxtSaveAsTemplateDescription": "Vossers Team Site Template",
            "ctl00$PlaceHolderMain$ctl03$CbSaveData": "on",
            "__spText1": "",
            "__spText2": ""
        };

        var options = {
            url: url,
            type: "POST",
            data: postParams,
            success: function (data, textStatus, XMLHttpRequest) {

                callback();

            }
        };

        $.ajax(options);

    }, "html");
}

Things to consider

When the page you are posting to is modified, for example by a SharePoint update, then it’s possible that your script breaks due to changes in form parameter names. This makes this technique a bit fragile. For this reason I recommend that you only consider using this technique once you have confirmed that it’s not possible to achieve what you want by using public APIs.

Written by jvossers

February 4, 2012 at 3:22 pm

SharePoint InlineSiteSettings 2010 – improved productivity for Administrators and Developers

leave a comment »

After having released SharePoint InlineSiteSettings for SharePoint 2007 a while ago, and having used a little desktop application called Launchy which is used to start desktop applications using just a few keystrokes, I decided to build an enhanced version of InlineSiteSettings, built for SharePoint 2010 with features similar to Launchy’s.

The end result is SharePoint InlineSiteSettings 2010, which can be downloaded from CodePlex at http://sitesettings2010.codeplex.com/

inlinesitesettings2010

The purpose of the solution is to improve productivity for SharePoint 2010 users who regularly access the Site Settings page, i.e. SharePoint Administrators and SharePoint Developers. It allows them to access the Site Settings in a dialog by pressing Ctrl+s, so no need to move your mouse to Site Actions, click it, click Site Settings, and wait for the full page to load.

As we all know, once the Site Settings page has been loaded, it can actually take a few seconds to spot the link you are looking for (as the links are not listed in alphabetical order), so what’s new in this version of SharePoint InlineSiteSettings is that users can start typing the title of the link they whish to navigate to, and with real-time filtering functionality, all links that do not match your filter will disappear from view. In addition to that, as soon as exactly one link is left that matches your filter, it will automatically redirect you to that page, as can be seen in the demo screencast below. As a result, navigating between administrative pages in SharePoint 2010 will be less painful.

SharePoint InlineSiteSettings 2010 is packaged as a Sandbox Solution, and does not depend on any server side code. The good thing about this is that it works on SharePoint Online (Office365).

Download SharePoint InlineSiteSettings 2010 from CodePlex

Written by jvossers

May 8, 2011 at 9:59 pm

Bypass caching with jQuery AJAX GET requests

with one comment

As I seem to use this trick quite often and I keep forgetting the exact details on how to implement it, I thought it would be good to document this.

Using jQuery, I often make ansynchronous GET requests to a custom ASHX handler in SharePoint’s _layouts folder which returns some data that I want to display. This data is always dynamic, but sometimes the browser tries to cache the results from the previous request, so you might not get the response you expected.

To avoid this, simply make the url for eacht request unique by adding a timestamp to it in javascript.

var url = '/_layouts/MyProject/MyHandler.ashx?unique=' + new Date().getTime();

Written by jvossers

January 11, 2011 at 10:41 am

Released: SharePoint WebPartSlices

with one comment

I have recently released my sixth CodePlex project (list of all my CodePlex projects), titled SharePoint WebPartSlices.

To all the jQuery fans – Sorry, no jQuery this time! SharePoint WebPartSlices is a server-side solution that allows users to transform all Web Parts on a page into IE8 Web Slices simply by adding the webslices=1 querystring parameter to the url of the page containing the web parts to be transformed, basically allowing you to add web parts to your IE8 Favorites Bar.

webpartslices1

VoilĂ  – No need to navigate to the original page to see the updated Web Part.

webpartslices2

Installation consists of a WSP deployment + Feature activation only.

SharePoint WebPartSlices on CodePlex

Written by jvossers

February 4, 2010 at 12:06 pm

jQuery Developer Frameworks for SharePoint

with 2 comments

If you are into developing SharePoint solutions using jQuery, you should really have a look at the following GREAT CodePlex projects. Both projects have been developed by real experts in the SharePoint & jQuery field 🙂

jPoint – Developed by a team lead by Will Lawrence (@willhlaw)

jPoint is an open source javascript API and script deployment framework for Sharepoint. It leverages the speed and agility of jQuery to manipulate Sharepoint forms and pages, communicate to Sharepoint webservices, and to build jPart plugins.

jQuery Library for SharePoint Web Services – Developed by Marc D Anderson (@sympmarc)

This is a jQuery library which abstracts SharePoint’s Web Services and makes them easier to use. It also includes functions which use the various Web Service operations to provide more useful (and cool) capabilities. It works entirely client side and requires no server install.

Written by jvossers

December 16, 2009 at 12:06 pm

Released: SharePoint LiveListData

with 20 comments

Last week I published my fourth CodePlex project, called SharePoint LiveListData. It is an “assembly-free”  solution which means that it contains no server side code. It is implemented as a jQuery plugin.

So what does it do? It uses AJAX to automatically reload any list-based Web Parts as soon as a change in the underlying list data is detected. You can also have your custom web parts refreshed, as long as they have a web part property that contains the ID of the list they depend on!

I have put online a screencast that demonstrates the the user experience.

Want to know how it works? Allow me to describe using some pseudo code..

  • OnDocumentLoaded
    • Make a single call to WebParts.asmx web service using AJAX to return an xml document with all web parts on the current page
    • Parse returned xml and find all web part nodes that contain a ListID element (which holds the value for the ListID web part property)
    • Create and populate a javascript object that contains a list of all ListIDs that we found in the returned xml, plus a list of all WebPartIDs per ListID, also retrieved from the xml (more or less creating a hashtable with the key being the ListID and the value being an array or WebPartIDs).
    • LOOP with interval = $configured_interval
      • Make a single call to Lists.asmx web service using AJAX to retrieve “LastDeleted” and “Modified” properties for each ListID in the hashtable that was created earlier.
      • For each ListID in hashtable
        • compare values for LastDeleted and Modified with those values retrieved as part of the previous loop iteration for this ListID (unless it’s the first iteration).
        • If a change in one of the two property values has been detected (indicating that someone inserted, updated or deleted an item) mark this ListID as “UpdatePending”, storing it on our javascript object that holds our ListIDs and WebPartIDs.
      • If any of the ListIDs are marked as UpdatePending
        • Make an AJAX request to page that is currently loaded in the browser (allowing us to get a fresh copy of the current page containing the new list data)
        • For each ListID marked as UpdatePending
          • For each WebPartID associated with ListID in our javascript hashtable object thingy
            • Replace div with matching WebPartID attribute in current document with “same” div in AJAX response (which contains the new list data).

This is basically how it works in a nutshell.

For examples on usage, check out the downloads tab on the SharePoint LiveListData CodePlex site, where you can also download the script!

Written by jvossers

November 3, 2009 at 11:40 pm