Jared Ottley

I’ve heard asked many times by customers and community members if there was a way to diff files in Alfresco and alas there isn’t an OTB way to do this.  A month ago the discussion came up again internally.  And I thought it might be fun to tackle this as side project just to see if/what was possible.  So I took an evening and hammered out a simple Java class that did a comparison between two text files.  Once I saw that I had at least the basics (annotate the differences between two files) and had gotten the question of basic possibility/difficulty out of the way I moved on to other projects.

Today almost the entire family is sick so I thought I’d pick up the project again, moving the Java class to a Java Backed web script.

The web script is a simple GET that takes the nodeRef of two files, or two versions of the same file and outputs a simple HTML page that highlights the differences between the two.  There are no complex algorithms that take into account shifts in blocks or identifies just the text in a line that has changed.  It is a simple line by line comparison of two pieces of content. It is not integrated in to Share or Explorer at this time.  I might take that as a separate sick day project (or accept any code contributions to add that).

I’ll admit right off that the code is ugly and repetitive.  But this is more of a Proof of Concept than a full production ready implementation (though it could definitely be used as such to provide a quick view of differences).

I’ve also probably bored you with the above so let’s just jump right in before I completely lose you…

Using The Web Script

The web script is called by the following URL:

alfresco/service/file/{protocol_1}/{identifier_1}/{id_1}/diff/{protocol_2}/{identifier_2}/{id_2}

For real world examples we’ll first look at comparing two files

alfresco/service/file/workspace/SpacesStore/dd83c9f6-81b7-462b-8a1a-1e9a2af251dd/diff/workspace/SpacesStore/ca65d129-6c2c-4ba0-936d-d7626f94f23a

Second comparing two versions of the same file

alfresco/service/file/workspace/SpacesStore/dd83c9f6-81b7-462b-8a1a-1e9a2af251dd/diff/versionStore/version2Store/ca65d129-6c2c-4ba0-936d-d7626f94f23a

What is returned is, as stated above, a simple HTML highlighting the differences

Each line that is different is highlighted in blue.  Simple and to the point.

The Code

This is just a little Declarative Web Script that reads the content line by line and then compares the hash of each line to see differences.  When a difference is found it is wrapped in HTML to annotate the difference so that when displayed, CSS can take care of highlighting the differences.

A couple of things that I think are important to note:

• File length: When comparing two files there is always the possibility that one is longer/shorter than the other.  To simplify the comparison, I just append lines with a single space to the shorter file, simplifying any computational work needed for the comparison caused by the difference in length.
  • I mentioned above that the appended line contains a single space.  This is done so the that the line appears in the output.  <div> tags with no content can be ignored by some browsers. The annotation/presentation uses a combination of <div> and <pre> tags.  The space is maintained in a <pre> tag forces the div element to be visible.
• Special Characters: Because the output for the comparison is targeted for HTML, it is important to escape all characters/strings that could be interpreted by the browser as presentation elements.  Apache Commons (included with Alfresco) has classes to help do this.
• Gotcha!: When I was initially testing the code, the file content kept appending files to the previous request.  So remember when defining a Collection as a class scoped variable to call clear() on the List to make sure it is empty before it gets reused.

This extension is available as an AMP. The source is available in the Google Code Project.

I’ve taken a bit of Holiday time to update the Alfresco PDF Toolkit.  Nate has been doing an outstanding job adding Watermarking, Digital Signatures, Encryption and cleaning up my messy code.  But it was time to add a little bit myself.

So I took sometime this evening to add in one of my planned actions: Insert PDF.  This action allows you to insert a PDF into another PDF at a specific page.

This is a pretty straight forward action to test:  From the Document Details page of the PDF you want to insert content into, select Run Action (This action can also be run through the rules engine or scripted).

From the list of Actions you’ll want to select Insert PDF.

Now you will want to set the parameters for the insert.  There are 4 parameters for an insert:

1. Name: This is the name of the new file that will be generated.  No extension is needed, it will automatically be added.
2. Destination: Space where the new file will be stored.
3. Insert at page: Where page 1 of the inserted PDF will start in the targeted PDF.
4. Insert: The PDF to insert into the targeted PDF

Finally, you’ll get a message summarizing the action you are taking

See pretty simple!

The latest amp and source can be found at the Alfresco PDF Toolkit project site.

Updated: Added new tested versions

For this post I want to share another policy from recent request from a customer.  The project was to help them develop a way to have usage quotas set to a default value when a new user/person was added to Alfresco. (There is an important distinction between the two.)  A few months ago I had a discussion about possible ways to implement this kind of functionality with a co-worker and had a few ideas brewing as we started the engagement.

First some background on quotas:

• The default quota in Alfresco is unlimited.  In other words, there is no limit in the amount (total size) of content a user can add/own in Alfresco.
• A quota can be set either on creation or at anytime during a users lifetime.
  • From within the UI a quota can be in either GB, MB or KB.
  • From an API  (Web Script, JavaScript, Java) it accepts the size in bytes.
• See http://wiki.alfresco.com/wiki/Usages_and_Quotas for additional details

When developing a behavior I continually reference Jeff Potts’s tutorial on implementing behaviors. His table of available policies is a great quick reference.  Of course the definitive source is the Alfresco source code, but not much has changed since Jeff wrote the article.

JavaScript Behavior

The first attempt to implementing this policy was to use a behavior implemented in JavaScript.  I used Jeff’s JavaScript example as the seed for my code.  In fact there was very little I needed to change (mostly just the business logic). It is a great outline to get you going.

Using JavaScript wasn’t completely successful.  The code did work up to a point and that point was setting the quota.  There is an undocumented (in the wiki) JS function that can be used to set quotas.

From the People class (note the comment):

/**
 * Set the content quota in bytes for a person.
 * Only the admin authority can set this value.
 *
 * @param person    Person to set quota against.
 * @param quota     As a string, in bytes, a value of "-1" means no quota is set
*/
public void setQuota(ScriptNode person, String quota)

During the transaction the quota was being set, but once the transaction was committed it was lost. The problem being (again see the comments) that the setQuota must be executed by an admin.  A quota must be set explicitly by an admin.

The JavaScript API lacks the ability to execute a script as one user but then run specific code in that script as another user.  This is done for security reasons (like being able to keep a user from uploading and then executing a malicious script).

While the script did not work as desired it still may be useful for something else.  So I’m including links to the context file and script as part of this post.

Java Behavior

Because we need to  set the quota as an admin user, we’ll switch to Java which provides a useful means to run code as one user, and execute specific parts as a different user.

Before we jump to that, let’s talk about some of the specifics of our policy:

First, there is not much difference in the structure needed for this behavior and the Max Version Policy I wrote about in a previous post.  So I used it as a template for this project.

Next, users/people in Alfresco are stored as nodes.  If you start to dig into the node browser you may be drawn to find your users in the user://alfrecoUserStore store.  This is, as the name suggestions, the Alfresco User Store which is used as the native Alfresco authentication source (alfrescoNTLM).  The nodes in this store are of type {http://www.alfresco.org/model/user/1.0}user.  Quotas are a property of {http://www.alfresco.org/model/content/1.0}person and are found in the workspace://SpacesStore under system -> people.

Alfresco has no specific policies for user nodes (like an onCreateUser policy), but since they are just nodes we can leverage the onCreateNode policy. Also because they are just nodes, when using an onCreateNode policy we don’t want the policy to be run every time a node is created.  We want to target cm:person nodes.  Otherwise, we would need to overcomplicate the code with additional tests to only only execute the business logic when the newly created node is of type cm:person.  So we can bind our policy to a specific type.  Similarly to the max version policy we initialize our behavior and bind it in the init method.

public void init() {

this.onCreateNode = new JavaBehaviour(this, "onCreateNode", NotificationFrequency.TRANSACTION_COMMIT);

this.policyComponent.bindClassBehaviour(QName.createQName(NamespaceService.ALFRESCO_URI, "onCreateNode"), ContentModel.TYPE_PERSON, this.onCreateNode);

}

In the init() above we bind our policy: QName.createQName(NamespaceService.ALFRESCO_URI, “onCreateNode”), the type: ContentModel.TYPE_PERSON and the behavior: this.onCreateNode together.

Next we need to implement the onCreateNode method from the OnCreateNodePolicy in our new class

public void onCreateNode(ChildAssociationRef childAssocRef) {

We can grab our reference to the newly created user node from the ChildAssociationRef parameter.

final NodeRef user = childAssocRef.getChildRef();

Notice that it is using the final modifier.  Variables from an outer class that are being referenced in an inner class must be defined as final.

For our default policy we also want to allow the default quota to be overwritten.  If an admin wants to set a different value for the quota at creation time we need to allow it. So we need to first get the value that was assigned to the user on the node at creation

long currentQuota = contentUsageService.getUserQuota((String) nodeService.getProperty(user,ContentModel.PROP_USERNAME));

The default value of no quota is -1.  If an admin has set a value for the quota it will be greater than 0.

if (currentQuota < 0) {

...business logic here...

}

Because quotas can only be set by an admin we need to use the runAs utility

AuthenticationUtil.runAs(

new AuthenticationUtil.RunAsWork<Object>() {

public Object doWork() throws Exception {

...code to be run as a different user...

}

}, "admin");

runAs takes two parameters: The first is the RunAsWork Object, which contains an inner class that has the code that needs to be run as another user.  Second the name of the user to execute the code as.

Now in our policy we can set the quota.  We’ll use the contentUsageService to set the new users quota, taking the username and the value of the quota as parameters. Also note that default value is in bytes which is read from the spring context file for the OTB default I’ve chosen 2GB (2147483648).

contentUsageService.setUserQuota((String) nodeService.getProperty(user, ContentModel.PROP_USERNAME), Long.parseLong(defaultQuota));

return user; 

RunAsWork is also looking for a return value which I’ve set as user.  We won’t being doing anything with this value so in this case it is an arbitrary return.

Installing

The policy is packaged as an AMP and is downloadable from the alfresco-defaultquota-policy project hosted on Google Code.  (See http://wiki.alfresco.com/wiki/Module_Management_Tool for detailed instructions on installing AMPs.)

The amp has been tested with Alfresco Enterprise 3.1.1 to 3.3.2.

I’ve only tested this on Enterprise 3.3.2.  I’ll look to expand my testing soon.  If you have a chance to try it on another version of Alfresco please let me know.  (In that case you’ll need to build the amp from source, changing the version.min/max property to include the version you’re targeting.)

So what next?

While this policy is limited to setting the user quota, your probably thinking what else can I use this for? I know I am!  Maybe your using a database or some other none supported user store in Alfresco and you want to populate the user node properties with details from that system.  Or you want to add them to specific groups based on some complex business logic.  Or interact with external systems when a user is created in Alfresco.  What are your ideas?

I also believe that this should work with any external authentication/synchronization of users into Alfresco.  I’ve not tested it, but it is the list of things to test next.

I’m always looking for feedback: let me know what worked or didn’t for you.