DDevelopment & Design

Testing NiFi Flow – The good, the bad and the ugly

Introduction

Some time has passed since we wrote our last blogpost about Apache NiFi where we pointed out what could be improved. It’s a very nice tool, so we are still using it, but we’ve found some other things that could be improved to make it even better. Of course, we could write another post where all we do is complain, but does that make the world better? Unfortunately not. So we decided that we could do better than that. We took the most painful issue and implemented a solution – that’s how NiFi Flow Tester was created.

Use case

Let’s assume you have to create a simple flow in NiFi according to some specification your client gave you:

  1. read some XML files from directory
  2. validate them (using XSD file)
  3. convert them from XML to JSON
  4. log if something failed
  5. pass it for further processing if everything went well

after studying documentation and some googling you end up with this flow: First you need to list all the files, then read their content, validate it, convert to JSON and pass it further. Looks great. Now it’s time for some tests – you have two options.

Test in NiFi directly – the bad

To test it manually, you need to copy some file to the input directory, wait to see what happens and if everything went well – you can verify it (again, manually) using ‘View data provenance’. Let’s try this approach. Something went wrong. Can you tell where? Something inside ValidateXml, but what exactly? So now to the LogAttribute -> View provenance data and check record attributes to find this one:

validatexml.invalid.error
The markup in the document following the root element must be well-formed.

Maybe there’s something wrong with XML file that your client gave you?

> cat data.txt

    Foo
    student
    31


    Invalid age
    student
    -11


    Bar
    student
    12

Looks like your client has some strange file format, where each line is a separate XML file. Ok, that’s fine you just need to add one more processor which splits text by each line and do the manual tests AGAIN… but at this point, you should have asked a question – is there a better way to do this? After all, we’re programmers and we love to write code.

Nifi Mock – the ugly

Nifi Mock library comes with a processor testing tool – TestRunner. Let’s use this to test our flow! TestRunner can only run one processor, but we can work it out. Let’s start with first one:

val listFileRunner = TestRunners.newTestRunner(new ListFile)
listFileRunner.setProperty(ListFile.DIRECTORY, s"$testDir/person/")
listFileRunner.run()
val listFileResults = listFileRunner.getFlowFilesForRelationship("success")

We create a runner with the processor, set a directory to read from, run it and get the results from the relationship. That was easy, let’s create another TestRunner with FetchFile processor, enqueue results from the previous step, run and collect results.

val fetchFileRunner = TestRunners.newTestRunner(new FetchFile)
listFileResults.foreach(f => fetchFileRunner.enqueue(f))
fetchFileRunner.run()
val fetchFileResults = fetchFileRunner.getFlowFilesForRelationship("success")

Great! Next one:

val splitTextRunner = TestRunners.newTestRunner(new SplitText)
splitTextRunner.setProperty(SplitText.LINE_SPLIT_COUNT, "1")
fetchFileResults.foreach(f => splitTextRunner.enqueue(f)) 
splitTextRunner.run()
val splitTextResults = splitTextRunner.getFlowFilesForRelationship(SplitText.REL_SPLITS)

Two more processors and we are done. And don’t forget to check all the runners and results names when you are done with copy-pasting this code! That’s not cool. I mean, we love to write code but this is too much boilerplate, isn’t it? I’m sure you saw the pattern here. We saw it too and that’s why we introduced a solution.

Nifi Flow Tester – the good

In our new library we have two ways to create flow. Today we will focus on the simple one, which is better for prototyping. First, we need to create new NifiFlowBuilder() and add some nodes to it:

new NifiFlowBuilder()
  .addNode(
    "ListFile",
    new ListFile,
    Map(ListFile.DIRECTORY.getName -> s"$testDir/person/")
  )
  .addNode("FetchFile", new FetchFile, Map())
  .addNode(
    "SplitText",
    new Split Text,
    Map(SplitText.LINE_SPLIT_COUNT.getName -> "1")
  )
  .addNode(
    "ValidateXml",
    new ValidateXml,
    Map(ValidateXml.SCHEMA_FILE.getName -> s"$testDir/person-schema.xsd")
  )
  .addNode(
    "TransformXml",
    new TransformXml,
    Map(TransformXml.XSLT_FILE_NAME.getName -> s"$testDir/xml-to-json.xsl")
  )

First, you need to specify the node name, which allows you to identify your node. It can be the same as the class name as long as you don’t use the same processor twice in flow. Then of course you need to specify the processor with all the parameters as simple Map[String, String]. The safest way to do this is to use processor’s class fields of type PropertyDescriptor. Unfortunately, they’re not always public, so sometimes you have written their name – instead of ListFile.DIRECTORY.getName we could write Input Directory.

When all the nodes are specified, we can add connections between them using node names. The first parameter is the source node, the second is a destination and the third is the selected relationship. Again, using processor class fields is less error prone but sometimes these fields are not public (for instance ListFile or FetchFile processor)

.addConnection("ListFile", "FetchFile", "success")
.addConnection("FetchFile", "SplitText", "success")
.addConnection("SplitText", "ValidateXml", SplitText.REL_SPLITS)
.addConnection("ValidateXml", "TransformXml", ValidateXml.REL_VALID)
.addOutputConnection("TransformXml", "success")

In the end, we add a connection to the output port to get the results. Everything looks good. Now just call build method to create flow. The entire code looks like this:

val flow = new NifiFlowBuilder()
      .addNode("ListFile", new ListFile, Map(ListFile.DIRECTORY.getName -> s"$testDir/person/"))
      .addNode("FetchFile", new FetchFile, Map())
      .addNode("SplitText", new SplitText, Map(SplitText.LINE_SPLIT_COUNT.getName -> "1"))
      .addNode("ValidateXml", new ValidateXml, Map(ValidateXml.SCHEMA_FILE.getName -> s"$testDir/person-schema.xsd"))
      .addNode("TransformXml", new TransformXml, Map(TransformXml.XSLT_FILE_NAME.getName -> s"$testDir/xml-to-json.xsl"))
      .addConnection("ListFile", "FetchFile", "success")
      .addConnection("FetchFile", "SplitText", "success")
      .addConnection( "SplitText", "ValidateXml", SplitText.REL_SPLITS)
      .addConnection("ValidateXml", "TransformXml", ValidateXml.REL_VALID)
      .addOutputConnection("TransformXml", "success")
      .build()

Now we just need to run the flow, collect the results and verify them:

flow.run() 
val files = flow.executionResult.outputFlowFiles 
files.head.assertContentEquals("""{"person":{"name":"Foo","type":"student","age":31}}""")

Disclaimer: this is not the best way to test if JSON is correct, but it was done for simplicity.

Conclusion

Apache NiFi seems to be perfect unless you start a serious data integration. Without the ability to test your changes fast, you will become extremely frustrated with clicking every time your client notices a bug. Sometimes it may be a bug of the NiFi itself, but you will never know it until you debug the code. That’s something our library can help you with. You can find it here: https://github.com/TouK/plumber

— Previous article

Loops performance in Groovy

Next article —

Not so easy functional programming in JavaScript

You May Also Like
DDevelopment & Design

Phonegap / Cordova and cross domain ssl request problem on android.

In one app I have participated, there was a use case:
  • User fill up a form.
  • User submit the form.
  • System send data via https to server and show a response.
During development there wasn’t any problem, but when we were going to release production version then some unsuspected situation occurred. I prepare the production version accordingly with standard flow for Android environment:
  • ant release
  • align
  • signing
During conduct tests on that version, every time I try to submit the form, a connection error appear. In that situation, at the first you should check whitelist in cordova settings. Every URL you want to connect to, must be explicit type in: 
res/xml/cordova.xml
If whitelist looks fine, the error is most likely caused by inner implementation of Android System. The Android WebView does not allow by default self-signed SSL certs. When app is debug-signed the SSL error is ignored, but if app is release-signed connection to untrusted services is blocked.



Workaround


You have to remember that secure connection to service with self-signed certificate is risky and unrecommended. But if you know what you are doing there is some workaround of the security problem. Behavior of method 
CordovaWebViewClient.onReceivedSslError
must be changed.


Thus add new class extended CordovaWebViewClient and override ‘onReceivedSslError’. I strongly suggest to implement custom onReceiveSslError as secure as possible. I know that the problem occours when app try connect to example.domain.com and in spite of self signed certificate the domain is trusted, so only for that case the SslError is ignored. 

public class MyWebViewClient extends CordovaWebViewClient {

   private static final String TAG = MyWebViewClient.class.getName();
   private static final String AVAILABLE_SLL_CN 
                               = "example.domain.com";

   public MyWebViewClient(DroidGap ctx) {
       super(ctx);
   }

   @Override
   public void onReceivedSslError(WebView view, 
                                  SslErrorHandler handler, 
                                  android.net.http.SslError error) {

       String errorSourceCName = error.getCertificate().
                                  getIssuedTo().getCName();

       if( AVAILABLE_SLL_CN.equals(errorSourceCName) ) {
           Log.i(TAG, "Detect ssl connection error: " + 
                       error.toString() + 
                       „ so the error is ignored”);

           handler.proceed();
           return;
       }

       super.onReceivedSslError(view, handler, error);
   }
}
Next step is forcing yours app to  use custom implementation of WebViewClient. 

public class Start extends DroidGap
{
   private static final String TAG = Start.class.getName();

   @Override
   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       super.setIntegerProperty("splashscreen", R.drawable.splash);
       super.init();

       MyWebViewClient myWebViewClient = new MyWebViewClient(this);
       myWebViewClient.setWebView(this.appView);

       this.appView.setWebViewClient(myWebViewClient);
       
       // yours code

   }
}
That is all ypu have to do if minSdk of yours app is greater or equals 8. In older version of Android there is no class 
android.net.http.SslError
So in class MyCordovaWebViewClient class there are errors because compliator doesn’t see SslError class. Fortunately Android is(was) open source, so it is easy to find source of the class. There is no inpediments to ‘upgrade’ app and just add the file to project. I suggest to keep original packages. Thus after all operations the source tree looks like:

Class SslError placed in source tree. 
 Now the app created in release mode can connect via https to services with self-signed SSl certificates.