Bug 57579

Created attachment 32467 [details]
Error instead of no sample showing

Hi,

I was trying to write a simple test script for our site and found interesting issue. I think it's a bug the new feature of not recording samples for HTTP-cached responses (https://issues.apache.org/bugzilla/show_bug.cgi?id=54778).

Steps to reproduce:

(1) Create test with 1 HTTP Sampler request for an URL which returns Expires & Cache-Control headers in HTTP response, like:
Response headers:
  HTTP/1.1 200 OK
  Date: Thu, 12 Feb 2015 22:09:52 GMT
  ...
  Vary: Accept-Encoding
  Expires: Sun, 09 Feb 2025 22:09:52 GMT
  Cache-Control: max-age=315360000, public
  ETag: "c7109969:dtagent7888VJDk:dtagent7888kDJV"
  Last-Modified: Wed, 30 Oct 2013 17:05:39 GMT
  Content-Type: text/css
  Content-Length: 320
  Connection: close

(2) Add "HTTP Cache Manager" element, check "Use Cache-Control / Expires header when processing GET requests" 

(3) Run the test with 1 thread, with 10 iterations (Loop count = 10).

Result:
First run executes HTTP request, server returns 200 + caching headers. Second request (and any subsequent) fails with Error in the JMeter. This was taken from element "View Results Tree":

"Sampler result" tab:
Thread Name: Liferay Authenticated Users Browsing 1-1
Sample Start: 1969-12-31 18:00:00 CST
Load time: 0
Latency: 0
Size in bytes: 413
Headers size in bytes: 0
Body size in bytes: 413
Sample Count: 1
Error Count: 1
Response code: Non HTTP response code: java.lang.NullPointerException
Response message: Non HTTP response message: null

Response headers:


HTTPSampleResult fields:
ContentType: 
DataEncoding: null

"Request" tab:
null

"Response data" tab:
java.lang.NullPointerException
	at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1142)
	at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1130)
	at org.apache.jmeter.threads.JMeterThread.process_sampler(JMeterThread.java:431)
	at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:258)
	at java.lang.Thread.run(Thread.java:745)

  

Expected:
No error is shown, no sample is recorded.

Workaround:
If you change the behavior of JMeter cache manager using this property:

cache_manager.cached_resource_mode=RETURN_200_CACHE

then script works without errors (samples with response time=0 are recorded as expected).

Details:
Seems like issue 54778 causes this, I debugged through the code and if the main sample URL is found in the JMeter cache:

org.apache.jmeter.protocol.http.sampler.HTTPAbstractImpl.updateSampleResultForResourceInCache():365
    ...
    protected HTTPSampleResult updateSampleResultForResourceInCache(HTTPSampleResult res) {
        switch (CACHED_RESOURCE_MODE) {
            case RETURN_NO_SAMPLE:
                return null; // line 365
            case RETURN_200_CACHE:
    ...

null is returned as the HTTPSampleResult. But then JMeter tries to set the label on this result:
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample():1142
    ...
    public SampleResult sample() {
        SampleResult res = null;
        try {
            res = sample(getUrl(), getMethod(), false, 0);
            res.setSampleLabel(getName()); // line 1142
            return res;
        } catch (Exception e) {
            return errorResult(e, new HTTPSampleResult());
        }
    }
    ...

This fails for NPE.

Note that if the same HTTP response headers are set on a HTTP request which is a sub-sample (for example originating from "Retrieve All Embedded Resource"), this works fine -- no error is shown, no sample is recorded.


I'm using OS X 10.10.2 which is not in the list of OSes.