How to modify the image in the JMeter script? - image

Question

I'm uploading the image with the following JMeter script. But we have the requirement to modify the image for every request so that virus scanner scans it every time. Can anyone please suggest how to modify the image? Thanks.
<HTTPSamplerProxy guiclass="HttpTestSampleGui" testclass="HTTPSamplerProxy" testname="HTTP Request" enabled="true">
<elementProp name="HTTPsampler.Files" elementType="HTTPFileArgs">
<collectionProp name="HTTPFileArgs.files">
<elementProp name="Sample.JPG" elementType="HTTPFileArg">
<stringProp name="File.path">Sample.JPG</stringProp>
<stringProp name="File.paramname">File</stringProp>
<stringProp name="File.mimetype">image/jpeg</stringProp>
</elementProp>
</collectionProp>
</elementProp>

Answer 1

You can use ImageIO class in order to add something to the original image
Add JSR223 PreProcessor as a child of the HTTP Request sampler which performs the image upload
Put the following code into "Script" area:
def image = javax.imageio.ImageIO.read(new File('Sample.jpg'))
def graphics = image.getGraphics()
graphics.setFont(graphics.getFont().deriveFont(16f))
graphics.drawString('User ' + ctx.getThreadNum() + '; iteration: ' + ctx.getVariables().getIteration(), 50, 50)
graphics.dispose()
javax.imageio.ImageIO.write(image, "jpg", new File("Sample.jpg"))
That's it, when you run your test the above code will add current user and iteration text to the upper-left corner of the image (the font color is white so if your image is white you won't be able to see it using your eyes)
More information on Groovy scripting in JMeter: Apache Groovy - Why and How You Should Use It
If any concurrency is assumed - consider making the copy of the image and updating the filename in the HTTP Request sampler otherwise you will run into race condition when multiple threads will be simultaneously writing into the same file so the image will get corrupt.