You can download a pre-compiled, ready-to-go version, right here
In Burp go to the "Extender" tab, then select the "Extensions" sub-tab and click "Add"
This is a Java extension, so select extension type "Java"
and as extension file, select the Jar file that comes with this extension (e.g.NakedBody-1.0.jar) Accept all defaults for the extension and you are good to go.
Go to the "HTTP history" sub-tab in the "Proxy" tab. Select one or more lines in the history and click the right mouse button. In the pop-up, select line "Naked Body" to display the save dialog of this extension.
Use the "Browse..." button to select the output directory (where to bury^H save the request/response bodies) Check or uncheck the options to save request bodies and/or response bodies
Finally, click "OK" to actually save the selected bodies.
The output filenames are built like so:
/"-req-" for request bodies, "-resp-" for response bodies.dat"Examples:
blackhole/2019-09-12_18-10-55-req-1.dat
blackhole/2019-09-12_18-10-55-req-2.dat
blackhole/2019-09-12_18-10-55-resp-2.dat
The first step would be to download the source code from here and extract the archive in a convenient place.
If you have Maven installed, then go to the top level directory of the extracted archive and type:
mvn package
At the end, you will find the Jar file in subdirectory target/
If you do not have Maven at hand, the process is slightly more complicated. First get version 1.7.22 of the Burp extender API. If all else fails, you could use the actual Burpsuite Jar instead of this API Jar.
Next, go to the subdirectory src/main/java of the extracted sources and compile the code by hand with something like this:
javac -cp <your-burp-api.jar> burp/*.java evilwan/nakedbody/*.java
followed by a packaging like this:
jar cvf your-naked-body.jar burp/*.class evilwan/nakedbody/*.class
This extension is distributed under a 3 clause BSD license.