How to include JSON response body in Spring Boot Actuator's Trace?

Question

Spring Boot Actuator's Trace does a good job of capturing input/output HTTP params, headers, users, etc. I'd like to expand it to also capture the body of the HTTP response, that way I can have a full view of what is coming in and going out of the the web layer. Looking at the TraceProperties, doesn't look like there is a way to configure response body capturing. Is there a "safe" way to capture the response body without messing up whatever character stream it is sending back?

Answer 1

Recently, I wrote a blog post about customization of Spring Boot Actuator's trace endpoint and while playing with Actuator, I was kinda surprised that response body isn't one of the supported properties to trace.

I thought I may need this feature and came up with a quick solution thanks to Logback's TeeFilter.

To duplicate output stream of the response, I copied and used TeeHttpServletResponse and TeeServletOutputStream without too much examination.

Then, just like I explained in the blog post, extended WebRequestTraceFilter like:

@Component
public class RequestTraceFilter extends WebRequestTraceFilter {

    RequestTraceFilter(TraceRepository repository, TraceProperties properties) {
        super(repository, properties);
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        TeeHttpServletResponse teeResponse = new TeeHttpServletResponse(response);

        filterChain.doFilter(request, teeResponse);

        teeResponse.finish();

        request.setAttribute("responseBody", teeResponse.getOutputBuffer());

        super.doFilterInternal(request, teeResponse, filterChain);
    }

    @Override
    protected Map<String, Object> getTrace(HttpServletRequest request) {
        Map<String, Object> trace = super.getTrace(request);

        byte[] outputBuffer = (byte[]) request.getAttribute("responseBody");

        if (outputBuffer != null) {
            trace.put("responseBody", new String(outputBuffer));
        }

        return trace;
    }
}

Now, you can see responseBody in the JSON trace endpoint serves.