Resulting report from BuildReport() was exceeding the provided maxSize limit

[astroza]

Description

Under packet loss stress, the rfc8888 interceptor was sending packets bigger than the maxSize limit, sometimes even bigger than the network MTU.

I found the next problems:

1. Ranging over a map is not deterministic (this applies only for the testing code)

   for i, log := range r.streams {
       if len(r.streams) > 1 && int(i) == len(r.streams)-1 {
           maxReportBlocksPerStream = maxReportBlocks % len(r.streams)
       }
       block := log.metricsAfter(now, int64(maxReportBlocksPerStream))
       report.ReportBlocks = append(report.ReportBlocks, block)
   }
   

   maxReportBlocksPerStream could be updated in the last iteration as well as the first one

2. r.streams is a "ssrc -> log" map, so the i variable will never be equal to len(r.streams)-1. i is not a array index

3. maxReportBlocksPerStream as maxReportBlocks / (len(r.streams)-1) will exceed the blocks limit. This is specially true when len(r.streams) is a small number

4. The tests were not catching the actual issue
   If you run the new test "MaxreportsPerStream 3 streams" with the old code, you will get

           	Error Trace:	/home/fastroza/src/interceptor/pkg/rfc8888/recorder_test.go:166
      	Error:      	"1746" is not less than "1200"
   

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.63%. Comparing base (ff2807d) to head (86db425).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #365      +/-   ##
==========================================
- Coverage   78.71%   78.63%   -0.09%     
==========================================
  Files          82       82              
  Lines        5169     5163       -6     
==========================================
- Hits         4069     4060       -9     
- Misses        927      929       +2     
- Partials      173      174       +1     

Flag	Coverage Δ
go	78.63% <100.00%> (-0.09%)	⬇️
wasm	76.07% <100.00%> (-0.03%)	⬇️

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[Sean-Der]

Nice catch :)

@mengelbart what you think? If I don't hear back in a day or two @astroza I will merge myself!

[mengelbart]

Thanks @astroza!