NDT-DEV email list created

Status: New
Owner: ----
Labels: Type-Defect Severity-Medium

New issue 161 by 
:
 Non-random Test Data risks compression
https://code.google.com/p/ndt/issues/detail?id=161

Reading the source, I noticed that the data that NDT sends in S2C and C2s  
tests is nonrandom.

From the Flash client:
      // Prepare the data to send to the server.
      for (var i:int = 0; i < NDTConstants.PREDEFINED_BUFFER_SIZE; i++) {
        _dataToSend.writeByte(i);
      }
https://code.google.com/p/ndt/source/browse/trunk/flash-client/src/TestC2S.as#168

From the C client:
    // ....Fill buffer upto NDTConstants.PREDEFNED_BUFFER_SIZE packets
    pkts = 0;
    k = 0;
    for (i = 0; i < (64*KILO_BITS); i++) {  // again buffer sizes differ.
      // Since the actual transmitted byte count is timed, it doesn't appear
      // that it is causing specific problems.
      while (!isprint(k & 0x7f))
        k++;
      buff[i] = (k++ % 0x7f);
    }
https://code.google.com/p/ndt/source/browse/trunk/src/test_c2s_clt.c#141

Because we're sending buffers of sequential bytes (and in the case of the C  
client, only printable ASCII characters), there is a risk that boxes on the  
network will compress the data and skew measurements.

We should modify the code for data generation so that we use a pseudorandom  
number generator with a periodicity of at least 64k, then take the last  
byte of each generated number as the next byte to place in the send buffer.

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