Missing activity in case of "broken" ActivityID in events

There is a bug in the BCL that generates 00 byte in an event ActivityID GUID that leads to stopping the parsing and "hidding" final activities.

Since each Start/Stop action is adding an activity, I was expecting to see them (i.e. /1/4/2000/xx/ instead of /1/4/2000/
However, the GUID seemed to contain the missing xx value like in the second 32 value -0010- or -0020-.

 23360 | 00d0c714-0000-0000-0000-00003d2d6f5a =       /1/4/2000/ > event   1 __ [ 1| Start] RequestStart
       |> http://localhost:5500/Products/Info/1990
 23360 | 00d0c714-0010-0000-0000-00002d2d6f5a =       /1/4/2000/ > event   7 __ [ 1| Start] RequestHeadersStart
       |QH[ 20]
 23360 | 00d0c714-0010-0000-0000-00002d2d6f5a =       /1/4/2000/ > event   8 __ [ 2|  Stop] RequestHeadersStop
      <|QH
 44048 | 00d0c714-0020-0000-0000-00001d2d6f5a =       /1/4/2000/ > event  11 __ [ 1| Start] ResponseHeadersStart
       |RH>
 44048 | 00d0c714-0020-0000-0000-00001d2d6f5a =       /1/4/2000/ > event  12 __ [ 2|  Stop] ResponseHeadersStop
  200 <|RH
 44048 | 00d0c714-0030-0000-0000-00000d2d6f5a =       /1/4/2000/ > event  13 __ [ 1| Start] ResponseContentStart
       |RC>
 44048 | 00d0c714-0030-0000-0000-00000d2d6f5a =       /1/4/2000/ > event  14 __ [ 2|  Stop] ResponseContentStop
      <|RC
 44048 | 00d0c714-0000-0000-0000-00003d2d6f5a =       /1/4/2000/ > event   2 __ [ 2|  Stop] RequestStop
  200 <|

These output were generated to analyze network events (HTTP, socket, security, DNS).

This happens only when a 12 bits value is stored AND the high bits are stored in the low nibble of a byte. The following code update in StartStopActivityComputer.cs seems to avoid the problem and supports the proposed fix in the BCL:

// Compute the number (little endian) (thus backwards).
for (int i = (int)numBytes - 1; 0 <= i; --i)
{
    value = (value << 8) + bytePtr[i];
}

// Print the value
sb.Append(separator).Append(value);

bytePtr += numBytes;        // Advance past the bytes.

// FIX: there is a special case for a value < 4096/0xFFF where the encoder made a mistake
// It is encoded with 1 nibble + 1 byte + 1 byte that contains 0 (hence stopping the parsing)
if ((value >= 0xFF) && (value < 0xFFF) && (bytePtr + 1 < endPtr) && (bytePtr[0] == 0) && (bytePtr[1] != 0))
{
    bytePtr++;  // Advance past the 00 byte
}

Note: feel free to use this test app to debug and validate the fix.

Start in src/TraceEvent/Computers/StartStopActivityComputer.cs around the activity-ID parsing at the referenced line. Use the linked dotnet-activity test app to reproduce the malformed GUID case and compare the output with the proposed BCL fix. Done means parsing continues past the embedded zero byte and the final activities appear in the activity path.