According to the Wire Compression specification:

Unknown compressors MUST yield a warning, as per the Connection String specification, and MUST NOT be included in the handshake.

The .NET/C# driver ignores unknown compressors, but does not log a warning as required by the spec.

To reproduce:

• Create a MongoClient using the connection string mongodb://localhost:27017/test?compressors=snoopy
• Observe that no warning is logged even if a trace source is configured

For comparison, consider the following Python output:

>>> from pymongo import MongoClient
>>> client = MongoClient("mongodb://localhost:37017/test?compressors=snoopy")
/usr/local/lib/python3.9/site-packages/pymongo/compression_support.py:55: UserWarning: Unsupported compressor: snoopy
  warnings.warn("Unsupported compressor: %s" % (compressor,))