fix(fastapi): invalid utf8 header values are now not breaking trace

[bwcgn]

Fix: Handle invalid UTF-8 in FastAPI middleware headers

Problem

The FastAPI middleware could crash with a UnicodeDecodeError when processing HTTP headers containing invalid UTF-8 byte sequences. This occurred in both request and response header processing where .decode() was called without error handling.

Solution

Added errors='replace' parameter to all .decode() calls for header keys and values. Invalid UTF-8 bytes are now replaced with the Unicode replacement character (�) instead of raising an exception.

Changes

• Updated request header decoding (line 18-19)
• Updated response header decoding (line 58-59)
• Both now use .decode('utf-8', errors='replace')

Impact

• Prevents crashes when processing malformed or non-UTF-8 headers
• Maintains observability even with invalid header data
• No breaking changes to existing functionality

[dynatrace-cla-bot]

All committers have signed the CLA.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bwcgn]

@dlopes7 Can this be patched? :)