logging: Add subsystem to log API (#19002)

Create new code paths for multiple subsystems in the code. This will
make maintaing this easier later.

Also introduce bugLogIf() for errors that should not happen in the first
place.

cmd/handler-utils.go

@@ -51,7 +51,7 @@ func parseLocationConstraint(r *http.Request) (location string, s3Error APIError
 	locationConstraint := createBucketLocationConfiguration{}
 	err := xmlDecoder(r.Body, &locationConstraint, r.ContentLength)
 	if err != nil && r.ContentLength != 0 {
-		logger.LogOnceIf(GlobalContext, err, "location-constraint-xml-parsing")
+		internalLogOnceIf(GlobalContext, err, "location-constraint-xml-parsing")
 		// Treat all other failures as XML parsing errors.
 		return "", ErrMalformedXML
 	} // else for both err as nil or io.EOF
@@ -191,7 +191,7 @@ func extractMetadata(ctx context.Context, mimesHeader ...textproto.MIMEHeader) (
 // extractMetadata extracts metadata from map values.
 func extractMetadataFromMime(ctx context.Context, v textproto.MIMEHeader, m map[string]string) error {
 	if v == nil {
-		logger.LogIf(ctx, errInvalidArgument)
+		bugLogIf(ctx, errInvalidArgument)
 		return errInvalidArgument
 	}
 
@@ -461,7 +461,7 @@ func proxyRequest(ctx context.Context, w http.ResponseWriter, r *http.Request, e
 		ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
 			success = false
 			if err != nil && !errors.Is(err, context.Canceled) {
-				logger.LogIf(GlobalContext, err)
+				replLogIf(GlobalContext, err)
 			}
 		},
 	})