Inconsistent handling of \r in protocol parser

[neilalexander]

Observed behavior

The handling of \r characters is not always consistent when they don't follow a \n. The behaviour here is different depending on whether we're using argBuf or not, and can cause unrelated characters to be dropped from the bytestring in some cases.

Pedantic mode avoids this issue somewhat, but it can result in unexpected \r characters being propagated which could cause a connection to be dropped.

Expected behavior

Better checking for characters other than \n when drop is set in the parser.

Server and client version

All

Host environment

No response

Steps to reproduce

No response