Uses std.encoding.sanitize, which returns the original string, if all code points are properly encoded. Note that the performance could still be improved considerably by iterating over multiple bytes at once, fast skipping over characters that don't have the most significant bit set.
The library is able to support simple TCP servers in the current state. The API is still mostly compatible with mainline vibe.d, but the driver systen has been replaced by the eventcore library and sockets/files/timers/... are now structs with automatic reference counting instead of GC collected classes. The stream interfaces have been removed for now.