Actually, it's to allow for non-NUL terminated strings.

A good example is when using a String supplied by a scripting language such as Ruby or JavaScript.

Normally, you might need to copy the string to add a NUL byte, or request that the scripting engine provide a NUL terminated string (which might result in the same action performed).

Using this optional approach, a potential copy of the data can be avoided.

Knowing nothing about this, I would guess that this is to allow sending binary data that contains embedded null bytes?

Though I guess it would be good to have nicer wrappers for the common case where you do only send text.

Probably they use length-prefixed strings internally (which is probably a requirement for taking a C web framework seriously), but allow C nul-terminated strings at the API boundary for convenience of use.

No it is not necessary. If no length is given, the string is assumed to be NULL-terminated.

It's a bit unfortunate that they use two code paths for that which are basically just copy & paste.

https://github.com/boazsegev/facil.io/blob/master/lib/facil/...

This approach moves an `if` statement out of the loop, so there's no need to repeat it.