Some of the warnings on the clang builders prompted me to take a closer look at the libconf branch.

• https://github.com/networkupstools/nut/blob/libconf/common/nutstream.cpp#L346

NutStream::status_t NutFile::putData(const std::string & data) has a comment that there is not a FILE* interface for writing arbitrary data. What about fwrite()?

• https://github.com/networkupstools/nut/blob/libconf/common/nutstream.cpp#L211

tempnam() should probably be replaced with mkstemp(). Then you won't need the hard-coded /var/tmp variable. (Some systems implement per-user $TMPDIR variables, which eliminate some corner cases and race conditions.)

• https://github.com/networkupstools/nut/blob/libconf/common/nutstream.cpp#L488

This expression won't do bit operations: ss << (packed && 0x000000ff) << ".";

Also, you should consider using the standard inet_?to? functions here, especially for the IPv6 address printer.