Add "dumpallzones" command to dump all zones in BIND9 format

[Daniel15]

Adds a new dumpallzones command to dump all zones in BIND9 format. This is useful to backup an entire ClouDNS account.

Technically this could be accomplished in an external script by calling cloudns_api.sh listzones followed by cloudns_api.sh dumpzone for every zone. However, dumpzone itself uses listzones to determine if the specified zone is a valid zone in the account. This means that calling dumpzone 20 times also calls listzones 20 times! That's a waste of API calls, particular in this case where we know the zone names are valid.

To fix this, I split the dump_zone function into two separate functions: dump_zone that does all the validation, and dump_zone_impl that actually does the zone export. dump_all_zones uses dump_zone_impl directly, as it does not need to perform any of the validation.

[tokiwinter]

Firstly, sorry this has taken an age for me to get to.

All good apart from one comment.

Thanks

[tokiwinter]

Could you please do something like:

if ! mkdir -p ${OUTPUT_DIR} >/dev/null 2>&1; then
  print_error "Unable to create output directory ${OUTPUT_DIR}"
  exit 1
fi

otherwise you'll end up with an unhandled error, best case a bunch of output files in the current directory, worst case a bunch of errors about not being able to write to some path.

Thanks!

[Daniel15]

Sure, I'll do that when I get some free time.

[Daniel15]

It's been a while, but I finally got around to updating this. Now it checks the return value of mkdir:

$ ./cloudns_api.sh dumpallzones /invalid-directory
Sun Apr 15 16:55:55 DST 2018: Error: Unable to create output directory /invalid-directory

Otherwise, when running normally, it outputs the name of each zone as it's dumped:

$ ./cloudns_api.sh dumpallzones /tmp/dns-zones
- d.sb
- dan.cx
- dan.net.au
...