Replace the custom DNS servers used in the "forward" system test with
new code based on the isctest.asyncserver module.
For ans6, instead of configuring the responses to send at runtime, set
them up when the server is started. Make sure the server supports
toggling response sending at runtime to enable simulating forwarder
timeouts as required by one of the checks.
For ans11, put most of the responses to be provided by that server into
a zone file, only retaining code modifying zone-based answers in the
form of a response handler, to improve code readability. Use explicit
domain names instead of variables as that server only handles a single
domain and fixed strings improve readability in this case. Make sure
the server supports toggling response sending at runtime to enable
simulating forwarder timeouts as required by one of the checks.
Migrate sendcmd() and its uses to the new way of sending control queries
to custom servers used in system tests.
This commit converts the license handling to adhere to the REUSE
specification. It specifically:
1. Adds used licnses to LICENSES/ directory
2. Add "isc" template for adding the copyright boilerplate
3. Changes all source files to include copyright and SPDX license
header, this includes all the C sources, documentation, zone files,
configuration files. There are notes in the doc/dev/copyrights file
on how to add correct headers to the new files.
4. Handle the rest that can't be modified via .reuse/dep5 file. The
binary (or otherwise unmodifiable) files could have license places
next to them in <foo>.license file, but this would lead to cluttered
repository and most of the files handled in the .reuse/dep5 file are
system test files.
Since following a delegation resets most fetch context state, address
marks (FCTX_ADDRINFO_MARK) set inside lib/dns/resolver.c are not
preserved when a delegation is followed. This is fine for full
recursive resolution but when named is configured with "forward first;"
and one of the specified forwarders times out, triggering a fallback to
full recursive resolution, that forwarder should no longer be consulted
at each delegation point subsequently reached within a given fetch
context.
Add a new badnstype_t enum value, badns_forwarder, and use it to mark a
forwarder as bad when it times out in a "forward first;" configuration.
Since the bad server list is not cleaned when a fetch context follows a
delegation, this prevents a forwarder from being queried again after
falling back to full recursive resolution. Yet, as each fetch context
maintains its own list of bad servers, this change does not cause a
forwarder timeout to prevent that forwarder from being used by other
fetch contexts.
