Allow config & checking of nameserver rotation option #48
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Fix up a couple of problems with configuring whether c-ares rotates between different name servers between requests. Firstly, ares_save_options() returns (in *optmask) the value of (channel->optmask & ARES_OPT_ROTATE), which doesn't necessarily indicate whether the channel is or is not actually doing rotation. This can be confusing/incorrect if: - the channel was originally configured without ARES_OPT_ROTATE (so it appears that the channel is not rotating) - the /etc/resolv.conf file includes the 'rotate' option (so the channel is actually performing rotation). Secondly, it is not possible to reliably configure a channel to not-rotate; leaving off ARES_OPT_ROTATE is not enough, since a 'rotate' option in /etc/resolv.conf will turn it on again. Therefore: - add an ARES_OPT_NOROTATE optmask value to allow explicit configuration of no-rotate behaviour - in ares_save_options(), report the value of channel->rotate as exactly one of (optmask & ARES_OPT_ROTATE) or (optmask & ARES_OPT_NOROTATE). In terms of back-compatibility: - existing apps that set ARES_OPT_ROTATE will continue to rotate, and to have ARES_OPT_ROTATE reported back from ares_save_options() - existing apps that don't set ARES_OPT_ROTATE will continue to use local config/defaults to decide whether to rotate, and will now get ARES_OPT_ROTATE or ARES_OPT_NOROTATE reported back from ares_save_options() rather than 0.
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Any thoughts? |
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The only thought I have about this, is if I think it looks like most of the existing code does the latter: it stores the current state. That seems to match what your patch here does, which makes 👍 it. |
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For discussion, particular around whether this is suitably back-compatible.