Hi Alex, On 08/06/18 01:57, Alex Zorin via Unbound-users wrote: > Hello, > > I'm using libunbound to perform iterative DNS lookups for a diagnostic > service: github.com/letsdebug/letsdebug . > > One of the problems I have is when one or more of a domain's authoritative > nameservers are timing out, ub_resolve takes an incredibly long time to give > up, something like ~10 minutes when the ub_ctx is configured with these > options:
If a timeout is needed, set a timeout. So the code calling libunbound sets the timeout it wants. And then cancels or ignores the return value of the lookup. For example, use ub_resolve_async(), and then ub_fd(ctx) put that file descriptor in select or poll, with a timeout that you want to select or poll. So, sketching code that would look like this: ub_resolve_async(ctx, name, type, class, 0, funcwhendone, &async_id); struct pollfd fds[1]; fds[0].fd = ub_fd(ctx); fds[0].events = POLLIN; fds[0].revents = 0; int r = poll(fds, 1, 180 * 1000); if(r == 0) /* timeout */ else if(r == -1) /* poll has a system error */ else ub_process(ctx); /* calls funcwhendone */ At timeout you could call ub_cancel(ctx, async_id) or just ignore the result when funcwhendone gets called (eventually). Or delete the context, you say you only use it once, this also removes that callback. Best regards, Wouter > > > https://github.com/letsdebug/letsdebug/blob/e56f10a5741445645c44a6d6683b9f085f657999/dns_util.go#L84-L116 > > I've tried to grok the meaning of > https://www.unbound.net/documentation/info_timeout.html but I'm not seeing > the solution after some weeks of pondering the problem.. > > Ideally I would like to place a deadline of something like 180 seconds on the > ub_resolve operation. I am using a fresh ub_ctx for each lookup, which is > done to avoid sharing any resolver state between lookups. > > Do you have any further guidance on the ability to restrict ub_resolve's > runtime? > > Thanks! > Alex >
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