Commits on Jul 18, 2017

1. call libc::res_init() in response to DNS failures …

   Go's DNS resolution often defers to the libc implementation, and glibc's
   resolver has a serious bug: https://sourceware.org/bugzilla/show_bug.cgi?id=984
   It will cache the contents of /etc/resolv.conf, which can put the client
   in a state where all DNS requests fail forever after a network change.
   The conditions where Go calls into libc are complicated and
   platform-specific, and the resolver cache involves thread-local state,
   so repros tend to be inconsistent. But when you hit this on your laptop
   on the subway or whatever, the effect is that everything is broken until
   you restart the process.
   
   One way to fix this would be to force using the pure-Go resolver
   (net.DefaultResolver.PreferGo = true), which refreshes /etc/resolv.conf
   every 5 seconds. I'm wary of doing that, because the Go devs went
   through an enormous amount of trouble to enable cgo fallback, for
   various platform- and environment-specific reasons. See all the comments
   in net/conf.go::initConfVal() and net/conf.go::hostLookupOrder() in the
   standard library.
   
   Instead, we're trying the same workaround that the Rust standard library
   chose, where we call libc::res_init() after DNS failures. See
   rust-lang/rust#41570. The downside here is
   that we have to remember to do this after we make network calls, and
   that we have to use cgo in the build, but the upside is that it should
   never break a DNS environment that was working before.

   

   oconnor663 committed Jul 18, 2017
   Configuration menu

   • View commit details
   • Copy full SHA for 9a3cbac
   • Browse repository at this point

   Copy the full SHA

   9a3cbac View commit details

   Browse the repository at this point in the history