tree aeee8fbf90e9e7044284a16cbdf08152f36fe710
parent ba2fdce6739b74c4150ef365e8e7af9c78d5b8a6
author Xiaochu Liu <xiaochu@chromium.org> 1562863866 -0700
committer Commit Bot <commit-bot@chromium.org> 1563567220 +0000

update_engine: call res_init and retry one extra time on unresolved host
libcurl error

Based on https://curl.haxx.se/docs/todo.html#updated_DNS_server_while_running:

"If /etc/resolv.conf gets updated while a program using libcurl is running, it
may cause name resolves to fail unless res_init() is called. We should
consider calling res_init() + retry once unconditionally on all name resolve
failures to mitigate against this."

This CL added following behavior:
On libcurl returns CURLE_COULDNT_RESOLVE_HOST error code:
1. we increase the max retry count by 1 for the first time it happens in the
lifetime of an LibcurlHttpFetcher object.
2. we call res_init unconditionally.

We also add UMA metrics to measure whether calling res_init helps
mitigate the unresolved host problem. WIP CL: https://chromium-review.googlesource.com/c/chromium/src/+/1698722

BUG=chromium:982813
TEST=FEATURES="test" emerge-kefka update_engine, tested on a device

Change-Id: Ia894eae93b3a0adbac1a831e657b75cba835dfa0