* middleware/proxy
Use connection pooling for communicating with an upstream, instead of
opening a new socket every time.
This makes the proxy more efficient and allowed for some cleanups.
* Some cleanups
* Some fixes
* more
* Kill pool
* Add nil check
* remove pool
While looking into the proxy middleware it appears that there are
several golint messages:
```
ubuntu@ubuntu:~/coredns$ golint middleware/proxy/
middleware/proxy/lookup.go:66:1: exported method Proxy.Forward should have comment or be unexported
middleware/proxy/proxy.go:24:6: exported type Client should have comment or be unexported
middleware/proxy/proxy.go:107:1: exported function Clients should have comment or be unexported
middleware/proxy/reverseproxy.go:10:6: exported type ReverseProxy should have comment or be unexported
middleware/proxy/reverseproxy.go:16:1: exported method ReverseProxy.ServeDNS should have comment or be unexported
middleware/proxy/upstream.go:42:6: exported type Options should have comment or be unexported
```
This fix addressed the above golint messages.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Changes large parts of proxy lookup mechanism.
The duplicate zone checking erroneous added a nameserver for each
zone we are auth. for, creating to many backend hosts. So even when a
host was determined do be Down() we still got an (identical) new one
from the list.
The Down() and failure checking for upstream hosts had data race in the
uh.Fails check - we now use atomic.LoadInt32 for that.
Use and debug the test/server.go test servers implementation in the
TestStubLookup test to prevent going out to the internet.
Also delete the stub cycle test. That test was wrong and did not test
what it needed to be testing. Deleted for now.
