plugin/host: parse file without holding lock (#2270)

* plugin/host: parse file without holding lock

Parse first and then swap the maps *while* holding the lock.

Signed-off-by: Miek Gieben <miek@miek.nl>

* add back in the parse function, but now purely for testing

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/hosts/hosts_test.go

@@ -2,6 +2,7 @@ package hosts
 
 import (
 	"context"
+	"io"
 	"strings"
 	"testing"
 
@@ -11,6 +12,8 @@ import (
 	"github.com/miekg/dns"
 )
 
+func (h *Hostsfile) parseReader(r io.Reader) { h.hmap = h.parse(r, h.inline) }
+
 func TestLookupA(t *testing.T) {
 	h := Hosts{Next: test.ErrorHandler(), Hostsfile: &Hostsfile{Origins: []string{"."}}}
 	h.parseReader(strings.NewReader(hostsExample))