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))

plugin/hosts/hostsfile.go

@@ -106,13 +106,17 @@ func (h *Hostsfile) readHosts() {
 		return
 	}
 
+	newMap := h.parse(file, h.inline)
+	log.Debugf("Parsed hosts file into %d entries", newMap.Len())
+
 	h.Lock()
-	defer h.Unlock()
-	h.parseReader(file)
 
+	h.hmap = newMap
 	// Update the data cache.
 	h.mtime = stat.ModTime()
 	h.size = stat.Size()
+
+	h.Unlock()
 }
 
 func (h *Hostsfile) initInline(inline []string) {
@@ -125,12 +129,6 @@ func (h *Hostsfile) initInline(inline []string) {
 	*h.hmap = *h.inline
 }
 
-func (h *Hostsfile) parseReader(r io.Reader) {
-	h.hmap = h.parse(r, h.inline)
-
-	log.Debugf("Parsed hosts file into %d entries", h.hmap.Len())
-}
-
 // Parse reads the hostsfile and populates the byName and byAddr maps.
 func (h *Hostsfile) parse(r io.Reader, override *hostsMap) *hostsMap {
 	hmap := newHostsMap()