1 files changed, 193 insertions, 0 deletions
diff --git a/plugin/hosts/hostsfile.go b/plugin/hosts/hostsfile.go
new file mode 100644
index 000000000..91e828099
--- /dev/null
+++ b/plugin/hosts/hostsfile.go
@@ -0,0 +1,193 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a modified version of net/hosts.go from the golang repo
+
+package hosts
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"net"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coredns/coredns/plugin"
+)
+
+const cacheMaxAge = 5 * time.Second
+
+func parseLiteralIP(addr string) net.IP {
+	if i := strings.Index(addr, "%"); i >= 0 {
+		// discard ipv6 zone
+		addr = addr[0:i]
+	}
+
+	return net.ParseIP(addr)
+}
+
+func absDomainName(b string) string {
+	return plugin.Name(b).Normalize()
+}
+
+// Hostsfile contains known host entries.
+type Hostsfile struct {
+	sync.Mutex
+
+	// list of zones we are authoritive for
+	Origins []string
+
+	// Key for the list of literal IP addresses must be a host
+	// name. It would be part of DNS labels, a FQDN or an absolute
+	// FQDN.
+	// For now the key is converted to lower case for convenience.
+	byNameV4 map[string][]net.IP
+	byNameV6 map[string][]net.IP
+
+	// Key for the list of host names must be a literal IP address
+	// including IPv6 address with zone identifier.
+	// We don't support old-classful IP address notation.
+	byAddr map[string][]string
+
+	expire time.Time
+	path   string
+	mtime  time.Time
+	size   int64
+}
+
+// ReadHosts determines if the cached data needs to be updated based on the size and modification time of the hostsfile.
+func (h *Hostsfile) ReadHosts() {
+	now := time.Now()
+
+	if now.Before(h.expire) && len(h.byAddr) > 0 {
+		return
+	}
+	stat, err := os.Stat(h.path)
+	if err == nil && h.mtime.Equal(stat.ModTime()) && h.size == stat.Size() {
+		h.expire = now.Add(cacheMaxAge)
+		return
+	}
+
+	var file *os.File
+	if file, _ = os.Open(h.path); file == nil {
+		return
+	}
+	defer file.Close()
+
+	h.Parse(file)
+
+	// Update the data cache.
+	h.expire = now.Add(cacheMaxAge)
+	h.mtime = stat.ModTime()
+	h.size = stat.Size()
+}
+
+// Parse reads the hostsfile and populates the byName and byAddr maps.
+func (h *Hostsfile) Parse(file io.Reader) {
+	hsv4 := make(map[string][]net.IP)
+	hsv6 := make(map[string][]net.IP)
+	is := make(map[string][]string)
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Bytes()
+		if i := bytes.Index(line, []byte{'#'}); i >= 0 {
+			// Discard comments.
+			line = line[0:i]
+		}
+		f := bytes.Fields(line)
+		if len(f) < 2 {
+			continue
+		}
+		addr := parseLiteralIP(string(f[0]))
+		if addr == nil {
+			continue
+		}
+		ver := ipVersion(string(f[0]))
+		for i := 1; i < len(f); i++ {
+			name := absDomainName(string(f[i]))
+			if plugin.Zones(h.Origins).Matches(name) == "" {
+				// name is not in Origins
+				continue
+			}
+			switch ver {
+			case 4:
+				hsv4[name] = append(hsv4[name], addr)
+			case 6:
+				hsv6[name] = append(hsv6[name], addr)
+			default:
+				continue
+			}
+			is[addr.String()] = append(is[addr.String()], name)
+		}
+	}
+	h.byNameV4 = hsv4
+	h.byNameV6 = hsv6
+	h.byAddr = is
+}
+
+// ipVersion returns what IP version was used textually
+func ipVersion(s string) int {
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '.':
+			return 4
+		case ':':
+			return 6
+		}
+	}
+	return 0
+}
+
+// LookupStaticHostV4 looks up the IPv4 addresses for the given host from the hosts file.
+func (h *Hostsfile) LookupStaticHostV4(host string) []net.IP {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	if len(h.byNameV4) != 0 {
+		if ips, ok := h.byNameV4[absDomainName(host)]; ok {
+			ipsCp := make([]net.IP, len(ips))
+			copy(ipsCp, ips)
+			return ipsCp
+		}
+	}
+	return nil
+}
+
+// LookupStaticHostV6 looks up the IPv6 addresses for the given host from the hosts file.
+func (h *Hostsfile) LookupStaticHostV6(host string) []net.IP {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	if len(h.byNameV6) != 0 {
+		if ips, ok := h.byNameV6[absDomainName(host)]; ok {
+			ipsCp := make([]net.IP, len(ips))
+			copy(ipsCp, ips)
+			return ipsCp
+		}
+	}
+	return nil
+}
+
+// LookupStaticAddr looks up the hosts for the given address from the hosts file.
+func (h *Hostsfile) LookupStaticAddr(addr string) []string {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	addr = parseLiteralIP(addr).String()
+	if addr == "" {
+		return nil
+	}
+	if len(h.byAddr) != 0 {
+		if hosts, ok := h.byAddr[addr]; ok {
+			hostsCp := make([]string, len(hosts))
+			copy(hostsCp, hosts)
+			return hostsCp
+		}
+	}
+	return nil
+}