memcached plugin: support unix sockets

closes #415

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Features
 - [#412](https://github.com/influxdb/telegraf/pull/412): Additional memcached stats. Thanks @mgresser!
 - [#410](https://github.com/influxdb/telegraf/pull/410): Additional redis metrics. Thanks @vlaadbrain!
+- [#415](https://github.com/influxdb/telegraf/issues/415): memcached plugin: support unix sockets
 
 ### Bugfixes
 - [#405](https://github.com/influxdb/telegraf/issues/405): Prometheus output cardinality issue

plugins/memcached/memcached.go

@@ -13,15 +13,17 @@ import (
 
 // Memcached is a memcached plugin
 type Memcached struct {
-	Servers []string
+	Servers     []string
+	UnixSockets []string
 }
 
 var sampleConfig = `
   # An array of address to gather stats about. Specify an ip on hostname
   # with optional port. ie localhost, 10.0.0.1:11211, etc.
   #
   # If no servers are specified, then localhost is used as the host.
-  servers = ["localhost"]
+  servers = ["localhost:11211"]
+  # unix_sockets = ["/var/run/memcached.sock"]
 `
 
 var defaultTimeout = 5 * time.Second
@@ -68,31 +70,49 @@ func (m *Memcached) Description() string {
 
 // Gather reads stats from all configured servers accumulates stats
 func (m *Memcached) Gather(acc plugins.Accumulator) error {
-	if len(m.Servers) == 0 {
+	if len(m.Servers) == 0 && len(m.UnixSockets) == 0 {
 		return m.gatherServer(":11211", acc)
 	}
 
 	for _, serverAddress := range m.Servers {
-		if err := m.gatherServer(serverAddress, acc); err != nil {
+		if err := m.gatherServer(serverAddress, false, acc); err != nil {
+			return err
+		}
+	}
+
+	for _, unixAddress := range m.UnixSockets {
+		if err := m.gatherServer(unixAddress, true, acc); err != nil {
 			return err
 		}
 	}
 
 	return nil
 }
 
-func (m *Memcached) gatherServer(address string, acc plugins.Accumulator) error {
-	_, _, err := net.SplitHostPort(address)
-	if err != nil {
-		address = address + ":11211"
-	}
+func (m *Memcached) gatherServer(
+	address string,
+	unix bool,
+	acc plugins.Accumulator,
+) error {
+	var conn net.Conn
+	if unix {
+		conn, err := net.DialTimeout("unix", address, defaultTimeout)
+		if err != nil {
+			return err
+		}
+		defer conn.Close()
+	} else {
+		_, _, err := net.SplitHostPort(address)
+		if err != nil {
+			address = address + ":11211"
+		}
 
-	// Connect
-	conn, err := net.DialTimeout("tcp", address, defaultTimeout)
-	if err != nil {
-		return err
+		conn, err = net.DialTimeout("tcp", address, defaultTimeout)
+		if err != nil {
+			return err
+		}
+		defer conn.Close()
 	}
-	defer conn.Close()
 
 	// Extend connection
 	conn.SetDeadline(time.Now().Add(defaultTimeout))