plugins/inputs/dovecot: Add support for unix domain sockets (#9223)

It's safer for dovecot to export metrics via a UDS instead of tcp port,
this will add support for that option.

### Required for all PRs:

<!-- Complete the tasks in the following list. Change [ ] to [x] to
show completion. -->

- [x] Updated associated README.md.
- [x] Wrote appropriate unit tests.

resolves #9215 

dovecot: Add support for unix domain sockets as well

plugins/inputs/dovecot/README.md

@@ -14,6 +14,9 @@ the [upgrading steps][upgrading].
   ## specify dovecot servers via an address:port list
   ##  e.g.
   ##    localhost:24242
+  ## or as an UDS socket
+  ##  e.g.
+  ##    /var/run/dovecot/old-stats
   ##
   ## If no servers are specified, then localhost is used as the host.
   servers = ["localhost:24242"]

plugins/inputs/dovecot/dovecot.go

@@ -78,12 +78,20 @@ func (d *Dovecot) Gather(acc telegraf.Accumulator) error {
 }
 
 func (d *Dovecot) gatherServer(addr string, acc telegraf.Accumulator, qtype string, filter string) error {
-	_, _, err := net.SplitHostPort(addr)
-	if err != nil {
-		return fmt.Errorf("%q on url %s", err.Error(), addr)
+	var proto string
+
+	if strings.HasPrefix(addr, "/") {
+		proto = "unix"
+	} else {
+		proto = "tcp"
+
+		_, _, err := net.SplitHostPort(addr)
+		if err != nil {
+			return fmt.Errorf("%q on url %s", err.Error(), addr)
+		}
 	}
 
-	c, err := net.DialTimeout("tcp", addr, defaultTimeout)
+	c, err := net.DialTimeout(proto, addr, defaultTimeout)
 	if err != nil {
 		return fmt.Errorf("enable to connect to dovecot server '%s': %s", addr, err)
 	}
@@ -108,7 +116,12 @@ func (d *Dovecot) gatherServer(addr string, acc telegraf.Accumulator, qtype stri
 		return fmt.Errorf("copying message failed for dovecot server '%s': %s", addr, err)
 	}
 
-	host, _, _ := net.SplitHostPort(addr)
+	var host string
+	if strings.HasPrefix(addr, "/") {
+		host = addr
+	} else {
+		host, _, _ = net.SplitHostPort(addr)
+	}
 
 	return gatherStats(&buf, acc, host, qtype)
 }

plugins/inputs/dovecot/dovecot_test.go

@@ -1,7 +1,12 @@
 package dovecot
 
 import (
+	"bufio"
 	"bytes"
+	"io"
+	"net"
+	"net/textproto"
+	"os"
 	"testing"
 	"time"
 
@@ -42,11 +47,49 @@ func TestDovecotIntegration(t *testing.T) {
 
 	var acc testutil.Accumulator
 
+	// Test type=global server=unix
+	addr := "/tmp/socket"
+	wait := make(chan int)
+	go func() {
+		defer close(wait)
+
+		la, err := net.ResolveUnixAddr("unix", addr)
+		require.NoError(t, err)
+
+		l, err := net.ListenUnix("unix", la)
+		require.NoError(t, err)
+		defer l.Close()
+		defer os.Remove(addr)
+
+		wait <- 0
+		conn, err := l.Accept()
+		require.NoError(t, err)
+		defer conn.Close()
+
+		readertp := textproto.NewReader(bufio.NewReader(conn))
+		_, err = readertp.ReadLine()
+		require.NoError(t, err)
+
+		buf := bytes.NewBufferString(sampleGlobal)
+		_, err = io.Copy(conn, buf)
+		require.NoError(t, err)
+	}()
+
+	// Wait for server to start
+	<-wait
+
+	d := &Dovecot{Servers: []string{addr}, Type: "global"}
+	err := d.Gather(&acc)
+	require.NoError(t, err)
+
+	tags := map[string]string{"server": addr, "type": "global"}
+	acc.AssertContainsTaggedFields(t, "dovecot", fields, tags)
+
 	// Test type=global
-	tags := map[string]string{"server": "dovecot.test", "type": "global"}
+	tags = map[string]string{"server": "dovecot.test", "type": "global"}
 	buf := bytes.NewBufferString(sampleGlobal)
 
-	err := gatherStats(buf, &acc, "dovecot.test", "global")
+	err = gatherStats(buf, &acc, "dovecot.test", "global")
 	require.NoError(t, err)
 
 	acc.AssertContainsTaggedFields(t, "dovecot", fields, tags)