Add more Go template functions

README.md

@@ -72,17 +72,17 @@ You can tell logspout to only include certain containers by setting filter param
 		--volume=/var/run/docker.sock:/var/run/docker.sock \
 		gliderlabs/logspout \
 		raw://192.168.10.10:5000?filter.name=*_db
-	
+
 	$ docker run \
 		--volume=/var/run/docker.sock:/var/run/docker.sock \
 		gliderlabs/logspout \
 		raw://192.168.10.10:5000?filter.id=3b6ba57db54a
-	
+
 	$ docker run \
 		--volume=/var/run/docker.sock:/var/run/docker.sock \
 		gliderlabs/logspout \
 		raw://192.168.10.10:5000?filter.sources=stdout%2Cstderr
-	
+
 	# Forward logs from containers with both label 'a' starting with 'x', and label 'b' ending in 'y'.
 	$ docker run \
 		--volume=/var/run/docker.sock:/var/run/docker.sock \
@@ -201,6 +201,15 @@ If you use multiline logging with raw, it's recommended to json encode the Data
 * `MULTILINE_FLUSH_AFTER` - maximum time between the first and last lines of a multiline log entry in milliseconds (default: 500)
 * `MULTILINE_SEPARATOR` - separator between lines for output (default: `\n`)
 
+##### Built-in Template Functions
+
+There are a few built in functions as well:
+
+* `join $string[] $sep` - Join concatenates the elements of a to create a single string. The separator string sep is placed between elements in the resulting string. Alias for [`strings.Join`][go.string.Join]. `{{ join . "-"}}`
+* `replace $string $old $new $count` - Replaces all occurrences of a string within another string. Alias for [`strings.Replace`][go.string.Replace]. `{{ replace .Container.Config.Hostname "-" "_" -1 }}`
+* `split $string $sep` - Splits a string into an array using a separator string. Alias for [`strings.Split`][go.string.Split]. `{{ split .Container.Config.Hostname "." }}`
+
+
 #### Raw Format
 
 The raw adapter has a function `toJSON` that can be used to format the message/fields to generate JSON-like output in a simple way, or full JSON output.
@@ -286,7 +295,7 @@ docker stack deploy --compose-file <name of your compose file> STACK
 ```
 
 More information about services and their mode of deployment can be found here:
-https://docs.docker.com/engine/swarm/how-swarm-mode-works/services/ 
+https://docs.docker.com/engine/swarm/how-swarm-mode-works/services/
 
 ### TLS Settings
 logspout supports modification of the client TLS settings via environment variables described below:

adapters/syslog/syslog.go

@@ -27,6 +27,12 @@ var (
 	econnResetErrStr string
 )
 
+var funcs = template.FuncMap{
+	"join": strings.Join,
+	"replace":  strings.Replace,
+	"split": strings.Split,
+}
+
 func init() {
 	hostname, _ = os.Hostname()
 	econnResetErrStr = fmt.Sprintf("write: %s", syscall.ECONNRESET.Error())
@@ -108,7 +114,7 @@ func NewSyslogAdapter(route *router.Route) (router.LogAdapter, error) {
 	default:
 		return nil, errors.New("unsupported syslog format: " + format)
 	}
-	tmpl, err := template.New("syslog").Parse(tmplStr)
+	tmpl, err := template.New("syslog").Funcs(funcs).Parse(tmplStr)
 	if err != nil {
 		return nil, err
 	}

adapters/syslog/syslog_test.go

@@ -13,6 +13,7 @@ import (
 	"testing"
 	"text/template"
 	"time"
+	"bytes"
 
 	_ "github.com/gliderlabs/logspout/transports/tcp"
 	_ "github.com/gliderlabs/logspout/transports/tls"
@@ -99,6 +100,64 @@ func TestSyslogReconnectOnClose(t *testing.T) {
 	}
 }
 
+func TestSyslogReplaceFunc(t *testing.T) {
+	in := "{{ replace \"oink oink oink\" \"k\" \"ky\" 2}}"
+	os.Setenv("SYSLOG_STRUCTURED_DATA", in)
+	adapter, err := newDummyAdapter()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	out := new(bytes.Buffer)
+	err = adapter.(*Adapter).tmpl.Execute(out, "")
+
+	if err != nil {
+		log.Fatalf("template error: %s\n", err)
+	}
+
+	expected := "<PRIORITY>1 TIMESTAMP HOSTNAME TAG PID - [oinky oinky oink] DATA\n"
+	check(t, adapter.(*Adapter).tmpl, expected, out.String())
+}
+
+func TestSyslogJoinFunc(t *testing.T) {
+	array := []string{"foo", "bar"}
+	in := "{{ join . \"-\" }}"
+	os.Setenv("SYSLOG_STRUCTURED_DATA", in)
+	adapter, err := newDummyAdapter()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	out := new(bytes.Buffer)
+	err = adapter.(*Adapter).tmpl.Execute(out, array)
+
+	if err != nil {
+		log.Fatalf("template error: %s\n", err)
+	}
+
+	expected :=  "<PRIORITY>1 TIMESTAMP HOSTNAME TAG PID - [foo-bar] DATA\n"
+	check(t, adapter.(*Adapter).tmpl, expected, out.String())
+}
+
+func TestSyslogSplitFunc(t *testing.T) {
+	in := "{{ index (split \"foo/bar\" \"/\") 1 }}"
+	os.Setenv("SYSLOG_STRUCTURED_DATA", in)
+	adapter, err := newDummyAdapter()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	out := new(bytes.Buffer)
+	err = adapter.(*Adapter).tmpl.Execute(out, "")
+
+	if err != nil {
+		log.Fatalf("template error: %s\n", err)
+	}
+
+	expected := "<PRIORITY>1 TIMESTAMP HOSTNAME TAG PID - [bar] DATA\n"
+	check(t, adapter.(*Adapter).tmpl, expected, out.String())
+}
+
 func TestHostnameDoesNotHaveLineFeed(t *testing.T) {
 	if err := ioutil.WriteFile(hostHostnameFilename, []byte(badHostnameContent), 0777); err != nil {
 		t.Fatal(err)
@@ -109,6 +168,22 @@ func TestHostnameDoesNotHaveLineFeed(t *testing.T) {
 	}
 }
 
+func newDummyAdapter()(router.LogAdapter, error) {
+	os.Setenv("SYSLOG_PRIORITY", "PRIORITY")
+	os.Setenv("SYSLOG_TIMESTAMP", "TIMESTAMP")
+	os.Setenv("SYSLOG_PID", "PID")
+	os.Setenv("SYSLOG_HOSTNAME", "HOSTNAME")
+	os.Setenv("SYSLOG_TAG", "TAG")
+	os.Setenv("SYSLOG_DATA", "DATA")
+	done := make(chan string)
+	addr, sock, srvWG := startServer("tcp", "", done)
+	defer srvWG.Wait()
+	defer os.Remove(addr)
+	defer sock.Close()
+	route := &router.Route{Adapter: "syslog+tcp", Address: addr}
+	return NewSyslogAdapter(route)
+}
+
 func startServer(n, la string, done chan<- string) (addr string, sock io.Closer, wg *sync.WaitGroup) {
 	if n == "udp" || n == "tcp" {
 		la = "127.0.0.1:0"