add stripDomain to template function (#10475)

* add stripDomain to template function

Signed-off-by: Ziqi Zhao <zzqwf12345@163.com>

docs/configuration/template_reference.md

@@ -76,6 +76,7 @@ versions.
 | graphLink  | expr | string | Returns path to graph view in the [expression browser](https://prometheus.io/docs/visualization/browser/) for the expression. |
 | tableLink  | expr | string | Returns path to tabular ("Table") view in the [expression browser](https://prometheus.io/docs/visualization/browser/) for the expression. |
 | parseDuration | string | float | Parses a duration string such as "1h" into the number of seconds it represents. |
+| stripDomain | string | string | Removes the domain part of a FQDN. Leaves port untouched. |
 
 ### Others
 

template/template.go

@@ -196,6 +196,21 @@ func NewTemplateExpander(
 				}
 				return host
 			},
+			"stripDomain": func(hostPort string) string {
+				host, port, err := net.SplitHostPort(hostPort)
+				if err != nil {
+					host = hostPort
+				}
+				ip := net.ParseIP(host)
+				if ip != nil {
+					return hostPort
+				}
+				host = strings.Split(host, ".")[0]
+				if port != "" {
+					return net.JoinHostPort(host, port)
+				}
+				return host
+			},
 			"humanize": func(i interface{}) (string, error) {
 				v, err := convertToFloat(i)
 				if err != nil {

template/template_test.go

@@ -480,6 +480,41 @@ func TestTemplateExpansion(t *testing.T) {
 			text:   "{{ printf \"%0.2f\" (parseDuration \"1h2m10ms\") }}",
 			output: "3720.01",
 		},
+		{
+			// Simple hostname.
+			text:   "{{ \"foo.example.com\" | stripDomain }}",
+			output: "foo",
+		},
+		{
+			// Hostname with port.
+			text:   "{{ \"foo.example.com:12345\" | stripDomain }}",
+			output: "foo:12345",
+		},
+		{
+			// Simple IPv4 address.
+			text:   "{{ \"192.0.2.1\" | stripDomain }}",
+			output: "192.0.2.1",
+		},
+		{
+			// IPv4 address with port.
+			text:   "{{ \"192.0.2.1:12345\" | stripDomain }}",
+			output: "192.0.2.1:12345",
+		},
+		{
+			// Simple IPv6 address.
+			text:   "{{ \"2001:0DB8::1\" | stripDomain }}",
+			output: "2001:0DB8::1",
+		},
+		{
+			// IPv6 address with port.
+			text:   "{{ \"[2001:0DB8::1]:12345\" | stripDomain }}",
+			output: "[2001:0DB8::1]:12345",
+		},
+		{
+			// Value can't be split into host and port.
+			text:   "{{ \"[2001:0DB8::1]::12345\" | stripDomain }}",
+			output: "[2001:0DB8::1]::12345",
+		},
 	})
 }