From 74e5b596da3a76a71671a182e3f0d56c687f2bcc Mon Sep 17 00:00:00 2001
From: Ziqi Zhao <zhaoziqi9146@gmail.com>
Date: Wed, 27 Apr 2022 17:30:05 +0800
Subject: [PATCH] add stripDomain to template function (#10475)

* add stripDomain to template function

Signed-off-by: Ziqi Zhao <zzqwf12345@163.com>
---
 docs/configuration/template_reference.md |  1 +
 template/template.go                     | 15 ++++++++++
 template/template_test.go                | 35 ++++++++++++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/docs/configuration/template_reference.md b/docs/configuration/template_reference.md
index 34557ecd8..5c96ee597 100644
--- a/docs/configuration/template_reference.md
+++ b/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
 
diff --git a/template/template.go b/template/template.go
index 696263998..4058ad3ae 100644
--- a/template/template.go
+++ b/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 {
diff --git a/template/template_test.go b/template/template_test.go
index 342a95112..45d1a66e7 100644
--- a/template/template_test.go
+++ b/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",
+		},
 	})
 }