CFE-3478: Add docs entry for isvalidip policy function

content/reference/functions/isvalidip.markdown

@@ -0,0 +1,69 @@
+---
+layout: default
+title: isvalidip
+aliases:
+  - "/reference-functions-isvalidip.html"
+---
+
+{{< CFEngine_function_prototype(address, version) >}}
+
+**Description:** Returns whether `address` is a valid IPv4 or IPv6 address.
+An optional second argument `version`, either `"ipv4"` or `"ipv6"`, restricts
+which IP version is accepted. By default, both are accepted.
+
+The whole string must be an IP address:
+
+- An IPv4 address consists of exactly four decimal numbers from 0 to 255,
+  separated by dots, e.g. `192.168.1.10`.
+- An IPv6 address consists of eight groups of 1 to 4 hexadecimal digits,
+  separated by colons, e.g. `2001:0db8:0000:0000:0000:0000:0000:0001`. One
+  sequence of zero groups may be shortened to `::`, e.g. `2001:db8::1`, and
+  the last two groups may be written as an IPv4 address, e.g.
+  `::ffff:192.0.2.128`.
+
+Host names, surrounding whitespace, ports (`1.2.3.4:80`), brackets
+(`[::1]`), subnet masks (`10.0.0.0/8`) and zone IDs (`fe80::1%eth0`) are not
+accepted.
+
+{{< CFEngine_function_attributes(address, version) >}}
+
+**Example:**
+
+```cfengine3
+bundle agent main
+{
+  vars:
+    "candidates"
+      slist => {
+        "1.2.3.4", "300.123.123.1", "FE80:CD00:0000:0CDE:1257:0000:211E:729C"
+      };
+
+  reports:
+    "'$(candidates)' is a valid IP address" if => isvalidip("$(candidates)");
+
+    "'$(candidates)' is a valid IPv4 address"
+      if => isvalidip("$(candidates)", "ipv4");
+
+    "'$(candidates)' is a valid IPv6 address"
+      if => isvalidip("$(candidates)", "ipv6");
+
+    "'$(candidates)' is not a valid IP address"
+      unless => isvalidip("$(candidates)");
+}
+```
+
+Output:
+
+```
+R: '1.2.3.4' is a valid IP address
+R: 'FE80:CD00:0000:0CDE:1257:0000:211E:729C' is a valid IP address
+R: '1.2.3.4' is a valid IPv4 address
+R: 'FE80:CD00:0000:0CDE:1257:0000:211E:729C' is a valid IPv6 address
+R: '300.123.123.1' is not a valid IP address
+```
+
+**See also:** `isipinsubnet()`, `iprange()`, `host2ip()`
+
+**History:**
+
+- Function added in 3.30.0.