support host port split of template functions

docs/07.Reference/7.02.Filters.md

@@ -2097,6 +2097,9 @@ package, and extra functions defined by Easegress:
   a URL query, equivalent to the `urlquery` template function.
 * **urlQueryUnescape**: performs the inverse transformation of `urlQueryEscape`,
   decoding a URL-encoded string back to its origin form.
+* **host**: host splits a network address of the form "host:port" and return host part by using `net.SplitHostPort`.
+* **port**: port splits a network address of the form "host:port" and return port part by using `net.SplitHostPort`.
+
 
 Easegress injects existing requests/responses of the current context into
 the template engine at runtime, so we can use `.requests.<namespace>.<field>`

pkg/filters/builder/extrafuncs.go

@@ -20,6 +20,7 @@ package builder
 import (
 	"encoding/json"
 	"fmt"
+	"net"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -156,6 +157,16 @@ var extraFuncs = template.FuncMap{
 		return username
 	},
 
+	"host": func(hostPort string) string {
+		addr, _, _ := net.SplitHostPort(hostPort)
+		return addr
+	},
+
+	"port": func(hostPort string) string {
+		_, port, _ := net.SplitHostPort(hostPort)
+		return port
+	},
+
 	"urlQueryUnescape": func(s string) string {
 		unescapedStr, err := url.QueryUnescape(s)
 		if err != nil {