wireguard: Config.WriteTo()

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/wireguard/config.go

@@ -1,17 +1,40 @@
 package wireguard
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"net/netip"
 	"strconv"
 	"strings"
+	"text/template"
 
 	"darvaza.org/core"
 	"gopkg.in/gcfg.v1"
 )
 
+var configTemplate = template.Must(template.New("config").Funcs(template.FuncMap{
+	"PrefixJoin": func(a []netip.Prefix, sep string) string {
+		s := make([]string, len(a))
+		for i, p := range a {
+			s[i] = p.String()
+		}
+		return strings.Join(s, sep)
+	},
+}).Parse(`[Interface]
+Address = {{.Interface.Address}}
+PrivateKey = {{.Interface.PrivateKey}}
+ListenPort = {{.Interface.ListenPort}}
+{{- range .Peer }}
+
+[Peer]
+PublicKey = {{.PublicKey}}
+Endpoint = {{.Endpoint}}
+AllowedIPs = {{ PrefixJoin .AllowedIPs ", "}}
+{{- end }}
+`))
+
 // Config represents a wgN.conf file
 type Config struct {
 	Interface InterfaceConfig
@@ -28,6 +51,17 @@ func (f *Config) Peers() int {
 	return len(f.Peer)
 }
 
+// WriteTo writes a Wireguard [Config] onto the provided [io.Writer]
+func (f *Config) WriteTo(w io.Writer) (int64, error) {
+	var buf bytes.Buffer
+
+	if err := configTemplate.Execute(&buf, f); err != nil {
+		return 0, err
+	}
+
+	return buf.WriteTo(w)
+}
+
 // InterfaceConfig represents the [Interface] section
 type InterfaceConfig struct {
 	Address    netip.Addr