Update docs

- Add an option for specifying a Libreswan version to install,
  using variable VPN_SWAN_VER. Currently supported values are
  4.15 and 5.0. This could be useful for users who want to
  install the older Libreswan version 4.

README-zh.md

@@ -162,6 +162,20 @@ https://gitlab.com/hwdsl2/setup-ipsec-vpn/-/raw/master/vpnsetup.sh
 
 如果无法下载，打开 [vpnsetup.sh](vpnsetup.sh)，然后点击右边的 `Raw` 按钮。按快捷键 `Ctrl/Cmd+A` 全选，`Ctrl/Cmd+C` 复制，然后粘贴到你喜欢的编辑器。
 </details>
+<details>
+<summary>
+我需要安装较旧版本的 Libreswan 版本 4。
+</summary>
+
+一般建议使用最新的 [Libreswan](https://libreswan.org/) 版本 5，它是本项目的默认版本。但是，如果你想要安装较旧版本的 Libreswan 版本 4：
+
+```bash
+wget https://get.vpnsetup.net -O vpn.sh
+sudo VPN_SWAN_VER=4.15 sh vpn.sh
+```
+
+**注：** 如果 Libreswan 版本 5 已经安装，你可能需要首先[卸载 VPN](docs/uninstall-zh.md)，然后安装 Libreswan 版本 4。或者，你也可以下载[升级脚本](#升级libreswan)，编辑它并指定 `SWAN_VER=4.15`，然后运行脚本。
+</details>
 
 ## 自定义 VPN 选项
 

README.md

@@ -162,6 +162,20 @@ https://gitlab.com/hwdsl2/setup-ipsec-vpn/-/raw/master/vpnsetup.sh
 
 If you are unable to download, open [vpnsetup.sh](vpnsetup.sh), then click the `Raw` button on the right. Press `Ctrl/Cmd+A` to select all, `Ctrl/Cmd+C` to copy, then paste into your favorite editor.
 </details>
+<details>
+<summary>
+I want to install the older Libreswan version 4.
+</summary>
+
+It is generally recommended to use the latest [Libreswan](https://libreswan.org/) version 5, which is the default version in this project. However, if you want to install the older Libreswan version 4:
+
+```bash
+wget https://get.vpnsetup.net -O vpn.sh
+sudo VPN_SWAN_VER=4.15 sh vpn.sh
+```
+
+**Note:** If Libreswan version 5 is already installed, you may need to first [Uninstall the VPN](docs/uninstall.md) before installing Libreswan version 4. Alternatively, download the [update script](#upgrade-libreswan), edit it to specify `SWAN_VER=4.15`, then run the script.
+</details>
 
 ## Customize VPN options
 

vpnsetup.sh

@@ -280,7 +280,7 @@ run_setup() {
       VPN_DNS_NAME="$VPN_DNS_NAME" VPN_CLIENT_NAME="$VPN_CLIENT_NAME" \
       VPN_PROTECT_CONFIG="$VPN_PROTECT_CONFIG" \
       VPN_CLIENT_VALIDITY="$VPN_CLIENT_VALIDITY" \
-      VPN_SKIP_IKEV2="$VPN_SKIP_IKEV2" \
+      VPN_SKIP_IKEV2="$VPN_SKIP_IKEV2" VPN_SWAN_VER="$VPN_SWAN_VER" \
       /bin/bash "$tmpdir/vpn.sh" || status=1
     else
       status=1

vpnsetup_alpine.sh

@@ -248,6 +248,18 @@ get_swan_ver() {
   if printf '%s' "$swan_ver_latest" | grep -Eq '^([3-9]|[1-9][0-9]{1,2})(\.([0-9]|[1-9][0-9]{1,2})){1,2}$'; then
     SWAN_VER="$swan_ver_latest"
   fi
+  if [ -n "$VPN_SWAN_VER" ]; then
+    if ! printf '%s\n%s' "4.15" "$VPN_SWAN_VER" | sort -C -V \
+      || ! printf '%s\n%s' "$VPN_SWAN_VER" "$SWAN_VER" | sort -C -V; then
+cat 1>&2 <<EOF
+Error: Libreswan version '$VPN_SWAN_VER' is not supported.
+       This script can install Libreswan 4.15+ or $SWAN_VER.
+EOF
+      exit 1
+    else
+      SWAN_VER="$VPN_SWAN_VER"
+    fi
+  fi
 }
 
 check_libreswan() {

vpnsetup_amzn.sh

@@ -266,6 +266,18 @@ get_swan_ver() {
   if printf '%s' "$swan_ver_latest" | grep -Eq '^([3-9]|[1-9][0-9]{1,2})(\.([0-9]|[1-9][0-9]{1,2})){1,2}$'; then
     SWAN_VER="$swan_ver_latest"
   fi
+  if [ -n "$VPN_SWAN_VER" ]; then
+    if ! printf '%s\n%s' "4.15" "$VPN_SWAN_VER" | sort -C -V \
+      || ! printf '%s\n%s' "$VPN_SWAN_VER" "$SWAN_VER" | sort -C -V; then
+cat 1>&2 <<EOF
+Error: Libreswan version '$VPN_SWAN_VER' is not supported.
+       This script can install Libreswan 4.15+ or $SWAN_VER.
+EOF
+      exit 1
+    else
+      SWAN_VER="$VPN_SWAN_VER"
+    fi
+  fi
 }
 
 check_libreswan() {

vpnsetup_centos.sh

@@ -368,6 +368,18 @@ get_swan_ver() {
   if printf '%s' "$swan_ver_latest" | grep -Eq '^([3-9]|[1-9][0-9]{1,2})(\.([0-9]|[1-9][0-9]{1,2})){1,2}$'; then
     SWAN_VER="$swan_ver_latest"
   fi
+  if [ -n "$VPN_SWAN_VER" ]; then
+    if ! printf '%s\n%s' "4.15" "$VPN_SWAN_VER" | sort -C -V \
+      || ! printf '%s\n%s' "$VPN_SWAN_VER" "$SWAN_VER" | sort -C -V; then
+cat 1>&2 <<EOF
+Error: Libreswan version '$VPN_SWAN_VER' is not supported.
+       This script can install Libreswan 4.15+ or $SWAN_VER.
+EOF
+      exit 1
+    else
+      SWAN_VER="$VPN_SWAN_VER"
+    fi
+  fi
 }
 
 check_libreswan() {

vpnsetup_ubuntu.sh

@@ -321,6 +321,18 @@ get_swan_ver() {
   if printf '%s' "$swan_ver_latest" | grep -Eq '^([3-9]|[1-9][0-9]{1,2})(\.([0-9]|[1-9][0-9]{1,2})){1,2}$'; then
     SWAN_VER="$swan_ver_latest"
   fi
+  if [ -n "$VPN_SWAN_VER" ]; then
+    if ! printf '%s\n%s' "4.15" "$VPN_SWAN_VER" | sort -C -V \
+      || ! printf '%s\n%s' "$VPN_SWAN_VER" "$SWAN_VER" | sort -C -V; then
+cat 1>&2 <<EOF
+Error: Libreswan version '$VPN_SWAN_VER' is not supported.
+       This script can install Libreswan 4.15+ or $SWAN_VER.
+EOF
+      exit 1
+    else
+      SWAN_VER="$VPN_SWAN_VER"
+    fi
+  fi
 }
 
 check_libreswan() {