feat: rebase static IP on gateway change

README.md

@@ -12,6 +12,7 @@
 - 多种打印机驱动可选
 - 驱动管理器（默认仅允许内网访问）
 - 网络和打印服务守护（断网自动切 DHCP，CUPS 卡死自动恢复）
+- 静态 IP 支持网关变更自愈：先切 DHCP，再按原静态 IP 尾号迁移到新网段
 - 支持一键卸载
 
 ## 快速安装
@@ -151,6 +152,9 @@ lpinfo -v | grep usb
 ### 手机发送打印任务很慢
 脚本已配置 `HostNameLookups Off` 解决此问题。如果仍然慢，检查网络连接。
 
+### 更换路由器或网关后找不到打印服务器
+网络守护会在连续检测失败后先切换到 DHCP 恢复连接。如果发现 DHCP 获取到的新网关和原静态网关不同，会保留原静态 IP 的最后一段，例如 `192.168.11.219` 的 `219`，自动改成新网段下的 `x.x.x.219`。
+
 ### 界面显示英文
 确保安装时下载了中文模板、中文首页和前端汉化脚本。重新运行安装脚本可以修复。
 

setup_cups.sh

@@ -1196,6 +1196,7 @@ install_watchdogs() {
     local current_interface=$(get_interface)
     local current_netmask=$(get_netmask)
     local current_dns=$(get_dns)
+    local current_host_octet="${current_ip##*.}"
     current_dns="${current_dns:-114.114.114.114 223.5.5.5}"
 
     local ping_targets="223.5.5.5 114.114.114.114"
@@ -1213,9 +1214,12 @@ STATIC_IP="$current_ip"
 STATIC_PREFIX="$current_netmask"
 STATIC_GATEWAY="$current_gateway"
 STATIC_DNS="$current_dns"
+STATIC_HOST_OCTET="$current_host_octet"
 PING_TARGETS="$ping_targets"
 FAIL_THRESHOLD=3
 DHCP_AFTER_FAILURE=1
+REBASE_STATIC_ON_GATEWAY_CHANGE=1
+REBASE_WAIT_SECONDS=20
 LOG_FILE="/var/log/cups-watchdog/network.log"
 MAX_LOG_SIZE_KB=256
 EOF

watchdog/network-watchdog.sh

@@ -3,6 +3,8 @@
 # Network watchdog for the CUPS print server.
 # Default behavior: when connectivity checks fail repeatedly, switch the
 # configured interface back to DHCP so the box can regain network access.
+# If DHCP reveals a different gateway, the script can rebuild the static IP
+# with the new network prefix while keeping the old host octet.
 #
 # Edit /etc/cups-watchdog/network-watchdog.conf to set STATIC_IP,
 # STATIC_PREFIX, STATIC_GATEWAY and STATIC_DNS. You can also run:
@@ -20,9 +22,12 @@ STATIC_IP=""
 STATIC_PREFIX="24"
 STATIC_GATEWAY=""
 STATIC_DNS="114.114.114.114 223.5.5.5"
+STATIC_HOST_OCTET=""
 PING_TARGETS="223.5.5.5 114.114.114.114"
 FAIL_THRESHOLD=3
 DHCP_AFTER_FAILURE=1
+REBASE_STATIC_ON_GATEWAY_CHANGE=1
+REBASE_WAIT_SECONDS=20
 LOG_FILE="/var/log/cups-watchdog/network.log"
 MAX_LOG_SIZE_KB=256
 
@@ -71,6 +76,56 @@ detect_interface() {
     ip route show default 2>/dev/null | awk '{print $5; exit}'
 }
 
+current_ipv4_for_interface() {
+    local iface="$1"
+
+    ip -4 -o addr show dev "$iface" scope global 2>/dev/null | awk '{split($4, a, "/"); print a[1]; exit}'
+}
+
+current_prefix_for_interface() {
+    local iface="$1"
+
+    ip -4 -o addr show dev "$iface" scope global 2>/dev/null | awk '{split($4, a, "/"); print a[2]; exit}'
+}
+
+current_gateway_for_interface() {
+    local iface="$1"
+    local gateway
+
+    gateway="$(ip route show default dev "$iface" 2>/dev/null | awk '{print $3; exit}')"
+    if [ -z "$gateway" ]; then
+        gateway="$(ip route show default 2>/dev/null | awk '{print $3; exit}')"
+    fi
+    echo "$gateway"
+}
+
+last_octet() {
+    local ip="$1"
+
+    case "$ip" in
+        *.*.*.*) echo "${ip##*.}" ;;
+        *) echo "" ;;
+    esac
+}
+
+prefix24() {
+    local ip="$1"
+
+    case "$ip" in
+        *.*.*.*) echo "${ip%.*}" ;;
+        *) echo "" ;;
+    esac
+}
+
+valid_host_octet() {
+    local octet="$1"
+
+    case "$octet" in
+        ''|*[!0-9]*) return 1 ;;
+    esac
+    [ "$octet" -ge 1 ] 2>/dev/null && [ "$octet" -le 254 ] 2>/dev/null
+}
+
 nm_connection_for_interface() {
     local iface="$1"
     nmcli -t -f NAME,DEVICE con show --active 2>/dev/null | awk -F: -v iface="$iface" '$2 == iface {print $1; exit}'
@@ -141,6 +196,70 @@ configure_dhcp() {
     fi
 }
 
+set_config_value() {
+    local key="$1"
+    local value="$2"
+    local tmp_file
+
+    if [ ! -f "$CONFIG_FILE" ]; then
+        mkdir -p "$(dirname "$CONFIG_FILE")" 2>/dev/null || true
+        : > "$CONFIG_FILE" 2>/dev/null || return 1
+    fi
+
+    tmp_file="${CONFIG_FILE}.tmp.$$"
+    if grep -q "^${key}=" "$CONFIG_FILE" 2>/dev/null; then
+        awk -v key="$key" -v value="$value" '
+            BEGIN { q = sprintf("%c", 34) }
+            $0 ~ "^" key "=" { print key "=" q value q; next }
+            { print }
+        ' "$CONFIG_FILE" > "$tmp_file" && mv "$tmp_file" "$CONFIG_FILE"
+    else
+        printf '%s="%s"\n' "$key" "$value" >> "$CONFIG_FILE"
+    fi
+    chmod 600 "$CONFIG_FILE" 2>/dev/null || true
+}
+
+wait_for_dhcp_network() {
+    local iface="$1"
+    local i=0
+    local ip
+    local gateway
+
+    while [ "$i" -lt "${REBASE_WAIT_SECONDS:-20}" ]; do
+        ip="$(current_ipv4_for_interface "$iface")"
+        gateway="$(current_gateway_for_interface "$iface")"
+        if [ -n "$ip" ] && [ -n "$gateway" ]; then
+            echo "$ip $gateway"
+            return 0
+        fi
+        i=$((i + 1))
+        sleep 1
+    done
+
+    return 1
+}
+
+candidate_ip_in_use() {
+    local iface="$1"
+    local candidate_ip="$2"
+    local current_ip="$3"
+
+    [ "$candidate_ip" = "$current_ip" ] && return 1
+
+    if command -v arping >/dev/null 2>&1; then
+        # arping duplicate-address detection returns success when no reply is seen.
+        arping -D -I "$iface" -c 2 -w 3 "$candidate_ip" >/dev/null 2>&1
+        [ "$?" != "0" ] && return 0
+        return 1
+    fi
+
+    if ping -c 1 -W 1 "$candidate_ip" >/dev/null 2>&1; then
+        return 0
+    fi
+
+    return 1
+}
+
 configure_static_nmcli() {
     local iface="$1"
     local conn
@@ -243,6 +362,105 @@ configure_static() {
     fi
 }
 
+rebase_static_after_dhcp() {
+    local iface="$1"
+    local dhcp_state
+    local dhcp_ip
+    local dhcp_gateway
+    local dhcp_prefix
+    local host_octet
+    local base_prefix
+    local candidate_ip
+    local old_static_ip="$STATIC_IP"
+    local old_static_gateway="$STATIC_GATEWAY"
+    local old_static_prefix="$STATIC_PREFIX"
+    local old_static_dns="$STATIC_DNS"
+    local current_dns
+
+    [ "${REBASE_STATIC_ON_GATEWAY_CHANGE:-1}" = "1" ] || return 0
+
+    if [ -z "${STATIC_IP:-}" ] || [ -z "${STATIC_GATEWAY:-}" ]; then
+        log_msg "skip static rebase: STATIC_IP or STATIC_GATEWAY is empty"
+        return 0
+    fi
+
+    dhcp_state="$(wait_for_dhcp_network "$iface" 2>/dev/null || true)"
+    if [ -z "$dhcp_state" ]; then
+        log_msg "skip static rebase: DHCP did not provide an IP and gateway in time"
+        return 0
+    fi
+
+    dhcp_ip="$(echo "$dhcp_state" | awk '{print $1}')"
+    dhcp_gateway="$(echo "$dhcp_state" | awk '{print $2}')"
+    if [ "$dhcp_gateway" = "$STATIC_GATEWAY" ]; then
+        log_msg "DHCP gateway is still $dhcp_gateway; keep DHCP recovery without rebasing static IP"
+        return 0
+    fi
+
+    host_octet="${STATIC_HOST_OCTET:-$(last_octet "$STATIC_IP")}"
+    if ! valid_host_octet "$host_octet"; then
+        log_msg "skip static rebase: invalid STATIC_HOST_OCTET '$host_octet'"
+        return 0
+    fi
+
+    base_prefix="$(prefix24 "$dhcp_ip")"
+    [ -n "$base_prefix" ] || base_prefix="$(prefix24 "$dhcp_gateway")"
+    if [ -z "$base_prefix" ]; then
+        log_msg "skip static rebase: cannot derive IPv4 /24 prefix from DHCP state"
+        return 0
+    fi
+
+    candidate_ip="${base_prefix}.${host_octet}"
+    if candidate_ip_in_use "$iface" "$candidate_ip" "$dhcp_ip"; then
+        log_msg "skip static rebase: candidate $candidate_ip appears to be in use; staying on DHCP"
+        return 0
+    fi
+
+    dhcp_prefix="$(current_prefix_for_interface "$iface")"
+    STATIC_IP="$candidate_ip"
+    STATIC_GATEWAY="$dhcp_gateway"
+    STATIC_PREFIX="${dhcp_prefix:-$STATIC_PREFIX}"
+    current_dns="$(grep -E '^nameserver ' /etc/resolv.conf 2>/dev/null | awk '{print $2}' | head -n2 | tr '\n' ' ')"
+    STATIC_DNS="${current_dns:-$STATIC_DNS}"
+
+    log_msg "gateway changed from $old_static_gateway to $STATIC_GATEWAY; rebasing static IP from $old_static_ip to $STATIC_IP/$STATIC_PREFIX"
+    configure_static
+    sleep 3
+
+    if connectivity_ok; then
+        set_config_value "STATIC_IP" "$STATIC_IP" || true
+        set_config_value "STATIC_GATEWAY" "$STATIC_GATEWAY" || true
+        set_config_value "STATIC_PREFIX" "$STATIC_PREFIX" || true
+        set_config_value "STATIC_DNS" "$STATIC_DNS" || true
+        set_config_value "STATIC_HOST_OCTET" "$host_octet" || true
+        set_config_value "PING_TARGETS" "$STATIC_GATEWAY 223.5.5.5 114.114.114.114" || true
+        log_msg "static rebase succeeded: $STATIC_IP via $STATIC_GATEWAY"
+        return 0
+    fi
+
+    STATIC_IP="$old_static_ip"
+    STATIC_GATEWAY="$old_static_gateway"
+    STATIC_PREFIX="$old_static_prefix"
+    STATIC_DNS="$old_static_dns"
+    log_msg "static rebase to $candidate_ip failed connectivity check; falling back to DHCP"
+    configure_dhcp
+}
+
+recover_after_failure() {
+    local iface
+    local fallback_iface
+
+    fallback_iface="$(detect_interface)"
+    configure_dhcp || return 1
+    iface="$(detect_interface)"
+    [ -n "$iface" ] || iface="$fallback_iface"
+    if [ -z "$iface" ]; then
+        log_msg "skip static rebase: network interface not found after DHCP recovery"
+        return 1
+    fi
+    rebase_static_after_dhcp "$iface"
+}
+
 connectivity_ok() {
     local iface
     local gateway
@@ -288,7 +506,7 @@ check_network() {
 
     log_msg "connectivity failed ($fail_count/$FAIL_THRESHOLD)"
     if [ "$fail_count" -ge "$FAIL_THRESHOLD" ] && [ "$DHCP_AFTER_FAILURE" = "1" ]; then
-        configure_dhcp
+        recover_after_failure
         echo 0 > "$count_file"
     fi
 }