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app: Require link carrier to consider Ethernet uplink active

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A static IPv4 (e.g. the hotspot gateway address on eth0) was wrongly
classified as a DHCP uplink on stacks where ip(8) omits the "dynamic"
flag, and a NO-CARRIER interface with any address was reported as up.
Gate probeEthernet on /sys/class/net/<iface>/carrier == 1, and accept
either the dynamic flag or a finite valid_lft as the DHCP signal so
BusyBox's ip output is handled too.
This commit is contained in:
nemunaire 2026-05-02 11:37:28 +08:00
commit 92b6113d72
1 changed files with 28 additions and 9 deletions
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37
internal/app/network.go
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@ -3,18 +3,33 @@ package app
import (
"fmt"
"log"
"os"
"os/exec"
"strings"
"github.com/nemunaire/repeater/internal/models"
)
// probeEthernet reports the wired uplink state of iface by parsing
// `ip -4 -o addr show dev <iface>`. An IPv4 line carrying the "dynamic" flag
// (set by ip(8) on addresses with a finite valid_lft) is treated as a
// DHCP-assigned lease — that's the signal we use to decide whether the box
// already has connectivity through Ethernet.
// hasCarrier reports whether the kernel sees an active link on iface.
// `/sys/class/net/<iface>/carrier` is "1" when the link layer is up; reading
// it on an admin-down interface yields EINVAL, which we treat the same way.
func hasCarrier(iface string) bool {
data, err := os.ReadFile("/sys/class/net/" + iface + "/carrier")
if err != nil {
return false
}
return strings.TrimSpace(string(data)) == "1"
}
// probeEthernet reports the wired uplink state of iface. Active requires both
// a live link (`carrier == 1`) and a DHCP-assigned IPv4 — detected either by
// the `dynamic` flag emitted by full iproute2, or by a finite `valid_lft`
// (which BusyBox's `ip` does emit even when it omits the flag).
func probeEthernet(iface string) (*models.EthernetStatus, error) {
if !hasCarrier(iface) {
return &models.EthernetStatus{Active: false, Interface: iface}, nil
}
out, err := exec.Command("ip", "-4", "-o", "addr", "show", "dev", iface).Output()
if err != nil {
return nil, fmt.Errorf("ip addr show %s: %w", iface, err)
@ -23,7 +38,7 @@ func probeEthernet(iface string) (*models.EthernetStatus, error) {
fields := strings.Fields(line)
var addr string
hasInet := false
hasDynamic := false
isDHCP := false
for i, f := range fields {
switch f {
case "inet":
@ -32,10 +47,14 @@ func probeEthernet(iface string) (*models.EthernetStatus, error) {
addr = fields[i+1]
}
case "dynamic":
hasDynamic = true
isDHCP = true
case "valid_lft":
if i+1 < len(fields) && fields[i+1] != "forever" {
isDHCP = true
}
}
}
if hasInet && hasDynamic {
if hasInet && isDHCP {
if slash := strings.IndexByte(addr, '/'); slash >= 0 {
addr = addr[:slash]
}
@ -60,7 +79,7 @@ func ensureUplink(iface string) *models.EthernetStatus {
log.Printf("DHCP address %s on %s, leaving wpa_supplicant alone", eth.IPv4, iface)
return eth
}
log.Printf("No DHCP address on %s, starting wpa_supplicant", iface)
log.Printf("No usable DHCP uplink on %s (carrier or lease missing), starting wpa_supplicant", iface)
if out, err := exec.Command("service", "wpa_supplicant", "start").CombinedOutput(); err != nil {
log.Printf("Failed to start wpa_supplicant: %v: %s", err, strings.TrimSpace(string(out)))
}