fix(agent): strip invalid UTF-8 from battery names (#2241)

Battery names come from firmware (sysfs model_name on Linux), which does not
guarantee valid UTF-8. The hub decodes agent payloads using the default
fxamacker/cbor decode mode, which rejects invalid UTF-8, so a single bad byte
in a battery name makes the hub drop the entire payload and mark the system
down until the agent is downgraded.

agent/battery/battery.go

@@ -33,7 +33,10 @@ var errNoBatteries = errors.New("no readable batteries")
 func normalizeBatteries(batteries []Battery) []Battery {
 	nameCounts := make(map[string]int, len(batteries))
 	for i := range batteries {
-		name := strings.TrimSpace(batteries[i].Name)
+		// Names come from firmware (e.g. sysfs model_name) and are not guaranteed to
+		// be valid UTF-8. Invalid bytes are rejected when the hub decodes the CBOR
+		// payload, which drops every metric for the system, so strip them here.
+		name := strings.TrimSpace(strings.ToValidUTF8(batteries[i].Name, ""))
 		if name == "" {
 			name = "Battery " + strconv.Itoa(i+1)
 		}

agent/battery/battery_test.go

@@ -2,6 +2,7 @@ package battery
 
 import (
 	"testing"
+	"unicode/utf8"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -33,3 +34,15 @@ func TestNormalizeBatteriesFallbackNames(t *testing.T) {
 	bats := normalizeBatteries([]Battery{{}, {}, {Name: "Mouse"}, {Name: "Mouse"}})
 	assert.Equal(t, []string{"Battery 1", "Battery 2", "Mouse", "Mouse (2)"}, []string{bats[0].Name, bats[1].Name, bats[2].Name, bats[3].Name})
 }
+
+func TestNormalizeBatteriesStripsInvalidUTF8(t *testing.T) {
+	// Firmware occasionally reports names that are not valid UTF-8 (a ThinkPad
+	// reporting "LNV-5B11K63024@\xd0" in model_name is a real example).
+	bats := normalizeBatteries([]Battery{{Name: "LNV-5B11K63024@\xd0"}, {Name: "\xff\xfe"}})
+	assert.Equal(t, "LNV-5B11K63024@", bats[0].Name)
+	// A name made up entirely of invalid bytes falls back to the generic name.
+	assert.Equal(t, "Battery 2", bats[1].Name)
+	for _, b := range bats {
+		assert.True(t, utf8.ValidString(b.Name))
+	}
+}