fix(go): avoid gb32960 decimal float tails

go/vehicle-gateway/internal/protocol/gb32960/parser_test.go

@@ -2,8 +2,10 @@ package gb32960
 
 import (
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"math"
+	"strings"
 	"testing"
 
 	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
@@ -213,6 +215,54 @@ func TestParseFrameKeepsParsingRealFuelCellReportUntilUnknownExtension(t *testin
 	}
 }
 
+func TestScaledDecimalFieldsDoNotLeakBinaryFloatTails(t *testing.T) {
+	unit := parseDriveMotorData([]byte{
+		0x01,
+		0x01,
+		0x02,
+		0x5d,
+		0x6c, 0xc6,
+		0x4e, 0x20,
+		0x64,
+		0x15, 0xb8,
+		0x27, 0x6e, // 10094 -> 9.4A after -1000 offset.
+	})
+	data, err := json.Marshal(unit)
+	if err != nil {
+		t.Fatal(err)
+	}
+	text := string(data)
+	if !strings.Contains(text, `"controller_current_a":9.4`) {
+		t.Fatalf("controller_current_a should render as 9.4 without float tail: %s", text)
+	}
+	if strings.Contains(text, "999999") || strings.Contains(text, "000000000000") {
+		t.Fatalf("scaled decimal field leaked binary float tail: %s", text)
+	}
+
+	aux := parseGdFCAuxiliaryData([]byte{
+		0x01,
+		0x01, 0x74,
+		0x00, 0x05,
+		0xff, 0xff,
+		0x00, 0x05,
+		0x01, 0x74,
+		0xff, 0xff,
+		0x00, 0x05,
+		0x00, 0x84, // 132 -> 13.2V.
+	})
+	data, err = json.Marshal(aux)
+	if err != nil {
+		t.Fatal(err)
+	}
+	text = string(data)
+	if !strings.Contains(text, `"low_voltage_battery_voltage_v":13.2`) {
+		t.Fatalf("low voltage should render as 13.2 without float tail: %s", text)
+	}
+	if strings.Contains(text, "13.200000000000") {
+		t.Fatalf("auxiliary scaled decimal leaked binary float tail: %s", text)
+	}
+}
+
 func assertFloatField(t *testing.T, env envelope.FrameEnvelope, key string, want float64) {
 	t.Helper()
 	got, ok := env.Fields[key].(float64)