Modbus: add shared block reading (#30846)

plugin/modbus_test.go

@@ -0,0 +1,53 @@
+package plugin
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"github.com/evcc-io/evcc/util/modbus"
+	gridx "github.com/grid-x/modbus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// huaweiGridBlock mirrors the shared grid block of the huawei-sun2000-hybrid
+// template: 16 registers (32 bytes) starting at 37107.
+var huaweiGridBlock = modbus.Block{Register: 37107, Count: 16}
+
+func op(addr, length uint16) modbus.RegisterOperation {
+	return modbus.RegisterOperation{FuncCode: gridx.FuncCodeReadHoldingRegisters, Addr: addr, Length: length}
+}
+
+// TestExtractBlock verifies that each Huawei grid register is sliced from the
+// block payload at the correct offset and decodes to the expected value.
+func TestExtractBlock(t *testing.T) {
+	payload := make([]byte, 2*huaweiGridBlock.Count)
+	// power @ 37113 (offset 12), int32 = 1234 W
+	binary.BigEndian.PutUint32(payload[12:], uint32(int32(1234)))
+	// imported energy @ 37121 (offset 28), uint32 = 567890
+	binary.BigEndian.PutUint32(payload[28:], 567890)
+
+	power, err := huaweiGridBlock.Extract(op(37113, 2), payload)
+	require.NoError(t, err)
+	powerDec, err := (modbus.Register{Type: "holding", Decode: "int32"}).DecodeFunc()
+	require.NoError(t, err)
+	assert.Equal(t, 1234.0, powerDec(power))
+
+	energy, err := huaweiGridBlock.Extract(op(37121, 2), payload)
+	require.NoError(t, err)
+	energyDec, err := (modbus.Register{Type: "holding", Decode: "uint32"}).DecodeFunc()
+	require.NoError(t, err)
+	assert.Equal(t, 567890.0, energyDec(energy))
+}
+
+func TestExtractBlockBounds(t *testing.T) {
+	payload := make([]byte, 2*huaweiGridBlock.Count)
+
+	// register outside the block is rejected
+	_, err := huaweiGridBlock.Extract(op(37200, 2), payload)
+	require.Error(t, err)
+
+	// short payload is rejected
+	_, err = huaweiGridBlock.Extract(op(37121, 2), payload[:10])
+	require.Error(t, err)
+}