feat(proto): 自 go-hua 迁入长度前缀封包协议编解码

- 8 字节头(4 字节 ID/校验 + 4 字节长度, 小端序) + CRC32 校验版本
- 附测试、examples/proto 例程与包 README(含 Decode reader 复用告诫)

proto/proto_test.go

@@ -0,0 +1,90 @@
+package proto
+
+import (
+	"bufio"
+	"bytes"
+	"net"
+	"testing"
+)
+
+func TestEncodeDecode(t *testing.T) {
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	want := []byte("hello proto")
+	go func() {
+		data, err := Encode(want)
+		if err != nil {
+			t.Errorf("Encode: %v", err)
+			server.Close()
+			return
+		}
+		server.Write(data)
+	}()
+
+	got, err := Decode(bufio.NewReader(client))
+	if err != nil {
+		t.Fatalf("Decode: %v", err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Errorf("Decode = %q, want %q", got, want)
+	}
+}
+
+func TestEncodeDecodeCrc32(t *testing.T) {
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	want := []byte("hello crc32")
+	go func() {
+		data, err := EncodeCrc32(want)
+		if err != nil {
+			t.Errorf("EncodeCrc32: %v", err)
+			server.Close()
+			return
+		}
+		server.Write(data)
+	}()
+
+	got, err := DecodeCrc32(bufio.NewReader(client))
+	if err != nil {
+		t.Fatalf("DecodeCrc32: %v", err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Errorf("DecodeCrc32 = %q, want %q", got, want)
+	}
+}
+
+func TestDecodeCrc32Corrupted(t *testing.T) {
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	go func() {
+		data, _ := EncodeCrc32([]byte("payload"))
+		data[len(data)-1] ^= 0xFF // 篡改数据
+		server.Write(data)
+	}()
+
+	_, err := DecodeCrc32(bufio.NewReader(client))
+	if err == nil {
+		t.Error("篡改数据后 DecodeCrc32 应返回错误")
+	}
+}
+
+func TestEncodeHeaderFormat(t *testing.T) {
+	// 头 8 字节：[0:4] 为 CRC/ID，[4:8] 为小端长度
+	data, err := EncodeCrc32([]byte("abcd"))
+	if err != nil {
+		t.Fatalf("EncodeCrc32: %v", err)
+	}
+	length := int(data[4]) | int(data[5])<<8 | int(data[6])<<16 | int(data[7])<<24
+	if length != 4 {
+		t.Errorf("长度字段 = %d, want 4", length)
+	}
+	if len(data) != int(PakHeadLen)+4 {
+		t.Errorf("报文总长 = %d, want %d", len(data), PakHeadLen+4)
+	}
+}