feat: add iterator

reader.go

@@ -0,0 +1,67 @@
+package spb
+
+import "io"
+
+type Iterator struct {
+	r                  io.Reader
+	structlen, reallen uint32
+	i                  uint32
+	v                  []byte
+}
+
+// NewReader 迭代器形式读取而非一次解析完
+func NewReader(r io.Reader) (it Iterator, err error) {
+	it.structlen, it.reallen, err = ReadNum(r)
+	if err != nil {
+		return
+	}
+	if it.structlen <= 1 || it.structlen >= uint32(1)<<20 {
+		err = ErrInvalidStructLen
+		return
+	}
+	it.r = r
+	return
+}
+
+// Next 是否有下一个
+func (it *Iterator) Next() bool {
+	if it.i >= it.structlen {
+		return false
+	}
+	var offset, datalen, n uint32
+	var err error
+	offset, n, err = ReadNum(it.r)
+	it.reallen += n
+	if err != nil {
+		return false
+	}
+	datalen, n, err = ReadNum(it.r)
+	it.reallen += n
+	if err != nil {
+		return false
+	}
+	if datalen == 0 {
+		return false
+	}
+	if datalen > offset {
+		return false
+	}
+	it.v = append(it.v[:0], make([]byte, datalen)...)
+	x, err := it.r.Read(it.v)
+	it.reallen += uint32(x)
+	if err != nil {
+		return false
+	}
+	it.i += offset
+	return true
+}
+
+// Bytes 本次迭代的原始值
+func (it *Iterator) Bytes() []byte {
+	return it.v
+}
+
+// String 将本次迭代的值解释为 string
+func (it *Iterator) String() string {
+	return string(it.v)
+}