refactor(xconf): add kv reader

kv/loader.go

@@ -7,6 +7,11 @@ import (
 	"sync"
 )
 
+// Getter 主动获取指定confPath的数据
+type Getter interface {
+	Get(ctx context.Context, confPath string) ([]byte, error)
+}
+
 // Loader kv加载基础接口
 // todo Loder实现Reader接口完全对接到io.Reader，将远程的首次加载流程直接对接到xconf的WithReader
 type Loader interface {

kv/reader.go

@@ -0,0 +1,42 @@
+package kv
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"time"
+)
+
+type reader struct {
+	Getter
+	p       string
+	timeout time.Duration
+	reader  io.Reader
+}
+
+// NewReader 返回一个kv reader
+func NewReader(getter Getter, path string, timeout time.Duration) io.Reader {
+	return &reader{Getter: getter, p: path, timeout: timeout}
+}
+
+func (r *reader) do() error {
+	ctx, cancel := context.WithTimeout(context.Background(), r.timeout)
+	defer cancel()
+	bb, err := r.Getter.Get(ctx, r.p)
+	if err != nil {
+		return err
+	}
+	r.reader = bytes.NewReader(bb)
+	return nil
+}
+
+// Read 实现io.Reader接口
+func (r *reader) Read(p []byte) (n int, err error) {
+	if r.reader == nil {
+		err = r.do()
+		if err != nil {
+			return 0, err
+		}
+	}
+	return r.reader.Read(p)
+}