config: minor changes to split config and watcher files

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

watcher.go

@@ -0,0 +1,103 @@
+package file
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"reflect"
+
+	"github.com/unistack-org/micro/v3/codec"
+	"github.com/unistack-org/micro/v3/config"
+	"github.com/unistack-org/micro/v3/util/jitter"
+	rutil "github.com/unistack-org/micro/v3/util/reflect"
+)
+
+type fileWatcher struct {
+	path  string
+	opts  config.Options
+	wopts config.WatchOptions
+	done  chan struct{}
+	vchan chan map[string]interface{}
+	echan chan error
+}
+
+func (w *fileWatcher) run() {
+	ticker := jitter.NewTicker(w.wopts.MinInterval, w.wopts.MaxInterval)
+	defer ticker.Stop()
+
+	src := w.opts.Struct
+	if w.wopts.Struct != nil {
+		src = w.wopts.Struct
+	}
+
+	for {
+		select {
+		case <-w.done:
+			return
+		case <-ticker.C:
+			dst, err := rutil.Zero(src)
+			if err == nil {
+				var fp *os.File
+				if fp, err = os.OpenFile(w.path, os.O_RDONLY, os.FileMode(0400)); err != nil {
+					w.echan <- fmt.Errorf("failed to open: %s, error: %w", w.path, err)
+					return
+				}
+				var buf []byte
+				buf, err = ioutil.ReadAll(io.LimitReader(fp, int64(codec.DefaultMaxMsgSize)))
+				if err == nil {
+					err = w.opts.Codec.Unmarshal(buf, dst)
+				}
+				if err != nil {
+					_ = fp.Close()
+					w.echan <- err
+					return
+				}
+				err = fp.Close()
+			}
+			if err != nil {
+				w.echan <- err
+				return
+			}
+			srcmp, err := rutil.StructFieldsMap(src)
+			if err != nil {
+				w.echan <- err
+				return
+			}
+			dstmp, err := rutil.StructFieldsMap(dst)
+			if err != nil {
+				w.echan <- err
+				return
+			}
+			for sk, sv := range srcmp {
+				if reflect.DeepEqual(dstmp[sk], sv) {
+					delete(dstmp, sk)
+				}
+			}
+			if len(dstmp) > 0 {
+				w.vchan <- dstmp
+				src = dst
+			}
+		}
+	}
+}
+
+func (w *fileWatcher) Next() (map[string]interface{}, error) {
+	select {
+	case <-w.done:
+		break
+	case err := <-w.echan:
+		return nil, err
+	case v, ok := <-w.vchan:
+		if !ok {
+			break
+		}
+		return v, nil
+	}
+	return nil, config.ErrWatcherStopped
+}
+
+func (w *fileWatcher) Stop() error {
+	close(w.done)
+	return nil
+}