[#73] Uploader, downloader structures refactoring

Signed-off-by: Marina Biryukova <m.biryukova@yadro.com>

internal/handler/filter.go

@@ -0,0 +1,57 @@
+package handler
+
+import (
+	"bytes"
+	"fmt"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-http-gw/internal/logs"
+	"git.frostfs.info/TrueCloudLab/frostfs-http-gw/utils"
+	"github.com/valyala/fasthttp"
+	"go.uber.org/zap"
+)
+
+func filterHeaders(l *zap.Logger, header *fasthttp.RequestHeader) (map[string]string, error) {
+	var err error
+	result := make(map[string]string)
+	prefix := []byte(utils.UserAttributeHeaderPrefix)
+
+	header.VisitAll(func(key, val []byte) {
+		// checks that the key and the val not empty
+		if len(key) == 0 || len(val) == 0 {
+			return
+		}
+
+		// checks that the key has attribute prefix
+		if !bytes.HasPrefix(key, prefix) {
+			return
+		}
+
+		// removing attribute prefix
+		clearKey := bytes.TrimPrefix(key, prefix)
+
+		clearKey = utils.TransformIfSystem(clearKey)
+
+		// checks that the attribute key is not empty
+		if len(clearKey) == 0 {
+			return
+		}
+
+		// check if key gets duplicated
+		// return error containing full key name (with prefix)
+		if _, ok := result[string(clearKey)]; ok {
+			err = fmt.Errorf("key duplication error: %s", string(key))
+			return
+		}
+
+		// make string representation of key / val
+		k, v := string(clearKey), string(val)
+
+		result[k] = v
+
+		l.Debug(logs.AddAttributeToResultObject,
+			zap.String("key", k),
+			zap.String("val", v))
+	})
+
+	return result, err
+}