fix S3 per-user-directory Policy (#6443)

* fix S3 per-user-directory Policy

* Delete docker/config.json

* add tests

* remove logs

* undo modifications of weed/shell/command_volume_balance.go

* remove modifications of docker-compose

* fix failing test

---------

Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>

weed/s3api/s3_constants/header.go

@@ -17,9 +17,10 @@
 package s3_constants
 
 import (
-	"github.com/gorilla/mux"
 	"net/http"
 	"strings"
+
+	"github.com/gorilla/mux"
 )
 
 // Standard S3 HTTP request constants
@@ -72,6 +73,16 @@ func GetBucketAndObject(r *http.Request) (bucket, object string) {
 	return
 }
 
+func GetPrefix(r *http.Request) string {
+	query := r.URL.Query()
+	prefix := query.Get("prefix")
+	if !strings.HasPrefix(prefix, "/") {
+		prefix = "/" + prefix
+	}
+
+	return prefix
+}
+
 var PassThroughHeaders = map[string]string{
 	"response-cache-control":       "Cache-Control",
 	"response-content-disposition": "Content-Disposition",