miniogw: make ListObjects/V2 aware of easier cases

This change changes listObjectsExhaustive (that ListObjects /
ListObjectsV2 is using) to not list too many items if it doesn't have
to. Specifically, if the prefix contains forward slashes, it will always
try to limit the scope of its listing by listing from the last forward
slash in the prefix.

Updates storj/customer-issues#184

Change-Id: Iae3fa0bc509cf089404a348bdaa9bae1c127966e

miniogw/gateway.go

@@ -462,13 +462,17 @@ func (layer *gatewayLayer) listObjectsExhaustive(
 	// have to comply with (*uplink.Project).ListObjects' API.
 	var listPrefix string
 
-	if strings.HasSuffix(prefix, "/") {
-		listPrefix = prefix
+	// There is a good chance we don't need to list the entire bucket if the
+	// prefix contains forward slashes! If it does, let's list from the last
+	// one. If the satellite doesn't give us anything after that chopped-off
+	// prefix, we won't return anything anyway.
+	if i := strings.LastIndex(prefix, "/"); i != -1 {
+		listPrefix = prefix[:i] + "/"
 	}
 
 	list := project.ListObjects(ctx, bucket, &uplink.ListObjectsOptions{
 		Prefix:    listPrefix,
-		Recursive: delimiter != "/" || (strings.Contains(prefix, "/") && !strings.HasSuffix(prefix, "/")),
+		Recursive: delimiter != "/",
 		System:    true,
 		Custom:    layer.compatibilityConfig.IncludeCustomMetadataListing,
 	})