Handle the scenario where the listing is truncated but the "NextMarke…

…r" key is missing from the server response. In such cases, use the last listed item as the "NextMarker" value (issue #122)

Documentation:
https://docs.aws.amazon.com/AmazonS3/latest/API/API_ListObjects.html

src/xml/s3propparser.cpp

@@ -53,7 +53,8 @@ struct S3PropParser::Internal{
     S3ListingMode::S3ListingMode _s3_listing_mode;
 
     bool istruncated = false;
-    std::string nextmarker = "";
+    std::string nextmarker;
+    std::string nextmarker_last_key;
 
     int start_elem(const std::string &elem){
         // new tag, clean content;
@@ -110,20 +111,21 @@ struct S3PropParser::Internal{
             prefix = current;
             if(inside_com_prefix){  // all keys would have been processed by now, just common prefixes left, use as DIRs
                 DAVIX_SLOG(DAVIX_LOG_TRACE, DAVIX_LOG_XML, "push new common prefix {}", current.c_str());
+                // Save key for "truncated reply with missing NextMarker" scenario
+                nextmarker_last_key = current;
                 current = current.erase(current.size()-1,1);
                 property.filename = current.erase(0, prefix_to_remove.size());
                 property.info.mode =  0755 | S_IFDIR;
                 property.info.mode &= ~(S_IFREG);
                 props.push_back(property);
                 prop_count++;
-                if (istruncated) {
-                    nextmarker = current;
-                }
             }
         }
 
         // new name new fileprop
         if( StrUtil::compare_ncase(name_prop, elem) ==0){
+            // Save key for "truncated reply with missing NextMarker" scenario
+            nextmarker_last_key = current;
 
             if(_s3_listing_mode == S3ListingMode::Flat) {  // flat mode
                 property.filename = current.erase(0,prefix.size());
@@ -271,7 +273,15 @@ std::deque<FileProperties> & S3PropParser::getProperties(){
 }
 
 std::string S3PropParser::getNextMarker() {
-    return (d_ptr->istruncated ? d_ptr->nextmarker : "");
+    if (d_ptr->istruncated) {
+        if (!d_ptr->nextmarker.empty()) {
+            return d_ptr->nextmarker;
+        }
+
+        return d_ptr->nextmarker_last_key;
+    }
+
+    return "";
 }