Support large opds result listings without an OOM

lib/OpdsParser/OpdsParser.h

@@ -2,6 +2,7 @@
 #include <Print.h>
 #include <expat.h>
 
+#include <functional>
 #include <string>
 #include <vector>
 
@@ -73,24 +74,13 @@ class OpdsParser final : public Print {
 
   operator bool() { return !error(); }
 
-  /**
-   * Get the parsed entries (both navigation and book entries).
-   * @return Vector of OpdsEntry entries
-   */
-  const std::vector<OpdsEntry>& getEntries() const& { return entries; }
-  std::vector<OpdsEntry> getEntries() && { return std::move(entries); }
-
-  /**
-   * Get only book entries (legacy compatibility).
-   * @return Vector of book entries
-   */
-  std::vector<OpdsEntry> getBooks() const;
-
   /**
    * Clear all parsed entries.
    */
   void clear();
 
+  std::function<void(OpdsEntry)> onEntryParsed;
+
  private:
   // Expat callbacks
   static void XMLCALL startElement(void* userData, const XML_Char* name, const XML_Char** atts);
@@ -105,7 +95,6 @@ class OpdsParser final : public Print {
   static const char* findAttribute(const XML_Char** atts, const char* name);
 
   XML_Parser parser = nullptr;
-  std::vector<OpdsEntry> entries;
   OpdsEntry currentEntry;
   std::string currentText;