diff --git a/payload_state.h b/payload_state.h
index 46711b6..14f0f50 100644
--- a/payload_state.h
+++ b/payload_state.h
@@ -79,7 +79,9 @@
   }
 
   inline std::string GetCurrentUrl() override {
-    return candidate_urls_.size() ? candidate_urls_[url_index_] : "";
+    return candidate_urls_.size() && candidate_urls_[payload_index_].size()
+               ? candidate_urls_[payload_index_][url_index_]
+               : "";
   }
 
   inline uint32_t GetUrlFailureCount() override {
@@ -368,7 +370,9 @@
   void ResetRollbackVersion();
 
   inline uint32_t GetUrlIndex() {
-    return url_index_;
+    return url_index_ ? std::min(candidate_urls_[payload_index_].size() - 1,
+                                 url_index_)
+                      : 0;
   }
 
   // Computes the list of candidate URLs from the total list of payload URLs in
@@ -420,6 +424,9 @@
   // Loads the persisted scattering wallclock-based wait period.
   void LoadScatteringWaitPeriod();
 
+  // Get the total size of all payloads.
+  int64_t GetPayloadSize();
+
   // The global state of the system.
   SystemState* system_state_;
 
@@ -468,12 +475,15 @@
   // we resume from the same value in case of a process restart.
   int full_payload_attempt_number_;
 
+  // The index of the current payload.
+  size_t payload_index_ = 0;
+
   // The index of the current URL.  This type is different from the one in the
   // accessor methods because PrefsInterface supports only int64_t but we want
   // to provide a stronger abstraction of uint32_t.  Each update to this value
   // is persisted so we resume from the same value in case of a process
   // restart.
-  int64_t url_index_;
+  size_t url_index_;
 
   // The count of failures encountered in the current attempt to download using
   // the current URL (specified by url_index_).  Each update to this value is
@@ -543,7 +553,7 @@
 
   // The ordered list of the subset of payload URL candidates which are
   // allowed as per device policy.
-  std::vector<std::string> candidate_urls_;
+  std::vector<std::vector<std::string>> candidate_urls_;
 
   // This stores a blacklisted version set as part of rollback. When we rollback
   // we store the version of the os from which we are rolling back from in order