Manifest age check when requesting parts

This is an additional check that should eliminate the
spurious part problem.

Author: jamescowens

src/scraper_net.cpp

@@ -24,6 +24,7 @@ std::map<uint256, std::pair<int64_t, std::unique_ptr<CScraperManifest>>> CScrape
 CCriticalSection CScraperManifest::cs_mapManifest;
 extern unsigned int SCRAPER_MISBEHAVING_NODE_BANSCORE;
 extern int64_t SCRAPER_DEAUTHORIZED_BANSCORE_GRACE_PERIOD;
+extern int64_t SCRAPER_CMANIFEST_RETENTION_TIME;
 extern unsigned int nScraperSleep;
 extern AppCacheSectionExt mScrapersExt;
 extern std::atomic<int64_t> nSyncTime;
@@ -546,7 +547,10 @@ bool CScraperManifest::RecvManifest(CNode* pfrom, CDataStream& vRecv)
         manifest.Complete();
     } else {
         /* else request missing parts from the sender */
-        manifest.UseAsSource(pfrom);
+        // Note: As an additional buffer to prevent spurious part receipts, if the manifest timestamp is within nScraperSleep of expiration (i.e.
+        // about to go on the pending delete list, then do not request missing parts, as it is possible that the manifest will be deleted
+        // by the housekeeping loop in between the receipt of the manifest, request for parts, and receipt of parts otherwise.
+        if (manifest.nTime >= GetAdjustedTime() - SCRAPER_CMANIFEST_RETENTION_TIME + (int64_t) nScraperSleep / 1000) manifest.UseAsSource(pfrom);
     }
     return true;
 }