From 8e13789e8f6d689a36b426d6cb75b543a5073026 Mon Sep 17 00:00:00 2001
From: Abs62 <ottomann@yandex.ru>
Date: Tue, 6 Oct 2020 17:52:30 +0300
Subject: [PATCH] Zim: Handle clusters in random order case

---
 zim.cc | 48 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 11 deletions(-)

diff --git a/zim.cc b/zim.cc
index aee2fd10..3cce0fd8 100644
--- a/zim.cc
+++ b/zim.cc
@@ -191,6 +191,7 @@ private:
   ZIM_header zimHeader;
   Cache cache[ CACHE_SIZE ];
   int stamp;
+  QVector< QPair< quint64, quint32 > > clusterOffsets;
 
   void clearCache();
 };
@@ -270,6 +271,27 @@ bool ZimFile::open()
   if( read( reinterpret_cast< char * >( &zimHeader ), sizeof( zimHeader ) ) != sizeof( zimHeader ) )
     return false;
 
+// Clusters in zim file may be placed in random order.
+// We create sorted offsets list to calculate clusters size.
+
+  clusterOffsets.resize( zimHeader.clusterCount );
+  QVector< quint64 > offs;
+  offs.resize( zimHeader.clusterCount );
+
+  seek( zimHeader.clusterPtrPos );
+  qint64 size = zimHeader.clusterCount * sizeof( quint64 );
+  if( read( reinterpret_cast< char * >( offs.data() ), size) != size )
+  {
+    vector< string > names;
+    getFilenames( names );
+    throw exCantReadFile( names[ 0 ] );
+  }
+
+  for( quint32 i = 0; i < zimHeader.clusterCount; i++ )
+    clusterOffsets[ i ] = QPair< quint64, quint32 >( offs.at( i ), i );
+
+  qSort( clusterOffsets );
+
   return true;
 }
 
@@ -312,24 +334,25 @@ string ZimFile::getClusterData( quint32 cluster_nom )
 
   // Cache miss, read data from file
 
-  // Read cluster pointers
-
-  quint64 clusters[ 2 ];
-  seek( zimHeader.clusterPtrPos + cluster_nom * 8 );
-  if( read( reinterpret_cast< char * >( clusters ), sizeof(clusters) ) != sizeof(clusters) )
-    return string();
-
   // Calculate cluster size
 
   quint64 clusterSize;
-  if( cluster_nom < zimHeader.clusterCount - 1 )
-    clusterSize = clusters[ 1 ] - clusters[ 0 ];
+  quint32 nom;
+  for( nom = 0; nom < zimHeader.clusterCount; nom++ )
+    if( clusterOffsets.at( nom ).second == cluster_nom )
+      break;
+
+  if( nom >= zimHeader.clusterCount ) // Invalid cluster nom
+    return string();
+
+  if( nom < zimHeader.clusterCount - 1 )
+    clusterSize = clusterOffsets.at( nom + 1 ).first - clusterOffsets.at( nom ).first;
   else
-    clusterSize = size() - clusters[ 0 ];
+    clusterSize = size() - clusterOffsets.at( nom ).first;
 
   // Read cluster data
 
-  seek( clusters[ 0 ] );
+  seek( clusterOffsets.at( nom ).first );
 
   char compressionType;
   if( !getChar( &compressionType ) )
@@ -356,6 +379,9 @@ string ZimFile::getClusterData( quint32 cluster_nom )
   else
     return string();
 
+  if( decompressedData.empty() )
+    return string();
+
   // Check BLOBs number in the cluster
   // We cache multi-element clusters only