EPUB: workaround ZIP files with corrupted central directories

If the main reading method (using zip header at the end of the
archive) fails, we can try using the alternative method already
used when this zip header is missing ("truncated"), which uses
local zip headers met along while scanning the zip.

Author: poire-z

crengine/src/lvstream.cpp

@@ -2097,6 +2097,10 @@ struct ZipHd2
     lUInt16     getZIPAttr() { return _Attr_and_Offset[0]; }
     lUInt32     getAttr() { return _Attr_and_Offset[1] | ((lUInt32)_Attr_and_Offset[2]<<16); }
     lUInt32     getOffset() { return _Attr_and_Offset[3] | ((lUInt32)_Attr_and_Offset[4]<<16); }
+    void        setOffset(lUInt32 offset) {
+        _Attr_and_Offset[3] = (lUInt16)(offset & 0xFFFF);
+        _Attr_and_Offset[4] = (lUInt16)(offset >> 16);
+    }
     void byteOrderConv()
     {
         //
@@ -2489,14 +2493,20 @@ class LVZipDecodeStream : public LVNamedStream
 
 class LVZipArc : public LVArcContainerBase
 {
+protected:
+    // whether the alternative "truncated" method was used, or is to be used
+    bool m_alt_reading_method = false;
 public:
+    bool usedAltReadingMethod() { return m_alt_reading_method; }
+    void useAltReadingMethod() { m_alt_reading_method = true; }
+
     virtual LVStreamRef OpenStream( const wchar_t * fname, lvopen_mode_t /*mode*/ )
     {
         if ( fname[0]=='/' )
             fname++;
         int found_index = -1;
         for (int i=0; i<m_list.length(); i++) {
-            if ( !lStr_cmp( fname, m_list[i]->GetName() ) ) {
+            if ( m_list[i]->GetName() != NULL && !lStr_cmp( fname, m_list[i]->GetName() ) ) {
                 if ( m_list[i]->IsContainer() ) {
                     // found directory with same name!!!
                     return LVStreamRef();
@@ -2592,6 +2602,18 @@ class LVZipArc : public LVArcContainerBase
         }
 
         truncated = !found;
+
+        // If the main reading method (using zip header at the end of the
+        // archive) failed, we can try using the alternative method used
+        // when this zip header is missing ("truncated"), which uses
+        // local zip headers met along while scanning the zip.
+        if (m_alt_reading_method)
+            truncated = true; // do as if truncated
+        else if (truncated) // archive detected as truncated
+            // flag that, so there's no need to try that alt method,
+            // as it was used on first scan
+            m_alt_reading_method = true;
+
         if (truncated)
             NextPosition=0;
 
@@ -2612,6 +2634,11 @@ class LVZipArc : public LVArcContainerBase
 
             if (truncated)
             {
+                // The offset (that we don't find in a local header, but
+                // that we will store in the ZipHeader we're building)
+                // happens to be the current position here.
+                lUInt32 offset = (lUInt32)m_stream->GetPos();
+
                 m_stream->Read( &ZipHd1, ZipHd1_size, &ReadSize);
                 ZipHd1.byteOrderConv();
 
@@ -2636,6 +2663,10 @@ class LVZipArc : public LVArcContainerBase
                 ZipHeader.NameLen=ZipHd1.getNameLen();
                 ZipHeader.AddLen=ZipHd1.getAddLen();
                 ZipHeader.Method=ZipHd1.getMethod();
+                ZipHeader.setOffset(offset);
+                // We may get a last invalid record with NameLen=0, which shouldn't hurt.
+                // If it does, use:
+                // if (ZipHeader.NameLen == 0) break;
             } else {
 
                 m_stream->Read( &ZipHeader, ZipHeader_size, &ReadSize);
@@ -2742,8 +2773,17 @@ class LVZipArc : public LVArcContainerBase
                 return NULL;
         LVZipArc * arc = new LVZipArc( stream );
         int itemCount = arc->ReadContents();
+        if ( itemCount > 0 && arc->usedAltReadingMethod() ) {
+            printf("CRE WARNING: zip file truncated: going on with possibly partial content.\n");
+        }
+        else if ( itemCount <= 0 && !arc->usedAltReadingMethod() ) {
+            printf("CRE WARNING: zip file corrupted or invalid: trying alternative processing...\n");
+            arc->useAltReadingMethod();
+            itemCount = arc->ReadContents();
+        }
         if ( itemCount <= 0 )
         {
+            printf("CRE WARNING: zip file corrupted or invalid: processing failure.\n");
             delete arc;
             return NULL;
         }