implement PDiff patching for compressed files

Some additional files like 'Contents' are very big and should therefore
kept compressed on the disk, which apt-file did in the past. It also
implemented pdiff patching of these files by un- and recompressing these
files on-the-fly, with this commit we can do the same – but we can do
this in both pdiff patching styles (client and server merging) and
secured by hashes.

Hashes are in so far slightly complicated as we can't compare the hashes
of the compressed files as we might compress them differently than the
server would (different compressor versions, options, …), so we must
compare the hashes of the uncompressed content.

While this commit has changes in public headers, the classes it changes
are marked as hidden, so nobody can use them directly, which means the
ABI break is internal only.

1 files changed, 1 insertions, 4 deletions

diff --git a/apt-pkg/acquire-item.h b/apt-pkg/acquire-item.h
index d6bcdafcb..6d58f2ba9 100644
--- a/apt-pkg/acquire-item.h
+++ b/apt-pkg/acquire-item.h
@@ -409,7 +409,7 @@ class APT_HIDDEN pkgAcqMetaBase : public pkgAcqTransactionItem		/*{{{*/
    /** \brief The index files which should be looked up in the meta-index
     *  and then downloaded.
     */
-   std::vector<IndexTarget> const IndexTargets;
+   std::vector<IndexTarget> IndexTargets;
 
    /** \brief If \b true, the index's signature is currently being verified.
     */
@@ -944,9 +944,6 @@ class APT_HIDDEN pkgAcqIndex : public pkgAcqBaseIndex
    /** \brief Do the changes needed to fetch via AptByHash (if needed) */
    void InitByHashIfNeeded();
 
-   /** \brief Auto select the right compression to use */
-   void AutoSelectCompression();
-
    /** \brief Schedule file for verification after a IMS hit */
    void ReverifyAfterIMS();