a hit on Release files means the indexes will be hits too

If we get a IMSHit for the Transaction-Manager (= the InRelease file or
as its still supported fallback Release + Release.gpg combo) we can
assume that every file we would queue based on this manager, but already
have locally is current and hence would get an IMSHit, too. We therefore
save us and the server the trouble and skip the queuing in this case.
Beside speeding up repetative executions of 'apt-get update' this way we
also avoid hitting hashsum errors if the indexes are in fact already
updated, but the Release file isn't yet as it is the case on well
behaving mirrors as Release files is updated last.

The implementation is a bit harder than the theory makes it sound as we
still have to keep reverifying the Release files (e.g. to detect now expired
once to avoid an attacker being able to silently stale us) and have to
handle cases in which the Release file hits, but some indexes aren't
present (e.g. user added a new foreign architecture).

1 files changed, 15 insertions, 13 deletions

diff --git a/apt-pkg/acquire-item.h b/apt-pkg/acquire-item.h
index c2759b792..148728b3c 100644
--- a/apt-pkg/acquire-item.h
+++ b/apt-pkg/acquire-item.h
@@ -74,10 +74,15 @@ class pkgAcquire::Item : public WeakPointable
 
    /** \brief Insert this item into its owner's queue.
     *
+    *  The method is designed to check if the request would end
+    *  in an IMSHit and if it determines that it would, it isn't
+    *  queueing the Item and instead sets it to completion instantly.
+    *
     *  \param Item Metadata about this item (its URI and
     *  description).
+    *  \return true if the item was inserted, false if IMSHit was detected
     */
-   void QueueURI(ItemDesc &Item);
+   virtual bool QueueURI(ItemDesc &Item);
 
    /** \brief Remove this item from its owner's queue. */
    void Dequeue();
@@ -392,9 +397,6 @@ class pkgAcqMetaBase  : public pkgAcquire::Item				/*{{{*/
     */
    bool AuthPass;
 
-   // required to deal gracefully with problems caused by incorrect ims hits
-   bool IMSHit;
-
    /** \brief The URI of the signature file.  Unlike Desc.URI, this is
     *  never modified; it is used to determine the file that is being
     *  downloaded.
@@ -457,7 +459,11 @@ class pkgAcqMetaBase  : public pkgAcquire::Item				/*{{{*/
    virtual std::string GetFinalFilename() const;
 
  public:
+   // This refers more to the Transaction-Manager than the actual file
+   bool IMSHit;
+
    virtual std::string DescURI() {return RealURI; };
+   virtual bool QueueURI(pkgAcquire::ItemDesc &Item);
 
    // transaction code
    void Add(Item *I);
@@ -479,10 +485,7 @@ class pkgAcqMetaBase  : public pkgAcquire::Item				/*{{{*/
                   indexRecords* MetaIndexParser,
 		  std::string const &RealURI,
                   HashStringList const &ExpectedHashes=HashStringList(),
-                  pkgAcqMetaBase *TransactionManager=NULL)
-      : Item(Owner, ExpectedHashes, TransactionManager),
-        MetaIndexParser(MetaIndexParser), IndexTargets(IndexTargets),
-        AuthPass(false), IMSHit(false), RealURI(RealURI) {};
+                  pkgAcqMetaBase *TransactionManager=NULL);
 };
 									/*}}}*/
 /** \brief An acquire item that downloads the detached signature	{{{
@@ -652,9 +655,7 @@ class pkgAcqBaseIndex : public pkgAcquire::Item
                    pkgAcqMetaBase *TransactionManager,
                    struct IndexTarget const * const Target,
                    HashStringList const &ExpectedHashes,
-                   indexRecords *MetaIndexParser)
-      : Item(Owner, ExpectedHashes, TransactionManager), Target(Target), 
-        MetaIndexParser(MetaIndexParser) {};
+                   indexRecords *MetaIndexParser);
 };
 									/*}}}*/
 /** \brief An item that is responsible for fetching an index file of	{{{
@@ -691,6 +692,7 @@ class APT_HIDDEN pkgAcqDiffIndex : public pkgAcqBaseIndex
    /** \brief Get the full pathname of the final file for the current URI */
    virtual std::string GetFinalFilename() const;
 
+   virtual bool QueueURI(pkgAcquire::ItemDesc &Item);
  public:
    // Specialized action members
    virtual void Failed(std::string Message,pkgAcquire::MethodConfig *Cnf);
@@ -714,7 +716,6 @@ class APT_HIDDEN pkgAcqDiffIndex : public pkgAcqBaseIndex
     *  false otherwise.
     */
    bool ParseDiffIndex(std::string IndexDiffFile);
-   
 
    /** \brief Create a new pkgAcqDiffIndex.
     *
@@ -733,6 +734,8 @@ class APT_HIDDEN pkgAcqDiffIndex : public pkgAcqBaseIndex
                    struct IndexTarget const * const Target,
                    HashStringList const &ExpectedHashes,
                    indexRecords *MetaIndexParser);
+ private:
+   APT_HIDDEN void QueueOnIMSHit() const;
 };
 									/*}}}*/
 /** \brief An item that is responsible for fetching client-merge patches {{{
@@ -1008,7 +1011,6 @@ class APT_HIDDEN pkgAcqIndex : public pkgAcqBaseIndex
    virtual std::string GetFinalFilename() const;
 
    public:
-   
    // Specialized action members
    virtual void Failed(std::string Message,pkgAcquire::MethodConfig *Cnf);
    virtual void Done(std::string Message,unsigned long long Size,