do not request files if we expect an IMS hit

If we have a file on disk and the hashes are the same in the new Release
file and the old one we have on disk we know that if we ask the server
for the file, we will at best get an IMS hit – at worse the server
doesn't support this and sends us the (unchanged) file and we have to
run all our checks on it again for nothing. So, we can save ourselves
(and the servers) some unneeded requests if we figure this out on our
own.

1 files changed, 50 insertions, 27 deletions

diff --git a/apt-pkg/acquire-item.cc b/apt-pkg/acquire-item.cc
index 13e971e9f..511bbbc64 100644
--- a/apt-pkg/acquire-item.cc
+++ b/apt-pkg/acquire-item.cc
@@ -119,6 +119,16 @@ static bool AllowInsecureRepositories(indexRecords const * const MetaIndexParser
    return false;
 }
 									/*}}}*/
+static HashStringList GetExpectedHashesFromFor(indexRecords * const Parser, std::string const MetaKey)/*{{{*/
+{
+   if (Parser == NULL)
+      return HashStringList();
+   indexRecords::checkSum * const R = Parser->Lookup(MetaKey);
+   if (R == NULL)
+      return HashStringList();
+   return R->Hashes;
+}
+									/*}}}*/
 
 // all ::HashesRequired and ::GetExpectedHashes implementations		/*{{{*/
 /* ::GetExpectedHashes is abstract and has to be implemented by all subclasses.
@@ -372,6 +382,25 @@ bool pkgAcqDiffIndex::TransactionState(TransactionStates const state)
 }
 									/*}}}*/
 
+class APT_HIDDEN NoActionItem : public pkgAcquire::Item			/*{{{*/
+/* The sole purpose of this class is having an item which does nothing to
+   reach its done state to prevent cleanup deleting the mentioned file.
+   Handy in cases in which we know we have the file already, like IMS-Hits. */
+{
+   IndexTarget const * const Target;
+   public:
+   virtual std::string DescURI() const {return Target->URI;};
+   virtual HashStringList GetExpectedHashes()  const {return HashStringList();};
+
+   NoActionItem(pkgAcquire * const Owner, IndexTarget const * const Target) :
+      pkgAcquire::Item(Owner), Target(Target)
+   {
+      Status = StatDone;
+      DestFile = GetFinalFileNameFromURI(Target->URI);
+   }
+};
+									/*}}}*/
+
 // Acquire::Item::Item - Constructor					/*{{{*/
 APT_IGNORE_DEPRECATED_PUSH
 pkgAcquire::Item::Item(pkgAcquire * const Owner) :
@@ -644,12 +673,7 @@ pkgAcqTransactionItem::~pkgAcqTransactionItem()				/*{{{*/
 									/*}}}*/
 HashStringList pkgAcqTransactionItem::GetExpectedHashesFor(std::string const MetaKey) const	/*{{{*/
 {
-   if (TransactionManager->MetaIndexParser == NULL)
-      return HashStringList();
-   indexRecords::checkSum * const R = TransactionManager->MetaIndexParser->Lookup(MetaKey);
-   if (R == NULL)
-      return HashStringList();
-   return R->Hashes;
+   return GetExpectedHashesFromFor(TransactionManager->MetaIndexParser, MetaKey);
 }
 									/*}}}*/
 
@@ -939,6 +963,23 @@ void pkgAcqMetaBase::QueueIndexes(bool const verify)			/*{{{*/
 	    return;
 	 }
 
+	 if (RealFileExists(GetFinalFileNameFromURI((*Target)->URI)))
+	 {
+	    if (TransactionManager->LastMetaIndexParser != NULL)
+	    {
+	       HashStringList const newFile = GetExpectedHashesFromFor(TransactionManager->MetaIndexParser, (*Target)->MetaKey);
+	       HashStringList const oldFile = GetExpectedHashesFromFor(TransactionManager->LastMetaIndexParser, (*Target)->MetaKey);
+	       if (newFile == oldFile)
+	       {
+		  // we have the file already, no point in trying to acquire it again
+		  new NoActionItem(Owner, *Target);
+		  continue;
+	       }
+	    }
+	 }
+	 else
+	    trypdiff = false; // no file to patch
+
 	 // check if we have patches available
 	 trypdiff &= TransactionManager->MetaIndexParser->Exists((*Target)->MetaKey + ".diff/Index");
       }
@@ -1085,20 +1126,6 @@ string pkgAcqMetaClearSig::Custom600Headers() const
 }
 									/*}}}*/
 // pkgAcqMetaClearSig::Done - We got a file				/*{{{*/
-class APT_HIDDEN DummyItem : public pkgAcquire::Item
-{
-   IndexTarget const * const Target;
-   public:
-   virtual std::string DescURI() const {return Target->URI;};
-   virtual HashStringList GetExpectedHashes()  const {return HashStringList();};
-
-   DummyItem(pkgAcquire * const Owner, IndexTarget const * const Target) :
-      pkgAcquire::Item(Owner), Target(Target)
-   {
-      Status = StatDone;
-      DestFile = GetFinalFileNameFromURI(Target->URI);
-   }
-};
 void pkgAcqMetaClearSig::Done(std::string const &Message,
                               HashStringList const &Hashes,
                               pkgAcquire::MethodConfig const * const Cnf)
@@ -1131,8 +1158,8 @@ void pkgAcqMetaClearSig::Done(std::string const &Message,
 	 // We got an InRelease file IMSHit, but we haven't one, which means
 	 // we had a valid Release/Release.gpg combo stepping in, which we have
 	 // to 'acquire' now to ensure list cleanup isn't removing them
-	 new DummyItem(Owner, &DetachedDataTarget);
-	 new DummyItem(Owner, &DetachedSigTarget);
+	 new NoActionItem(Owner, &DetachedDataTarget);
+	 new NoActionItem(Owner, &DetachedSigTarget);
       }
    }
 }
@@ -1578,11 +1605,7 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
    HashStringList LocalHashes;
    // try avoiding calculating the hash here as this is costly
    if (TransactionManager->LastMetaIndexParser != NULL)
-   {
-      indexRecords::checkSum * const R = TransactionManager->LastMetaIndexParser->Lookup(Target->MetaKey);
-      if (R != NULL)
-	 LocalHashes = R->Hashes;
-   }
+      LocalHashes = GetExpectedHashesFromFor(TransactionManager->LastMetaIndexParser, Target->MetaKey);
    if (LocalHashes.usable() == false)
    {
       FileFd fd(CurrentPackagesFile, FileFd::ReadOnly);