don't ask server if we have entire file in partial/

We have this situation in cases were parts of the transaction are
refused (e.g. in a hashsum mismatch) and rerun the update (e.g. in the
hope that we get a mirror which is synced this time).

Previously we would ask the server with an if-range and in the best case
recieve a 416 in response (less featureful server might end up giving us
the entire file again or we get the wrong file this time giving us a
hashsum mismatch…), which is a waste of time if we know already by
checking the hashsums that we got the complete and correct file.

4 files changed, 81 insertions, 31 deletions

diff --git a/methods/server.cc b/methods/server.cc
index 322b8d94c..b323ef4f3 100644
--- a/methods/server.cc
+++ b/methods/server.cc
@@ -419,36 +419,66 @@ void ServerMethod::SigTerm(int)
    depth. */
 bool ServerMethod::Fetch(FetchItem *)
 {
-   if (Server == 0)
+   if (Server == nullptr || QueueBack == nullptr)
       return true;
 
-   // Queue the requests
-   int Depth = -1;
-   for (FetchItem *I = Queue; I != 0 && Depth < (signed)PipelineDepth; 
-	I = I->Next, Depth++)
-   {
-      if (Depth >= 0)
-      {
-	 // If pipelining is disabled, we only queue 1 request
-	 if (Server->Pipeline == false)
-	    break;
-	 // if we have no hashes, do at most one such request
-	 // as we can't fixup pipeling misbehaviors otherwise
-	 else if (I->ExpectedHashes.usable() == false)
-	    break;
-      }
-      
+   // If pipelining is disabled, we only queue 1 request
+   auto const AllowedDepth = Server->Pipeline ? PipelineDepth : 0;
+   // how deep is our pipeline currently?
+   decltype(PipelineDepth) CurrentDepth = 0;
+   for (FetchItem const *I = Queue; I != QueueBack; I = I->Next)
+      ++CurrentDepth;
+
+   do {
       // Make sure we stick with the same server
-      if (Server->Comp(I->Uri) == false)
+      if (Server->Comp(QueueBack->Uri) == false)
+	 break;
+
+      bool const UsableHashes = QueueBack->ExpectedHashes.usable();
+      // if we have no hashes, do at most one such request
+      // as we can't fixup pipeling misbehaviors otherwise
+      if (CurrentDepth != 0 && UsableHashes == false)
 	 break;
-      if (QueueBack == I)
+
+      if (UsableHashes && FileExists(QueueBack->DestFile))
       {
-	 QueueBack = I->Next;
-	 SendReq(I);
-	 continue;
+	 FileFd partial(QueueBack->DestFile, FileFd::ReadOnly);
+	 Hashes wehave(QueueBack->ExpectedHashes);
+	 if (QueueBack->ExpectedHashes.FileSize() == partial.FileSize())
+	 {
+	    if (wehave.AddFD(partial) &&
+		  wehave.GetHashStringList() == QueueBack->ExpectedHashes)
+	    {
+	       FetchResult Res;
+	       Res.Filename = QueueBack->DestFile;
+	       Res.ResumePoint = QueueBack->ExpectedHashes.FileSize();
+	       URIStart(Res);
+	       // move item to the start of the queue as URIDone will
+	       // always dequeued the first item in the queue
+	       if (Queue != QueueBack)
+	       {
+		  FetchItem *Prev = Queue;
+		  for (; Prev->Next != QueueBack; Prev = Prev->Next)
+		     /* look for the previous queue item */;
+		  Prev->Next = QueueBack->Next;
+		  QueueBack->Next = Queue;
+		  Queue = QueueBack;
+		  QueueBack = Prev->Next;
+	       }
+	       Res.TakeHashes(wehave);
+	       URIDone(Res);
+	       continue;
+	    }
+	    else
+	       RemoveFile("Fetch-Partial", QueueBack->DestFile);
+	 }
       }
-   }
-   
+      auto const Tmp = QueueBack;
+      QueueBack = QueueBack->Next;
+      SendReq(Tmp);
+      ++CurrentDepth;
+   } while (CurrentDepth <= AllowedDepth && QueueBack != nullptr);
+
    return true;
 }
 									/*}}}*/
diff --git a/test/integration/framework b/test/integration/framework
index 213169a98..2a78e6194 100644
--- a/test/integration/framework
+++ b/test/integration/framework
@@ -1505,6 +1505,14 @@ testmarkedmanual() {
 	msggroup
 }
 
+catfile() {
+	if [ "${1##*.}" = 'deb' ]; then
+		stat >&2 "$1" || true
+		file >&2 "$1" || true
+	else
+		cat >&2 "$1" || true
+	fi
+}
 msgfailoutput() {
 	msgreportheader 'msgfailoutput'
 	local MSG="$1"
@@ -1514,7 +1522,7 @@ msgfailoutput() {
 		echo >&2
 		while [ -n "$2" ]; do shift; done
 		echo "#### Complete file: $1 ####"
-		cat >&2 "$1" || true
+		catfile "$1"
 		echo '#### grep output ####'
 	elif [ "$1" = 'test' ]; then
 		echo >&2
@@ -1529,7 +1537,7 @@ msgfailoutput() {
 					ls >&2 "$2" || true
 				elif test -e "$2"; then
 					echo "#### Complete file: $2 ####"
-					cat >&2 "$2" || true
+					catfile "$2"
 				fi
 			fi
 		}
@@ -1543,12 +1551,12 @@ msgfailoutput() {
 		echo >&2
 		while [ -n "$2" ]; do
 			echo "#### Complete file: $2 ####"
-			cat >&2 "$2" || true
+			catfile "$2"
 			shift
 		done
 		echo '#### cmp output ####'
 	fi
-	cat >&2 "$OUTPUT"
+	catfile "$OUTPUT"
 	msgfail "$MSG"
 }
 
diff --git a/test/integration/test-apt-update-transactions b/test/integration/test-apt-update-transactions
index 884838038..d8154b283 100755
--- a/test/integration/test-apt-update-transactions
+++ b/test/integration/test-apt-update-transactions
@@ -44,7 +44,8 @@ testrun() {
 	signreleasefiles
 
 	onehashbroken() {
-		testfailure aptget update
+		rm -rf rootdir/var/lib/apt/lists/partial
+		testfailure aptget update -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::http=1
 		# each file generates two messages with this string
 		testequal '2' grep --count 'Hash Sum mismatch' rootdir/tmp/testfailure.output
 		testfileequal "$1" "$(listcurrentlistsdirectory)"
diff --git a/test/integration/test-pdiff-usage b/test/integration/test-pdiff-usage
index f219b9193..9c7946083 100755
--- a/test/integration/test-pdiff-usage
+++ b/test/integration/test-pdiff-usage
@@ -30,7 +30,7 @@ echo 'hacked' > aptarchive/hacked-i386
 compressfile aptarchive/hacked-i386
 
 wasmergeused() {
-	testsuccess apt update "$@" -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::http=1 -o Debug::pkgAcquire=1
+	testsuccess apt update "$@"
 
 	msgtest 'No intermediate patch files' 'still exist'
 	local EDS="$(find rootdir/var/lib/apt/lists -name '*.ed' -o -name '*.ed.*')"
@@ -224,6 +224,14 @@ SHA256-Download:
 	testsuccessequal "$(cat "${PKGFILE}")
 " aptcache show apt oldstuff
 
+	# we reuse the entire state of the previous test here
+	msgmsg "Testcase: good files from previous fails are picked up from partial: $*"
+	wasmergeused "$@"
+	testfailure grep '^GET /Packages.diff/Index HTTP/1.1' rootdir/tmp/testsuccess.output
+	testnopackage oldstuff
+	testsuccessequal "$(cat Packages-future)
+" aptcache show apt newstuff futurestuff
+
 	# we reuse the archive state of the previous test here
 	msgmsg "Testcase: downloading a patch fails, but successful fallback: $*"
 	rm -rf rootdir/var/lib/apt/lists
@@ -294,7 +302,7 @@ SHA256-Download:
  $(sha256sum "${PATCHFILE}.gz" | cut -d' ' -f 1) $(stat -c%s "${PATCHFILE}.gz")000 $(basename "${PATCHFILE}.gz")" > "$PATCHINDEX"
 	generatereleasefiles '+1hour'
 	signreleasefiles
-	testsuccess apt update -o Debug::pkgAcquire::Diffs=1 "$@"
+	testsuccess apt update "$@"
 	cp -f rootdir/tmp/testsuccess.output rootdir/tmp/aptupdate.output
 	testsuccess grep 'bytes (Limit is' rootdir/tmp/aptupdate.output
 	testnopackage oldstuff
@@ -303,6 +311,9 @@ SHA256-Download:
 }
 echo 'Debug::pkgAcquire::Diffs "true";
 Debug::Acquire::Transaction "true";
+Debug::pkgAcquire::Worker "true";
+Debug::Acquire::http "true";
+Debug::pkgAcquire "true";
 Debug::pkgAcquire::rred "true";' > rootdir/etc/apt/apt.conf.d/rreddebug.conf
 
 testcase() {