if file is inaccessible for _apt, disable privilege drop in acquire

We had a very similar method previously for our own private usage, but
with some generalisation we can move this check into the acquire system
proper so that all frontends profit from this compatibility change.

As we are disabling a security feature here a warning is issued and
frontends are advised to consider reworking their download logic if
possible.

Note that this is implemented as an all or nothing situation: We can't
just (not) drop privileges for a subset of the files in a fetcher, so in
case you have to download some files with and some without you need to
use two fetchers.

2 files changed, 7 insertions, 4 deletions

diff --git a/test/integration/test-acquire-same-file-multiple-times b/test/integration/test-acquire-same-file-multiple-times
index 526765521..a850f897c 100755
--- a/test/integration/test-acquire-same-file-multiple-times
+++ b/test/integration/test-acquire-same-file-multiple-times
@@ -14,10 +14,9 @@ filedown() {
 	msgtest 'Downloading the same URI twice over file' "$1"
 	testsuccess --nomsg apthelper download-file file:///$APTARCHIVE/foo ./downloaded/foo1 '' file:///$APTARCHIVE/foo ./downloaded/foo2 '' -o Debug::pkgAcquire::Worker=1
 	cp rootdir/tmp/testsuccess.output download.log
-	#cat download.log
 	testsuccess cmp $TESTFILE ./downloaded/foo1
 	testsuccess cmp ./downloaded/foo1 ./downloaded/foo2
-	#testequal '1' grep -c '200%20URI%20Start' ./download.log
+	testequal '1' grep -c '200%20URI%20Start' ./download.log
 	testequal '1' grep -c '201%20URI%20Done' ./download.log
 	rm -f ./downloaded/foo1 ./downloaded/foo2
 }
diff --git a/test/integration/test-apt-get-changelog b/test/integration/test-apt-get-changelog
index 6ca05d0fa..502920617 100755
--- a/test/integration/test-apt-get-changelog
+++ b/test/integration/test-apt-get-changelog
@@ -47,8 +47,12 @@ testsuccessequal "'http://localhost:8080/main/f/foo/foo_1.0.changelog' foo.chang
 'http://localhost:8080/main/libb/libbar/libbar_1.0.changelog' libbar.changelog" aptget changelog foo libbar --print-uris -o Acquire::Changelogs::URI::Override::Label::Debian='http://localhost:8080/CHANGEPATH.changelog'
 
 releasechanger 'Changelogs' 'no'
-testequal 'E: Failed to fetch changelog:/foo.changelog  Changelog unavailable for foo=1.0
-' aptget changelog foo -qq -d
+if [ "$(id -u)" = '0' ]; then
+	testfailuremsg "W: Can't drop privileges for downloading as file 'foo.changelog' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
+E: Failed to fetch changelog:/foo.changelog  Changelog unavailable for foo=1.0" aptget changelog foo -d
+else
+	testfailuremsg 'E: Failed to fetch changelog:/foo.changelog  Changelog unavailable for foo=1.0' aptget changelog foo -d
+fi
 
 sed -i '/^Changelogs: / d' $(find rootdir/var/lib/apt/lists -name '*Release')
 releasechanger 'Label' 'Testcases'