Parse last line in deb file correctly by adding a newline

While merging apt-pkg and apt-inst libraries the codepath of handling
deb files in apt-pkg was adapted to use the 'old' code from apt-inst
instead of fork&exec of dpkg-deb -I. The information we get this way
forms the main part of the package stanza, but we add a few
semi-optional fields to the stanza to make it look and work more
like a stanza we got from a repository.

Just be careful with the area where these two parts touch as if,
hypothetically, we would stip all newlines around the parts,
but forget to add a newline between them later, the two lines around
the merge would stick a bit too close together forming one which could
result in fun parsing errors if this merged line was previously e.g. a
well-formed Depends line and has now extra fluff attached.

This codepath has a history with too many newlines (#802553) though,
so how likely is it really that it will some day lack one you may ask.

References: 6089a4b17c61ef30b2efc00e270b0907f51f352a

2 files changed, 5 insertions, 1 deletions

diff --git a/apt-pkg/deb/debindexfile.cc b/apt-pkg/deb/debindexfile.cc
index 43317d314..e1698e151 100644
--- a/apt-pkg/deb/debindexfile.cc
+++ b/apt-pkg/deb/debindexfile.cc
@@ -189,7 +189,7 @@ bool debDebPkgFileIndex::GetContent(std::ostream &content, std::string const &de
    while (isspace_ascii(Control[0]))
       Control++;
 
-   content << Control;
+   content << Control << '\n';
    content << "Filename: " << debfile << "\n";
    content << "Size: " << std::to_string(Buf.st_size) << "\n";
 
diff --git a/test/integration/test-apt-get-install-deb b/test/integration/test-apt-get-install-deb
index 002c1aef8..7fa5ca3e7 100755
--- a/test/integration/test-apt-get-install-deb
+++ b/test/integration/test-apt-get-install-deb
@@ -168,12 +168,16 @@ createpkg 'trailing-newline' '' '
 createpkg 'double-trailing-newline' '' '
 
 '
+createpkg 'last-line-parse' '' 'Pre-Depends: pkg-as-it-should-be
+'
 
 echo 'Package: /pkg-/
 Pin: release a=experimental
 Pin-Priority: 501' > rootdir/etc/apt/preferences.d/pinit
 
+testfailuremsg 'E: Unable to correct problems, you have held broken packages.' aptget install -q=0 ./incoming/pkg-last-line-parse_0_all.deb
 testsuccess aptget install ./incoming/pkg-as-it-should-be_0_all.deb
+testsuccess aptget install ./incoming/pkg-last-line-parse_0_all.deb
 testsuccess aptget install "$(readlink -f ./incoming/pkg-leading-newline_0_all.deb)"
 testsuccess aptget install ./incoming/pkg-trailing-newline_0_all.deb
 testsuccess aptget install ./incoming/pkg-double-trailing-newline_0_all.deb