Support records larger than 32kb in 'apt show'

The default buffer size for pkgTagFile is 32kb which should be big
enough for everything… expect for enormous lists of provides,
resulting in:

$ apt show librust-winapi-dev
E: Unable to parse package file /var/lib/apt/lists/ftp.br.debian.org_debian_dists_unstable_main_binary-amd64_Packages (2)
E: Internal Error, Unable to parse a package record

The "apt-cache show" codepath uses instead a max size for all files,
which seems a bit excessive, but works – using the max size for the file
in question seems most appropriate.

The patch is written for the 1.6.y series as a rewrite of the related
code in the 1.7.y series (commit bf53f39c9a0221b670ffff74053ed36fc502d5a0)
removed this problem before it was reported.

Closes: #905527
LP: #1787120
(cherry picked from commit 409ceec9ed30cbebd8ece1ef7ce667ab5a32f9df)

2 files changed, 35 insertions, 2 deletions

diff --git a/apt-private/private-show.cc b/apt-private/private-show.cc
index cd7a2a064..d96335977 100644
--- a/apt-private/private-show.cc
+++ b/apt-private/private-show.cc
@@ -177,9 +177,9 @@ static bool DisplayRecordV2(pkgCacheFile &CacheFile, pkgCache::VerIterator const
 
    // Read the record
    pkgTagSection Tags;
-   pkgTagFile TagF(&PkgF);
+   pkgTagFile TagF(&PkgF, Vf->Size);
 
-   if (TagF.Jump(Tags, V.FileList()->Offset) == false)
+   if (TagF.Jump(Tags, Vf->Offset) == false)
       return _error->Error("Internal Error, Unable to parse a package record");
 
    // make size nice
diff --git a/test/integration/test-apt-cli-show b/test/integration/test-apt-cli-show
index 754b3aa5f..54aaee4b8 100755
--- a/test/integration/test-apt-cli-show
+++ b/test/integration/test-apt-cli-show
@@ -7,10 +7,18 @@ TESTDIR="$(readlink -f "$(dirname "$0")")"
 setupenvironment
 configarchitecture 'i386' 'amd64'
 
+generatelotsofnames() {
+	for i in $(seq 0 10000); do
+		printf ', this-is-a-long-pkg-name-%s (= 0.a.long.version)' "$i"
+	done
+}
+
 DESCR='Some description
  That has multiple lines'
 insertpackage 'unstable' 'foo' 'all' '1.0' '' '' "$DESCR"
 insertpackage 'unstable' 'bar' 'i386,amd64' '1' '' '' "$DESCR"
+insertpackage 'unstable' 'large' 'all' '1' "Provides: pkga$(generatelotsofnames)" '' "$DESCR"
+insertpackage 'unstable' 'large2' 'all' '1' "Provides: foobar, pkga$(generatelotsofnames)" '' "$DESCR"
 insertinstalledpackage 'foo' 'all' '1.0'
 
 setupaptarchive
@@ -54,6 +62,31 @@ Description: Some description
  That has multiple lines
 " apt show bar:amd64
 
+testsuccessequal "Package: large
+Version: 1
+Priority: optional
+Section: other
+Maintainer: Joe Sixpack <joe@example.org>
+Installed-Size: 43.0 kB
+Provides: pkga$(generatelotsofnames)
+Download-Size: unknown
+APT-Sources: file:$APTARCHIVE unstable/main all Packages
+Description: Some description
+ That has multiple lines
+" apt show large
+testsuccessequal "Package: large2
+Version: 1
+Priority: optional
+Section: other
+Maintainer: Joe Sixpack <joe@example.org>
+Installed-Size: 43.0 kB
+Provides: foobar, pkga$(generatelotsofnames)
+Download-Size: unknown
+APT-Sources: file:$APTARCHIVE unstable/main all Packages
+Description: Some description
+ That has multiple lines
+" apt show large2
+
 # this is the default, but disabled by the testcases
 testsuccess apt show foo -o Apt::Cmd::Disable-Script-Warning=0
 cp rootdir/tmp/testsuccess.output aptshow.output