Initial support for snapshot servers, apt --snapshot option

Provide snapshot support for offical Debian and Ubuntu archives.

There are two ways to enable snapshots for sources:

1. Add Snapshot: yes to your sources file ([snapshot=yes]). This
   will allow you to specify a snapshot to use when updating or
   installing using the --snapshot,-S option.

2. Add Snapshot: ID to your sources files to request a specific
   snapshot for this source.

Snapshots are discovered using Label and Origin fields in the Release
file of the main source, hence you need to have updated the source at
least once before you can use snapshots.

The Release file may also declare a snapshots server to use, similar
to Changelogs, it can contain a Snapshots field with the values:

1. `Snapshots: https://example.com/@SNAPSHOTID@` where `@SNAPSHOTID@`
   is a placeholder that is replaced with the requested snapshot id

2. `Snapshots: no` to disable snapshot support for this source.
   Requesting snapshots for this source will result in a failure
   to load the source.

The implementation adds a SHADOWED option to deb source entries,
and marks the main entry as SHADOWED when a snapshot has been
requested, which will cause it to be updated, but not included
in the generated cache.

The concern here was that we need to keep generating the shadowed
entries because the cleanup in `apt update` deletes any files not
queued for download, so we gotta keep downloading the main source.

This design is not entirely optimal, but avoids the pitfalls of
having to reimplement list cleanup.

Gaps:

- Ubuntu Pro repositories and PPAs are not yet supported.

12 files changed, 367 insertions, 4 deletions

diff --git a/apt-pkg/deb/debmetaindex.cc b/apt-pkg/deb/debmetaindex.cc
index c6005f1c8..4133540ab 100644
--- a/apt-pkg/deb/debmetaindex.cc
+++ b/apt-pkg/deb/debmetaindex.cc
@@ -123,6 +123,9 @@ class APT_HIDDEN debReleaseIndexPrivate					/*{{{*/
    time_t DateMaxFuture;
    time_t NotBefore;
 
+   std::string Snapshot;
+   std::string SnapshotsServer;
+
    std::vector<std::string> Architectures;
    std::vector<std::string> NoSupportForAll;
    std::vector<std::string> SupportedComponents;
@@ -479,6 +482,7 @@ bool debReleaseIndex::Load(std::string const &Filename, std::string * const Erro
    Suite = Section.FindS("Suite");
    Codename = Section.FindS("Codename");
    ReleaseNotes = Section.FindS("Release-Notes");
+   d->SnapshotsServer = Section.FindS("Snapshots");
    {
       std::string const archs = Section.FindS("Architectures");
       if (archs.empty() == false)
@@ -789,6 +793,18 @@ bool debReleaseIndex::SetDateMaxFuture(time_t const DateMaxFuture)
       return _error->Error(_("Conflicting values set for option %s regarding source %s %s"), "Date-Max-Future", URI.c_str(), Dist.c_str());
    return true;
 }
+bool debReleaseIndex::SetSnapshot(std::string const Snapshot)
+{
+   if (d->Snapshot.empty())
+      d->Snapshot = Snapshot;
+   else if (d->Snapshot != Snapshot)
+      return _error->Error(_("Conflicting values set for option %s regarding source %s %s"), "Snapshot", URI.c_str(), Dist.c_str());
+   return true;
+}
+std::string debReleaseIndex::GetSnapshotsServer() const
+{
+   return d->SnapshotsServer;
+}
 bool debReleaseIndex::SetSignedBy(std::string const &pSignedBy)
 {
    if (SignedBy.empty() == true && pSignedBy.empty() == false)
@@ -1123,6 +1139,17 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 	 return defVal;
       return StringToBool(opt->second, defVal);
    }
+   static std::string GetSnapshotOption(std::map<std::string, std::string> const &Options, char const * const name, const std::string defVal="")
+   {
+      std::map<std::string, std::string>::const_iterator const opt = Options.find(name);
+      if (opt == Options.end())
+	 return defVal;
+      int boolVal = StringToBool(opt->second, -1);
+      if (boolVal != -1)
+	 return boolVal ? _config->Find("APT::Snapshot") : "";
+      return opt->second;
+   }
+
 
    static std::vector<std::string> GetMapKeys(std::map<std::string, std::string> const &Options)
    {
@@ -1167,7 +1194,7 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
       return true;
    }
 
-   static debReleaseIndex * GetDebReleaseIndexBy(std::vector<metaIndex *> &List, std::string const &URI,
+   static debReleaseIndex * GetDebReleaseIndexBy(std::vector<metaIndex *> &List, std::string URI,
 			   std::string const &Dist, std::map<std::string, std::string> const &Options)
    {
       std::map<std::string, std::string> ReleaseOptions{{
@@ -1182,6 +1209,8 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 	 ReleaseOptions.emplace("ALLOW_WEAK", "true");
       if (GetBoolOption(Options, "allow-downgrade-to-insecure", _config->FindB("Acquire::AllowDowngradeToInsecureRepositories")))
 	 ReleaseOptions.emplace("ALLOW_DOWNGRADE_TO_INSECURE", "true");
+      if (GetBoolOption(Options, "SHADOWED", false))
+	 ReleaseOptions.emplace("SHADOWED", "true");
 
       auto InReleasePath = Options.find("inrelease-path");
       if (InReleasePath != Options.end())
@@ -1221,10 +1250,78 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
    }
 
    protected:
+   // This is a duplicate of pkgAcqChangelog::URITemplate()  with some changes to work 
+   // on metaIndex instead of cache structures, and using Snapshots
+   std::string SnapshotServer(debReleaseIndex const *Rls) const
+   {
+      if (Rls->GetLabel().empty() && Rls->GetOrigin().empty())
+	 return "";
+      std::string const serverConfig = "Acquire::Snapshots::URI";
+      std::string server;
+#define APT_EMPTY_SERVER        \
+   if (server.empty() == false) \
+   {                            \
+      if (server != "no")       \
+	 return server;         \
+      return "";                \
+   }
+#define APT_CHECK_SERVER(X, Y)                                                                     \
+   if (not Rls->Get##X().empty())                                                                  \
+   {                                                                                               \
+      std::string const specialServerConfig = serverConfig + "::" + Y + #X + "::" + Rls->Get##X(); \
+      server = _config->Find(specialServerConfig);                                                 \
+      APT_EMPTY_SERVER                                                                             \
+   }
+      // this way e.g. Debian-Security can fallback to Debian
+      APT_CHECK_SERVER(Label, "Override::")
+      APT_CHECK_SERVER(Origin, "Override::")
 
-   bool CreateItemInternal(std::vector<metaIndex *> &List, std::string const &URI,
+      server = Rls->GetSnapshotsServer();
+      APT_EMPTY_SERVER
+
+      APT_CHECK_SERVER(Label, "")
+      APT_CHECK_SERVER(Origin, "")
+#undef APT_CHECK_SERVER
+#undef APT_EMPTY_SERVER
+      return "";
+   }
+   bool CreateItemInternal(std::vector<metaIndex *> &List, std::string URI,
+			   std::string const &Dist, std::string const &Section,
+			   bool const &IsSrc, std::map<std::string, std::string> Options) const
+   {
+      auto Snapshot = GetSnapshotOption(Options, "snapshot");
+      if (not Snapshot.empty()) {
+	 std::map<std::string, std::string> SnapshotOptions = Options;
+
+	 Options.emplace("SHADOWED", "true");
+
+	 auto const Deb = GetDebReleaseIndexBy(List, URI, Dist, Options);
+	 std::string filename;
+	 if (not ReleaseFileName(Deb, filename))
+	    return _error->Error("Cannot identify snapshot server for %s %s - run update without snapshot id first", URI.c_str(), Dist.c_str());
+	 auto OldDeb = dynamic_cast<debReleaseIndex *>(Deb->UnloadedClone());
+	 if (not OldDeb->Load(filename, nullptr))
+	    return _error->Error("Cannot identify snapshot server for %s %s - run update without snapshot id first", URI.c_str(), Dist.c_str());
+	 auto Server = SnapshotServer(OldDeb);
+	 delete OldDeb;
+
+	 if (Server.empty())
+	    return _error->Error("Snapshots not supported for %s %s", URI.c_str(), Dist.c_str());
+
+	 auto SnapshotURI = SubstVar(Server, "@SNAPSHOTID@", Snapshot);
+
+	 if (not CreateItemInternalOne(List, SnapshotURI, Dist, Section, IsSrc, SnapshotOptions))
+	    return false;
+      }
+      if (not CreateItemInternalOne(List, URI, Dist, Section, IsSrc, Options))
+	 return false;
+
+
+      return true;
+   }
+   bool CreateItemInternalOne(std::vector<metaIndex *> &List, std::string URI,
 			   std::string const &Dist, std::string const &Section,
-			   bool const &IsSrc, std::map<std::string, std::string> const &Options) const
+			   bool const &IsSrc, std::map<std::string, std::string> Options) const
    {
       auto const Deb = GetDebReleaseIndexBy(List, URI, Dist, Options);
       if (Deb == nullptr)
@@ -1263,7 +1360,8 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 	  Deb->SetValidUntilMax(GetTimeOption(Options, "valid-until-max")) == false ||
 	  Deb->SetValidUntilMin(GetTimeOption(Options, "valid-until-min")) == false ||
 	  Deb->SetCheckDate(GetTriStateOption(Options, "check-date")) == false ||
-	  Deb->SetDateMaxFuture(GetTimeOption(Options, "date-max-future")) == false)
+	  Deb->SetDateMaxFuture(GetTimeOption(Options, "date-max-future")) == false ||
+	  Deb->SetSnapshot(GetSnapshotOption(Options, "snapshot")) == false)
 	 return false;
 
       std::map<std::string, std::string>::const_iterator const signedby = Options.find("signed-by");
diff --git a/apt-pkg/deb/debmetaindex.h b/apt-pkg/deb/debmetaindex.h
index 717f08e2b..a1a9c41b5 100644
--- a/apt-pkg/deb/debmetaindex.h
+++ b/apt-pkg/deb/debmetaindex.h
@@ -51,6 +51,8 @@ class APT_HIDDEN debReleaseIndex : public metaIndex
    bool SetValidUntilMax(time_t const Valid);
    bool SetCheckDate(TriState const CheckDate);
    bool SetDateMaxFuture(time_t const DateMaxFuture);
+   bool SetSnapshot(std::string Snapshot);
+   std::string GetSnapshotsServer() const; // As defined in the Release file
    bool SetSignedBy(std::string const &SignedBy);
    std::map<std::string, std::string> GetReleaseOptions();
 
diff --git a/apt-pkg/indexfile.cc b/apt-pkg/indexfile.cc
index f13b52940..1176903f4 100644
--- a/apt-pkg/indexfile.cc
+++ b/apt-pkg/indexfile.cc
@@ -121,6 +121,7 @@ std::string IndexTarget::Option(OptionKeys const EnumKey) const		/*{{{*/
       APT_CASE(ALLOW_WEAK);
       APT_CASE(ALLOW_DOWNGRADE_TO_INSECURE);
       APT_CASE(INRELEASE_PATH);
+      APT_CASE(SHADOWED);
 #undef APT_CASE
       case FILENAME:
       {
@@ -221,6 +222,8 @@ unsigned long pkgDebianIndexTargetFile::Size() const				/*{{{*/
 									/*}}}*/
 bool pkgDebianIndexTargetFile::Exists() const					/*{{{*/
 {
+   if (Target.OptionBool(IndexTarget::SHADOWED))
+      return false;
    return FileExists(IndexFileName());
 }
 									/*}}}*/
diff --git a/apt-pkg/indexfile.h b/apt-pkg/indexfile.h
index d0b045a9d..95cee5dbc 100644
--- a/apt-pkg/indexfile.h
+++ b/apt-pkg/indexfile.h
@@ -91,6 +91,7 @@ class APT_PUBLIC IndexTarget							/*{{{*/
       ALLOW_WEAK,
       ALLOW_DOWNGRADE_TO_INSECURE,
       INRELEASE_PATH,
+      SHADOWED,
    };
    std::string Option(OptionKeys const Key) const;
    bool OptionBool(OptionKeys const Key) const;
diff --git a/apt-pkg/init.cc b/apt-pkg/init.cc
index b9d9b15d2..f70dbf308 100644
--- a/apt-pkg/init.cc
+++ b/apt-pkg/init.cc
@@ -209,6 +209,9 @@ bool pkgInitConfig(Configuration &Cnf)
    Cnf.CndSet("Acquire::Changelogs::URI::Origin::Ubuntu", "https://changelogs.ubuntu.com/changelogs/pool/@CHANGEPATH@/changelog");
    Cnf.CndSet("Acquire::Changelogs::AlwaysOnline::Origin::Ubuntu", true);
 
+   Cnf.CndSet("Acquire::Snapshots::URI::Origin::Debian", "https://snapshot.debian.org/archive/debian/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Override::Label::Debian-Security", "https://snapshot.debian.org/archive/debian-security/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Origin::Ubuntu", "https://snapshot.ubuntu.com/ubuntu/@SNAPSHOTID@/");
 
    Cnf.CndSet("DPkg::Path", "/usr/sbin:/usr/bin:/sbin:/bin");
 
diff --git a/apt-pkg/sourcelist.cc b/apt-pkg/sourcelist.cc
index 0ac59fcfc..055cf4142 100644
--- a/apt-pkg/sourcelist.cc
+++ b/apt-pkg/sourcelist.cc
@@ -120,6 +120,7 @@ bool pkgSourceList::Type::ParseStanza(vector<metaIndex *> &List,	/*{{{*/
    mapping.insert(std::make_pair("Valid-Until-Max", std::make_pair("valid-until-max", false)));
    mapping.insert(std::make_pair("Check-Date", std::make_pair("check-date", false)));
    mapping.insert(std::make_pair("Date-Max-Future", std::make_pair("date-max-future", false)));
+   mapping.insert(std::make_pair("Snapshot", std::make_pair("snapshot", false)));
    mapping.insert(std::make_pair("Signed-By", std::make_pair("signed-by", false)));
    mapping.insert(std::make_pair("PDiffs", std::make_pair("pdiffs", false)));
    mapping.insert(std::make_pair("By-Hash", std::make_pair("by-hash", false)));
diff --git a/apt-private/private-cmndline.cc b/apt-private/private-cmndline.cc
index 765378ea2..980d00530 100644
--- a/apt-private/private-cmndline.cc
+++ b/apt-private/private-cmndline.cc
@@ -88,6 +88,7 @@ static bool addArgumentsAPTCache(std::vector<CommandLine::Args> &Args, char cons
    addArg('g', "generate", "APT::Cache::Generate", 0);
    addArg('t', "target-release", "APT::Default-Release", CommandLine::HasArg);
    addArg('t', "default-release", "APT::Default-Release", CommandLine::HasArg);
+   addArg('S', "snapshot", "APT::Snapshot", CommandLine::HasArg);
 
    addArg('p', "pkg-cache", "Dir::Cache::pkgcache", CommandLine::HasArg);
    addArg('s', "src-cache", "Dir::Cache::srcpkgcache", CommandLine::HasArg);
@@ -269,6 +270,7 @@ static bool addArgumentsAPTGet(std::vector<CommandLine::Args> &Args, char const
    addArg('m',"ignore-missing","APT::Get::Fix-Missing",0);
    addArg('t',"target-release","APT::Default-Release",CommandLine::HasArg);
    addArg('t',"default-release","APT::Default-Release",CommandLine::HasArg);
+   addArg('S', "snapshot", "APT::Snapshot", CommandLine::HasArg);
    addArg(0,"download","APT::Get::Download",0);
    addArg(0,"fix-missing","APT::Get::Fix-Missing",0);
    addArg(0,"ignore-hold","APT::Ignore-Hold",0);
diff --git a/doc/apt-get.8.xml b/doc/apt-get.8.xml
index f4d347c70..beecfd27c 100644
--- a/doc/apt-get.8.xml
+++ b/doc/apt-get.8.xml
@@ -528,6 +528,16 @@
      Configuration Item: <literal>APT::Get::List-Cleanup</literal>.</para></listitem>
      </varlistentry>
 
+     <varlistentry><term><option>-S</option></term>
+                   <term><option>--snapshot</option></term>
+     <listitem><para>This option controls the snapshot chosen for archives with <literal>Snapshot: enable</literal>
+             in the source entry. For example, <option>-S 20220102T030405Z</option> selects a snapshot from January 2nd,
+             2022 at 03:04:05 UTC.
+     Configuration Item: <literal>APT::Snapshot</literal>;
+     see also the &sources-list; manual page.
+     </para></listitem>
+     </varlistentry>
+
      <varlistentry><term><option>-t</option></term>
                    <term><option>--target-release</option></term>
                    <term><option>--default-release</option></term>
diff --git a/doc/apt.conf.5.xml b/doc/apt.conf.5.xml
index 189fb7d7d..e815a58a1 100644
--- a/doc/apt.conf.5.xml
+++ b/doc/apt.conf.5.xml
@@ -211,6 +211,10 @@ APT::Compressor::rev {
      version is available. Contains release name, codename or release version. Examples: 'stable', 'testing',
      'unstable', '&debian-stable-codename;', '&debian-testing-codename;', '4.0', '5.0*'. See also &apt-preferences;.</para></listitem>
      </varlistentry>
+     <varlistentry><term><option>Snapshot</option></term>
+         <listitem><para>Snapshot to use for all repositories configured with <literal>Snapshot: yes</literal>. See also &sources-list;, the <option>--snapshot</option> option that sets this value, and <option>Acquire::Snapshots::URI</option> below.</para></listitem>
+     </varlistentry>
+
 
      <varlistentry><term><option>Ignore-Hold</option></term>
      <listitem><para>Ignore held packages; this global option causes the problem resolver to
@@ -647,6 +651,26 @@ APT::Compressor::rev {
 	  this source can't be used to acquire changelog files from. Another source will be tried
 	  if available in this case.
 	</para></listitem>
+</varlistentry>
+
+     <varlistentry><term><option>Snapshots::URI</option> scope</term>
+	<listitem><para>
+	  Like changelogs, snapshots can only be acquired if an URI is known from where to get them.
+	  Preferable the Release file indicates this in a 'Snapshots' field. If this isn't
+	  available the Label/Origin field of the Release file is used to check if a
+	  <literal>Acquire::Snapshots::URI::Label::<replaceable>LABEL</replaceable></literal> or
+	  <literal>Acquire::Snapshots::URI::Origin::<replaceable>ORIGIN</replaceable></literal> option
+	  exists and if so this value is taken. The value in the Release file can be overridden
+	  with <literal>Acquire::Snapshots::URI::Override::Label::<replaceable>LABEL</replaceable></literal>
+	  or <literal>Acquire::Snapshots::URI::Override::Origin::<replaceable>ORIGIN</replaceable></literal>.
+
+      The value should be a normal URI to a directory, except that the snapshot ID replaced with the
+      placeholder <literal>@SNAPSHOTID</literal>.
+
+	  The special value '<literal>no</literal>' is available for this option indicating that
+	  this source cannot be used to acquire snapshots from. Another source will be tried
+	  if available in this case.
+	</para></listitem>
     </varlistentry>
 
    </variablelist>
diff --git a/doc/examples/configure-index b/doc/examples/configure-index
index 5ec209766..e6d7c31ea 100644
--- a/doc/examples/configure-index
+++ b/doc/examples/configure-index
@@ -59,6 +59,9 @@ APT
   VersionedKernelPackages "<LIST>"; // regular expressions to be protected from autoremoval (kernel uname will be appended)
   Protect-Kernels "<BOOL>"; // whether to protect installed kernels against autoremoval (default: true)
 
+  // Currently active snapshot
+  Snapshot "<STRING>";
+
   // Options for apt-get
   Get
   {
@@ -398,6 +401,14 @@ Acquire
     Override::Origin::* "<STRING>";
     Override::Label::* "<STRING>";
   };
+  Snapshots::URI
+  {
+    // Origin::Debian "https://snapshot.debian.org/snapshot/@SNAPSHOTID@/";
+    Origin::* "<STRING>";
+    Label::* "<STRING>";
+    Override::Origin::* "<STRING>";
+    Override::Label::* "<STRING>";
+  };
   Changelogs::AlwaysOnline "<BOOL>"; // even if the changelog file exists get it online (as the file is incomplete)
   Changelogs::AlwaysOnline::Origin::* "<BOOL>";
 };
diff --git a/doc/sources.list.5.xml b/doc/sources.list.5.xml
index 478694c77..4fa7a245b 100644
--- a/doc/sources.list.5.xml
+++ b/doc/sources.list.5.xml
@@ -392,6 +392,23 @@ Signed-By:
 		or, if that fails, a <filename>Release</filename> file and its associated <filename>Release.gpg</filename> file. By setting this option,
 		the specified path will be tried instead of the InRelease file,
 		and the fallback to <filename>Release</filename> files will be disabled.
+    </para></listitem>
+
+    <listitem><para><option>Snapshot</option> (<option>snapshot</option>)
+        allows selecting an earlier version of the archive from the snapshot service. Supported
+    values are: </para>
+        <itemizedlist>
+        <listitem>
+            <para><literal>enable</literal> to allow selecting a snapshot with the <option>--snapshot</option> option, or</para>
+        </listitem>
+        <listitem>
+            <para>a snapshot ID to select a specific snapshot.</para>
+        </listitem>
+    </itemizedlist>
+        <para>
+            Snapshot IDs are usually timestamps in the form of <literal>YYYYMMDDTHHMMSSZ</literal>, such as
+            <literal>20220102T030405Z</literal> which is the January 2nd, 2022 at 03:04:05 UTC, servers may
+            however support additional types of IDs, and APT does not perform any checks so far.
 	  </para></listitem>
 
        </itemizedlist>
diff --git a/test/integration/test-snapshot b/test/integration/test-snapshot
new file mode 100755
index 000000000..609e3ade0
--- /dev/null
+++ b/test/integration/test-snapshot
@@ -0,0 +1,191 @@
+#!/bin/sh
+set -e
+
+TESTDIR="$(readlink -f "$(dirname "$0")")"
+. "$TESTDIR/framework"
+
+setupenvironment
+configarchitecture 'amd64'
+
+buildsimplenativepackage 'awesome' 'native' '42' 'stable'
+buildsimplenativepackage 'foo' 'all' '1.0' 'stable'
+buildsimplenativepackage 'libbar' 'all' '1.0' 'stable'
+
+getlabelfromsuite() { echo 'Testcases'; }
+getoriginfromsuite() { echo 'Debian'; }
+
+setupaptarchive --no-update
+changetowebserver
+testsuccess aptget update
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris --snapshot OPTIONNOTSET
+
+# Enable the snapshot feature
+sed -i 's/http:/[snapshot=enable] http:/' rootdir/etc/apt/sources.list.d/*
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris
+
+for option in -S --snapshot; do
+testsuccessequal "'https://snapshot.debian.org/archive/debian/BANANA/dists/stable/InRelease' snapshot.debian.org_archive_debian_BANANA_dists_stable_InRelease 0 
+'https://snapshot.debian.org/archive/debian/BANANA/dists/stable/main/source/Sources.xz' snapshot.debian.org_archive_debian_BANANA_dists_stable_main_source_Sources 0 
+'https://snapshot.debian.org/archive/debian/BANANA/dists/stable/main/binary-amd64/Packages.xz' snapshot.debian.org_archive_debian_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'https://snapshot.debian.org/archive/debian/BANANA/dists/stable/main/binary-all/Packages.xz' snapshot.debian.org_archive_debian_BANANA_dists_stable_main_binary-all_Packages 0 
+'https://snapshot.debian.org/archive/debian/BANANA/dists/stable/main/i18n/Translation-en.xz' snapshot.debian.org_archive_debian_BANANA_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris $option BANANA
+done
+
+
+# Let us update for realz
+mkdir aptarchive/snapshot/BANANA -p
+cp -a aptarchive/dists aptarchive/snapshot/BANANA
+
+testsuccessequal "Hit:1 http://localhost:${APTHTTPPORT} stable InRelease
+Get:2 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable InRelease [$(stat -c %s aptarchive/dists/stable/InRelease) B]
+Get:3 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main Sources [$(stat -c %s aptarchive/dists/stable/main/source/Sources.gz) B]
+Get:4 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main amd64 Packages [$(stat -c %s aptarchive/dists/stable/main/binary-amd64/Packages.gz) B]
+Get:5 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main all Packages [$(stat -c %s aptarchive/dists/stable/main/binary-all/Packages.gz) B]
+Get:6 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main Translation-en [$(stat -c %s aptarchive/dists/stable/main/i18n/Translation-en.gz) B]
+Reading package lists..." \
+	aptget update  -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/" -SBANANA
+
+msgmsg "Cache constructed without snapshot"
+testsuccessequal "Package files:
+ 500 http://localhost:${APTHTTPPORT} stable/main all Packages
+     release o=Debian,a=stable,n=stable,l=Testcases,c=main,b=all
+     origin localhost
+ 500 http://localhost:${APTHTTPPORT} stable/main amd64 Packages
+     release o=Debian,a=stable,n=stable,l=Testcases,c=main,b=amd64
+     origin localhost
+Pinned packages:" \
+	aptcache policy  -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/" 
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/pool/awesome_42_amd64.deb' awesome_42_amd64.deb $(stat -c %s aptarchive/pool/awesome_42_amd64.deb) " \
+	aptget install --print-uris -qq awesome
+
+msgmsg "Cache constructed with snapshot"
+testsuccessequal "Package files:
+ 500 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main all Packages
+     release o=Debian,a=stable,n=stable,l=Testcases,c=main,b=all
+     origin localhost
+ 500 http://localhost:${APTHTTPPORT}/snapshot/BANANA stable/main amd64 Packages
+     release o=Debian,a=stable,n=stable,l=Testcases,c=main,b=amd64
+     origin localhost
+Pinned packages:" \
+	aptcache policy  -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/" -SBANANA
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/snapshot/BANANA/pool/awesome_42_amd64.deb' awesome_42_amd64.deb $(stat -c %s aptarchive/pool/awesome_42_amd64.deb) " \
+	aptget install --print-uris -qq awesome  -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/" -SBANANA
+
+
+releasechanger() {
+	# modifying the Release files in lists… bad stuff. Good that this is only a test…
+	sed -i "s#^${1}: .*#${1}: ${2}#" $(find rootdir/var/lib/apt/lists -name '*Release')
+	rm -f rootdir/var/cache/apt/*.bin
+}
+
+msgmsg "Origin: Ubuntu"
+releasechanger 'Origin' 'Ubuntu'
+testsuccessequal "'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/InRelease' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_InRelease 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/source/Sources.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_source_Sources 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/binary-amd64/Packages.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/binary-all/Packages.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_binary-all_Packages 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/i18n/Translation-en.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris $option BANANA
+
+msgmsg "Label: Debian"
+releasechanger 'Label' 'Debian'
+testsuccessequal "'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/InRelease' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_InRelease 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/source/Sources.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_source_Sources 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/binary-amd64/Packages.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/binary-all/Packages.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_binary-all_Packages 0 
+'https://snapshot.ubuntu.com/ubuntu/BANANA/dists/stable/main/i18n/Translation-en.xz' snapshot.ubuntu.com_ubuntu_BANANA_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris $option BANANA
+
+testsuccessequal "'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/InRelease' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris -o Acquire::Snapshots::URI::Label::Debian="http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/" -SBANANA
+
+msgmsg "Snapshots: set in the InRelease file"
+sed -i '/^Origin: / a\
+Snapshots: https://example.org/snapshots/@SNAPSHOTID@/' $(find rootdir/var/lib/apt/lists -name '*Release')
+rm -f rootdir/var/cache/apt/*.bin
+
+testsuccessequal "'https://example.org/snapshots/BANANA/dists/stable/InRelease' example.org_snapshots_BANANA_dists_stable_InRelease 0 
+'https://example.org/snapshots/BANANA/dists/stable/main/source/Sources.xz' example.org_snapshots_BANANA_dists_stable_main_source_Sources 0 
+'https://example.org/snapshots/BANANA/dists/stable/main/binary-amd64/Packages.xz' example.org_snapshots_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'https://example.org/snapshots/BANANA/dists/stable/main/binary-all/Packages.xz' example.org_snapshots_BANANA_dists_stable_main_binary-all_Packages 0 
+'https://example.org/snapshots/BANANA/dists/stable/main/i18n/Translation-en.xz' example.org_snapshots_BANANA_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris -SBANANA
+
+releasechanger 'Snapshots' 'no'
+testfailuremsg "E: Snapshots not supported for http://localhost:${APTHTTPPORT}/ stable
+E: Snapshots not supported for http://localhost:${APTHTTPPORT}/ stable
+E: The list of sources could not be read." aptget update --print-uris -S BANANA
+
+msgmsg "Snapshot URI configured in apt.conf"
+sed -i '/^Snapshots: / d' $(find rootdir/var/lib/apt/lists -name '*Release')
+releasechanger 'Label' 'Testcases'
+
+echo "Acquire::Snapshots::URI::Label::Testcases \"http://localhost:${APTHTTPPORT}/snapshot/@SNAPSHOTID@/\";" > rootdir/etc/apt/apt.conf.d/changelog.conf
+testsuccessequal "'http://localhost:${APTHTTPPORT}/dists/stable/InRelease' localhost:${APTHTTPPORT}_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/InRelease' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_InRelease 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_dists_stable_main_i18n_Translation-en 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/source/Sources.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_source_Sources 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/binary-amd64/Packages.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_binary-amd64_Packages 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/binary-all/Packages.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_binary-all_Packages 0 
+'http://localhost:${APTHTTPPORT}/snapshot/BANANA/dists/stable/main/i18n/Translation-en.xz' localhost:${APTHTTPPORT}_snapshot_BANANA_dists_stable_main_i18n_Translation-en 0 " aptget update --print-uris -SBANANA
+
+rm rootdir/etc/apt/apt.conf.d/changelog.conf
+
+exit 0
+msgmsg "Failure cases"
+
+# no @CHANGEPATH@ in the URI
+testequal 'E: Failed to fetch changelog:/foo.changelog  Changelog unavailable for foo=1.0' \
+	aptget update  -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/snapshot" -SBANANA
+
+testequal "E: Failed to fetch http://localhost:${APTHTTPPORT}/does/not/exist/main/f/foo/foo_1.0/change.txt  Changelog unavailable for foo=1.0 (404  Not Found)" \
+	aptget update -o Acquire::Snapshots::URI::Label::Testcases="http://localhost:${APTHTTPPORT}/does/not/exist/@SNAPSHOTID@" -SBANANA
+
+
+