Seed snapshot servers for well-known hosts

This will attempt to fallback to a per-server setting if we could
not determine a value from the release file.

2 files changed, 38 insertions, 9 deletions

diff --git a/apt-pkg/deb/debmetaindex.cc b/apt-pkg/deb/debmetaindex.cc
index 4133540ab..ddc246349 100644
--- a/apt-pkg/deb/debmetaindex.cc
+++ b/apt-pkg/deb/debmetaindex.cc
@@ -1295,20 +1295,42 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 
 	 Options.emplace("SHADOWED", "true");
 
+	 ::URI ArchiveURI(URI);
+	 // Trim trailing and leading / from the path because we don't want them when calculating snapshot url
+	 if (not ArchiveURI.Path.empty() && ArchiveURI.Path[ArchiveURI.Path.length() - 1] == '/')
+	    ArchiveURI.Path.erase(ArchiveURI.Path.length() - 1);
+	 if (not ArchiveURI.Path.empty() && ArchiveURI.Path[0] == '/')
+	    ArchiveURI.Path.erase(0, 1);
+	 std::string Server;
+
 	 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;
 
+	 // The Release file and config based on that should be the ultimate source of truth.
+	 if (ReleaseFileName(Deb, filename))
+	 {
+	    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());
+	    Server = SnapshotServer(OldDeb);
+	    delete OldDeb;
+	 }
 	 if (Server.empty())
+	 {
+	    // We did not find a server based on the release file.
+	    // Lookup a fallback based on the host. For a.b.c, this will try a.b.c, .b.c, and .c to allow generalization for cc.archive.ubuntu.com
+	    for (std::string Host = ArchiveURI.Host; not Host.empty() && Server.empty(); Host = Host.find(".", 1) != Host.npos ? Host.substr(Host.find(".", 1)) : "")
+	       Server = _config->Find("Acquire::Snapshots::URI::Host::" + Host);
+	    if (Server == "no")
+	       Server = "";
+	 }
+	 if (Server.empty())
+	 {
+	    if (filename.empty())
+	       return _error->Error("Cannot identify snapshot server for %s %s - run update without snapshot id first", URI.c_str(), Dist.c_str());
 	    return _error->Error("Snapshots not supported for %s %s", URI.c_str(), Dist.c_str());
-
-	 auto SnapshotURI = SubstVar(Server, "@SNAPSHOTID@", Snapshot);
+	 }
+	 auto SnapshotURI = SubstVar(SubstVar(Server, "@SNAPSHOTID@", Snapshot), "@PATH@", ArchiveURI.Path);
 
 	 if (not CreateItemInternalOne(List, SnapshotURI, Dist, Section, IsSrc, SnapshotOptions))
 	    return false;
diff --git a/apt-pkg/init.cc b/apt-pkg/init.cc
index f70dbf308..3990a1f39 100644
--- a/apt-pkg/init.cc
+++ b/apt-pkg/init.cc
@@ -212,6 +212,13 @@ bool pkgInitConfig(Configuration &Cnf)
    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@/");
+   // Preseeds by host
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::archive.ubuntu.com", "https://snapshot.ubuntu.com/@PATH@/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::deb.debian.org", "https://snapshot.debian.org/archive/@PATH@/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::.archive.ubuntu.com", "https://snapshot.ubuntu.com/@PATH@/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::security.ubuntu.com", "https://snapshot.ubuntu.com/@PATH@/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::ppa.launchpadcontent.net", "https://snapshot.ppa.launchpadcontent.net/@PATH@/@SNAPSHOTID@/");
+   Cnf.CndSet("Acquire::Snapshots::URI::Host::ppa.launchpad.net", "https://snapshot.ppa.launchpadcontent.net/@PATH@/@SNAPSHOTID@/");
 
    Cnf.CndSet("DPkg::Path", "/usr/sbin:/usr/bin:/sbin:/bin");