Add 'dist-clean' command to remove packages and list files

We assume all files in the 'listsdir' are candidates. Keep only files
ending with Release, Release.gpg, and InRelease.

Closes: #959093

2 files changed, 64 insertions, 13 deletions

diff --git a/apt-pkg/acquire.cc b/apt-pkg/acquire.cc
index cdb2c5257..727880e71 100644
--- a/apt-pkg/acquire.cc
+++ b/apt-pkg/acquire.cc
@@ -29,6 +29,7 @@
 #include <iostream>
 #include <memory>
 #include <numeric>
+#include <regex>
 #include <sstream>
 #include <string>
 #include <tuple>
@@ -825,11 +826,11 @@ pkgAcquire::Worker *pkgAcquire::WorkerStep(Worker *I)
    return I->NextAcquire;
 }
 									/*}}}*/
-// Acquire::Clean - Cleans a directory					/*{{{*/
+// Acquire::CleanDir - Cleans a directory					/*{{{*/
 // ---------------------------------------------------------------------
 /* This is a bit simplistic, it looks at every file in the dir and sees
-   if it is part of the download set. */
-bool pkgAcquire::Clean(string Dir)
+   if it matches the predicate or not. */
+bool pkgAcquire::CleanDir(string Dir, std::function<bool(char const*)> const &Keep, char const * const Caller)
 {
    // non-existing directories are by definition clean…
    if (DirectoryExists(Dir) == false)
@@ -853,22 +854,49 @@ bool pkgAcquire::Clean(string Dir)
 	  strcmp(E->d_name, "auxfiles") == 0 ||
 	  strcmp(E->d_name, "lost+found") == 0 ||
 	  strcmp(E->d_name, ".") == 0 ||
-	  strcmp(E->d_name, "..") == 0)
+	  strcmp(E->d_name, "..") == 0 ||
+	  Keep(E->d_name) == true)
 	 continue;
-
-      // Look in the get list and if not found nuke
-      if (std::any_of(Items.cbegin(), Items.cend(),
-	     [&E](pkgAcquire::Item const * const I) {
-		return flNotDir(I->DestFile) == E->d_name;
-	     }) == false)
-      {
-	 RemoveFileAt("pkgAcquire::Clean", dirfd, E->d_name);
-      }
+      RemoveFileAt(Caller, dirfd, E->d_name);
    }
    closedir(D);
    return true;
 }
 									/*}}}*/
+// Acquire::Clean - Cleans a directory of downloaded files             /*{{{*/
+// ---------------------------------------------------------------------
+/* This is a bit simplistic, it looks at every file in the dir and sees
+   if it is part of the download set. */
+bool pkgAcquire::Clean(string Dir)
+{
+   return CleanDir(
+      Dir,
+      // Look in the get list and if found then keep
+      [this](char const *FName) {
+         return std::any_of(Items.cbegin(), Items.cend(),
+            [FName](pkgAcquire::Item const * const I) {
+               return flNotDir(I->DestFile) == FName;
+            });
+      },
+      "pkgAcquire::Clean"
+   );
+}
+                           /*}}}*/
+// Acquire::CleanLists - Cleans a directory of list files             /*{{{*/
+// ---------------------------------------------------------------------
+/* */
+bool pkgAcquire::CleanLists(string Dir)
+{
+   return CleanDir(
+      Dir,
+      [](char const *FName) noexcept {
+         static const std::regex KeepPattern(".*_(Release|Release.gpg|InRelease)");
+         return std::regex_match(FName, KeepPattern);
+      },
+      "pkgAcquire::CleanLists"
+   );
+}
+                           /*}}}*/
 // Acquire::TotalNeeded - Number of bytes to fetch			/*{{{*/
 // ---------------------------------------------------------------------
 /* This is the total number of bytes needed */
diff --git a/apt-pkg/acquire.h b/apt-pkg/acquire.h
index 17b68768e..46115a27f 100644
--- a/apt-pkg/acquire.h
+++ b/apt-pkg/acquire.h
@@ -70,6 +70,7 @@
 #include <apt-pkg/weakptr.h>
 
 #include <chrono>
+#include <functional>
 #include <string>
 #include <vector>
 
@@ -330,6 +331,14 @@ class APT_PUBLIC pkgAcquire
     *  \return \b true if the directory exists and is readable.
     */
    bool Clean(std::string Dir);
+   
+   /** Deletes each package list and index file in the given directory.
+    *
+    *  \param Dir The directory to be cleaned.
+    *
+    *  \return \b true if the directory exists and is readable.
+    */
+   bool CleanLists(std::string Dir);
 
    /** \return the total size in bytes of all the items included in
     *  this download.
@@ -372,6 +381,20 @@ class APT_PUBLIC pkgAcquire
 
    private:
    APT_HIDDEN void Initialize();
+
+   /** Delete each entry in the given directory whose name does \em not match
+    *  a criterion.
+    *
+    *  \param Dir The directory to be cleaned.
+    *
+    *  \param KeepP A predicate telling to keep the named file; if it is
+    *  non-empty and returns true, the file is kept.
+    *
+    *  \param Caller Log name of the caller.
+    *
+    *  \return \b true if the directory exists and is readable.
+    */
+   APT_HIDDEN static bool CleanDir(std::string Dir, std::function<bool(char const*)> const &KeepP, char const * const Caller);
 };
 
 /** \brief Represents a single download source from which an item