allow a method to request auxiliary files

If a method needs a file to operate like e.g. mirror needs to get a list
of mirrors before it can redirect the the actual requests to them. That
could easily be solved by moving the logic into libapt directly, but by
allowing a method to request other methods to do something we can keep
this logic contained in the method and allow e.g. also methods which
perform binary patching or similar things.

Previously they would need to implement their own acquire system inside
the existing one which in all likelyhood will not support the same
features and methods nor operate with similar security compared to what
we have already running 'above' the requesting method. That said, to
avoid methods producing conflicts with "proper" files we are downloading
a new directory is introduced to keep the auxiliary files in.

[The message magic number 351 is a tribute to the german Grundgesetz
article 35 paragraph 1 which defines that all authorities of the
state(s) help each other on request.]

7 files changed, 229 insertions, 22 deletions

diff --git a/apt-pkg/acquire-item.cc b/apt-pkg/acquire-item.cc
index 9b163081b..611876dd2 100644
--- a/apt-pkg/acquire-item.cc
+++ b/apt-pkg/acquire-item.cc
@@ -16,6 +16,7 @@
 #include <config.h>
 
 #include <apt-pkg/acquire-item.h>
+#include <apt-pkg/acquire-worker.h>
 #include <apt-pkg/acquire.h>
 #include <apt-pkg/aptconfiguration.h>
 #include <apt-pkg/configuration.h>
@@ -34,6 +35,7 @@
 #include <algorithm>
 #include <ctime>
 #include <iostream>
+#include <memory>
 #include <numeric>
 #include <random>
 #include <sstream>
@@ -1070,6 +1072,12 @@ bool pkgAcquire::Item::IsRedirectionLoop(std::string const &NewURI)	/*{{{*/
 									/*}}}*/
 int pkgAcquire::Item::Priority()					/*{{{*/
 {
+   // Stage 0: Files requested by methods
+   // - they will usually not end up here, but if they do we make sure
+   //   to get them as soon as possible as they are probably blocking
+   //   the processing of files by the requesting method
+   if (dynamic_cast<pkgAcqAuxFile *>(this) != nullptr)
+      return 5000;
    // Stage 1: Meta indices and diff indices
    // - those need to be fetched first to have progress reporting working
    //   for the rest
@@ -3892,3 +3900,114 @@ string pkgAcqFile::Custom600Headers() const				/*{{{*/
 }
 									/*}}}*/
 pkgAcqFile::~pkgAcqFile() {}
+
+void pkgAcqAuxFile::Failed(std::string const &Message, pkgAcquire::MethodConfig const *const Cnf) /*{{{*/
+{
+   pkgAcqFile::Failed(Message, Cnf);
+   if (Status == StatIdle)
+      return;
+   if (RealFileExists(DestFile))
+      Rename(DestFile, DestFile + ".FAILED");
+   Worker->ReplyAux(Desc);
+}
+									/*}}}*/
+void pkgAcqAuxFile::Done(std::string const &Message, HashStringList const &CalcHashes, /*{{{*/
+			 pkgAcquire::MethodConfig const *const Cnf)
+{
+   pkgAcqFile::Done(Message, CalcHashes, Cnf);
+   if (Status == StatDone)
+      Worker->ReplyAux(Desc);
+   else if (Status == StatAuthError || Status == StatError)
+      Worker->ReplyAux(Desc);
+}
+									/*}}}*/
+std::string pkgAcqAuxFile::Custom600Headers() const /*{{{*/
+{
+   if (MaximumSize == 0)
+      return pkgAcqFile::Custom600Headers();
+   std::string maxsize;
+   strprintf(maxsize, "\nMaximum-Size: %llu", MaximumSize);
+   return pkgAcqFile::Custom600Headers().append(maxsize);
+}
+									/*}}}*/
+void pkgAcqAuxFile::Finished() /*{{{*/
+{
+   auto dirname = flCombine(_config->FindDir("Dir::State::lists"), "auxfiles/");
+   if (APT::String::Startswith(DestFile, dirname))
+   {
+      // the file is never returned by method requesting it, so fix up the permission now
+      if (FileExists(DestFile))
+      {
+	 ChangeOwnerAndPermissionOfFile("pkgAcqAuxFile", DestFile.c_str(), "root", ROOT_GROUP, 0644);
+	 if (Status == StatDone)
+	    return;
+      }
+   }
+   else
+   {
+      dirname = flNotFile(DestFile);
+      RemoveFile("pkgAcqAuxFile::Finished", DestFile);
+      RemoveFile("pkgAcqAuxFile::Finished", DestFile + ".FAILED");
+      rmdir(dirname.c_str());
+   }
+   DestFile.clear();
+}
+									/*}}}*/
+// GetAuxFileNameFromURI						/*{{{*/
+static std::string GetAuxFileNameFromURIInLists(std::string const &uri)
+{
+   // check if we have write permission for our usual location.
+   auto const dirname = flCombine(_config->FindDir("Dir::State::lists"), "auxfiles/");
+   char const * const filetag = ".apt-acquire-privs-test.XXXXXX";
+   std::string const tmpfile_tpl = flCombine(dirname, filetag);
+   std::unique_ptr<char, decltype(std::free) *> tmpfile { strdup(tmpfile_tpl.c_str()), std::free };
+   int const fd = mkstemp(tmpfile.get());
+   if (fd == -1 && errno == EACCES)
+      return "";
+   RemoveFile("GetAuxFileNameFromURI", tmpfile.get());
+   close(fd);
+   return flCombine(dirname, URItoFileName(uri));
+}
+static std::string GetAuxFileNameFromURI(std::string const &uri)
+{
+   auto const lists = GetAuxFileNameFromURIInLists(uri);
+   if (lists.empty() == false)
+      return lists;
+
+   std::string tmpdir_tpl;
+   strprintf(tmpdir_tpl, "%s/apt-auxfiles-XXXXXX", GetTempDir().c_str());
+   std::unique_ptr<char, decltype(std::free) *> tmpdir { strndup(tmpdir_tpl.data(), tmpdir_tpl.length()), std::free };
+   if (mkdtemp(tmpdir.get()) == nullptr)
+   {
+      _error->Errno("GetAuxFileNameFromURI", "mkdtemp of %s failed", tmpdir.get());
+      return flCombine("/nonexistent/auxfiles/", URItoFileName(uri));
+   }
+   chmod(tmpdir.get(), 0755);
+   auto const filename = flCombine(tmpdir.get(), URItoFileName(uri));
+   _error->PushToStack();
+   FileFd in(flCombine(flCombine(_config->FindDir("Dir::State::lists"), "auxfiles/"), URItoFileName(uri)), FileFd::ReadOnly);
+   if (in.IsOpen())
+   {
+      FileFd out(filename, FileFd::WriteOnly | FileFd::Create | FileFd::Exclusive);
+      CopyFile(in, out);
+   }
+   _error->RevertToStack();
+   return filename;
+}
+									/*}}}*/
+pkgAcqAuxFile::pkgAcqAuxFile(pkgAcquire::Item *const Owner, pkgAcquire::Worker *const Worker,
+			     std::string const &ShortDesc, std::string const &Desc, std::string const &URI,
+			     HashStringList const &Hashes, unsigned long long const MaximumSize) : pkgAcqFile(Owner->GetOwner(), URI, Hashes, Hashes.FileSize(), Desc, ShortDesc, "", GetAuxFileNameFromURI(URI), false),
+												   Owner(Owner), Worker(Worker), MaximumSize(MaximumSize)
+{
+   /* very bad failures can happen while constructing which causes
+      us to hang as the aux request is never answered (e.g. method not available)
+      Ideally we catch failures earlier, but a safe guard can't hurt. */
+   if (Status == pkgAcquire::Item::StatIdle || Status == pkgAcquire::Item::StatFetching)
+      return;
+   Failed(std::string("400 URI Failure\n") +
+	     "URI: " + URI + "\n" +
+	     "Filename: " + DestFile,
+	  nullptr);
+}
+pkgAcqAuxFile::~pkgAcqAuxFile() {}
diff --git a/apt-pkg/acquire-item.h b/apt-pkg/acquire-item.h
index cf227d1b5..46d79df92 100644
--- a/apt-pkg/acquire-item.h
+++ b/apt-pkg/acquire-item.h
@@ -1238,6 +1238,25 @@ class pkgAcqFile : public pkgAcquire::Item
    virtual ~pkgAcqFile();
 };
 									/*}}}*/
+class APT_HIDDEN pkgAcqAuxFile : public pkgAcqFile /*{{{*/
+{
+   pkgAcquire::Item *const Owner;
+   pkgAcquire::Worker *const Worker;
+   unsigned long long MaximumSize;
+
+   public:
+   virtual void Failed(std::string const &Message, pkgAcquire::MethodConfig const *const Cnf) APT_OVERRIDE;
+   virtual void Done(std::string const &Message, HashStringList const &CalcHashes,
+		     pkgAcquire::MethodConfig const *const Cnf) APT_OVERRIDE;
+   virtual std::string Custom600Headers() const APT_OVERRIDE;
+   virtual void Finished() APT_OVERRIDE;
+
+   pkgAcqAuxFile(pkgAcquire::Item *const Owner, pkgAcquire::Worker *const Worker,
+		 std::string const &ShortDesc, std::string const &Desc, std::string const &URI,
+		 HashStringList const &Hashes, unsigned long long const MaximumSize);
+   virtual ~pkgAcqAuxFile();
+};
+									/*}}}*/
 /** @} */
 
 #endif
diff --git a/apt-pkg/acquire-worker.cc b/apt-pkg/acquire-worker.cc
index 995750dea..1b1f4dc4c 100644
--- a/apt-pkg/acquire-worker.cc
+++ b/apt-pkg/acquire-worker.cc
@@ -192,7 +192,8 @@ bool pkgAcquire::Worker::ReadMessages()
 // ---------------------------------------------------------------------
 /* This takes the messages from the message queue and runs them through
    the parsers in order. */
-enum class APT_HIDDEN MessageType {
+enum class APT_HIDDEN MessageType
+{
    CAPABILITIES = 100,
    LOG = 101,
    STATUS = 102,
@@ -200,6 +201,7 @@ enum class APT_HIDDEN MessageType {
    WARNING = 104,
    URI_START = 200,
    URI_DONE = 201,
+   AUX_REQUEST = 351,
    URI_FAILURE = 400,
    GENERAL_FAILURE = 401,
    MEDIA_CHANGE = 403
@@ -512,6 +514,22 @@ bool pkgAcquire::Worker::RunMessages()
 	    break;
 	 }
 
+	 case MessageType::AUX_REQUEST:
+	 {
+	    if (Itm == nullptr)
+	    {
+	       _error->Error("Method gave invalid Aux Request message");
+	       break;
+	    }
+
+	    auto maxsizestr = LookupTag(Message, "MaximumSize", "");
+	    unsigned long long const MaxSize = maxsizestr.empty() ? 0 : strtoull(maxsizestr.c_str(), nullptr, 10);
+	    new pkgAcqAuxFile(Itm->Owner, this, LookupTag(Message, "Aux-ShortDesc", ""),
+			      LookupTag(Message, "Aux-Description", ""), LookupTag(Message, "Aux-URI", ""),
+			      GetHashesFromMessage("Aux-", Message), MaxSize);
+	    break;
+	 }
+
 	 case MessageType::URI_FAILURE:
 	 {
 	    if (Itm == nullptr)
@@ -772,6 +790,46 @@ bool pkgAcquire::Worker::QueueItem(pkgAcquire::Queue::QItem *Item)
    return true;
 }
 									/*}}}*/
+// Worker::ReplyAux - reply to an aux request from this worker		/*{{{*/
+bool pkgAcquire::Worker::ReplyAux(pkgAcquire::ItemDesc const &Item)
+{
+   if (OutFd == -1)
+      return false;
+
+   if (isDoomedItem(Item.Owner))
+      return true;
+
+   string Message = "600 URI Acquire\n";
+   Message.reserve(200);
+   Message += "URI: " + Item.URI;
+   if (RealFileExists(Item.Owner->DestFile))
+   {
+      if (Item.Owner->Status == pkgAcquire::Item::StatDone)
+      {
+	 std::string const SandboxUser = _config->Find("APT::Sandbox::User");
+	 ChangeOwnerAndPermissionOfFile("Worker::ReplyAux", Item.Owner->DestFile.c_str(),
+					SandboxUser.c_str(), ROOT_GROUP, 0600);
+	 Message += "\nFilename: " + Item.Owner->DestFile;
+      }
+      else
+      {
+	 // we end up here in case we would need root-rights to delete a file,
+	 // but we run the command as non-root… (yes, it is unlikely)
+	 Message += "\nFilename: " + flCombine("/nonexistent", Item.Owner->DestFile);
+      }
+   }
+   else
+      Message += "\nFilename: " + Item.Owner->DestFile;
+   Message += "\n\n";
+
+   if (Debug == true)
+      clog << " -> " << Access << ':' << QuoteString(Message, "\n") << endl;
+   OutQueue += Message;
+   OutReady = true;
+
+   return true;
+}
+									/*}}}*/
 // Worker::OutFdRead - Out bound FD is ready				/*{{{*/
 // ---------------------------------------------------------------------
 /* */
diff --git a/apt-pkg/acquire-worker.h b/apt-pkg/acquire-worker.h
index 8fc686880..3c5c1cef6 100644
--- a/apt-pkg/acquire-worker.h
+++ b/apt-pkg/acquire-worker.h
@@ -276,6 +276,7 @@ class pkgAcquire::Worker : public WeakPointable
     *  queue.
     */
    bool QueueItem(pkgAcquire::Queue::QItem *Item);
+   APT_HIDDEN bool ReplyAux(pkgAcquire::ItemDesc const &Item);
 
    /** \brief Start up the worker and fill in #Config.
     *
diff --git a/apt-pkg/acquire.cc b/apt-pkg/acquire.cc
index aabcb0aba..5fa456ce3 100644
--- a/apt-pkg/acquire.cc
+++ b/apt-pkg/acquire.cc
@@ -78,13 +78,13 @@ void pkgAcquire::Initialize()
 }
 									/*}}}*/
 // Acquire::GetLock - lock directory and prepare for action		/*{{{*/
-static bool SetupAPTPartialDirectory(std::string const &grand, std::string const &parent)
+static bool SetupAPTPartialDirectory(std::string const &grand, std::string const &parent, std::string const &postfix, mode_t const mode)
 {
-   std::string const partial = parent + "partial";
-   mode_t const mode = umask(S_IWGRP | S_IWOTH);
+   std::string const partial = parent + postfix;
+   mode_t const old_umask = umask(S_IWGRP | S_IWOTH);
    bool const creation_fail = (CreateAPTDirectoryIfNeeded(grand, partial) == false &&
 	 CreateAPTDirectoryIfNeeded(parent, partial) == false);
-   umask(mode);
+   umask(old_umask);
    if (creation_fail == true)
       return false;
 
@@ -100,7 +100,7 @@ static bool SetupAPTPartialDirectory(std::string const &grand, std::string const
             _error->WarningE("SetupAPTPartialDirectory", "chown to %s:root of directory %s failed", SandboxUser.c_str(), partial.c_str());
       }
    }
-   if (chmod(partial.c_str(), 0700) != 0)
+   if (chmod(partial.c_str(), mode) != 0)
       _error->WarningE("SetupAPTPartialDirectory", "chmod 0700 of directory %s failed", partial.c_str());
 
    _error->PushToStack();
@@ -117,10 +117,12 @@ bool pkgAcquire::Setup(pkgAcquireStatus *Progress, string const &Lock)
    if (Lock.empty())
    {
       string const listDir = _config->FindDir("Dir::State::lists");
-      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir) == false)
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir, "partial", 0700) == false)
 	 return _error->Errno("Acquire", _("List directory %spartial is missing."), listDir.c_str());
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir, "auxfiles", 0755) == false)
+	 return _error->Errno("Acquire", _("List directory %sauxfiles is missing."), listDir.c_str());
       string const archivesDir = _config->FindDir("Dir::Cache::Archives");
-      if (SetupAPTPartialDirectory(_config->FindDir("Dir::Cache"), archivesDir) == false)
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::Cache"), archivesDir, "partial", 0700) == false)
 	 return _error->Errno("Acquire", _("Archives directory %spartial is missing."), archivesDir.c_str());
       return true;
    }
@@ -137,14 +139,19 @@ bool pkgAcquire::GetLock(std::string const &Lock)
 
    if (Lock == listDir)
    {
-      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir) == false)
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir, "partial", 0700) == false)
 	 return _error->Errno("Acquire", _("List directory %spartial is missing."), listDir.c_str());
    }
    if (Lock == archivesDir)
    {
-      if (SetupAPTPartialDirectory(_config->FindDir("Dir::Cache"), archivesDir) == false)
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::Cache"), archivesDir, "partial", 0700) == false)
 	 return _error->Errno("Acquire", _("Archives directory %spartial is missing."), archivesDir.c_str());
    }
+   if (Lock == listDir || Lock == archivesDir)
+   {
+      if (SetupAPTPartialDirectory(_config->FindDir("Dir::State"), listDir, "auxfiles", 0755) == false)
+	 return _error->Errno("Acquire", _("List directory %sauxfiles is missing."), listDir.c_str());
+   }
 
    if (_config->FindB("Debug::NoLocking", false) == true)
       return true;
@@ -288,7 +295,6 @@ static bool CheckForBadItemAndFailIt(pkgAcquire::Item * const Item,
 	 "\nFilename: " + Item->DestFile +
 	 "\nFailReason: WeakHashSums";
 
-      auto SavedDesc = Item->GetItemDesc();
       Item->Status = pkgAcquire::Item::StatAuthError;
       Item->Failed(Message, Config);
       if (Log != nullptr)
@@ -303,7 +309,10 @@ void pkgAcquire::Enqueue(ItemDesc &Item)
    const MethodConfig *Config;
    string Name = QueueName(Item.URI,Config);
    if (Name.empty() == true)
+   {
+      Item.Owner->Status = pkgAcquire::Item::StatError;
       return;
+   }
 
    /* the check for running avoids that we produce errors
       in logging before we actually have started, which would
@@ -769,11 +778,12 @@ bool pkgAcquire::Clean(string Dir)
    for (struct dirent *E = readdir(D); E != nullptr; E = readdir(D))
    {
       // Skip some entries
-      if (strcmp(E->d_name,"lock") == 0 ||
-	  strcmp(E->d_name,"partial") == 0 ||
-	  strcmp(E->d_name,"lost+found") == 0 ||
-	  strcmp(E->d_name,".") == 0 ||
-	  strcmp(E->d_name,"..") == 0)
+      if (strcmp(E->d_name, "lock") == 0 ||
+	  strcmp(E->d_name, "partial") == 0 ||
+	  strcmp(E->d_name, "auxfiles") == 0 ||
+	  strcmp(E->d_name, "lost+found") == 0 ||
+	  strcmp(E->d_name, ".") == 0 ||
+	  strcmp(E->d_name, "..") == 0)
 	 continue;
 
       // Look in the get list and if not found nuke
diff --git a/apt-pkg/clean.cc b/apt-pkg/clean.cc
index 04a7c4910..1abc638ee 100644
--- a/apt-pkg/clean.cc
+++ b/apt-pkg/clean.cc
@@ -62,11 +62,12 @@ bool pkgArchiveCleaner::Go(std::string Dir,pkgCache &Cache)
    for (struct dirent *Dir = readdir(D); Dir != 0; Dir = readdir(D))
    {
       // Skip some files..
-      if (strcmp(Dir->d_name,"lock") == 0 ||
-	  strcmp(Dir->d_name,"partial") == 0 ||
-	  strcmp(Dir->d_name,"lost+found") == 0 ||
-	  strcmp(Dir->d_name,".") == 0 ||
-	  strcmp(Dir->d_name,"..") == 0)
+      if (strcmp(Dir->d_name, "lock") == 0 ||
+	  strcmp(Dir->d_name, "partial") == 0 ||
+	  strcmp(Dir->d_name, "auxfiles") == 0 ||
+	  strcmp(Dir->d_name, "lost+found") == 0 ||
+	  strcmp(Dir->d_name, ".") == 0 ||
+	  strcmp(Dir->d_name, "..") == 0)
 	 continue;
 
       struct stat St;
diff --git a/apt-pkg/init.cc b/apt-pkg/init.cc
index 207f0d902..5c34113e7 100644
--- a/apt-pkg/init.cc
+++ b/apt-pkg/init.cc
@@ -138,7 +138,6 @@ bool pkgInitConfig(Configuration &Cnf)
    Cnf.CndSet("Dir::State", STATE_DIR + 1);
    Cnf.CndSet("Dir::State::lists","lists/");
    Cnf.CndSet("Dir::State::cdroms","cdroms.list");
-   Cnf.CndSet("Dir::State::mirrors","mirrors/");
 
    // Cache
    Cnf.CndSet("Dir::Cache", CACHE_DIR + 1);