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.]

1 files changed, 59 insertions, 1 deletions

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				/*{{{*/
 // ---------------------------------------------------------------------
 /* */