Fix gpg decryption (#186)

After a multipart/encrypted part gets decrypted the result is usually a
`multipart/mixed` part (see enigmail).

Before this commit mime multiparts where handled only by
`g_mime_message_foreach`.  As a result the decrypted mime multiparts
where not processed.

This patch handles mime multiparts explicitly by removing the
`g_mime_message_foreach` invocations.  This might come at the cost of
reduced maintainability, in the case of radical gmime changes.  However,
gmime is pretty stable and that scenario is highly unlikely.

TODO: After decryption make any attachments available

lib/mu-msg-part.c

@@ -30,10 +30,6 @@
 #include "mu-msg-priv.h"
 #include "mu-msg-part.h"
 
-static gboolean handle_children (MuMsg *msg,
-				 GMimeMessage *mime_msg, MuMsgOptions opts,
-				 unsigned index, MuMsgPartForeachFunc func,
-				 gpointer user_data);
 struct _DoData {
 	GMimeObject *mime_obj;
 	unsigned    index;
@@ -151,6 +147,13 @@ accumulate_text (MuMsg *msg, MuMsgPart *part, GString **gstrp)
 		accumulate_text_part (msg, part, gstrp);
 }
 
+/* declaration, so we can use it earlier */
+static gboolean handle_mime_object (MuMsg *msg,
+				    GMimeObject *mobj, GMimeObject *parent,
+				    MuMsgOptions opts,
+				    unsigned index, MuMsgPartForeachFunc func,
+				    gpointer user_data);
+
 static char*
 get_text_from_mime_msg (MuMsg *msg, GMimeMessage *mmsg, MuMsgOptions opts,
 			unsigned index)
@@ -158,7 +161,11 @@ get_text_from_mime_msg (MuMsg *msg, GMimeMessage *mmsg, MuMsgOptions opts,
 	GString *gstr;
 
 	gstr = g_string_sized_new (4096);
-	handle_children (msg, mmsg, opts, index,
+	handle_mime_object (msg,
+	                    mmsg->mime_part,
+			    (GMimeObject *) mmsg,
+			    opts,
+			    0,
 			    (MuMsgPartForeachFunc)accumulate_text,
 			    &gstr);
 
@@ -304,13 +311,6 @@ get_disposition (GMimeObject *mobj)
 	return MU_MSG_PART_TYPE_NONE;
 }
 
-/* declaration, so we can use it in handle_encrypted_part */
-static gboolean handle_mime_object (MuMsg *msg,
-				    GMimeObject *mobj, GMimeObject *parent,
-				    MuMsgOptions opts,
-				    unsigned index, MuMsgPartForeachFunc func,
-				    gpointer user_data);
-
 #define SIG_STATUS_REPORT "sig-status-report"
 
 /* call 'func' with information about this MIME-part */
@@ -474,14 +474,37 @@ handle_message_part (MuMsg *msg, GMimeMessagePart *mimemsgpart, GMimeObject *par
 		GMimeMessage *mmsg; /* this may return NULL for some messages */
 		mmsg = g_mime_message_part_get_message (mimemsgpart);
 		if (mmsg)
-			return handle_children
+			return handle_mime_object (msg,
-				(msg, mmsg,
+			                           mmsg->mime_part,
-				 opts, index, func, user_data);
+			                           (GMimeObject *) mmsg,
+			                           opts,
+			                           index,
+			                           func,
+			                           user_data);
 	}
 
 	return TRUE;
 }
 
+static gboolean
+handle_multipart (MuMsg *msg,
+                  GMimeMultipart *mpart, GMimeObject *parent, MuMsgOptions opts,
+                  unsigned index, MuMsgPartForeachFunc func, gpointer user_data)
+{
+	gboolean res;
+	GMimeObject *part;
+	guint i;
+
+	res = TRUE;
+	for (i = 0; i < mpart->children->len; i++) {
+		part = (GMimeObject *) mpart->children->pdata[i];
+		res &= handle_mime_object (msg, part, (GMimeObject *) mpart,
+		                           opts, ++index, func, user_data);
+	}
+
+	return res;
+}
+
 
 static gboolean
 handle_mime_object (MuMsg *msg,
@@ -505,50 +528,10 @@ handle_mime_object (MuMsg *msg,
 		return handle_encrypted_part
 			(msg, GMIME_MULTIPART_ENCRYPTED (mobj),
 			 parent, opts, index, func, user_data);
-	return TRUE;
+	else if (GMIME_IS_MULTIPART (mobj))
-}
+		return handle_multipart
-
+			(msg, GMIME_MULTIPART (mobj),
-struct _ForeachData {
+			 parent, opts, index, func, user_data);
-	MuMsgPartForeachFunc func;
-	gpointer             user_data;
-	MuMsg                *msg;
-	unsigned             index;
-	MuMsgOptions         opts;
-
-};
-typedef struct _ForeachData ForeachData;
-
-static void
-each_child (GMimeObject *parent, GMimeObject *part,
-	    ForeachData *fdata)
-{
-	handle_mime_object (fdata->msg,
-			    part,
-			    parent,
-			    fdata->opts,
-			    fdata->index++,
-			    fdata->func,
-			    fdata->user_data);
-}
-
-
-static gboolean
-handle_children (MuMsg *msg,
-		 GMimeMessage *mime_msg, MuMsgOptions opts,
-		 unsigned index, MuMsgPartForeachFunc func,
-		 gpointer user_data)
-{
-	ForeachData fdata;
-
- 	fdata.func	= func;
-	fdata.user_data = user_data;
-	fdata.opts	= opts;
-	fdata.msg	= msg;
-	fdata.index	= 0;
-
-	g_mime_message_foreach (mime_msg, (GMimeObjectForeachFunc)each_child,
-				&fdata);
-
 	return TRUE;
 }
 
@@ -562,8 +545,13 @@ mu_msg_part_foreach (MuMsg *msg, MuMsgOptions opts,
 	if (!mu_msg_load_msg_file (msg, NULL))
 		return FALSE;
 
-	return handle_children (msg, msg->_file->_mime_msg,
+	return handle_mime_object (msg,
-				opts, 0, func, user_data);
+	                           msg->_file->_mime_msg->mime_part,
+	                           (GMimeObject *) msg->_file->_mime_msg,
+	                           opts,
+	                           0,
+	                           func,
+	                           user_data);
 }