message: refactor/improve attachment heuristic a bit

Also check for X-MS-Has-Attach

lib/message/mu-message-part.cc

@@ -158,3 +158,31 @@ MessagePart::is_encrypted() const noexcept
 {
 	return mime_object().is_multipart_encrypted();
 }
+
+bool /* heuristic */
+MessagePart::looks_like_attachment() const noexcept
+{
+	auto matches=[](const MimeContentType& ctype,
+			const std::initializer_list<std::pair<const char*, const char*>>& ctypes) {
+		return std::find_if(ctypes.begin(), ctypes.end(), [&](auto&& item){
+			return ctype.is_type(item.first, item.second); }) != ctypes.end();
+	};
+
+	const auto ctype{mime_object().content_type()};
+	if (!ctype)
+		return false; // no content-type: not an attachment.
+
+	// we consider some parts _not_ to be attachments regardless of disposition
+	if  (matches(*ctype,{{"application", "pgp-keys"}}))
+		return false;
+
+	// we consider some parts to be attachments regardless of disposition
+	if  (matches(*ctype,{{"image", "*"},
+			     {"audio", "*"},
+			     {"application", "*"},
+			     {"application", "x-patch"}}))
+		return true;
+
+	// otherwise, rely on the disposition
+	return is_attachment();
+}

lib/message/mu-message-part.hh

@@ -105,13 +105,23 @@ public:
 	/**
 	 * Does this part have an "attachment" disposition? Otherwise it is
 	 * "inline". Note that does *not* map 1:1 to a message's HasAttachment
-	 * flag.
+	 * flag (which uses looks_like_attachment())
 	 *
 	 * @return true or false.
 	 */
 	bool is_attachment() const noexcept;
 
 
+	/**
+	 * Does this part appear to be an attachment from an end-users point of
+	 * view? This uses some heuristics to guess. Some parts for which
+	 * is_attachment() is true may not "really" be attachments, and
+	 * vice-versa
+	 *
+	 * @return true or false.
+	 */
+	bool looks_like_attachment() const noexcept;
+
 	/**
 	 * Is this part signed?
 	 *

lib/message/mu-message.cc

@@ -340,45 +340,6 @@ get_mailing_list(const MimeMessage& mime_msg)
 	return to_string_opt_gchar(std::move(res));
 }
 
-static bool /* heuristic */
-looks_like_attachment(const MimeObject& parent,
-		      const MimePart& part, const MimeContentType& ctype)
-{
-	constexpr std::array<std::pair<const char*, const char*>, 4> att_types = {{
-			{"image", "*"},
-			{"audio", "*"},
-			{"application", "*"},
-			{"application", "x-patch"}
-		}};
-
-	if (parent) { /* crypto multipart children are not considered attachments */
-		if (const auto parent_ctype{parent.content_type()}; parent_ctype) {
-			if (parent_ctype->is_type("multipart", "signed") ||
-			    parent_ctype->is_type("multipart", "encrypted"))
-				return false;
-		}
-	}
-
-	/* we also consider patches, images, audio, and non-pgp-signature
-	 * application attachments to be attachments... */
-	if (ctype.is_type("*", "pgp-signature"))
-		return false; /* don't consider as a signature */
-
-	if (ctype.is_type("text", "*") &&
-	    (ctype.is_type("*", "plain") || ctype.is_type("*", "html")))
-		return false; /* not a signature */
-
-	/* if not one of those special types, consider it any attachment
-	 * if it says so */
-	if (part.is_attachment())
-		return true;
-
-	const auto it = seq_find_if(att_types, [&](auto&& item){
-		return ctype.is_type(item.first, item.second);
-	});
-	return it != att_types.cend(); /* if found, it's an attachment */
-}
-
 static void
 append_text(Option<std::string>& str, Option<std::string> app)
 {
@@ -403,19 +364,38 @@ accumulate_text(const MimePart& part, Message::Private& info,
 		append_text(info.body_html, part.to_string());
 }
 
+
+static bool /* heuristic */
+looks_like_attachment(const MimeObject& parent, const MessagePart& mpart)
+{
+	if (parent) { /* crypto multipart children are not considered attachments */
+		if (const auto parent_ctype{parent.content_type()}; parent_ctype) {
+			if (parent_ctype->is_type("multipart", "signed") ||
+			    parent_ctype->is_type("multipart", "encrypted"))
+				return false;
+		}
+	}
+
+	return mpart.looks_like_attachment();
+}
+
+
 static void
 process_part(const MimeObject& parent, const MimePart& part,
-	     Message::Private& info)
+	     Message::Private& info, const MessagePart& mpart)
 {
 	const auto ctype{part.content_type()};
 	if (!ctype)
 		return;
 
-	if (looks_like_attachment(parent, part, *ctype))
 	// flag as calendar, if not already
 	if (none_of(info.flags & Flags::Calendar) &&
 	    ctype->is_type("text", "calendar"))
 		info.flags |= Flags::Calendar;
+
+	// flag as attachment, if not already.
+	if (none_of(info.flags & Flags::HasAttachment) &&
+	    looks_like_attachment(parent, mpart))
 		info.flags |= Flags::HasAttachment;
 
 	// if there are text parts, gather.
@@ -499,7 +479,7 @@ handle_object(const MimeObject& parent,
 		info.parts.emplace_back(obj);
 
 	if (obj.is_part())
-		process_part(parent, obj, info);
+		process_part(parent, obj, info, info.parts.back());
 	else if (obj.is_message_part())
 		process_message_part(obj, info);
 	else if (obj.is_multipart_signed())
@@ -553,6 +533,16 @@ process_message(const MimeMessage& mime_msg, const std::string& path,
 	info.mailing_list = get_mailing_list(mime_msg);
 	if (info.mailing_list)
 		info.flags |= Flags::MailingList;
+
+	// Microsoft override; outlook message can tell us directly
+	// wther
+	const auto ms_atthdr{mime_msg.header("X-MS-Has-Attach")};
+	if (ms_atthdr) {
+		if (*ms_atthdr == "yes")
+			info.flags |= Flags::HasAttachment;
+		else
+			info.flags &= ~Flags::HasAttachment;
+	}
 }
 
 static Mu::Result<std::string>

lib/message/test-mu-message.cc

@@ -20,6 +20,7 @@
 #include "mu-message.hh"
 #include "mu-mime-object.hh"
 #include <glib.h>
+#include <regex>
 
 using namespace Mu;
 
@@ -569,7 +570,45 @@ Moi,
 		       part.mime_type().value_or("boo").c_str());
 }
 
+static void
+test_message_ms_attach()
+{
+	const std::string msgtext =
+R"(Date: Thu, 31 Jul 2008 14:57:25 -0400
+From: "John Milton" <jm@example.com>
+Subject: Fere libenter homines id quod volunt credunt
+To: "Julius Caesar" <jc@example.com>
+Message-id: <3BE9E6535E3029448670913581E7A1A20D852173@emss35m06.us.lmco.com>
+X-MS-Has-Attach:
+MIME-version: 1.0
+Content-type: text/plain; charset=us-ascii
+Content-transfer-encoding: 7BIT
 
+OF Mans First Disobedience, and the Fruit
+Of that Forbidden Tree, whose mortal tast
+Brought Death into the World, and all our woe,
+With loss of Eden, till one greater Man
+)";
+
+	{
+		auto message{Message::make_from_text(msgtext)};
+		g_assert_true(!!message);
+		g_assert_true(message->flags() == (Flags::None));
+	}
+
+	{
+		const auto text2 = std::regex_replace(
+			msgtext, std::regex{"X-MS-Has-Attach:"},
+			"X-MS-Has-Attach: yes");
+
+		g_message("%s", text2.c_str());
+
+		auto message{Message::make_from_text(text2)};
+
+		g_assert_true(!!message);
+		g_assert_true(message->flags() == (Flags::HasAttachment));
+	}
+}
 
 
 static void
@@ -841,6 +880,8 @@ main(int argc, char* argv[])
 			test_message_multipart_mixed_rfc822);
 	g_test_add_func("/message/message/detect-attachment",
 			test_message_detect_attachment);
+	g_test_add_func("/message/message/x-ms-has-attach",
+			test_message_ms_attach);
 	g_test_add_func("/message/message/calendar",
 			test_message_calendar);
 	g_test_add_func("/message/message/fail",