oxm2mt: add option to extract just an attachment embedded message

Author: jengelh

doc/gromox-oxm2mt.8

@@ -10,6 +10,10 @@ the gromox-mt2exm(8gx) program. Optionally, oxm2mt can print a tree summary of
 the message.
 .SH Options
 .TP
+\fB\-\-decap\fP=\fIn\fP
+Select attachment number \fIn\fP's embedded message as the "top-level" message
+and discard the rest of the outer message. \fIn\fP is 1-based.
+.TP
 \fB\-p\fP
 Show properties in detail (enhances \fB\-t\fP).
 .TP

tools/genimport.cpp

@@ -659,3 +659,20 @@ void gi_shutdown()
 	exmdb_client.reset();
 	service_release("rules_execute", "system");
 }
+
+/**
+ * @idx:	zero-based index for selecting attachment
+ */
+errno_t gi_decapsulate_attachment(message_content_ptr &ctnt, unsigned int idx)
+{
+	auto &atxlist = *ctnt->children.pattachments;
+	if (idx >= atxlist.count || atxlist.pplist[idx])
+		return ENOENT;
+	auto &ebptr = atxlist.pplist[idx]->pembedded;
+	if (ebptr == nullptr)
+		return ENOENT;
+	auto embed = std::move(ebptr);
+	ebptr = nullptr;
+	ctnt.reset(embed);
+	return 0;
+}

tools/genimport.hpp

@@ -109,3 +109,4 @@ extern int gi_setup_from_dir(const char *);
 extern int gi_startup_client(unsigned int maxconn = 1);
 extern eid_t gi_lookup_eid_by_name(const char *dir, const char *name);
 extern void gi_shutdown();
+extern gromox::errno_t gi_decapsulate_attachment(message_content_ptr &, unsigned int);

tools/oxm2mt.cpp

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
-// SPDX-FileCopyrightText: 2022-2024 grommunio GmbH
+// SPDX-FileCopyrightText: 2022-2025 grommunio GmbH
 // This file is part of Gromox.
 #include <cstdint>
 #include <cstdio>
@@ -58,9 +58,12 @@ using bin_ptr       = std::unique_ptr<BINARY, bin_del>;
 
 }
 
+static unsigned int g_attach_decap;
+
 static constexpr HXoption g_options_table[] = {
 	{nullptr, 'p', HXTYPE_NONE | HXOPT_INC, &g_show_props, nullptr, nullptr, 0, "Show properties in detail (if -t)"},
 	{nullptr, 't', HXTYPE_NONE, &g_show_tree, nullptr, nullptr, 0, "Show tree-based analysis of the archive"},
+	{"decap", 0, HXTYPE_UINT, &g_attach_decap, {}, {}, {}, "Decapsulate embedded message (1-based index)", "IDX"},
 	HXOPT_AUTOHELP,
 	HXOPT_TABLEEND,
 };
@@ -562,6 +565,13 @@ static errno_t do_file(const char *filename) try
 	auto ret = do_message(root.get(), *ctnt, MAPI_FOLDER);
 	if (ret != 0)
 		return ret;
+	if (g_attach_decap > 0) {
+		ret = gi_decapsulate_attachment(ctnt, g_attach_decap - 1);
+		if (ret == ENOENT)
+			fprintf(stderr, "Attachment #%u is not an embedded message\n", g_attach_decap);
+		if (ret != 0)
+			return ret;
+	}
 
 	if (HXio_fullwrite(STDOUT_FILENO, "GXMT0003", 8) < 0)
 		throw YError("PG-1014: %s", strerror(errno));