Fix fopen() on windows to cope with long filenames (part of #1755).

7 files changed, 123 insertions, 2 deletions

diff --git a/src/lib/cross.h b/src/lib/cross.h
index cc066488a..bdcae3537 100644
--- a/src/lib/cross.h
+++ b/src/lib/cross.h
@@ -67,6 +67,7 @@ extern bool running_32_on_64 ();
 extern void unprivileged ();
 extern boost::filesystem::path config_path ();
 extern boost::filesystem::path directory_containing_executable ();
+extern boost::filesystem::path fix_long_path (boost::filesystem::path path);
 namespace dcpomatic {
 	std::string get_process_id ();
 }
diff --git a/src/lib/cross_linux.cc b/src/lib/cross_linux.cc
index 510bce8c3..816573230 100644
--- a/src/lib/cross_linux.cc
+++ b/src/lib/cross_linux.cc
@@ -420,3 +420,11 @@ dcpomatic::get_process_id ()
 {
 	return dcp::raw_convert<string>(getpid());
 }
+
+
+boost::filesystem::path
+fix_long_path (boost::filesystem::path path)
+{
+	return path;
+}
+
diff --git a/src/lib/cross_osx.cc b/src/lib/cross_osx.cc
index fc8ccd4a8..bd31541c5 100644
--- a/src/lib/cross_osx.cc
+++ b/src/lib/cross_osx.cc
@@ -607,3 +607,10 @@ dcpomatic::get_process_id ()
 {
 	return dcp::raw_convert<string>(getpid());
 }
+
+
+boost::filesystem::path
+fix_long_path (boost::filesystem::path path)
+{
+	return path;
+}
diff --git a/src/lib/cross_windows.cc b/src/lib/cross_windows.cc
index 04ee26271..d97550ca9 100644
--- a/src/lib/cross_windows.cc
+++ b/src/lib/cross_windows.cc
@@ -26,6 +26,7 @@
 #include "config.h"
 #include "exceptions.h"
 #include "dcpomatic_assert.h"
+#include "util.h"
 #include <dcp/raw_convert.h>
 #include <glib.h>
 extern "C" {
@@ -234,6 +235,36 @@ disk_writer_path ()
 #endif
 
 
+/** Windows can't "by default" cope with paths longer than 260 characters, so if you pass such a path to
+ *  any boost::filesystem method it will fail.  There is a "fix" for this, which is to prepend
+ *  the string \\?\ to the path.  This will make it work, so long as:
+ *  - the path is absolute.
+ *  - the path only uses backslashes.
+ *  - individual path components are "short enough" (probably less than 255 characters)
+ *
+ *  See https://www.boost.org/doc/libs/1_57_0/libs/filesystem/doc/reference.html under
+ *  "Warning: Long paths on Windows" for some details.
+ *
+ *  Our fopen_boost uses this method to get this fix, but any other calls to boost::filesystem
+ *  will not unless this method is explicitly called to pre-process the pathname.
+ */
+boost::filesystem::path
+fix_long_path (boost::filesystem::path long_path)
+{
+	using namespace boost::filesystem;
+	path fixed = "\\\\?\\";
+	/* We have to make the path canonical but we can't call canonical() on the long path
+	 * as it will fail.  So we'll sort of do it ourselves (possibly badly).
+	 */
+	if (long_path.is_absolute()) {
+		fixed += long_path.make_preferred();
+	} else {
+		fixed += boost::filesystem::current_path() / long_path.make_preferred();
+	}
+	return fixed;
+}
+
+
 /* Apparently there is no way to create an ofstream using a UTF-8
    filename under Windows.  We are hence reduced to using fopen
    with this wrapper.
@@ -242,8 +273,8 @@ FILE *
 fopen_boost (boost::filesystem::path p, string t)
 {
         wstring w (t.begin(), t.end());
-	/* c_str() here should give a UTF-16 string */
-        return _wfopen (p.c_str(), w.c_str ());
+	/* c_str() on fixed here should give a UTF-16 string */
+	return _wfopen (fix_long_path(p).c_str(), w.c_str());
 }
 
 
diff --git a/src/lib/util.cc b/src/lib/util.cc
index 65bfd4534..8a039764d 100644
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -1193,3 +1193,4 @@ start_of_thread (string)
 
 }
 #endif
+
diff --git a/test/windows_test.cc b/test/windows_test.cc
new file mode 100644
index 000000000..4d07d5fdf
--- /dev/null
+++ b/test/windows_test.cc
@@ -0,0 +1,72 @@
+/*
+    Copyright (C) 2021 Carl Hetherington <cth@carlh.net>
+
+    This file is part of DCP-o-matic.
+
+    DCP-o-matic is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    DCP-o-matic is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DCP-o-matic.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+
+#include "lib/cross.h"
+#include "lib/util.h"
+#include <boost/filesystem.hpp>
+#include <boost/test/unit_test.hpp>
+#include <iostream>
+
+
+BOOST_AUTO_TEST_CASE (fix_long_path_test)
+{
+#ifdef DCPOMATIC_WINDOWS
+	BOOST_CHECK_EQUAL (fix_long_path("c:\\foo"), "\\\\?\\c:\\foo");
+	BOOST_CHECK_EQUAL (fix_long_path("c:\\foo\\bar"), "\\\\?\\c:\\foo\\bar");
+	boost::filesystem::path fixed_bar = "\\\\?\\";
+	fixed_bar += boost::filesystem::current_path();
+	fixed_bar /= "bar";
+	BOOST_CHECK_EQUAL (fix_long_path("bar"), fixed_bar);
+#else
+	BOOST_CHECK_EQUAL (fix_long_path("foo/bar/baz"), "foo/bar/baz");
+#endif
+}
+
+
+#ifdef DCPOMATIC_WINDOWS
+BOOST_AUTO_TEST_CASE (windows_long_filename_test)
+{
+	using namespace boost::filesystem;
+
+	path too_long = current_path() / "build\\test\\a\\really\\very\\long\\filesystem\\path\\indeed\\that\\will\\be\\so\\long\\that\\windows\\cannot\\normally\\cope\\with\\it\\unless\\we\\add\\this\\crazy\\prefix\\and\\then\\magically\\it\\can\\do\\it\\fine\\I\\dont\\really\\know\\why\\its\\like\\that\\but\\hey\\it\\is\\so\\here\\we\\are\\what\\can\\we\\do\\other\\than\\bodge\\it";
+
+	BOOST_CHECK (too_long.string().length() > 260);
+	boost::system::error_code ec;
+	create_directories (too_long, ec);
+	BOOST_CHECK (ec);
+
+	path fixed_path = fix_long_path(too_long);
+	create_directories (fixed_path, ec);
+	BOOST_CHECK (!ec);
+
+	auto file = fopen_boost(too_long / "hello", "w");
+	BOOST_REQUIRE (file);
+	fprintf (file, "Hello_world");
+	fclose (file);
+
+	file = fopen_boost(too_long / "hello", "r");
+	BOOST_REQUIRE (file);
+	char buffer[64];
+	fscanf (file, "%63s", buffer);
+	BOOST_CHECK_EQUAL (strcmp(buffer, "Hello_world"), 0);
+}
+#endif
+
diff --git a/test/wscript b/test/wscript
index 4303db835..e2628ecd8 100644
--- a/test/wscript
+++ b/test/wscript
@@ -138,6 +138,7 @@ def build(bld):
                  video_level_test.cc
                  video_mxf_content_test.cc
                  vf_kdm_test.cc
+                 windows_test.cc
                  writer_test.cc
                  zipper_test.cc
                  """