From 8a1da1da65ba0e6a6fb915c73ff6e6a81da349f2 Mon Sep 17 00:00:00 2001 From: Carl Hetherington Date: Tue, 24 Nov 2020 23:01:04 +0100 Subject: [PATCH] Fix the behaviour of FileGroup when seeking too far. Previously, if you did a seek off the end of the file group, the seek would return an error. This is not what fseek() does; it returns no error, and preserves the file pointer (returned by ftell()) as if the seek had been successful. fread()s after a too-far seek return no data, of course. Parsing some files (the example used to find the bug was a H264 MP4) involves a seek which is to the byte after the end of the mp4 file. If this fails the whole header parsing fails and DCP-o-matic refuses to use the file. --- src/lib/file_group.cc | 10 ++++++++-- test/file_group_test.cc | 11 +++++++++-- 2 files changed, 17 insertions(+), 4 deletions(-) diff --git a/src/lib/file_group.cc b/src/lib/file_group.cc index 9863a21cb..04e23b6b2 100644 --- a/src/lib/file_group.cc +++ b/src/lib/file_group.cc @@ -135,12 +135,18 @@ FileGroup::seek (int64_t pos, int whence) const if (sub_pos < int64_t (len)) { break; } - sub_pos -= len; ++i; + if (i < _paths.size()) { + /* If we've run out of files we need to seek off the end of the last file */ + sub_pos -= len; + } } if (i == _paths.size ()) { - return -1; + /* Seeking too far isn't an error; we'll seek too far in the last file which + * will "pass on" fseek()'s behaviour to our caller. + */ + i--; } ensure_open_path (i); diff --git a/test/file_group_test.cc b/test/file_group_test.cc index cfcaacfc2..05127828c 100644 --- a/test/file_group_test.cc +++ b/test/file_group_test.cc @@ -92,8 +92,15 @@ BOOST_AUTO_TEST_CASE (file_group_test) BOOST_CHECK_EQUAL (fg.read (test, total_length * 3), total_length - pos); BOOST_CHECK_EQUAL (memcmp (data + pos, test, total_length - pos), 0); - /* Bad seek */ - BOOST_CHECK_EQUAL (fg.seek (total_length * 2, SEEK_SET), -1); + /* Seeking off the end of the file should not give an error */ + BOOST_CHECK_EQUAL (fg.seek (total_length * 2, SEEK_SET), total_length * 2); + /* and attempting to read should return nothing */ + BOOST_CHECK_EQUAL (fg.read (test, 64), 0); + /* but the requested seek should be remembered, so if we now go back (relatively) */ + BOOST_CHECK_EQUAL (fg.seek (-total_length * 2, SEEK_CUR), 0); + /* we should be at the start again */ + BOOST_CHECK_EQUAL (fg.read (test, 64), 64); + BOOST_CHECK_EQUAL (memcmp (data, test, 64), 0); /* SEEK_SET */ BOOST_CHECK_EQUAL (fg.seek (999, SEEK_SET), 999); -- 2.30.2