From: Carl Hetherington <cth@carlh.net>
Date: Tue, 6 Oct 2020 23:02:47 +0000 (+0200)
Subject: Fix errors when over-reading a "large" amount from FileGroups on
X-Git-Tag: v2.15.104~31
X-Git-Url: https://main.carlh.net/gitweb/?p=dcpomatic.git;a=commitdiff_plain;h=e5277d4042b896c4b50c694fba0f1afb47337f45

Fix errors when over-reading a "large" amount from FileGroups on
Windows.  I haven't been able to find any conclusive explanation for
why this stuff happens;

https://stackoverflow.com/questions/7241168/safe-maximum-number-of-records-read-by-fread

is one possible lead.
---

diff --git a/src/lib/file_group.cc b/src/lib/file_group.cc
index 3e8a7b79c..9863a21cb 100644
--- a/src/lib/file_group.cc
+++ b/src/lib/file_group.cc
@@ -37,6 +37,7 @@ using std::cout;
 FileGroup::FileGroup ()
 	: _current_path (0)
 	, _current_file (0)
+	, _current_size (0)
 {
 
 }
@@ -45,6 +46,7 @@ FileGroup::FileGroup ()
 FileGroup::FileGroup (boost::filesystem::path p)
 	: _current_path (0)
 	, _current_file (0)
+	, _current_size (0)
 {
 	_paths.push_back (p);
 	ensure_open_path (0);
@@ -95,6 +97,7 @@ FileGroup::ensure_open_path (size_t p) const
 	if (_current_file == 0) {
 		throw OpenFileError (_paths[_current_path], errno, OpenFileError::READ);
 	}
+	_current_size = boost::filesystem::file_size (_paths[_current_path]);
 }
 
 int64_t
@@ -155,7 +158,15 @@ FileGroup::read (uint8_t* buffer, int amount) const
 {
 	int read = 0;
 	while (true) {
-		int const this_time = fread (buffer + read, 1, amount - read, _current_file);
+		int64_t to_read = amount - read;
+#ifdef DCPOMATIC_WINDOWS
+		/* If we over-read from the file by too much on Windows we get a errno=22 rather than an feof condition,
+		 * for unknown reasons.  So if we're going to over-read, we need to do it by a little bit, so that feof
+		 * still gets triggered but there is no errno=22.
+		 */
+		to_read = std::min(to_read, static_cast<int64_t>(_current_size - _ftelli64(_current_file) + 1));
+#endif
+		int const this_time = fread (buffer + read, 1, to_read, _current_file);
 		read += this_time;
 		if (read == amount) {
 			/* Done */
diff --git a/src/lib/file_group.h b/src/lib/file_group.h
index 800d9a059..21499f563 100644
--- a/src/lib/file_group.h
+++ b/src/lib/file_group.h
@@ -52,6 +52,7 @@ private:
 	/** Index of path that we are currently reading from */
 	mutable size_t _current_path;
 	mutable FILE* _current_file;
+	mutable size_t _current_size;
 };
 
 #endif