Prevent download hang if filename exceeds fs limit

If the name template ends up generating a path where the filename itself
exceeds the limits of the file system (e.g. 255 characters for NTFS on
Windows, 255 bytes for most Linux filesystems), the try..catch block to
handle race-condition file moves in MoveToSaveFolder unhelpfully ends up
causing an infinite loop.

Add a test for the correct behaviour of an IOException being thrown and
adjust MoveToSaveFolder to check for the existence of a file in the
destination path if an IOException has been caught, re-throwing if it
has been thrown for a different reason.

Resolves issue #259.

Classes/DownloadHandler.cs

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2007-2020 Matt Robinson
+ * Copyright © 2007-2024 Matt Robinson
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
@@ -227,7 +227,7 @@ private void DownloadProgThread()
                 }
                 catch (IOException ioExp)
                 {
-                    this.DownloadError(Provider.ErrorType.LocalProblem, "Encountered an error saving the downloaded file.  " + ioExp.Message + "  You may need to select a new location for saving downloaded programmes under Options -> Main Options.");
+                    this.DownloadError(Provider.ErrorType.LocalProblem, "Encountered an error saving the downloaded file.  " + ioExp.Message.TrimEnd('.') + ".  You may need to select a new location for saving downloaded programmes or adjust the file name format under Options -> Main Options.");
                     return;
                 }
                 catch (UnauthorizedAccessException unAuthExp)

Classes/Model/Download.cs

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2008-2020 Matt Robinson
+ * Copyright © 2008-2024 Matt Robinson
  * Copyright © 2017-2018 Neil Blanchard
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
@@ -428,12 +428,9 @@ public static string MoveToSaveFolder(string formatString, Programme progInfo, E
                     {
                         OsUtils.MoveFile(sourceFile, savePath);
                     }
-                    catch (IOException e)
+                    catch (IOException)
                     {
-                        // We only want to handle IOException itself as a
-                        // number of IOException subclasses are thrown for
-                        // other cases we don't want to handle
-                        if (e.GetType() == typeof(IOException))
+                        if (File.Exists(savePath))
                         {
                             // Destination file created since File.Exists check
                             continue;

Test/Classes/Model/TestDownload.cs

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2020 Matt Robinson
+ * Copyright © 2020-2024 Matt Robinson
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
@@ -154,5 +154,28 @@ public void MoveToSaveFolderLongPath()
                 destFile,
                 Download.MoveToSaveFolder(@"%progname%", prog, episode, tempLong, "mp3", sourceFile));
         }
+
+        /// <summary>
+        /// Test that MoveToSaveFolder will throw an IOException if the destination
+        /// file ends up with a name longer than the filesystem supports.
+        /// </summary>
+        [Fact]
+        public void MoveToSaveFolderLongFileName()
+        {
+            string tempBase = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
+            Directory.CreateDirectory(tempBase);
+            string sourceFile = Path.GetTempFileName();
+
+            var prog = new Programme();
+            prog.Name = new string('P', 500);
+
+            var episode = new Episode();
+            episode.Name = "EN";
+
+            string destFile = Path.Combine(tempBase, prog.Name + ".mp3");
+
+            Assert.Throws<IOException>(() =>
+                Download.MoveToSaveFolder(@"%progname%", prog, episode, tempBase, "mp3", sourceFile));
+        }
     }
 }