Returning a stream from File OpenRead

Question

I m in the process of writing a WCF service that will allow an ASP Net web site to retrieve files  based on this article   My problem is that when I return the stream  it s blank   For simplicity  I ve isolated the code into a simple winforms app to try and find what the problem is with returning a stream and this is the code        private Stream TestStream                 Stream fs   File OpenRead   c  testdocument docx            return fs                This method converts the filestream into a byte array so that when it is         used in my ASP Net project the file can be sent using response Write     private void Test                             System IO MemoryStream data   new System IO MemoryStream            System IO Stream str   TestStream             str CopyTo data           byte   buf   new byte data Length           data Read buf  0  buf Length                                  The result of this code is that buf is 12 587 bytes long  the correct length of the file  but it just contains 0 s   The Word document opens without problems if I try it  am I missing something obvious

User · Answer

Options    Use data Seek as suggested by ken2k Use the somewhat simpler Position property   data Position   0   Use the ToArray call in MemoryStream to make your life simpler to start with   byte   buf   data ToArray       The third option would be my preferred approach   Note that you should have a using statement to close the file stream automatically  and optionally for the MemoryStream   and I d add a using directive for System IO to make your code cleaner   byte   buf  using  MemoryStream data   new MemoryStream          using  Stream file   TestStream                  file CopyTo data           buf   data ToArray                Use buf   You might also want to create an extension method on Stream to do this for you in one place  e g   public static byte   CopyToArray this Stream input        using  MemoryStream memoryStream   new MemoryStream                  input CopyTo memoryStream           return memoryStream ToArray              Note that this doesn t close the input stream

User · Answer

Try changing your code to this   private void Test                     System IO MemoryStream data   new System IO MemoryStream TestStream          byte   buf   new byte data Length       data Read buf  0  buf Length

User · Answer

You need      str CopyTo data       data Position   0     reset to beginning     byte   buf   new byte data Length       data Read buf  0  buf Length       And since your Test   method is imitating the client it ought to Close   or Dispose   the str Stream  And the memoryStream too  just out of principal

User · Answer

You forgot to seek   str CopyTo data   data Seek 0  SeekOrigin Begin       lt -- missing line byte   buf   new byte data Length   data Read buf  0  buf Length

User · Answer

You forgot to reset the position of the memory stream   private void Test                     System IO MemoryStream data   new System IO MemoryStream        System IO Stream str   TestStream         str CopyTo data          Reset memory stream     data Seek 0  SeekOrigin Begin       byte   buf   new byte data Length       data Read buf  0  buf Length                              Update   There is one more thing to note  It usually pays not to ignore the return values of methods  A more robust implementation should check how many bytes have been read after the call returns   private void Test                     using MemoryStream data   new MemoryStream                  using Stream str   TestStream                         str CopyTo data                        Reset memory stream         data Seek 0  SeekOrigin Begin           byte   buf   new byte data Length           int bytesRead   data Read buf  0  buf Length            Debug Assert bytesRead    data Length                       String Format  Expected to read  0  bytes  but read  1                             data Length  bytesRead

[c#] Returning a stream from File.OpenRead()

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