Encode a FileStream to base64 with c

Question

I know how to encode   decode a simple string to   from base64    But how would I do that if the data is already been written to a FileStream object  Let s say I have only access to the FileStream object not to the previously stored original data in it  How would I encode a FileStream to base64 before I flush the FileStream to a file    Ofc I could just open my file and encode   decode it after I have written the FileStream to the file  but I would like to do this all in one single step without doing two file operations one after another  The file could be larger and it would also take double time to load  encode and save it again after it was just saved a short time before    Maybe someone of you knows a better solution  Can I convert the FileStream to a string  encode the string and then convert the string back to a FileStream for example or what would I do and how would such a code look like

User · Answer

Since the file will be larger  you don t have very much choice in how to do this  You cannot process the file in place since that will destroy the information you need to use  You have two options that I can see    Read in the entire file  base64 encode  re-write the encoded data  Read the file in smaller pieces  encoding as you go along  Encode to a temporary file in the same directory  When you are finished  delete the original file  and rename the temporary file    Of course  the whole point of streams is to avoid this sort of scenario  Instead of creating the content and stuffing it into a file stream  stuff it into a memory stream  Then encode that and only then save to disk

User · Answer

When dealing with large streams  like a file sized over 4GB - you don t want to load the file into memory  as a Byte    because not only is it very slow  but also may cause a crash as even in 64-bit processes a Byte   cannot exceed 2GB  or 4GB with gcAllowVeryLargeObjects   Fortunately there s a neat helper in  NET called ToBase64Transform which processes a stream in chunks  For some reason Microsoft put it in System Security Cryptography and it implements ICryptoTransform  for use with CryptoStream   but disregard that   quot a rose by any other name    quot   just because you aren t performing any cryprographic tasks  You use it with CryptoStream like so  using System Security Cryptography  using System IO       using  FileStream   inputFile      new FileStream    quot C  VeryLargeFile bin quot   FileMode Open  FileAccess Read  FileShare None  bufferSize  1024   1024  useAsync  true        When using  useAsync  true  you get better performance with buffers much larger than the default 4096 bytes  using  CryptoStream base64Stream   new CryptoStream  inputFile  new ToBase64Transform    CryptoStreamMode Read     using  FileStream   outputFile     new FileStream    quot C  VeryLargeBase64File txt quot   FileMode CreateNew  FileAccess Write  FileShare None  bufferSize  1024   1024  useAsync  true           await base64Stream CopyToAsync  outputFile   ConfigureAwait false

User · Answer

You may try something like that       public Stream ConvertToBase64 Stream stream                Byte   inArray   new Byte  int stream Length           Char   outArray   new Char  int  stream Length   1 34            stream Read inArray  0   int stream Length           Convert ToBase64CharArray inArray  0  inArray Length  outArray  0           return new MemoryStream Encoding UTF8 GetBytes outArray

User · Answer

A simple Stream extension method would do the job   public static class StreamExtensions       public static string ConvertToBase64 this Stream stream                var bytes   new Byte  int stream Length            stream Seek 0  SeekOrigin Begin           stream Read bytes  0   int stream Length            return Convert ToBase64String bytes             The methods for Read  and also Write  and optimized for the respective class  whether is file stream  memory stream  etc   and will do the work for you  For simple task like this  there is no need of readers  and etc   The only drawback is that the stream is copied into byte array  but that is how the conversion to base64 via Convert ToBase64String works unfortunately

User · Answer

An easy one as an extension method  public static class Extensions       public static Stream ConvertToBase64 this Stream stream                byte   bytes          using  var memoryStream   new MemoryStream                          stream CopyTo memoryStream               bytes   memoryStream ToArray                       string base64   Convert ToBase64String bytes           return new MemoryStream Encoding UTF8 GetBytes base64

User · Answer

You can also encode bytes to Base64  How to get this from a stream see here  How to convert an Stream into a byte   in C    Or I think it should be also possible to use the  ToString   method and encode this

[c#] Encode a FileStream to base64 with c#

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