How to convert base64 value from a database to a stream with C#

Question

I have some base64 stored in a database (that are actually images) that needs to be uploaded to a third party. I would like to upload them using memory rather than saving them as an image then posting it to a server. Does anyone here know how to convert base64 to a stream?

How can I change this code:

var fileInfo = new FileInfo(fullFilePath); var fileContent = new StreamContent(fileInfo.OpenRead());

to fill the StreamContent object with a base64 interpretation of an image file instead.

    private static StreamContent FileMultiPartBody(string fullFilePath)
    {
        var fileInfo = new FileInfo(fullFilePath);

        var fileContent = new StreamContent(fileInfo.OpenRead());

        // Manually wrap the string values in escaped quotes.
        fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
        {
            FileName = string.Format("\"{0}\"", fileInfo.Name),
            Name = "\"name\"",
        };
        fileContent.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg");

        return fileContent;
    }

http://stackoverflow.com/questions/351126/convert-a-string-to-stream and StreamContent will accept a stream, that doesn't have to be a file, you should be able to hand it the resulting stream and go from there. — tbddeveloper, Jul 20 '15 at 19:07

score 62 · Accepted Answer · answered Jul 20 '15 at 19:18

62

You'll want to do something like this, once you've gotten the string from the database:

var bytes = Convert.FromBase64String(base64encodedstring);
var contents = new StreamContent(new MemoryStream(bytes));
// Whatever else needs to be done here.

answered Jul 20 '15 at 19:18

willaien

2,647
15
24

score 13 · Answer 2 · answered Mar 04 '16 at 11:43

Just as an alternative approach, which works well with large streams (saves the intermediate byte array):

// using System.Security.Cryptography
// and assumes the input stream is b64Stream
var stream = new CryptoStream(b64Stream, new FromBase64Transform(), CryptoStreamMode.Read);
return new StreamContent(stream);

score 7 · Answer 3 · answered May 29 '22 at 10:20

7

var stream = new MemoryStream(Convert.FromBase64String(base64));

answered May 29 '22 at 10:20

Mohammad Fazeli

648
10
13

Your answer could be improved by adding more information on what the code does and how it helps the OP. – Tyler2P May 30 '22 at 13:53

How to convert base64 value from a database to a stream with C#

3 Answers3