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;
    }

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
– tbddeveloper, Commented Jul 20, 2015 at 19:07

willaien · Accepted Answer · 2015-07-20 19:18:43Z

75

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, 2015 at 19:18

willaien

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DigitalDan · Accepted Answer · 2016-03-04 11:43:44Z

20

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);

answered Mar 4, 2016 at 11:43

DigitalDan

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Mohammad Fazeli · Accepted Answer · 2022-05-29 10:20:40Z

14

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

answered May 29, 2022 at 10:20

Mohammad Fazeli

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1 Comment

Tyler2P Over a year ago

Your answer could be improved by adding more information on what the code does and how it helps the OP.

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