The input is not a valid Base-64 string as it contains a non-base64 character

Question

I have a REST service that reads a file and sends it to another console application after converting it to Byte array and then to Base64 string. This part works, but when th

Answer 1

And some times it started with double quotes, most of the times when you call API from dotNetCore 2 for getting file

string string64 = string64.Replace(@"""", string.Empty);
byte[] bytes = Convert.ToBase64String(string64);

Answer 2

I arranged a similar context as you described and I faced the same error. I managed to get it working by removing the " from the beginning and the end of the content and by replacing \/ with /.

Here is the code snippet:

var result = client.Execute(request);
var response = result.Content
    .Substring(1, result.Content.Length - 2)
    .Replace(@"\/","/");
byte[] d = Convert.FromBase64String(response);

As an alternative, you might consider using XML for the response format:

[WebGet(UriTemplate = "ReadFile/Convert", ResponseFormat = WebMessageFormat.Xml)]  
public string ExportToExcel() { //... }

On the client side:

request.AddHeader("Accept", "application/xml");
request.AddHeader("Content-Type", "application/xml");
request.OnBeforeDeserialization = resp => { resp.ContentType = "application/xml"; };

var result = client.Execute(request);
var doc = new System.Xml.XmlDocument();
doc.LoadXml(result.Content);
var xml = doc.InnerText;
byte[] d = Convert.FromBase64String(xml);

Answer 3

We can remove unnecessary string input in front of the value.

string convert = hdnImage.Replace("data:image/png;base64,", String.Empty);

byte[] image64 = Convert.FromBase64String(convert);

Answer 4

As Alex Filipovici mentioned the issue was a wrong encoding. The file I read in was UTF-8-BOM and threw the above error on Convert.FromBase64String(). Changing to UTF-8 did work without problems.

Answer 5

var spl = item.Split('/')[1];
var format =spl.Split(';')[0];           
stringconvert=item.Replace($"data:image/{format};base64,",String.Empty);