The input is not a valid Base-64 string as it contains a non-base 64 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 the same stream is received at the application  it gets manipulated and is no longer a valid Base64 string  Some junk characters are getting introduced into the stream   The exception received when converting the stream back to Byte is      The input is not a valid Base-64 string as it contains a non-base 64   character  more than two padding characters  or a non-white space   character among the padding characters   At Service    WebGet UriTemplate    ReadFile Convert   ResponseFormat   WebMessageFormat Json     public string ExportToExcel             string filetoexport    D   SomeFile xls         byte   data   File ReadAllBytes filetoexport         var s   Convert ToBase64String data         return s        At Application          var client   new RestClient  http   localhost 56877 User            var request   new RestRequest  ReadFile Convert   RestSharp Method GET          request AddHeader  Accept    application Json           request AddHeader  Content-Type    application Json           request OnBeforeDeserialization   resp   gt   resp ContentType       application Json            var result   client Execute request          byte   d   Convert FromBase64String result Content

User · Answer

Very possibly it s getting converted to a modified Base64  where the   and   characters are changed to - and    See http   en wikipedia org wiki Base64 Implementations and history  If that s the case  you need to change it back   string converted   base64String Replace  -         converted   converted Replace

User · Answer

Remove the unnecessary string through Regex Regex regex new Regex   quot    w    -   base64  quot    base64File regex Replace base64File string Empty

User · Answer

Since you re returning a string as JSON  that string will include the opening and closing quotes in the raw response  So your response should probably look like    abc123XYZ      or whatever   You can try confirming this with Fiddler   My guess is that the result Content is the raw string  including the quotes  If that s the case  then result Content will need to be deserialized before you can use it

User · Answer

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

User · Answer

Check if your image data contains some header information at the beginning   imageCode    data image png base64 iVBORw0KGgoAAAANSUhEUgAAAMgAAABkC      This will cause the above error   Just remove everything in front of and including the first comma  and you good to go   imageCode    iVBORw0KGgoAAAANSUhEUgAAAMgAAABkC

User · Answer

Just in case you don t know the type of uploaded image  and you just you need to remove its base64 header    var imageParts   model ImageAsString Split      ToList lt string gt        Exclude the header from base64 by taking second element in List   byte   Image   Convert FromBase64String imageParts 1

User · Answer

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   gt    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

User · Answer

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

User · Answer

var spl   item Split      1   var format  spl Split      0              stringconvert item Replace   data image  format  base64   String Empty

User · Answer

I get this error because a field was varbinary in sqlserver table instead of varchar

User · Answer

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

User · Answer

Probably the string would be like this data image jpeg base64  9j 4QN8RXh    First split for   and get the second token  var StrAfterSlash   Face Split      1    Then Split for   and get the first token which will be the format  In my case it s jpeg  var ImageFormat  StrAfterSlash Split      0    Then remove the line data image jpeg base64  for the collected format CleanFaceData Face Replace   quot data image  ImageFormat   base64  quot  string Empty

[c#] The input is not a valid Base-64 string as it contains a non-base 64 character

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