How to create a binary blob from atob - currently getting different bytes
I have a binary Excel file generated on the server that I am returning from C # WebMethod using Convert.ToBase64String (FileData) called from JavaScript / JQuery $ ajax call. I have confirmed that the base64 string data is getting to the client, but when I try to convert it to a binary block and store it, the bytes stored on disk are not the same as on the server. (I get a lot of 0xC3 bytes, etc., which looks suspicious like doubled utf8 bytes)
$.ajax({
type: "POST",
contentType: "application/json;",
dataType: "json",
processData: false,
data: "{ inputData: \"" + dataString + "\" }",
url: "Api.aspx/GetExcel",
success: ...
Success handler code includes:
var excelBlob = new Blob([atob(msg.d)], { type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;' });
...
var a = document.createElement('a');
...
a.href = window.URL.createObjectURL(excelBlob);
a.setAttribute('download', 'Excel.xlsx');
When it finishes downloading, it has the wrong byte values. Binary comparison to source shows it is close but has C3 and similar values inserted or tagged in place.
Is there something I am doing wrong or missing to get the Base64 string correctly converted to a binary blob client?
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The new Blob constructor encodes any strings it encounters as UTF-8 ( http://dev.w3.org/2006/webapi/FileAPI/#constructorBlob ). Since you are dealing with binary data, this is converted to multibyte UTF-8 representations.
Instead, you need to convert your data to a byte array before moving on to the Blob constructor.
The following code works for me in Chrome:
var binary = atob(base64)
var array = new Uint8Array(binary.length)
for( var i = 0; i < binary.length; i++ ) { array[i] = binary.charCodeAt(i) }
new Blob([array])
This says that I don't know how well it atob
renders in browsers (I guess the reason is that mozilla provides much longer example code https://developer.mozilla.org/en-US/docs/Web/API/ WindowBase64 / Base64_encoding_and_decoding # Solution_.232_.E2.80.93_rewriting_atob% 28% 29_and_btoa% 28% 29_using_TypedArrays_and_UTF-8 ).
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