C# Blazor, ExcelDataReader Memory Stream gives Invalid Signature, FileStream does not - Stack Overflow

Trying to figure out why I am unable to read a MemoryStream using ExcelDataReader. If I hard code the path to the CSV file and pass the stream as a FileStream it works. My problem is that I am getting the file from Blazor using <InputFile OnChange="LoadFile" accept=".csv,.xlsx,.xls" /> which only provides me an IBrowserFile, which gives me a Stream, not a FileStream. When I attempt to pass this in the following code (which works on this file if I pass a FileStream) I get an "Invalid Signature" exception.

The code:

using (var memoryStream = new MemoryStream())
{
    System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);

    // Copy the file data to the memory stream
    await browserFile.OpenReadStream().CopyToAsync(memoryStream);
    memoryStream.Position = 0; // Reset stream position to the beginning
    var config = new ExcelReaderConfiguration
    {
        FallbackEncoding = System.Text.Encoding.UTF8 // Default encoding
    };
    // Exception happens here, CreateReader...
    using var reader = ExcelReaderFactory.CreateReader(memoryStream, config);
    var result = reader.AsDataSet(new ExcelDataSetConfiguration()
    {
        ConfigureDataTable = _ => new ExcelDataTableConfiguration()
        {
            UseHeaderRow = true // Use the first row as column names
        }
    });
}

The body of the exception is:

ExcelDataReader.Exceptions.HeaderException
  HResult=0x80131500
  Message=Invalid file signature.
  Source=ExcelDataReader
  StackTrace:
   at ExcelDataReader.ExcelReaderFactory.CreateReader(Stream fileStream, ExcelReaderConfiguration configuration)
   at CollectXScore.Web.Utilities.ExcelCSVFileReader.<LoadFile>d__1.MoveNext() in mycode.cs:line 44

  This exception was originally thrown at this call stack:
    [External Code]

When make the call this way it works for the same file:

FileStream source = File.Open("C:\\myfilepath\\" + browserFile.Name, FileMode.Open);
using var reader = ExcelReaderFactory.CreateReader(source);

What am I doing wrong?

Trying to figure out why I am unable to read a MemoryStream using ExcelDataReader. If I hard code the path to the CSV file and pass the stream as a FileStream it works. My problem is that I am getting the file from Blazor using <InputFile OnChange="LoadFile" accept=".csv,.xlsx,.xls" /> which only provides me an IBrowserFile, which gives me a Stream, not a FileStream. When I attempt to pass this in the following code (which works on this file if I pass a FileStream) I get an "Invalid Signature" exception.

The code:

using (var memoryStream = new MemoryStream())
{
    System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);

    // Copy the file data to the memory stream
    await browserFile.OpenReadStream().CopyToAsync(memoryStream);
    memoryStream.Position = 0; // Reset stream position to the beginning
    var config = new ExcelReaderConfiguration
    {
        FallbackEncoding = System.Text.Encoding.UTF8 // Default encoding
    };
    // Exception happens here, CreateReader...
    using var reader = ExcelReaderFactory.CreateReader(memoryStream, config);
    var result = reader.AsDataSet(new ExcelDataSetConfiguration()
    {
        ConfigureDataTable = _ => new ExcelDataTableConfiguration()
        {
            UseHeaderRow = true // Use the first row as column names
        }
    });
}

The body of the exception is:

ExcelDataReader.Exceptions.HeaderException
  HResult=0x80131500
  Message=Invalid file signature.
  Source=ExcelDataReader
  StackTrace:
   at ExcelDataReader.ExcelReaderFactory.CreateReader(Stream fileStream, ExcelReaderConfiguration configuration)
   at CollectXScore.Web.Utilities.ExcelCSVFileReader.<LoadFile>d__1.MoveNext() in mycode.cs:line 44

  This exception was originally thrown at this call stack:
    [External Code]

When make the call this way it works for the same file:

FileStream source = File.Open("C:\\myfilepath\\" + browserFile.Name, FileMode.Open);
using var reader = ExcelReaderFactory.CreateReader(source);

What am I doing wrong?

• c#
• stream
• blazor
• exceldatareader

Share Improve this question Follow edited Jan 2 at 19:38 Age of Empires asked Jan 2 at 19:02 Age of EmpiresAge of Empires 13577 bronze badges 5

• How are you rendering in Blazor? – GH DevOps Commented Jan 2 at 19:17
• @GHDevOps This is a server side Blazor app. I use the <Input> to get the stream and then use ExcelDataReader to read the data. Once it has been parsed I am displaying it in a Grid. But I never get to the rendering. It is blowing up on the CreateReader when I use the stream from the IBrowserFile. – Age of Empires Commented Jan 2 at 19:32
• which works on this file if I pass a FileStream - can you share the working code? Are you sure the file is really encoded in Encoding.UTF8 or could there be a BOM specifying some other encoding? Also, is there any chance the file is larger than the default long maxAllowedSize = 512000? – dbc Commented Jan 2 at 19:33
• You wrote, If I hard code the path to the CSV file but is the file actually a CSV file? I checked the source for ExcelReaderFactory.CreateReader(Stream fileStream, ExcelReaderConfiguration configuration = null), it seems to be xls or xlsx files. For CSV files you need to use CreateCsvReader(). – dbc Commented Jan 2 at 19:45
• Looks like the IDE was doing something funky. I exited the IDE, removed the UTF-8 reference and now seems to be working. Sry! – Age of Empires Commented Jan 2 at 20:07

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1 Answer 1

Sorted by: Reset to default 0

Looks like this was the IDE being stupid, and potentially the reference to UTF-8. This code did work for the CSV file now:

System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
 using var source = new MemoryStream();
 await file.OpenReadStream().CopyToAsync(source);
 source.Position = 0;

 using var reader = ExcelReaderFactory.CreateCsvReader(source);
 var result = reader.AsDataSet(new ExcelDataSetConfiguration()
 {
     ConfigureDataTable = _ => new ExcelDataTableConfiguration()
     {
         UseHeaderRow = true // Use the first row as column names
     }
 });

Where file is the the IBrowserFile reference.