Returning SpreadsheetGear workbook stream from WebMethod

Question

I would like to provide a web service that lets me download certain Excel workbooks. These Excel workbooks are SpreadsheetGear objects that may be modified with data. I don't want to write them as a file and return the file. Instead, I'd like to stream them into the browser so the user gets a downloaded file.

Here is my attempt that does not work, drawn from this guide from SpreadsheetGear's site:

[System.Web.Services.WebMethod(
  Description = "Returns a stream for the excel file")]
    public ActionResult downloadTemplate(string excelFileName)
    {
        var workbook = makeSpreadsheetGearWorkbookFrom(excelFileName);
        // Save workbook to an Open XML (XLSX) workbook stream.
        System.IO.Stream stream = workbook.SaveToStream(
            SpreadsheetGear.FileFormat.OpenXMLWorkbook);

        // Reset stream's current position back to the beginning.
        stream.Seek(0, System.IO.SeekOrigin.Begin);

        return new FileStreamResult(stream,
            "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    }

I get the following error:

The web service returned the following result:

500 - Internal Server Error
System.InvalidOperationException: There was an error generating the XML document. ---> System.InvalidOperationException: System.Web.Mvc.FileStreamResult cannot be serialized because it does not have a parameterless constructor.
  at System.Xml.Serialization.TypeDesc.CheckSupported () [0x0001c] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.TypeScope.GetTypeDesc (System.Type type, System.Reflection.MemberInfo source, System.Boolean directReference, System.Boolean throwOnError) [0x0006a] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.TypeScope.GetTypeDesc (System.Type type) [0x00000] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializationWriter.CreateUnknownTypeException (System.Type type) [0x00039] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializationWriter.CreateUnknownTypeException (System.Object o) [0x00007] in <611e64636ff745389933c69c817b2d4a>:0 
  at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write3_ActionResult (System.String n, System.String ns, System.Web.Mvc.ActionResult o, System.Boolean isNullable, System.Boolean needType) [0x00048] in <3fa7e61a58e74ec08df7a46ab2fb8972>:0 
  at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write7_ActionResult (System.Object o) [0x00028] in <3fa7e61a58e74ec08df7a46ab2fb8972>:0 
  at Microsoft.Xml.Serialization.GeneratedAssembly.ActionResultSerializer.Serialize (System.Object objectToSerialize, System.Xml.Serialization.XmlSerializationWriter writer) [0x00000] in <3fa7e61a58e74ec08df7a46ab2fb8972>:0 
  at System.Xml.Serialization.XmlSerializer.Serialize (System.Xml.XmlWriter xmlWriter, System.Object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, System.String encodingStyle, System.String id) [0x00098] in <611e64636ff745389933c69c817b2d4a>:0 
   StackTraceEnd
  at System.Xml.Serialization.XmlSerializer.Serialize (System.Xml.XmlWriter xmlWriter, System.Object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, System.String encodingStyle, System.String id) [0x0012f] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializer.Serialize (System.Xml.XmlWriter xmlWriter, System.Object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces, System.String encodingStyle) [0x00000] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializer.Serialize (System.Xml.XmlWriter xmlWriter, System.Object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces) [0x00000] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializer.Serialize (System.IO.TextWriter textWriter, System.Object o, System.Xml.Serialization.XmlSerializerNamespaces namespaces) [0x00015] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Xml.Serialization.XmlSerializer.Serialize (System.IO.TextWriter textWriter, System.Object o) [0x00000] in <611e64636ff745389933c69c817b2d4a>:0 
  at System.Web.Services.Protocols.XmlReturnWriter.Write (System.Web.HttpResponse response, System.IO.Stream outputStream, System.Object returnValue) [0x00079] in <11189ae945ae429a8c10c5e8a65a097a>:0 
  at System.Web.Services.Protocols.HttpServerProtocol.WriteReturns (System.Object[] returnValues, System.IO.Stream outputStream) [0x0003f] in <11189ae945ae429a8c10c5e8a65a097a>:0 
  at System.Web.Services.Protocols.WebServiceHandler.WriteReturns (System.Object[] returnValues) [0x00051] in <11189ae945ae429a8c10c5e8a65a097a>:0 
  at System.Web.Services.Protocols.WebServiceHandler.Invoke () [0x000cc] in <11189ae945ae429a8c10c5e8a65a097a>:0

How should I approach this?

score 1 · Accepted Answer · answered Oct 27 '17 at 00:48

Solved the problem by returning a list of bytes instead of a StreamResult, like so:

public byte[] downloadTemplate(string excelFileName)
    //...
    byte[] modelData = toByteArray(stream);
    return modelData;
}

public byte[] toByteArray(System.IO.Stream stream)
{
    using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
    {
        stream.CopyTo(ms);
        return ms.ToArray();
    }
}

It is easy to put the byte array into a JObject and then into an XML Envelope.

Returning SpreadsheetGear workbook stream from WebMethod

1 Answers1