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Overview

The OnlyOfficeHandler.ashx is an ASP.NET HTTP handler that processes document-related requests for the OnlyOffice Control library. It implements the IHttpHandler interface and provides three main actions for document management.

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Handler Endpoint

OnlyOfficeHandler.ashx?action={action}

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Available Actions

The handler supports three primary actions, specified via the action query parameter:

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download

Downloads a document file from the server storage. 
GET OnlyOfficeHandler.ashx?action=download&fileId={fileId}
Learn more about document download →

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callback

Receives document status updates from OnlyOffice Document Server when users edit or save documents. 
POST OnlyOfficeHandler.ashx?action=callback&fileId={fileId}
Learn more about document callback →

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proxy

Proxies external document requests to handle CORS restrictions and security validation. 
GET OnlyOfficeHandler.ashx?action=proxy&url={url}
Learn more about document proxy →

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Error Handling

If an invalid or missing action is provided, the handler returns:
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statusCode
number
default:"400"
HTTP status code indicating bad request
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body
string
default:"Invalid action"
Error message in plain text format

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Example Error Response

HTTP/1.1 400 Bad Request
Content-Type: text/plain

Invalid action

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File Storage

All document files are stored in the ~/App_Data/uploads directory. The handler automatically creates this directory if it doesn’t exist.

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File Naming Convention

Files are stored with the pattern: {fileId}.{extension} For example:
  • doc123.docx
  • sheet456.xlsx
  • presentation789.pptx

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Implementation Details

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Namespace

OnlyOfficeControl.Controls.OnlyOfficeEditorBundle

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Class

public class OnlyOfficeHandler : IHttpHandler
{
    public bool IsReusable => false;
}

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Handler Registration

Ensure the handler is registered in your web.config: 
<system.webServer>
  <handlers>
    <add name="OnlyOfficeHandler" 
         verb="*" 
         path="OnlyOfficeHandler.ashx" 
         type="OnlyOfficeControl.Controls.OnlyOfficeEditorBundle.OnlyOfficeHandler" />
  </handlers>
</system.webServer>

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Security Considerations

The handler processes file operations and external requests. Ensure proper authentication and authorization are implemented at the application level before allowing access to this handler.

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TLS Configuration

The handler enforces secure connections for external requests: 
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | 
                                       SecurityProtocolType.Tls11 | 
                                       SecurityProtocolType.Tls;

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Next Steps

Download Action

Learn how to download documents from storage

Callback Action

Handle document save callbacks from OnlyOffice

Proxy Action

Proxy external document requests

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