Can a web application send additional information after streaming a file to the browser?

Problem

Your web application uses OfficeWriter to generate and stream a document or spreadsheet to the browser. Subsequently, you want to send additional instructions to the browser to update the web page, display a pop-up confirmation message, or re-direct to another web page.

Solution

It is not possible for a web application to stream a file to the browser and subsequently send additional information in the same response. This limitation is a consequence of the request-response nature of web programming and is not specific to OfficeWriter. The same limitation applies to any web application which performs media streaming or file downloading.

The HTTP protocol mandates that there can be only one response to each request. A response consists of HTTP headers and content. The HTTP headers provides information about the file and optionally specifies how it should be handled. In the case of file downloading, the response’s content must contain only file data. If there are non-file data in the response, such as HTML code to update the web page or perform additional actions, the foreign data would be taken to be part of the file, causing the file to be corrupted.

After a web application streams a file to the browser using OfficeWriter’s Save method, attempting to redirect to another web page may generate the following error: “Cannot redirect after HTTP headers have been sent.” This is because OfficeWriter’s Save method sets the appropriate HTTP headers before streaming the file and the instruction to redirect requires another set of HTTP headers.

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