Скачать или смотреть Solving the RestSharp Request.AddFile Parameter Order Issue

Learn how to manually control header order when using RestSharp to send multipart/form-data, ensuring your REST endpoint receives the request correctly.
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Solving the RestSharp Request.AddFile Parameter Order Issue

If you're working with RESTful services, you might occasionally run into the issue where your requests don't adhere to the expected format. This post addresses a specific problem encountered when using the RestSharp library for sending a CSV file to a REST endpoint. The receiving server is sensitive to the order of the headers within the request body, particularly the position of Content-Disposition relative to Content-Type. In this guide, we'll break down how to resolve this problem effectively.

Understanding the Problem

When using RestSharp to send a POST request with a CSV file, you might notice that the library automatically adds headers for you, sometimes in the wrong order. The server you’re trying to communicate with may expect the Content-Disposition header to appear immediately after the multipart form boundary.

The Problematic Order

Here's the order in which RestSharp is adding the headers:

[[See Video to Reveal this Text or Code Snippet]]

The Required Order

The server requires this instead:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

In order to rectify this, you have to manually assemble the request body. The following code demonstrates how to accomplish this:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code

Set Up the Header: The first line explicitly states the Content-Type header with the desired boundary.

Build the Body:

A StringBuilder is used to build the multipart form-data body.

You start with the boundary followed immediately by the Content-Disposition header.

Add the Content-Type header for the file, this time after Content-Disposition.

Finally, append the file content followed by the closing boundary.

This method gives you the control you need over the header order, ensuring the request matches what the server expects.

Conclusion

In cases where libraries like RestSharp impose certain automatic behaviors that conflict with external requirements, manual intervention becomes necessary. By constructing the request body yourself, you can dictate the order of the headers, thereby ensuring compliance with the server’s expectations.

Next time you face similar issues, remember this solution for a seamless interaction with your REST endpoints. Happy coding!