Why is My Go Web Server Redirecting POST Requests to GET?

Go Web Server Automatically Redirecting POST Requests

Many developers have encountered an issue where their Go web server automatically redirects POST requests, resulting in unexpected behavior. This phenomenon arises when the server receives a POST request for a specific URL but responds with a 301 (Moved Permanently) status code, triggering a subsequent GET request to a different URL.

To understand the root cause, it's essential to delve into the behavior of Go's http.ServeMux type. By default, ServeMux will automatically redirect requests to the root of a subtree if the request includes a trailing slash in the URL. For instance, if a handler is registered for "/myurl/", any request to "/myurl" (without the trailing slash) will be redirected to "/myurl/".

In the example provided, the PHandler is registered to handle requests to "/myurl/". However, the user's browser was directed to "/myurl" without the trailing slash. As a result, ServeMux detected this discrepancy and issued a 301 redirect to the correct URL, effectively converting the POST request into a GET request.

To resolve this issue, consider the following solutions:

• Ensure that the URL your browser accesses matches the registered path for the handler. In this case, direct the browser to "/myurl/" instead of "/myurl".
• If you do not require a subtree handler but solely need a handler for a specific path, register the handler only for that path without the trailing slash, such as "http.HandleFunc("/myurl", PHandler)".
• Register both paths to the handler to handle both "/myurl" and "/myurl/". Use the function "http.HandleFunc("/myurl/", PHandler)".

Remember that browsers typically do not repeat POST requests after a redirect to preserve the security of sensitive data.

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