Why Are request.URL.Host and request.URL.Scheme Blank in Relative HTTP Requests?

Determining URL Host and Scheme in Development Server: Why Are They Blank?

When accessing an HTTP server from a relative path, as is common in development environments, certain URL attributes may appear blank. Specifically, request.URL.Host and request.URL.Scheme may return empty values.

Why Does This Occur?

Relative HTTP requests, typically issued by browsers when accessing the server locally, lack explicit host and scheme information. This contrasts with absolute URLs used by HTTP proxies, which include these details in the request. In the case of relative requests, only the raw URL is available in the http.Request.URL object.

Accessing the HTTP Host

To retrieve the HTTP host, you can access the Host attribute of the http.Request struct. This provides the hostname and port specified in the request's Host header.

Distinguishing Relative and Absolute URLs

You can determine whether a request uses a relative or absolute URL by calling the IsAbs() method on http.Request.URL. If IsAbs() returns false, the URL is relative and does not contain host or scheme information.

Example Using Netcat

To demonstrate the difference, you can use netcat to send an HTTP request with a relative path.

cat my-http-request-file | nc localhost 8080

The my-http-request-file should contain the following contents, formatted as an HTTP request:

GET / HTTP/1.1
Host: localhost:8080

This request will return blank r.URL.Host and r.URL.Scheme values in the handler.

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