I am having trouble understanding ProxyFromEnvironment and ProxyURL in net/http package. Can someone please explain me when and why these two functionalities are used?
My current understanding (at least for ProxyFromEnvironment) is that this is used to get the URL of a PROXY Server from the Environment Variables and this PROXY Server is used to make HTTP Requests.
Both functions are related to how you use the http.Transport mechanism.
One can be used to allow the transport to dynamically retrieve the proxy settings from the environment, the other can be used to provide a static URL to be used by the transport for the proxy every time.
ProxyFromEnvironment is a func that returns a URL describing the proxy that is configured in the Environment; it can be assigned to the Transport.Proxy field, and every time the Transport makes a request, the Proxy will depend on the values in the Environment.
ProxyURL is a func that returns a general func which returns the given URL every time it is invoked; it can be used to generate a helper function to assign to the Transport.Proxy field, so that your Transport has a consistent Proxy every time the Transport makes a request.