Very similar to the request structure, responses also contain a start-line that is designated as the response status-line. The response may include a message body and header fields, just as the request message is capable of doing. The following data is included within the response line:

• HTTP-Version (RFC-7230 2.6): Similar to the request HTTP-Version field in the request-line, the HTTP-Version is the protocol major and minor version in which the server is responding.

• Status-Code (RFC-7231 6): The response status-code is a three-digit integer code that explains the response of the server. There are five different classes of status codes, namely informational (1xx), successful (2xx), redirection (3xx),  client Error (4xx) and server error (5xx).

• Reason-Phrase: The reason-phrase of the response status-line should be ignored by the client, as it is a textual explanation concerning the status of the request.

Within Go, there is an http.Response type which contains all of the previously enumerated elements within the status-line as well as a response header structure and a message body. Typically, if you are developing a web application in Go, you will generally only interface with the response type through the http.ResponseWriter type defined (https://golang.org/pkg/net/http/#ResponseWriter), which is an interface. This interface allows the developer to populate the message header fields with the Header method, and write the status-line in the message with the WriteHeader method. If the response requires a message body in the response message, the http.ResponseWriter interface has a Write method which will send the raw data as the response message body.

When looking at web application frameworks, it is important to keep in mind the bare essentials of the protocol. The HTTP protocol is a very simple text-based protocol, consisting of request and response messages that were designed to be stateless. However, some very interesting and complex systems and services have been built on top of this simple protocol. When we talk about web frameworks and Echo, we need to keep in mind how the features will affect our application, which in the end is a simple text-based protocol.