In order to get a resource from a HTTP server, a HTTP client initiates a HTTP request addressed to that server. When the HTTP server receives that request, it constructs a HTTP response back to the client. The header portions of HTTP requests and HTTP responses are in plain-text format.
Whenever a resource is available, the client will be able to extract it from the response. However, if the resource is unavailable, the client will be able to get a status within the HTTP response. Given that, the client can then decide on any further actions.
HTTP requests and responses are not encrypted. In order to secure the communication between a HTTP client and server, HTTPS has to be used. In addition to defining the communication protocol, HTTPS includes how encryption is performed on data that is communicated between the client and server.