HTTP messages
| [HTTP messages | MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Messages) |
HTTP messages are the mechanism used to exchange data between a server and a client in the HTTP protocol. There are two types of messages: requests sent by the client to trigger an action on the server, and responses, the answer that the server sends in response to a request.
Both requests and responses share a similar structure:
- A start-line is a single line that describes the HTTP version along with the request method or the outcome of the request.
- An optional set of HTTP headers containing metadata that describes the message. For example, a request for a resource might include the allowed formats of that resource, while the response might include headers to indicate the actual format returned.
- An empty line indicating the metadata of the message is complete.
- An optional body containing data associated with the message. This might be POST data to send to the server in a request, or some resource returned to the client in a response. Whether a message contains a body or not is determined by the start-line and HTTP headers.