What is HTTP/0.9 request?

HTTP/0.9 is a one-line protocol. Its main points are:

• Initial version of HTTP - a simple client-server, request-response, telenet-friendly protocol
• Request nature: single-line (method + path for requested document)
• Methods supported: GET only
• Response type: hypertext only
• Connection nature: terminated immediately after the response
• No HTTP headers (cannot transfer other content type files), No status/error codes, No URLs, No versioning

For details see the article
Evolution of HTTP — HTTP/0.9, HTTP/1.0, HTTP/1.1, Keep-Alive, Upgrade, and HTTPS.

An example of a HTTP/0.9 request: