😀 HTTP/1.1 Upgrade header

Abstract

The Upgrade header field is a HTTP header field introduced in HTTP/1.1. In the exchange, the client begins by making a cleartext request, which is later upgraded to a newer http protocol version or switched to a different protocol.

Use cases:

• WebSocket uses this mechanism to set up a connection with a HTTP server in a compatible way.
• HTTP/2 uses this to setup a compatible HTTP connection.

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references:

• Wikipedia

16 Sep 2017