HTTP |
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Request methods |
Header fields |
Response status codes |
Security access control methods |
Security vulnerabilities |
The Upgrade header field is an 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. A connection upgrade must be requested by the client; if the server wants to enforce an upgrade it may send a 426 Upgrade Required
response. The client can then send a new request with the appropriate upgrade headers while keeping the connection open.