In the following, `\n' refers to a linefeed and `\t' refers to a horizontal tab; requests are what the client sends and responses are what the server sends. In general, the connection is governed by the client--the server does not send responses without first receiving requests to do so; see section Introduction to Responses for more details of this convention.
It is typical, early in the connection, for the client to transmit a
Valid-responses request, containing all the responses it
supports, followed by a valid-requests request, which elicits
from the server a Valid-requests response containing all the
requests it understands. In this way, the client and server each find
out what the other supports before exchanging large amounts of data
(such as file contents).
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