https://github.com/ooni/minivpn/blob/5254d6892315db9d6c9b325d2575f1d7700828ee/internal/model/session.go#L8package model

// NegotiationState is the state of the session negotiation.
type NegotiationState int

const (
// S_ERROR means there was some form of protocol error.
S_ERROR = NegotiationState(iota) - 1

// S_UNDEF is the undefined state.
S_UNDEF

// S_INITIAL means we're ready to begin the three-way handshake.
S_INITIAL

// S_PRE_START means we're waiting for acknowledgment from the remote.
S_PRE_START

// S_START means we've done the three-way handshake.
S_START

// S_SENT_KEY means we have sent the local part of the key_source2 random material.
S_SENT_KEY

// S_GOT_KEY means we have got the remote part of key_source2.
S_GOT_KEY

// S_ACTIVE means the control channel was established.
S_ACTIVE

// S_GENERATED_KEYS means the data channel keys have been generated.
S_GENERATED_KEYS

)

// String maps a [SessionNegotiationState] to a string.
func (sns NegotiationState) String() string {
switch sns {
case S_UNDEF:
return "S_UNDEF"
case S_INITIAL:
return "S_INITIAL"
case S_PRE_START:
return "S_PRE_START"
case S_START:
return "S_START"
case S_SENT_KEY:
return "S_SENT_KEY"
case S_GOT_KEY:
return "S_GOT_KEY"
case S_ACTIVE:
return "S_ACTIVE"
case S_GENERATED_KEYS:
return "S_GENERATED_KEYS"
case S_ERROR:
return "S_ERROR"
default:
return "S_INVALID"
}
}