add connection gating interfaces and types. (#139)

connmgr/gater.go

+package connmgr
+
+import (
+	ma "github.com/multiformats/go-multiaddr"
+
+	"github.com/libp2p/go-libp2p-core/control"
+	"github.com/libp2p/go-libp2p-core/network"
+	"github.com/libp2p/go-libp2p-core/peer"
+)
+
+// ConnectionGater can be implemented by a type that supports active
+// inbound or outbound connection gating.
+//
+// ConnectionGaters are active, whereas ConnManagers tend to be passive.
+//
+// A ConnectionGater will be consulted during different states in the lifecycle
+// of a connection being established/upgraded. Specific functions will be called
+// throughout the process, to allow you to intercept the connection at that stage.
+//
+//  InterceptPeerDial is called on an imminent outbound peer dial request, prior
+//  to the addresses of that peer being available/resolved. Blocking connections
+//  at this stage is typical for blacklisting scenarios.
+//
+//  InterceptAddrDial is called on an imminent outbound dial to a peer on a
+//  particular address. Blocking connections at this stage is typical for
+//  address filtering.
+//
+//  InterceptAccept is called as soon as a transport listener receives an
+//  inbound connection request, before any upgrade takes place. Transports who
+//  accept already secure and/or multiplexed connections (e.g. possibly QUIC)
+//  MUST call this method regardless, for correctness/consistency.
+//
+//  InterceptSecured is called for both inbound and outbound connections,
+//  after a security handshake has taken place and we've authenticated the peer.
+//
+//  InterceptUpgraded is called for inbound and outbound connections, after
+//  libp2p has finished upgrading the connection entirely to a secure,
+//  multiplexed channel.
+//
+// This interface can be used to implement *strict/active* connection management
+// policies, such as hard limiting of connections once a maximum count has been
+// reached, maintaining a peer blacklist, or limiting connections by transport
+// quotas.
+//
+// EXPERIMENTAL: a DISCONNECT protocol/message will be supported in the future.
+// This allows gaters and other components to communicate the intention behind
+// a connection closure, to curtail potential reconnection attempts.
+//
+// For now, InterceptUpgraded can return a non-zero DisconnectReason when
+// blocking a connection, but this interface is likely to change in the future
+// as we solidify this feature. The reason why only this method can handle
+// DisconnectReasons is that we require stream multiplexing capability to open a
+// control protocol stream to transmit the message.
+type ConnectionGater interface {
+
+	// InterceptPeerDial tests whether we're permitted to Dial the specified peer.
+	//
+	// This is called by the network.Network implementation when dialling a peer.
+	InterceptPeerDial(p peer.ID) (allow bool)
+
+	// InterceptAddrDial tests whether we're permitted to dial the specified
+	// multiaddr for the given peer.
+	//
+	// This is called by the network.Network implementation after it has
+	// resolved the peer's addrs, and prior to dialling each.
+	InterceptAddrDial(peer.ID, ma.Multiaddr) (allow bool)
+
+	// InterceptAccept tests whether an incipient inbound connection is allowed.
+	//
+	// This is called by the upgrader, or by the transport directly (e.g. QUIC,
+	// Bluetooth), straight after it has accepted a connection from its socket.
+	InterceptAccept(network.ConnMultiaddrs) (allow bool)
+
+	// InterceptSecured tests whether a given connection, now authenticated,
+	// is allowed.
+	//
+	// This is called by the upgrader, after it has performed the security
+	// handshake, and before it negotiates the muxer, or by the directly by the
+	// transport, at the exact same checkpoint.
+	InterceptSecured(network.Direction, peer.ID, network.ConnMultiaddrs) (allow bool)
+
+	// InterceptUpgraded tests whether a fully capable connection is allowed.
+	//
+	// At this point, the connection a multiplexer has been selected.
+	// When rejecting a connection, the gater can return a DisconnectReason.
+	// Refer to the godoc on the ConnectionGater type for more information.
+	//
+	// NOTE: the go-libp2p implementation currently IGNORES the disconnect reason.
+	InterceptUpgraded(network.Conn) (allow bool, reason control.DisconnectReason)
+}

control/disconnect.go

+package control
+
+// DisconnectReason communicates the reason why a connection is being closed.
+//
+// A zero value stands for "no reason" / NA.
+//
+// This is an EXPERIMENTAL type. It will change in the future. Refer to the
+// connmgr.ConnectionGater godoc for more info.
+type DisconnectReason int