Propose a backoff system for managing interdependent timers.

backoff/backoff.go

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+// Package backoff provides facilities for working with interdependent backoff timers.
+//
+// This package is motivated by https://github.com/libp2p/go-libp2p-swarm/issues/37.
+//
+// We would like to associate backoff logic to each component of a multiaddr.
+// For instance, consider a typical multiaddr of the form IP/transport/protocol.
+// The backoff associated with IP dictates whether any multiaddr
+// using that IP can be dialed (regardless of transport and protocol).
+// The backoff associated with IP and transport dictates whether
+// any multiaddr using that IP and transport can be dialed (regardless of protocol).
+// And so on.
+//
+// Furthermore, we stipulate that software components that utilize backoffs on multiaddrs
+// should share the backoff timers in order to benefit from each other's learnings.
+//
+// To this end, this package provides the definition of a backoff timer (as the interface BackoffTimer),
+// as well as an interface for a shared set of backoff timers, called SharedBackoffs.
+package backoff
+
+import (
+	"time"
+
+	ma "github.com/multiformats/go-multiaddr"
+)
+
+// SharedBackoffs maintains backoff timers that are shared by multiple IPFS components.
+// Some of the timers are correlated. If this is the case, the relationships are documented in the access methods below.
+type SharedBackoffs interface {
+
+	// Timers for dialing multiaddresses.
+
+	// IP returns the timer associated with a given IP address.
+	// If the argument multiaddr does not start with an IP component, a panic is thrown.
+	// The IP timer should be backed off, if it is determined that the IP itself is unreachable
+	// (e.g. in response to a "no route to IP" error).
+	// The IP timer should be cleared whenever any successful connection to this IP is established.
+	IP(ma.Multiaddr) BackoffTimer
+
+	// Transport returns the timer associated with a given IP address and a transport (TCP, UDP, etc.).
+	// If the argument multiaddr does not start with an IP and transport components, a panic is thrown.
+	// The IP/Transport timer should be backed off, if it is determined that the IP is reachable but the transport is not.
+	// The IP/Transport timer should be cleared whenever any successful connection to this IP/transport pair is established.
+	// The IP/Transport timer will report a clear state whenever the IP and  IP/Transport timers are both clear.
+	Transport(ma.Multiaddr) BackoffTimer
+
+	// Swarm returns the timer associated with a given IP address, a transport (TCP, UDP, etc.) and the swarm service.
+	// If the argument multiaddr does not start with an IP and transport components, a panic is thrown.
+	// The IP/Transport/Swarm timer should be backed off, if it is determined that the IP is reachable
+	// using the given transport, but the swarm service is not supported.
+	// The IP/Transport/Swarm timer should be cleared whenever any successful connection to the IP/transport pair is established
+	// and the swarm service is available.
+	// The IP/Transport/Swarm timer will report a clear state whenever the respective IP, IP/Transport and IP/Transport/Swarm
+	// timers are all clear.
+	Swarm(ma.Multiaddr) BackoffTimer
+
+	// Protocol returns the timer associated with a given IP address, transport (TCP, UDP, etc.) and
+	// protocol, supported through the swarm service.
+	// If the argument multiaddr does not start with an IP, transport and protocol components, a panic is thrown.
+	// The IP/Transport/Swarm/Protocol timer should be backed off, if it is determined that the IP is reachable
+	// using the given transport, the swarm service is supported, but the protocol is not.
+	// The IP/Transport/Swarm/Protocol timer should be cleared whenever any successful connection to the protocol
+	// is established through the swarm service on the given IP/transport.
+	// The IP/Transport/Swarm/Protocol timer will report a clear state whenever the respective
+	// IP, IP/Transport and IP/Transport/Swarm, and IP/Transport/Swarm/Protocol timers are all clear.
+	Protocol(ma.Multiaddr) BackoffTimer
+
+	// Other shared backoff timers should be added here.
+}
+
+// BackoffTimer is a user-facing interface to a backoff timer.
+type BackoffTimer interface {
+	// Wait blocks until the timer and all of its ancestors (parent, grandparent, etc.), if any, have been cleared.
+	Wait()
+	// TimeToClear returns the duration remaining until the back off state is cleared.
+	// Zero or negative durations indicate that the state is already cleared.
+	TimeToClear() time.Duration
+	// Clear clears this timer and returns instantaneously.
+	// For example, a user might call this function after a successul connection attempt.
+	Clear()
+	// Backoff places the timer in backing off state and returns instantaneously.
+	// For example, a user might call this function after an unsuccessful connection attempt.
+	Backoff()
+}