pool: implement optional penalty box mechanic.

pool.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"math"
 	"slices"
 	"strings"
 	"sync"
@@ -26,7 +27,9 @@ type SimplePool struct {
 	eventMiddleware []func(IncomingEvent)
 
 	// custom things not often used
-	SignatureChecker func(Event) bool
+	signatureChecker func(Event) bool
+	penaltyBoxMu     sync.Mutex
+	penaltyBox       map[string][2]float64
 }
 
 type DirectedFilters struct {
@@ -73,6 +76,42 @@ func (h WithAuthHandler) ApplyPoolOption(pool *SimplePool) {
 	pool.authHandler = h
 }
 
+// WithPenaltyBox just sets the penalty box mechanism so relays that fail to connect
+// or that disconnect will be ignored for a while and we won't attempt to connect again.
+func WithPenaltyBox() withPenaltyBoxOpt { return withPenaltyBoxOpt{} }
+
+type withPenaltyBoxOpt struct{}
+
+func (h withPenaltyBoxOpt) ApplyPoolOption(pool *SimplePool) {
+	pool.penaltyBox = make(map[string][2]float64)
+	go func() {
+		sleep := 30.0
+		for {
+			time.Sleep(time.Duration(sleep) * time.Second)
+
+			pool.penaltyBoxMu.Lock()
+			nextSleep := 300.0
+			for url, v := range pool.penaltyBox {
+				remainingSeconds := v[1]
+				remainingSeconds -= sleep
+				if remainingSeconds <= 0 {
+					pool.penaltyBox[url] = [2]float64{v[0], 0}
+					continue
+				} else {
+					pool.penaltyBox[url] = [2]float64{v[0], remainingSeconds}
+				}
+
+				if remainingSeconds < nextSleep {
+					nextSleep = remainingSeconds
+				}
+			}
+
+			sleep = nextSleep
+			pool.penaltyBoxMu.Unlock()
+		}
+	}()
+}
+
 // WithEventMiddleware is a function that will be called with all events received.
 // more than one can be passed at a time.
 type WithEventMiddleware func(IncomingEvent)
@@ -84,6 +123,7 @@ func (h WithEventMiddleware) ApplyPoolOption(pool *SimplePool) {
 var (
 	_ PoolOption = (WithAuthHandler)(nil)
 	_ PoolOption = (WithEventMiddleware)(nil)
+	_ PoolOption = WithPenaltyBox()
 )
 
 func (pool *SimplePool) EnsureRelay(url string) (*Relay, error) {
@@ -91,27 +131,44 @@ func (pool *SimplePool) EnsureRelay(url string) (*Relay, error) {
 	defer namedLock(nm)()
 
 	relay, ok := pool.Relays.Load(nm)
-	if ok && relay.IsConnected() {
+	if ok && relay == nil {
+		if pool.penaltyBox != nil {
+			pool.penaltyBoxMu.Lock()
+			defer pool.penaltyBoxMu.Unlock()
+			v, _ := pool.penaltyBox[nm]
+			if v[1] > 0 {
+				return nil, fmt.Errorf("in penalty box, %fs remaining", v[1])
+			}
+		}
+	} else if ok && relay.IsConnected() {
 		// already connected, unlock and return
 		return relay, nil
-	} else {
-		var err error
-		// we use this ctx here so when the pool dies everything dies
-		ctx, cancel := context.WithTimeout(pool.Context, time.Second*15)
-		defer cancel()
-
-		opts := make([]RelayOption, 0, 1+len(pool.eventMiddleware))
-		if pool.SignatureChecker != nil {
-			opts = append(opts, WithSignatureChecker(pool.SignatureChecker))
-		}
-
-		if relay, err = RelayConnect(ctx, nm, opts...); err != nil {
-			return nil, fmt.Errorf("failed to connect: %w", err)
-		}
-
-		pool.Relays.Store(nm, relay)
-		return relay, nil
 	}
+
+	// try to connect
+	var err error
+	// we use this ctx here so when the pool dies everything dies
+	ctx, cancel := context.WithTimeout(pool.Context, time.Second*15)
+	defer cancel()
+
+	opts := make([]RelayOption, 0, 1+len(pool.eventMiddleware))
+	if pool.signatureChecker != nil {
+		opts = append(opts, WithSignatureChecker(pool.signatureChecker))
+	}
+
+	if relay, err = RelayConnect(ctx, nm, opts...); err != nil {
+		if pool.penaltyBox != nil {
+			// putting relay in penalty box
+			pool.penaltyBoxMu.Lock()
+			defer pool.penaltyBoxMu.Unlock()
+			v, _ := pool.penaltyBox[nm]
+			pool.penaltyBox[nm] = [2]float64{v[0] + 1, 30.0 + math.Pow(2, v[0]+1)}
+		}
+		return nil, fmt.Errorf("failed to connect: %w", err)
+	}
+
+	pool.Relays.Store(nm, relay)
+	return relay, nil
 }
 
 // SubMany opens a subscription with the given filters to multiple relays