Add load balancing network dialer

mtglib/network/load_balanced.go

@@ -0,0 +1,55 @@
+package network
+
+import (
+	"context"
+	"math/rand"
+	"net"
+	"net/url"
+)
+
+type loadBalancedDialer struct {
+	dialers []Dialer
+}
+
+func (l loadBalancedDialer) Dial(network, address string) (net.Conn, error) {
+	return l.DialContext(context.Background(), network, address)
+}
+
+func (l loadBalancedDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	length := len(l.dialers)
+	start := rand.Intn(length)
+	moved := false
+
+	for i := start; i != start || !moved; i = (i + 1) % length {
+		moved = true
+		if conn, err := l.dialers[i].DialContext(ctx, network, address); err == nil {
+			return conn, nil
+		}
+	}
+
+	return nil, ErrCannotDialWithAllProxies
+}
+
+func NewLoadBalancedDialer(baseDialer Dialer, proxyURLs []*url.URL) (Dialer, error) {
+	switch len(proxyURLs) {
+	case 0:
+		return baseDialer, nil
+	case 1:
+		return NewSocks5Dialer(baseDialer, proxyURLs[0])
+	}
+
+	dialers := []Dialer{}
+
+	for _, u := range proxyURLs {
+		dialer, err := NewSocks5Dialer(newProxyDialer(baseDialer, u), u)
+		if err != nil {
+			return nil, err
+		}
+
+		dialers = append(dialers, dialer)
+	}
+
+	return loadBalancedDialer{
+		dialers: dialers,
+	}, nil
+}