Add new admin panel, failover, dns fallback, providers, limiters. Update XHTTP

dns/transport/fallback/strategy.go

@@ -0,0 +1,73 @@
+package fallback
+
+import (
+	"context"
+
+	mDNS "github.com/miekg/dns"
+	"github.com/sagernet/sing-box/adapter"
+	E "github.com/sagernet/sing/common/exceptions"
+	"github.com/sagernet/sing/common/logger"
+)
+
+type ExchangeStrategy = func(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error)
+
+func parallelStrategy(servers []adapter.DNSTransport, logger logger.ContextLogger) ExchangeStrategy {
+	return func(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
+		queryCtx, cancel := context.WithCancel(ctx)
+		defer cancel()
+		type result struct {
+			response *mDNS.Msg
+			err      error
+		}
+		results := make(chan result)
+		for _, server := range servers {
+			go func() {
+				response, err := server.Exchange(queryCtx, message)
+				select {
+				case results <- result{response, err}:
+				case <-queryCtx.Done():
+				}
+			}()
+		}
+		var lastErr error
+		for range servers {
+			select {
+			case result := <-results:
+				if result.err != nil {
+					lastErr = result.err
+					continue
+				}
+				return result.response, nil
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			}
+		}
+		return nil, lastErr
+	}
+}
+
+func sequentialStrategy(servers []adapter.DNSTransport, logger logger.ContextLogger) ExchangeStrategy {
+	return func(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
+		var lastErr error
+		for _, server := range servers {
+			response, err := server.Exchange(ctx, message)
+			if err != nil {
+				lastErr = err
+				continue
+			}
+			return response, nil
+		}
+		return nil, lastErr
+	}
+}
+
+func CreateStrategy(strategy string, servers []adapter.DNSTransport, logger logger.ContextLogger) (ExchangeStrategy, error) {
+	switch strategy {
+	case "parallel":
+		return parallelStrategy(servers, logger), nil
+	case "", "sequential":
+		return sequentialStrategy(servers, logger), nil
+	default:
+		return nil, E.New("strategy not found: ", strategy)
+	}
+}