wireguard-go/conn/multipath_bind.go

/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2017-2025 WireGuard LLC. All Rights Reserved.
 */

package conn

import (
	"fmt"
	"net"
	"sync"
)

// MultiPathBind implements Bind interface but sends packets through multiple network paths
type MultiPathBind struct {
	mu    sync.RWMutex
	binds []Bind
	// Store the primary bind for receive operations (only one bind receives)
	primaryBind Bind
}

// NewMultiPathBind creates a new multi-path bind with multiple underlying binds
func NewMultiPathBind(binds []Bind) *MultiPathBind {
	if len(binds) == 0 {
		panic("MultiPathBind requires at least one bind")
	}
	
	return &MultiPathBind{
		binds:       binds,
		primaryBind: binds[0], // Use first bind as primary for receiving
	}
}

// Open puts all binds into listening state
func (mpb *MultiPathBind) Open(port uint16) (fns []ReceiveFunc, actualPort uint16, err error) {
	mpb.mu.Lock()
	defer mpb.mu.Unlock()

	// Open primary bind first to get the actual port and receive functions
	fns, actualPort, err = mpb.primaryBind.Open(port)
	if err != nil {
		return nil, 0, fmt.Errorf("failed to open primary bind: %w", err)
	}

	// Open additional binds on the same port
	for i, bind := range mpb.binds[1:] {
		_, bindPort, bindErr := bind.Open(actualPort)
		if bindErr != nil {
			// If any bind fails, close already opened binds
			mpb.primaryBind.Close()
			for j := 0; j < i; j++ {
				mpb.binds[j+1].Close()
			}
			return nil, 0, fmt.Errorf("failed to open bind %d: %w", i+1, bindErr)
		}
		// Verify all binds use the same port
		if bindPort != actualPort {
			mpb.primaryBind.Close()
			for j := 0; j <= i; j++ {
				mpb.binds[j+1].Close()
			}
			return nil, 0, fmt.Errorf("bind %d opened on different port %d vs %d", i+1, bindPort, actualPort)
		}
	}

	return fns, actualPort, nil
}

// Close closes all underlying binds
func (mpb *MultiPathBind) Close() error {
	mpb.mu.Lock()
	defer mpb.mu.Unlock()

	var firstErr error
	for i, bind := range mpb.binds {
		if err := bind.Close(); err != nil && firstErr == nil {
			firstErr = fmt.Errorf("failed to close bind %d: %w", i, err)
		}
	}
	return firstErr
}

// SetMark sets the mark for all underlying binds
func (mpb *MultiPathBind) SetMark(mark uint32) error {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()

	for i, bind := range mpb.binds {
		if err := bind.SetMark(mark); err != nil {
			return fmt.Errorf("failed to set mark on bind %d: %w", i, err)
		}
	}
	return nil
}

// Send sends the same packets through ALL configured network paths
func (mpb *MultiPathBind) Send(bufs [][]byte, ep Endpoint) error {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()

	var firstErr error
	successCount := 0

	// Send through all binds
	for i, bind := range mpb.binds {
		if err := bind.Send(bufs, ep); err != nil {
			if firstErr == nil {
				firstErr = fmt.Errorf("bind %d failed: %w", i, err)
			}
		} else {
			successCount++
		}
	}

	// Consider it successful if at least one path succeeded
	if successCount > 0 {
		return nil
	}
	
	return firstErr
}

// ParseEndpoint uses the primary bind to parse endpoints
func (mpb *MultiPathBind) ParseEndpoint(s string) (Endpoint, error) {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()
	return mpb.primaryBind.ParseEndpoint(s)
}

// BatchSize returns the minimum batch size among all binds
func (mpb *MultiPathBind) BatchSize() int {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()

	if len(mpb.binds) == 0 {
		return 1
	}

	minBatchSize := mpb.binds[0].BatchSize()
	for _, bind := range mpb.binds[1:] {
		if size := bind.BatchSize(); size < minBatchSize {
			minBatchSize = size
		}
	}
	return minBatchSize
}

// BindToInterface binds specific binds to specific interfaces
// This is a helper method for configuring each bind to use different interfaces
func (mpb *MultiPathBind) BindToInterface(bindIndex int, interfaceIndex uint32, blackhole bool) error {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()

	if bindIndex >= len(mpb.binds) {
		return fmt.Errorf("bind index %d out of range (have %d binds)", bindIndex, len(mpb.binds))
	}

	bind := mpb.binds[bindIndex]
	if binder, ok := bind.(BindSocketToInterface); ok {
		// Try IPv4 first
		if err := binder.BindSocketToInterface4(interfaceIndex, blackhole); err != nil {
			// If IPv4 fails, try IPv6
			if err := binder.BindSocketToInterface6(interfaceIndex, blackhole); err != nil {
				return fmt.Errorf("failed to bind to interface %d: %w", interfaceIndex, err)
			}
		}
		return nil
	}
	
	return fmt.Errorf("bind %d does not support interface binding", bindIndex)
}

// GetBindCount returns the number of configured network paths
func (mpb *MultiPathBind) GetBindCount() int {
	mpb.mu.RLock()
	defer mpb.mu.RUnlock()
	return len(mpb.binds)
}