Update

vendor/tailscale.com/appc/conn25.go

@@ -0,0 +1,110 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package appc
+
+import (
+	"net/netip"
+	"sync"
+
+	"tailscale.com/tailcfg"
+)
+
+// Conn25 holds the developing state for the as yet nascent next generation app connector.
+// There is currently (2025-12-08) no actual app connecting functionality.
+type Conn25 struct {
+	mu         sync.Mutex
+	transitIPs map[tailcfg.NodeID]map[netip.Addr]netip.Addr
+}
+
+const dupeTransitIPMessage = "Duplicate transit address in ConnectorTransitIPRequest"
+
+// HandleConnectorTransitIPRequest creates a ConnectorTransitIPResponse in response to a ConnectorTransitIPRequest.
+// It updates the connectors mapping of TransitIP->DestinationIP per peer (tailcfg.NodeID).
+// If a peer has stored this mapping in the connector Conn25 will route traffic to TransitIPs to DestinationIPs for that peer.
+func (c *Conn25) HandleConnectorTransitIPRequest(nid tailcfg.NodeID, ctipr ConnectorTransitIPRequest) ConnectorTransitIPResponse {
+	resp := ConnectorTransitIPResponse{}
+	seen := map[netip.Addr]bool{}
+	for _, each := range ctipr.TransitIPs {
+		if seen[each.TransitIP] {
+			resp.TransitIPs = append(resp.TransitIPs, TransitIPResponse{
+				Code:    OtherFailure,
+				Message: dupeTransitIPMessage,
+			})
+			continue
+		}
+		tipresp := c.handleTransitIPRequest(nid, each)
+		seen[each.TransitIP] = true
+		resp.TransitIPs = append(resp.TransitIPs, tipresp)
+	}
+	return resp
+}
+
+func (c *Conn25) handleTransitIPRequest(nid tailcfg.NodeID, tipr TransitIPRequest) TransitIPResponse {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.transitIPs == nil {
+		c.transitIPs = make(map[tailcfg.NodeID]map[netip.Addr]netip.Addr)
+	}
+	peerMap, ok := c.transitIPs[nid]
+	if !ok {
+		peerMap = make(map[netip.Addr]netip.Addr)
+		c.transitIPs[nid] = peerMap
+	}
+	peerMap[tipr.TransitIP] = tipr.DestinationIP
+	return TransitIPResponse{}
+}
+
+func (c *Conn25) transitIPTarget(nid tailcfg.NodeID, tip netip.Addr) netip.Addr {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.transitIPs[nid][tip]
+}
+
+// TransitIPRequest details a single TransitIP allocation request from a client to a
+// connector.
+type TransitIPRequest struct {
+	// TransitIP is the intermediate destination IP that will be received at this
+	// connector and will be replaced by DestinationIP when performing DNAT.
+	TransitIP netip.Addr `json:"transitIP,omitzero"`
+
+	// DestinationIP is the final destination IP that connections to the TransitIP
+	// should be mapped to when performing DNAT.
+	DestinationIP netip.Addr `json:"destinationIP,omitzero"`
+}
+
+// ConnectorTransitIPRequest is the request body for a PeerAPI request to
+// /connector/transit-ip and can include zero or more TransitIP allocation requests.
+type ConnectorTransitIPRequest struct {
+	// TransitIPs is the list of requested mappings.
+	TransitIPs []TransitIPRequest `json:"transitIPs,omitempty"`
+}
+
+// TransitIPResponseCode appears in TransitIPResponse and signifies success or failure status.
+type TransitIPResponseCode int
+
+const (
+	// OK indicates that the mapping was created as requested.
+	OK TransitIPResponseCode = 0
+
+	// OtherFailure indicates that the mapping failed for a reason that does not have
+	// another relevant [TransitIPResponsecode].
+	OtherFailure TransitIPResponseCode = 1
+)
+
+// TransitIPResponse is the response to a TransitIPRequest
+type TransitIPResponse struct {
+	// Code is an error code indicating success or failure of the [TransitIPRequest].
+	Code TransitIPResponseCode `json:"code,omitzero"`
+	// Message is an error message explaining what happened, suitable for logging but
+	// not necessarily suitable for displaying in a UI to non-technical users. It
+	// should be empty when [Code] is [OK].
+	Message string `json:"message,omitzero"`
+}
+
+// ConnectorTransitIPResponse is the response to a ConnectorTransitIPRequest
+type ConnectorTransitIPResponse struct {
+	// TransitIPs is the list of outcomes for each requested mapping. Elements
+	// correspond to the order of [ConnectorTransitIPRequest.TransitIPs].
+	TransitIPs []TransitIPResponse `json:"transitIPs,omitempty"`
+}