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appc,feature/conn25,net: Add DNS response interception for conn25

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The new version of app connector (conn25) needs to read DNS responses
for domains it is interested in and store and swap out IP addresses.

Add a hook to dns manager to enable this.
Give the conn25 updated netmaps so that it knows when to assign
connecting addresses and from what pool.
Assign an address when we see a DNS response for a domain we are
interested in, but don't do anything with the address yet.

Updates tailscale/corp#34252

Signed-off-by: Fran Bull <fran@tailscale.com>
This commit is contained in:
Fran Bull
2026-01-28 14:07:08 -08:00
committed by franbull
parent cae54e2046
commit 3b737edbf1
11 changed files with 1000 additions and 292 deletions
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appc/conn25.go
-101
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@@ -5,9 +5,7 @@ package appc
import (
"cmp"
"net/netip"
"slices"
"sync"
"tailscale.com/tailcfg"
"tailscale.com/types/appctype"
@@ -15,105 +13,6 @@ import (
"tailscale.com/util/set"
)
// 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"`
}
const AppConnectorsExperimentalAttrName = "tailscale.com/app-connectors-experimental"
// PickSplitDNSPeers looks at the netmap peers capabilities and finds which peers