save mapresponses

Signed-off-by: Kristoffer Dalby <[email protected]>

hscontrol/mapper/mapper.go

@@ -4,7 +4,10 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
+	"io/fs"
 	"net/url"
+	"os"
+	"path"
 	"sort"
 	"strings"
 	"sync"
@@ -18,6 +21,7 @@ import (
 	"github.com/klauspost/compress/zstd"
 	"github.com/rs/zerolog/log"
 	"github.com/samber/lo"
+	"tailscale.com/envknob"
 	"tailscale.com/smallzstd"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/dnstype"
@@ -29,6 +33,8 @@ const (
 	reservedResponseHeaderSize = 4
 )
 
+var debugDumpMapResponsePath = envknob.String("HEADSCALE_DEBUG_DUMP_MAPRESPONSE_PATH")
+
 type Mapper struct {
 	db *db.HSDatabase
 
@@ -413,6 +419,22 @@ func (m Mapper) marshalMapResponse(
 			Msg("Cannot marshal map response")
 	}
 
+	if debugDumpMapResponsePath != "" {
+		perms := fs.FileMode(0o755)
+		mPath := path.Join(debugDumpMapResponsePath, machine.Hostname)
+		err := os.MkdirAll(mPath, perms)
+		if err != nil {
+			panic(err)
+		}
+
+		now := time.Now().Unix()
+
+		err = os.WriteFile(path.Join(mPath, fmt.Sprintf("%d.json", now)), jsonBody, perms)
+		if err != nil {
+			panic(err)
+		}
+	}
+
 	var respBody []byte
 	if compression == util.ZstdCompression {
 		respBody = zstdEncode(jsonBody)