add overwrite option

Author: lanrat

README.md

@@ -22,7 +22,7 @@ An example Docker configuration for Unbound is provided in the `unbound/` direct
 
 ## Example
 
-```
+```console
 ./allxfr -dry-run
 ROOT g.root-servers.net. xfr size: 22017 records in 1.334s
 mr. ns-mr.nic.tn. (41.228.63.70) xfr size: 444 records in 337ms
@@ -51,7 +51,7 @@ sv. cir.red.sv. (168.243.254.1) xfr size: 1514 records in 883ms
 
 ## Usage
 
-```
+```console
 Usage of ./allxfr:
   -dry-run
         only test if xfr is allowed by retrieving one envelope
@@ -61,6 +61,8 @@ Usage of ./allxfr:
         nameserver to use for manually querying of records not in zone file
   -out string
         directory to save found zones in (default "zones")
+  -overwrite
+        if zone already exists on disk, overwrite it with newer data
   -parallel uint
         number of parallel zone transfers to perform (default 10)
   -psl
@@ -77,6 +79,6 @@ Usage of ./allxfr:
 
 ## Building
 
-```
+```console
 go build
 ```

axfr.go

@@ -146,6 +146,12 @@ func axfrToFile(zone string, ip net.IP, nameserver string) (int64, error) {
 	} else {
 		filename = fmt.Sprintf("%s/%s.zone.gz", *saveDir, zone[:len(zone)-1])
 	}
+	if !*overwrite {
+		if _, err := os.Stat(filename); err != nil && !os.IsNotExist(err) {
+			return 0, nil
+		}
+	}
+
 	filenameTmp := fmt.Sprintf("%s.tmp", filename)
 	var bufWriter *bufio.Writer
 

main.go

@@ -12,16 +12,17 @@ import (
 )
 
 var (
-	parallel = flag.Uint("parallel", 10, "number of parallel zone transfers to perform")
-	saveDir  = flag.String("out", "zones", "directory to save found zones in")
-	verbose  = flag.Bool("verbose", false, "enable verbose output")
-	zonefile = flag.String("zonefile", "", "use the provided zonefile instead of getting the root zonefile")
-	ns       = flag.String("ns", "", "nameserver to use for manually querying of records not in zone file")
-	saveAll  = flag.Bool("save-all", false, "attempt AXFR from every nameserver for a given zone and save all answers")
-	psl      = flag.Bool("psl", false, "attempt AXFR from zones listed in the public suffix list, requires -ns flag")
-	ixfr     = flag.Bool("ixfr", false, "attempt an IXFR instead of AXFR")
-	dryRun   = flag.Bool("dry-run", false, "only test if xfr is allowed by retrieving one envelope")
-	retry    = flag.Int("retry", 3, "number of times to retry failed operations")
+	parallel  = flag.Uint("parallel", 10, "number of parallel zone transfers to perform")
+	saveDir   = flag.String("out", "zones", "directory to save found zones in")
+	verbose   = flag.Bool("verbose", false, "enable verbose output")
+	zonefile  = flag.String("zonefile", "", "use the provided zonefile instead of getting the root zonefile")
+	ns        = flag.String("ns", "", "nameserver to use for manually querying of records not in zone file")
+	saveAll   = flag.Bool("save-all", false, "attempt AXFR from every nameserver for a given zone and save all answers")
+	psl       = flag.Bool("psl", false, "attempt AXFR from zones listed in the public suffix list, requires -ns flag")
+	ixfr      = flag.Bool("ixfr", false, "attempt an IXFR instead of AXFR")
+	dryRun    = flag.Bool("dry-run", false, "only test if xfr is allowed by retrieving one envelope")
+	retry     = flag.Int("retry", 3, "number of times to retry failed operations")
+	overwrite = flag.Bool("overwrite", false, "if zone already exists on disk, overwrite it with newer data")
 )
 
 var (