fuzzing: allow setup function to be called (#3175)

This allows to fuzzing of more interesting targets that require setup.
Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/cache/fuzz.go

@@ -8,5 +8,5 @@ import (
 
 // Fuzz fuzzes cache.
 func Fuzz(data []byte) int {
-	return fuzz.Do(New(), data)
+	return fuzz.Do(New(), nil, data)
 }

plugin/chaos/fuzz.go

@@ -9,5 +9,5 @@ import (
 // Fuzz fuzzes cache.
 func Fuzz(data []byte) int {
 	c := Chaos{}
-	return fuzz.Do(c, data)
+	return fuzz.Do(c, nil, data)
 }

plugin/file/fuzz.go

@@ -15,7 +15,7 @@ func Fuzz(data []byte) int {
 	zone, _ := Parse(strings.NewReader(fuzzMiekNL), name, "stdin", 0)
 	f := File{Next: test.ErrorHandler(), Zones: Zones{Z: map[string]*Zone{name: zone}, Names: []string{name}}}
 
-	return fuzz.Do(f, data)
+	return fuzz.Do(f, nil, data)
 }
 
 const fuzzMiekNL = `

plugin/pkg/fuzz/do.go

@@ -11,7 +11,12 @@ import (
 )
 
 // Do will fuzz p - used by gofuzz. See Makefile.fuzz for comments and context.
-func Do(p plugin.Handler, data []byte) int {
+func Do(p plugin.Handler, fn SetupFunc, data []byte) int {
+	if fn != nil {
+		if err := fn(); err != nil {
+			panic("fuzz: " + err.Error())
+		}
+	}
 	ctx := context.TODO()
 	r := new(dns.Msg)
 	if err := r.Unpack(data); err != nil {

plugin/pkg/fuzz/setup.go

+package fuzz
+
+// SetupFunc can be given to Do to perform a one time setup of the fuzzing
+// environment. This function is called on every fuzz, it is your
+// responsibility to make it idempotent. If SetupFunc returns an error, panic
+// is called with that error.
+//
+// There isn't a ShutdownFunc, because fuzzing is supposed to be run for a long
+// time and there isn't any hook to call it from.
+type SetupFunc func() error

plugin/rewrite/fuzz.go

@@ -17,5 +17,5 @@ func Fuzz(data []byte) int {
 	}
 	r := Rewrite{Rules: rules}
 
-	return fuzz.Do(r, data)
+	return fuzz.Do(r, nil, data)
 }

plugin/whoami/fuzz.go

@@ -9,5 +9,5 @@ import (
 // Fuzz fuzzes cache.
 func Fuzz(data []byte) int {
 	w := Whoami{}
-	return fuzz.Do(w, data)
+	return fuzz.Do(w, nil, data)
 }