Support fuzzing unexported fields

fuzz.go

@@ -23,6 +23,7 @@ import (
 	"regexp"
 	"sync"
 	"time"
+	"unsafe"
 
 	"github.com/google/gofuzz/bytesource"
 	"strings"
@@ -33,14 +34,15 @@ type fuzzFuncMap map[reflect.Type]reflect.Value
 
 // Fuzzer knows how to fill any object with random fields.
 type Fuzzer struct {
-	fuzzFuncs         fuzzFuncMap
-	defaultFuzzFuncs  fuzzFuncMap
-	r                 *rand.Rand
-	nilChance         float64
-	minElements       int
-	maxElements       int
-	maxDepth          int
-	skipFieldPatterns []*regexp.Regexp
+	fuzzFuncs             fuzzFuncMap
+	defaultFuzzFuncs      fuzzFuncMap
+	r                     *rand.Rand
+	nilChance             float64
+	minElements           int
+	maxElements           int
+	maxDepth              int
+	allowUnexportedFields bool
+	skipFieldPatterns     []*regexp.Regexp
 
 	fuzzLock sync.Mutex
 }
@@ -57,12 +59,13 @@ func NewWithSeed(seed int64) *Fuzzer {
 			reflect.TypeOf(&time.Time{}): reflect.ValueOf(fuzzTime),
 		},
 
-		fuzzFuncs:   fuzzFuncMap{},
-		r:           rand.New(rand.NewSource(seed)),
-		nilChance:   .2,
-		minElements: 1,
-		maxElements: 10,
-		maxDepth:    100,
+		fuzzFuncs:             fuzzFuncMap{},
+		r:                     rand.New(rand.NewSource(seed)),
+		nilChance:             .2,
+		minElements:           1,
+		maxElements:           10,
+		maxDepth:              100,
+		allowUnexportedFields: false,
 	}
 	return f
 }
@@ -186,7 +189,14 @@ func (f *Fuzzer) MaxDepth(d int) *Fuzzer {
 	return f
 }
 
-// Skip fields which match the supplied pattern. Call this multiple times if needed
+// AllowUnexportedFields decides whether to do fuzz on the unexported fields,
+// i.e. the fields that start with lower case letter.
+func (f *Fuzzer) AllowUnexportedFields(flag bool) *Fuzzer {
+	f.allowUnexportedFields = flag
+	return f
+}
+
+// SkipFieldsWithPattern Skip fields which match the supplied pattern. Call this multiple times if needed
 // This is useful to skip XXX_ fields generated by protobuf
 func (f *Fuzzer) SkipFieldsWithPattern(pattern *regexp.Regexp) *Fuzzer {
 	f.skipFieldPatterns = append(f.skipFieldPatterns, pattern)
@@ -263,7 +273,10 @@ func (fc *fuzzerContext) doFuzz(v reflect.Value, flags uint64) {
 	defer func() { fc.curDepth-- }()
 
 	if !v.CanSet() {
-		return
+		if !fc.fuzzer.allowUnexportedFields || !v.CanAddr() {
+			return
+		}
+		v = reflect.NewAt(v.Type(), unsafe.Pointer(v.UnsafeAddr())).Elem()
 	}
 
 	if flags&flagNoCustomFuzz == 0 {

fuzz_test.go

@@ -483,6 +483,34 @@ func TestFuzz_Maxdepth(t *testing.T) {
 	}
 }
 
+func TestFuzzer_AllowUnexportedFields(t *testing.T) {
+	type S struct {
+		stringField string
+	}
+
+	f := New().NilChance(0)
+
+	obj := S{}
+	f.Fuzz(&obj)
+	if obj.stringField != "" {
+		t.Errorf("Expected obj.stringField to be empty")
+	}
+
+	f.AllowUnexportedFields(true)
+	obj = S{}
+	f.Fuzz(&obj)
+	if obj.stringField == "" {
+		t.Errorf("Expected stringFiled not empty")
+	}
+
+	f.AllowUnexportedFields(false)
+	obj = S{}
+	f.Fuzz(&obj)
+	if obj.stringField != "" {
+		t.Errorf("Expected obj.stringField to be empty")
+	}
+}
+
 func TestFuzz_SkipPattern(t *testing.T) {
 	obj := &struct {
 		S1    string