walkers: writing some bytes

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

walker/walkers/writeBytesFuzz/fuzz.go

@@ -1,17 +1,59 @@
 package writeBytesFuzz
 
 import (
+	"crypto/rand"
+	"fmt"
 	"os"
 
 	"git.thisco.de/vbatts/fuzz-walker/walker"
+	"github.com/hashicorp/errwrap"
 )
 
 func init() {
 	walker.RegisterFuzzFunc(Name, FuzzFunc)
+	// malloc early
+	for _, size := range sizes {
+		bufs[size] = make([]byte, size)
+	}
+}
+
+var bufs = map[int][]byte{}
+var sizes = []int{1, 9, 33, 65, 129, 257} // going with common int sizes + 1
+var randomized = false
+
+// this need only be run once
+func randomize(b map[int][]byte) error {
+	for size := range b {
+		_, err := rand.Read(b[size])
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 const Name = "writeBytesFuzz"
 
 func FuzzFunc(path string, info os.FileInfo) error {
+	if !info.Mode().IsRegular() {
+		return nil
+	}
+	if !randomized {
+		if err := randomize(bufs); err != nil {
+			return err
+		}
+	}
+	fd, err := os.OpenFile(path, os.O_WRONLY, os.ModePerm)
+	if err != nil {
+		return err
+	}
+	defer fd.Close()
+
+	for size, buf := range bufs {
+		_, err := fd.Write(buf)
+		if err != nil {
+			return errwrap.Wrapf(fmt.Sprintf("failed writing %d random bytes to %q: {{err}}", size, path), err)
+		}
+	}
 	return nil
 }

walker/walkers/writeNumFuzz/fuzz.go

@@ -13,5 +13,8 @@ func init() {
 const Name = "writeNumFuzz"
 
 func FuzzFunc(path string, info os.FileInfo) error {
+	if !info.Mode().IsRegular() {
+		return nil
+	}
 	return nil
 }