use fuzzing helper functions to generate transport parameter seed corpus

fuzzing/internal/helper/helper.go

@@ -0,0 +1,37 @@
+package helper
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// NthBit gets the n-th bit of a byte (counting starts at 0).
+func NthBit(val uint8, n int) bool {
+	if n < 0 || n > 7 {
+		panic("invalid value for n")
+	}
+	return val>>n&0x1 == 1
+}
+
+// WriteCorpusFile writes data to a corpus file in directory path.
+// The filename is calculated from the SHA1 sum of the file contents.
+func WriteCorpusFile(path string, data []byte) error {
+	// create the directory, if it doesn't exist yet
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		if err := os.MkdirAll(path, os.ModePerm); err != nil {
+			return err
+		}
+	}
+	hash := sha1.Sum(data)
+	return ioutil.WriteFile(filepath.Join(path, hex.EncodeToString(hash[:])), data, 0644)
+}
+
+// WriteCorpusFileWithPrefix writes data to a corpus file in directory path.
+// In many fuzzers, the first n bytes are used to control.
+// This function prepends n zero-bytes to the data.
+func WriteCorpusFileWithPrefix(path string, data []byte, n int) error {
+	return WriteCorpusFile(path, append(make([]byte, n), data...))
+}