implement a function to export a corpus file

The file name of that file is calculated to be the SHA1 sum of the contents.

fuzzing/internal/helper/export.go

@@ -0,0 +1,29 @@
+package helper
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// 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...))
+}

fuzzing/internal/helper/export_test.go

@@ -0,0 +1,60 @@
+package helper
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("exporting", func() {
+	var dir string
+
+	BeforeEach(func() {
+		var err error
+		dir, err = ioutil.TempDir("", "fuzzing-helper")
+		Expect(err).ToNot(HaveOccurred())
+		fmt.Fprintf(GinkgoWriter, "Created temporary directory %s", dir)
+	})
+
+	AfterEach(func() {
+		Expect(dir).ToNot(BeEmpty())
+		Expect(os.RemoveAll(dir)).To(Succeed())
+	})
+
+	It("writes a file", func() {
+		const data = "lorem ipsum"
+		// calculated by running sha1sum on the generated file
+		const expectedShaSum = "bfb7759a67daeb65410490b4d98bb9da7d1ea2ce"
+		Expect(WriteCorpusFile(dir, []byte("lorem ipsum"))).To(Succeed())
+		path := filepath.Join(dir, expectedShaSum)
+		Expect(path).To(BeARegularFile())
+		b, err := ioutil.ReadFile(path)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(string(b)).To(Equal(data))
+	})
+
+	It("writes a file and prepends data", func() {
+		const data = "lorem ipsum"
+		// calculated by running sha1sum on the generated file
+		const expectedShaSum = "523f5cab80fab0c7889dbf50dd310ab8c8879f9c"
+		const prefixLen = 7
+		Expect(WriteCorpusFileWithPrefix(dir, []byte("lorem ipsum"), prefixLen)).To(Succeed())
+		path := filepath.Join(dir, expectedShaSum)
+		Expect(path).To(BeARegularFile())
+		b, err := ioutil.ReadFile(path)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(b[:prefixLen]).To(Equal(make([]byte, prefixLen)))
+		Expect(string(b[prefixLen:])).To(Equal(data))
+	})
+
+	It("creates the directory, if it doesn't yet", func() {
+		subdir := filepath.Join(dir, "corpus")
+		Expect(subdir).ToNot(BeADirectory())
+		Expect(WriteCorpusFile(subdir, []byte("lorem ipsum"))).To(Succeed())
+		Expect(subdir).To(BeADirectory())
+	})
+})

fuzzing/internal/helper/helper_suite_test.go

@@ -0,0 +1,13 @@
+package helper
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+func TestHelper(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Helper Suite")
+}