Create tokengen.go

cbonello · cbonello · commit b183c051c99d · 2013-09-08T22:19:28.000+05:30
diff --git a/tokengen.go b/tokengen.go
@@ -0,0 +1,43 @@
+package csrf
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+)
+
+const (
+	rawTokenLength = 32
+)
+
+var (
+	tokenLength = base64.StdEncoding.EncodedLen(rawTokenLength)
+)
+
+// A token is generated by reading rawTokenLength bytes
+// from crypto/rand and encoding that as base64.
+func generateToken() string {
+	bytes := make([]byte, rawTokenLength)
+	_, _ = io.ReadFull(rand.Reader, bytes)
+
+	// I'm not sure how to handle the error from the above call.
+	// It shouldn't EVER really happen,
+	// as we check for the availablity of crypto/random
+	// in the init() function
+	// and both /dev/urandom and CryptGenRandom()
+	// should be inexhaustible.
+
+	return base64.StdEncoding.EncodeToString(bytes)
+}
+
+func init() {
+	// Check that cryptographically secure PRNG is available
+	// In case it's not, panic.
+	buf := make([]byte, 1)
+	_, err := io.ReadFull(rand.Reader, buf)
+
+	if err != nil {
+		panic(fmt.Sprintf("crypto/rand is unavailable: Read() failed with %#v", err))
+	}
+}
