Move top level packages to internal.

internal/luhn/luhn.go

@@ -0,0 +1,72 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+// All rights reserved. Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+// Package luhn generates and validates Luhn mod N check digits.
+package luhn
+
+import (
+	"fmt"
+	"strings"
+)
+
+// An alphabet is a string of N characters, representing the digits of a given
+// base N.
+type Alphabet string
+
+var (
+	Base32 Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
+)
+
+// Generate returns a check digit for the string s, which should be composed
+// of characters from the Alphabet a.
+func (a Alphabet) Generate(s string) (rune, error) {
+	if err := a.check(); err != nil {
+		return 0, err
+	}
+
+	factor := 1
+	sum := 0
+	n := len(a)
+
+	for i := range s {
+		codepoint := strings.IndexByte(string(a), s[i])
+		if codepoint == -1 {
+			return 0, fmt.Errorf("Digit %q not valid in alphabet %q", s[i], a)
+		}
+		addend := factor * codepoint
+		if factor == 2 {
+			factor = 1
+		} else {
+			factor = 2
+		}
+		addend = (addend / n) + (addend % n)
+		sum += addend
+	}
+	remainder := sum % n
+	checkCodepoint := (n - remainder) % n
+	return rune(a[checkCodepoint]), nil
+}
+
+// Validate returns true if the last character of the string s is correct, for
+// a string s composed of characters in the alphabet a.
+func (a Alphabet) Validate(s string) bool {
+	t := s[:len(s)-1]
+	c, err := a.Generate(t)
+	if err != nil {
+		return false
+	}
+	return rune(s[len(s)-1]) == c
+}
+
+// check returns an error if the given alphabet does not consist of unique characters
+func (a Alphabet) check() error {
+	cm := make(map[byte]bool, len(a))
+	for i := range a {
+		if cm[a[i]] {
+			return fmt.Errorf("Digit %q non-unique in alphabet %q", a[i], a)
+		}
+		cm[a[i]] = true
+	}
+	return nil
+}

internal/luhn/luhn_test.go

@@ -0,0 +1,61 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+// All rights reserved. Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package luhn_test
+
+import (
+	"testing"
+
+	"github.com/syncthing/syncthing/internal/luhn"
+)
+
+func TestGenerate(t *testing.T) {
+	// Base 6 Luhn
+	a := luhn.Alphabet("abcdef")
+	c, err := a.Generate("abcdef")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c != 'e' {
+		t.Errorf("Incorrect check digit %c != e", c)
+	}
+
+	// Base 10 Luhn
+	a = luhn.Alphabet("0123456789")
+	c, err = a.Generate("7992739871")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c != '3' {
+		t.Errorf("Incorrect check digit %c != 3", c)
+	}
+}
+
+func TestInvalidString(t *testing.T) {
+	a := luhn.Alphabet("ABC")
+	_, err := a.Generate("7992739871")
+	t.Log(err)
+	if err == nil {
+		t.Error("Unexpected nil error")
+	}
+}
+
+func TestBadAlphabet(t *testing.T) {
+	a := luhn.Alphabet("01234566789")
+	_, err := a.Generate("7992739871")
+	t.Log(err)
+	if err == nil {
+		t.Error("Unexpected nil error")
+	}
+}
+
+func TestValidate(t *testing.T) {
+	a := luhn.Alphabet("abcdef")
+	if !a.Validate("abcdefe") {
+		t.Errorf("Incorrect validation response for abcdefe")
+	}
+	if a.Validate("abcdefd") {
+		t.Errorf("Incorrect validation response for abcdefd")
+	}
+}