Fix yet another bug in VarintSize, add test

varint.go

@@ -11,7 +11,7 @@ func VarintSize(num int) int {
 	bits := bits.Len(uint(num))
 	q, r := bits/7, bits%7
 	size := q
-	if r > 0 {
+	if r > 0 || size == 0 {
 		size++
 	}
 	return size
@@ -19,7 +19,7 @@ func VarintSize(num int) int {
 
 // CodeToVarint converts an integer to a varint-encoded []byte
 func CodeToVarint(num int) []byte {
-	buf := make([]byte, bits.Len(uint(num))/7+1)
+	buf := make([]byte, VarintSize(num))
 	n := binary.PutUvarint(buf, uint64(num))
 	return buf[:n]
 }

varint_test.go

+package multiaddr
+
+import "testing"
+
+func expectVarint(t *testing.T, x, expected int) {
+	size := VarintSize(x)
+	if size != expected {
+		t.Fatalf("expected varintsize of %d to be %d, got %d", x, expected, size)
+	}
+}
+
+func TestVarintSize(t *testing.T) {
+	expectVarint(t, (1<<7)-1, 1)
+	expectVarint(t, 0, 1)
+	expectVarint(t, 1<<7, 2)
+}