From a0557075ec3c84e6dd18d13aca6596ca3a7ed689 Mon Sep 17 00:00:00 2001
From: Kevin Atkinson <k@kevina.org>
Date: Thu, 26 Jul 2018 12:50:11 -0400
Subject: [PATCH] Add prefix type that guarantees a valid multibase prefix.

---
 prefix.go      | 28 ++++++++++++++++++++++++++++
 prefix_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 prefix.go
 create mode 100644 prefix_test.go

diff --git a/prefix.go b/prefix.go
new file mode 100644
index 0000000..92ad4f8
--- /dev/null
+++ b/prefix.go
@@ -0,0 +1,28 @@
+package multibase
+
+import ()
+
+type Prefix struct {
+	enc Encoding
+}
+
+func NewPrefix(e Encoding) (Prefix, error) {
+	_, err := Encode(e, nil)
+	if err != nil {
+		return Prefix{-1}, err
+	}
+	return Prefix{e}, nil
+}
+
+func (p Prefix) Encoding() Encoding {
+	return p.enc
+}
+
+func (p Prefix) Encode(data []byte) string {
+	str, err := Encode(p.enc, data)
+	if err != nil {
+		// should not happen
+		panic(err)
+	}
+	return str
+}
diff --git a/prefix_test.go b/prefix_test.go
new file mode 100644
index 0000000..e0214cd
--- /dev/null
+++ b/prefix_test.go
@@ -0,0 +1,29 @@
+package multibase
+
+import (
+	"testing"
+)
+
+func TestInvalidPrefix(t *testing.T) {
+	_, err := NewPrefix('q')
+	if err == nil {
+		t.Error("expected failure")
+	}
+}
+
+func TestPrefix(t *testing.T) {
+	for _, base := range Encodings {
+		prefix,err := NewPrefix(base)
+		if err != nil {
+			t.Fatalf("NewPrefix(%c) failed: %v", base, err)
+		}
+		str1, err := Encode(base, sampleBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		str2 := prefix.Encode(sampleBytes)
+		if str1 != str2 {
+			t.Errorf("encoded string mismatch: %s != %s", str1, str2)
+		}
+	}
+}