add hash list and use it in multihash command

multihash.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"sort"
 
 	b58 "github.com/jbenet/go-base58"
 )
@@ -81,6 +82,13 @@ func init() {
 		Codes[c] = name
 		DefaultLengths[c] = int(n)
 	}
+
+	// Initialize NamesList
+	NamesList = make([]string, 0, len(Names))
+	for k, _ := range Names {
+		NamesList = append(NamesList, k)
+	}
+	sort.Strings(NamesList)
 }
 
 // Names maps the name of a hash to the code
@@ -104,6 +112,8 @@ var Names = map[string]uint64{
 	"shake-256":    SHAKE_256,
 }
 
+var NamesList []string
+
 // Codes maps a hash code to it's name
 var Codes = map[uint64]string{
 	ID:           "id",

multihash_test.go

@@ -49,6 +49,20 @@ var testCases = []TestCase{
 	TestCase{"4bca2b137edc580fe50a88983ef860ebaca36c857b1f492839d6d7392452a63c82cbebc68e3b70a2a1480b4bb5d437a7cba6ecf9d89f9ff3ccd14cd6146ea7e7", 0x14, "sha3-512"},
 }
 
+func TestNamesList(t *testing.T) {
+	if len(NamesList) != len(Names) {
+		t.Fatal("lengths are different, NamesList: %d; Names: %d",
+			len(NamesList), len(Names))
+	}
+
+	for _, v := range NamesList {
+		_, ok := Names[v]
+		if !ok {
+			t.Fatal("entry: %s not contained in Names", v)
+		}
+	}
+}
+
 func (tc TestCase) Multihash() (Multihash, error) {
 	ob, err := hex.DecodeString(tc.hex)
 	if err != nil {

opts/opts.go

@@ -35,7 +35,7 @@ var FlagValues = struct {
 	Algorithms []string
 }{
 	Encodings:  []string{"raw", "hex", "base58", "base64"},
-	Algorithms: []string{"sha1", "sha2-256", "sha2-512", "sha3"},
+	Algorithms: mh.NamesList,
 }
 
 // SetupFlags adds multihash related options to given flagset.