Drop DefaultLengths; can now get from Hash.Size.

Discussed in
#136 (comment)

multihash.go

@@ -80,7 +80,6 @@ func init() {
 		name := fmt.Sprintf("blake2b-%d", n*8)
 		Names[name] = c
 		Codes[c] = name
-		DefaultLengths[c] = int(n)
 	}
 
 	// Add blake2s (32 codes)
@@ -89,7 +88,6 @@ func init() {
 		name := fmt.Sprintf("blake2s-%d", n*8)
 		Names[name] = c
 		Codes[c] = name
-		DefaultLengths[c] = int(n)
 	}
 }
 
@@ -142,28 +140,6 @@ var Codes = map[uint64]string{
 	MD5:                       "md5",
 }
 
-// DefaultLengths maps a hash code to it's default length
-var DefaultLengths = map[uint64]int{
-	IDENTITY:     -1,
-	SHA1:         20,
-	SHA2_256:     32,
-	SHA2_512:     64,
-	SHA3_224:     28,
-	SHA3_256:     32,
-	SHA3_384:     48,
-	SHA3_512:     64,
-	DBL_SHA2_256: 32,
-	KECCAK_224:   28,
-	KECCAK_256:   32,
-	MURMUR3_128:  4,
-	KECCAK_384:   48,
-	KECCAK_512:   64,
-	SHAKE_128:    32,
-	SHAKE_256:    64,
-	X11:          64,
-	MD5:          16,
-}
-
 func uvarint(buf []byte) (uint64, []byte, error) {
 	n, c, err := varint.FromUvarint(buf)
 	if err != nil {

sum.go

@@ -2,7 +2,6 @@ package multihash
 
 import (
 	"errors"
-	"fmt"
 )
 
 // ErrSumNotSupported is returned when the Sum function code is not implemented
@@ -30,11 +29,7 @@ func Sum(data []byte, code uint64, length int) (Multihash, error) {
 
 	// Deal with any truncation.
 	if length < 0 {
-		var ok bool
-		length, ok = DefaultLengths[code]
-		if !ok {
-			return nil, fmt.Errorf("no default length for code %d", code)
-		}
+		length = hasher.Size()
 	}
 	if len(sum) < length {
 		return nil, ErrLenTooLarge

sum_test.go

@@ -131,11 +131,7 @@ func TestTooLargeLength(t *testing.T) {
 
 func TestBasicSum(t *testing.T) {
 	for code, name := range multihash.Codes {
-		defaultLen, ok := multihash.DefaultLengths[code]
-		if !ok {
-			defaultLen = 32
-		}
-		_, err := multihash.Sum([]byte("test"), code, defaultLen)
+		_, err := multihash.Sum([]byte("test"), code, -1)
 		switch err {
 		case multihash.ErrSumNotSupported, nil:
 		default: