Adds JWS encode and decode

It also adds interfaces Signer and HS256 and RS256 implementation.

jwt/base64.go

@@ -3,30 +3,61 @@ package jwt
 import (
 	"encoding/base64"
 	"fmt"
-	"strings"
 )
 
-// Base64Encode encodes a payload of data as a string, like specified
-// in RFC 7515 (no trailing '='
-func Base64Encode(b []byte) string {
-	return strings.TrimRight(base64.URLEncoding.EncodeToString(b), "=")
+// Base64EncodedBufferLen return the size needed to encode the
+// Base64Encode (padding '=' would be added, can be stripped with
+// Base64DecodedStrippedLen
+func Base64EncodedBufferLen(n int) int {
+	return base64.URLEncoding.EncodedLen(n)
 }
 
-// Base64Decode decodes a payload of data as a []byte, like specified
-// in RFC 7515 (no trailing '=')
-func Base64Decode(s string) ([]byte, error) {
-	switch len(s) % 4 {
+// Base64EncodedStrippedLen return the size of the encoded slice with no
+// padding.
+func Base64EncodedStrippedLen(n int) int {
+	eN := Base64EncodedBufferLen(n)
+	mod := n % 3
+	if mod == 0 {
+		return eN
+	}
+	return eN - (3 - mod)
+}
+
+// Base64DecodedStrippedLen returns the size of the data, without 0
+// bit padding, from the stripped length n.
+func Base64DecodedStrippedLen(n int) int {
+	return Base64DecodedLenFromStripped(n) + n - ((n+3)/4)*4
+}
+
+// Base64DecodedLenFromStripped returns the size of the data, with 0
+// bit padding, from the stripped length n.
+func Base64DecodedLenFromStripped(n int) int {
+	return base64.URLEncoding.DecodedLen(4 * ((n + 3) / 4))
+}
+
+// Base64Decode decodes a payload of data as a []byte, from a stripped
+// '=' encoded string.
+func Base64Decode(dst, src []byte) error {
+	switch len(src) % 4 {
+	// in this case, we have to copy the src, in order to allow decode part of the input
 	case 2:
-		s += "=="
+		oldSrc := src
+		src = make([]byte, len(src)+2)
+		copy(src, oldSrc)
+		src[len(src)-2] = '='
+		src[len(src)-1] = '='
 	case 3:
-		s += "="
+		oldSrc := src
+		src = make([]byte, len(src)+1)
+		copy(src, oldSrc)
+		src[len(src)-1] = '='
 	case 1:
-		return nil, fmt.Errorf("jwt: Invalid base64 string (length:%d %% 4 == 1): '%s'", len(s), s)
+		return fmt.Errorf("jwt: Invalid base64 string (length:%d %% 4 == 1): '%s'", len(src), src)
 	}
-	d, err := base64.URLEncoding.DecodeString(s)
+	_, err := base64.URLEncoding.Decode(dst, src)
 	if err != nil {
-		return nil, fmt.Errorf("jwt: %s", err)
+		return fmt.Errorf("jwt: %s", err)
 	}
-	return d, nil
 
+	return nil
 }