Better errors for EncodeMulti and DecodeMulti. Closes #1.

2 files changed, 42 insertions, 2 deletions

diff --git a/securecookie.go b/securecookie.go
index 1c743fc..e997fbd 100644
--- a/securecookie.go
+++ b/securecookie.go
@@ -363,12 +363,15 @@ func CodecsFromPairs(keyPairs ...[]byte) []Codec {
 // key rotation.
 func EncodeMulti(name string, value interface{},
 	codecs ...Codec) (string, error) {
+	var errors MultiError
 	for _, codec := range codecs {
 		if encoded, err := codec.Encode(name, value); err == nil {
 			return encoded, nil
+		} else {
+			errors = append(errors, err)
 		}
 	}
-	return "", errors.New("securecookie: the value could not be encoded")
+	return "", errors
 }
 
 // DecodeMulti decodes a cookie value using a group of codecs.
@@ -377,10 +380,34 @@ func EncodeMulti(name string, value interface{},
 // key rotation.
 func DecodeMulti(name string, value string, dst interface{},
 	codecs ...Codec) error {
+	var errors MultiError
 	for _, codec := range codecs {
 		if err := codec.Decode(name, value, dst); err == nil {
 			return nil
+		} else {
+			errors = append(errors, err)
 		}
 	}
-	return errors.New("securecookie: the value could not be decoded")
+	return errors
+}
+
+// MultiError groups multiple errors.
+type MultiError []error
+
+func (m MultiError) Error() string {
+	s := ""
+	for k, v := range m {
+		if v != nil && k == 0 {
+			s = v.Error()
+		}
+	}
+	switch len(m) {
+	case 0:
+		return "(0 errors)"
+	case 1:
+		return s
+	case 2:
+		return s + " (and 1 other error)"
+	}
+	return fmt.Sprintf("%s (and %d other errors)", s, len(m)-1)
 }
diff --git a/securecookie_test.go b/securecookie_test.go
index 0187ba0..099c290 100644
--- a/securecookie_test.go
+++ b/securecookie_test.go
@@ -10,6 +10,7 @@ import (
 	"crypto/sha256"
 	"errors"
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -131,6 +132,18 @@ func TestEncoding(t *testing.T) {
 	}
 }
 
+func TestMultiError(t *testing.T) {
+	s1, s2 := New(nil, nil), New(nil, nil)
+	_, err := EncodeMulti("sid", "value", s1, s2)
+	if len(err.(MultiError)) != 2 {
+		t.Errorf("Expected 2 errors, got %s.", err)
+	} else {
+		if strings.Index(err.Error(), "hash key is not set") == -1 {
+			t.Errorf("Expected missing hash key error, got %s.", err.Error())
+		}
+	}
+}
+
 // ----------------------------------------------------------------------------
 
 type FooBar struct {