fix http header binding failure bug #885 (#887)

core/mapping/unmarshaler.go

@@ -43,7 +43,8 @@ type (
 	UnmarshalOption func(*unmarshalOptions)
 
 	unmarshalOptions struct {
-		fromString bool
+		fromString   bool
+		canonicalKey func(key string) string
 	}
 
 	keyCache map[string][]string
@@ -321,9 +322,12 @@ func (u *Unmarshaler) processNamedField(field reflect.StructField, value reflect
 	if err != nil {
 		return err
 	}
-
+	k := key
+	if u.opts.canonicalKey != nil {
+		k = u.opts.canonicalKey(key)
+	}
 	fullName = join(fullName, key)
-	mapValue, hasValue := getValue(m, key)
+	mapValue, hasValue := getValue(m, k)
 	if hasValue {
 		return u.processNamedFieldWithValue(field, value, mapValue, key, opts, fullName)
 	}
@@ -621,6 +625,12 @@ func WithStringValues() UnmarshalOption {
 	}
 }
 
+func WithCanonicalKeyFunc(f func(string) string) UnmarshalOption {
+	return func(opt *unmarshalOptions) {
+		opt.canonicalKey = f
+	}
+}
+
 func fillDurationValue(fieldKind reflect.Kind, value reflect.Value, dur string) error {
 	d, err := time.ParseDuration(dur)
 	if err != nil {