Add XML payload support

Fixes #238

vendor/github.com/clbanning/mxj/misc.go

@@ -0,0 +1,86 @@
+// Copyright 2016 Charles Banning. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file
+
+// misc.go - mimic functions (+others) called out in:
+//          https://groups.google.com/forum/#!topic/golang-nuts/jm_aGsJNbdQ
+// Primarily these methods let you retrive XML structure information.
+
+package mxj
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Return the root element of the Map. If there is not a single key in Map,
+// then an error is returned.
+func (mv Map) Root() (string, error) {
+	mm := map[string]interface{}(mv)
+	if len(mm) != 1 {
+		return "", fmt.Errorf("Map does not have singleton root. Len: %d.", len(mm))
+	}
+	for k, _ := range mm {
+		return k, nil
+	}
+	return "", nil
+}
+
+// If the path is an element with sub-elements, return a list of the sub-element
+// keys.  (The list is alphabeticly sorted.)  NOTE: Map keys that are prefixed with
+// '-', a hyphen, are considered attributes; see m.Attributes(path).
+func (mv Map) Elements(path string) ([]string, error) {
+	e, err := mv.ValueForPath(path)
+	if err != nil {
+		return nil, err
+	}
+	switch e.(type) {
+	case map[string]interface{}:
+		ee := e.(map[string]interface{})
+		elems := make([]string, len(ee))
+		var i int
+		for k, _ := range ee {
+			if len(attrPrefix) > 0 && strings.Index(k, attrPrefix) == 0 {
+				continue // skip attributes
+			}
+			elems[i] = k
+			i++
+		}
+		elems = elems[:i]
+		// alphabetic sort keeps things tidy
+		sort.Strings(elems)
+		return elems, nil
+	}
+	return nil, fmt.Errorf("no elements for path: %s", path)
+}
+
+// If the path is an element with attributes, return a list of the attribute
+// keys.  (The list is alphabeticly sorted.)  NOTE: Map keys that are not prefixed with
+// '-', a hyphen, are not treated as attributes; see m.Elements(path). Also, if the
+// attribute prefix is "" - SetAttrPrefix("") or PrependAttrWithHyphen(false) - then
+// there are no identifiable attributes.
+func (mv Map) Attributes(path string) ([]string, error) {
+	a, err := mv.ValueForPath(path)
+	if err != nil {
+		return nil, err
+	}
+	switch a.(type) {
+	case map[string]interface{}:
+		aa := a.(map[string]interface{})
+		attrs := make([]string, len(aa))
+		var i int
+		for k, _ := range aa {
+			if len(attrPrefix) == 0 || strings.Index(k, attrPrefix) != 0 {
+				continue // skip non-attributes
+			}
+			attrs[i] = k[len(attrPrefix):]
+			i++
+		}
+		attrs = attrs[:i]
+		// alphabetic sort keeps things tidy
+		sort.Strings(attrs)
+		return attrs, nil
+	}
+	return nil, fmt.Errorf("no attributes for path: %s", path)
+}