Add XmlCheckIsValid toggle

After the value is encoded, the XML is checked to insure that it is valid.  Requires giithub.com/clbanning/mxj/v2.

anyxml.go

@@ -49,21 +49,24 @@
 		  <element>true</element>
 		</mydoc>
 
-An example of encoding a map[interface{}]interface{} value with mixed key types is 
+An example of encoding a map[interface{}]interface{} value with mixed key types is
 in anyxml/examples/goofy_map.go.
 */
 package anyxml
 
 import (
 	"encoding/xml"
 	"reflect"
+
+	// "github.com/clbanning/mxj"
+	"github.com/clbanning/mxj/v2"
 )
 
 // Default missingElementTag value.
 var missingElemTag = "element"
 
 // MissingElementTag is used to set the lable to be used
-// for values that are not map[string]interface{} type.  By default 
+// for values that are not map[string]interface{} type.  By default
 // the tag label "element" is used. The default can be reset by
 // passing an empty string, "", argument: MissingElementTag("").
 func MissingElementTag(s string) {
@@ -127,6 +130,12 @@ func Xml(v interface{}, rootTag ...string) ([]byte, error) {
 		b = []byte(*s)
 	}
 
+	if xmlCheckIsValid {
+		if _, err = mxj.NewMapXml(b); err != nil {
+			return nil, err
+		}
+	}
+
 	return b, err
 }
 
@@ -190,5 +199,11 @@ func XmlIndent(v interface{}, prefix, indent string, rootTag ...string) ([]byte,
 		b = []byte(*s)
 	}
 
+	if xmlCheckIsValid {
+		if _, err = mxj.NewMapXml(b); err != nil {
+			return nil, err
+		}
+	}
+
 	return b, err
 }

go.mod

@@ -0,0 +1,3 @@
+module github.com/clbanning/anymxj/v2
+
+go 1.15

isvalid_test.go

@@ -0,0 +1,28 @@
+package anyxml
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+)
+
+func TestXmlCheckIsValid(t *testing.T) {
+	fmt.Println("================== TestXmlCheckIsValid")
+
+	data := []byte(`{"":"empty", "$invalid":"hex$", "entities":"<>&", "nil": null}`)
+	m := make(map[string]interface{})
+	err := json.Unmarshal(data, &m)
+	if err != nil {
+		t.Fatal("json.Unmarshal err;", err)
+	}
+	fmt.Printf("%v\n", m)
+
+	XmlCheckIsValid()
+	if _, err := Xml(m); err == nil {
+		t.Fatal("Xml err: nil")
+	}
+
+	if _, err := XmlIndent(m, "", "   "); err == nil {
+		t.Fatal("Xml err: nil")
+	}
+}

readme.md

@@ -17,6 +17,10 @@ See mxj package documentation for caveats, etc.
 Since some values, such as arrays, may require injecting tag labels to generate the XML, unmarshaling
 the resultant XML is not necessarily symmetric, i.e., you cannot get the original value back without some manipulation.
 
+<h4>Dependencies</h4>
+
+   import  github.com/clbanning/mxj/v2
+
 <h4>Documentation</h4>
 
 http://godoc.org/github.com/clbanning/anyxml

xml.go

@@ -159,6 +159,20 @@ func escapeChars(s string) string {
 	return string(b)
 }
 
+// From clbanning/mxj issue #88
+// xmlCheckIsValid set switch to force decoding the encoded XML to
+// see if it is valid XML.
+var xmlCheckIsValid bool
+
+// XmlCheckIsValid forces the encoded XML to be checked for validity.
+func XmlCheckIsValid(b ...bool) {
+	if len(b) == 1 {
+		xmlCheckIsValid = b[0]
+		return
+	}
+	xmlCheckIsValid = !xmlCheckIsValid
+}
+
 // where the work actually happens
 // returns an error if an attribute is not atomic
 // patched with new version in github.com/clbanning/mxj - 2015.11.15
@@ -199,7 +213,7 @@ func mapToXmlIndent(doIndent bool, s *string, key string, value interface{}, pp
 		var n int
 		var ss string
 		for k, v := range vv {
-			if k[:1] == "-" {
+			if len(k) > 0 && k[:1] == "-" {
 				switch v.(type) {
 				case string:
 					ss = v.(string)
@@ -267,7 +281,7 @@ func mapToXmlIndent(doIndent bool, s *string, key string, value interface{}, pp
 		elemlist := make([][2]interface{}, len(vv))
 		n = 0
 		for k, v := range vv {
-			if k[:1] == "-" {
+			if len(k) > 0 && k[:1] == "-" {
 				continue
 			}
 			elemlist[n][0] = k