Add support for [BODY] placeholder and basic JSON path support

Note that arrays are not currently supported, same with asterisks

jsonpath/jsonpath.go

@@ -0,0 +1,30 @@
+package jsonpath
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+func Eval(path string, b []byte) string {
+	var object map[string]interface{}
+	err := json.Unmarshal(b, &object)
+	if err != nil {
+		return ""
+	}
+	return walk(path, object)
+}
+
+func walk(path string, object map[string]interface{}) string {
+	keys := strings.Split(path, ".")
+	targetKey := keys[0]
+	// if there's only one key and the target key is that key, then return its value
+	if len(keys) == 1 {
+		return fmt.Sprintf("%v", object[targetKey])
+	}
+	// if there's more than one key, then walk deeper
+	if len(keys) > 0 {
+		return walk(strings.Replace(path, fmt.Sprintf("%s.", targetKey), "", 1), object[targetKey].(map[string]interface{}))
+	}
+	return ""
+}