Fixed json bom handling when serializing/deserializing json

src/BizTalkPlatformManagementTool/Services/JsonFileStore.cs

@@ -1,4 +1,5 @@
 using System.IO;
+using System.Runtime.Serialization;
 using System.Runtime.Serialization.Json;
 using System.Text;
 
@@ -6,6 +7,8 @@ namespace BizTalkPlatformManagementTool.Services
 {
     public static class JsonFileStore
     {
+        private static readonly Encoding Utf8NoBom = new UTF8Encoding(false);
+
         public static void Save<T>(string path, T value)
         {
             Directory.CreateDirectory(Path.GetDirectoryName(Path.GetFullPath(path)));
@@ -17,8 +20,8 @@ namespace BizTalkPlatformManagementTool.Services
             using (var stream = new MemoryStream())
             {
                 serializer.WriteObject(stream, value);
-                var json = Encoding.UTF8.GetString(stream.ToArray());
-                File.WriteAllText(path, json, Encoding.UTF8);
+                var json = Utf8NoBom.GetString(stream.ToArray());
+                File.WriteAllText(path, json, Utf8NoBom);
             }
         }
 
@@ -29,10 +32,55 @@ namespace BizTalkPlatformManagementTool.Services
                 UseSimpleDictionaryFormat = true
             });
 
-            using (var stream = File.OpenRead(path))
+            var json = NormalizeJson(File.ReadAllText(path, Encoding.UTF8));
+            using (var stream = new MemoryStream(Utf8NoBom.GetBytes(json)))
             {
-                return (T)serializer.ReadObject(stream);
+                try
+                {
+                    return (T)serializer.ReadObject(stream);
+                }
+                catch (SerializationException ex)
+                {
+                    throw new InvalidDataException("Failed to load JSON file '" + path + "'. " + DescribeJsonStart(json), ex);
+                }
             }
         }
+
+        private static string NormalizeJson(string json)
+        {
+            if (string.IsNullOrEmpty(json))
+            {
+                return json;
+            }
+
+            if (json[0] == '\uFEFF')
+            {
+                json = json.Substring(1);
+            }
+
+            if (json.StartsWith("\u00EF\u00BB\u00BF"))
+            {
+                json = json.Substring(3);
+            }
+
+            return json;
+        }
+
+        private static string DescribeJsonStart(string json)
+        {
+            if (string.IsNullOrWhiteSpace(json))
+            {
+                return "The file is empty or contains only whitespace.";
+            }
+
+            var trimmed = json.TrimStart();
+            var first = trimmed.Length == 0 ? '\0' : trimmed[0];
+            if (first != '{' && first != '[')
+            {
+                return "The first JSON character is '" + first + "' instead of '{' or '['.";
+            }
+
+            return "The file starts with valid JSON syntax but could not be deserialized into the expected model.";
+        }
     }
 }