Detect end of json object using Newtonsoft.Json

Question

I have a string that starts with a JSON object but after the end of which the string goes on (something like {"a":"fdfsd","b":5}ghresd). The text afterward can contain any character and the JSON can be anything allowed for a JSON.

I would like to deserialize the JSON object and know where it ends because I want to process the rest of the string afterward, how do I do that, preferably using Newtonsoft.Json?

You might find the answers to my earlier, related question helpful, although in that case I was working in JavaScript: https://stackoverflow.com/questions/54608178/how-do-i-parse-json-sprinkled-unpredictably-into-a-string — R. Davidson, Apr 03 '19 at 19:57
Does the string contain } after the json-object? Hopefully not. Then you could use Parse with yourString.SubString(0,yourString.LastIndexOf('}')) as parameter. — Nikolaus, Apr 03 '19 at 19:58
How about getting everything from the first `{` and then the last index of `}`... this could be your json and the rest you can deal with then. Also you could verify it's valid json as well using `JToken.Parse`... — Trevor, Apr 03 '19 at 19:58
You can discard the characters after the end as shown in [Discarding garbage characters after json object with Json.Net](https://stackoverflow.com/q/37172263/3744182), however `JsonTextReader` buffers its content, and doesn't have any mechanism to report the current character position. — dbc, Apr 03 '19 at 20:01
@R.Davidson I was aware of the possibility to do this, but hoped for an easier solution, thanks anyway — Tobias Brohl, Apr 03 '19 at 20:01
@TobiasBrohl true, but what about the additional content the OP needs, still, the string will have to be parsed... — Trevor, Apr 03 '19 at 20:02
@dbc thanks, but that won't help me either, due to the limitation mentioned — Tobias Brohl, Apr 03 '19 at 20:03
@Nikolaus Yes it can contain curly brackets and any other character, so it wont work that way — Tobias Brohl, Apr 03 '19 at 20:06
Related unanswered question: [How to get detailed position information from JsonTextReader](https://stackoverflow.com/q/53108483). Maybe you could open an enhancement request on https://github.com/JamesNK/Newtonsoft.Json/issues asking to track the position in the underlying text reader? — dbc, Apr 03 '19 at 20:10
@Tobias Brohl the meaning of OP in this context is 'Original Poster'. — Theodor Zoulias, Apr 03 '19 at 23:09

score 4 · Accepted Answer · answered Apr 03 '19 at 20:11

You could make use of the SupportMultipleContent property, for example:

var json = "{\"a\":\"fdfsd\",\"b\":5}ghresd";

var reader = new JsonTextReader(new StringReader(json));
reader.SupportMultipleContent = true;

//Read the first JSON fragment
reader.Read();

var serializer = new JsonSerializer();
var result = serializer.Deserialize(reader);

//Or if you have a class to deserialise into:
//var result = serializer.Deserialize<YourClassHere>(reader);

//Line position is where the reader got up to in the JSON string
var extraData = json.Substring(reader.LinePosition);

Checking this but seems great – Tobias Brohl Apr 03 '19 at 20:13 — Tobias Brohl, Apr 03 '19 at 20:13

Smičius Mantas · Answer 2 · 2020-05-10T15:32:02.717

This piece of code might not work as expected if your json has multiple lines:

var extraData = json.Substring(reader.LinePosition);

You might need to consider adding additional check:

if(reader.LineNumber != 1)
  throw new NotSupportedException("Multiline JSON objects are not supported.");

Or you can take that value from private field using Reflection:

var charPosition = (int)reader.GetType().GetField("_charPos", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(reader);

JsonTextReader source code

Detect end of json object using Newtonsoft.Json

2 Answers2