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How to parse a complicated nested JSON string in C#?

I have an ugly JSON string that is getting returned from an API that looks like this (this is the result of Console.Write on the string):
{"d":"\"\\\"\\\\\\\"[{\\\\\\\\\\\\\\\"foo\\\\\\\\\\\\\\\":15,\\\\\\\\\\\\\\\"bar\\\\\\\\\\\\\\\":null}]\\\\\\\"\\\"\\n\""}
I am trying to parse this into a C# object in the simplest way possible, so I can access properties like foo and bar. But I am having a difficult time doing this.
I have tried parsing it a number of ways, including:
// code to get the response string
client.Headers.Add(HttpRequestHeader.ContentType, "application/json");
var serializedData = "{data: 'data'}";
var responseString = client.UploadString(url, "POST", serializedData);
// parse the response string
dynamic obj = Newtonsoft.Json.JsonConvert.DeserializeObject(jsonString);
This allows me to access the value of d, which is the actual string I need to parse. I then tried to parse that separately using JArray.Parse(obj["d"]), but I get an error saying that obj["d"] is not an array.
Unfortunately, I have no access to the API itself so can't modify how it's serializing the data it's returning.
Any suggestions?

You can replace all New Line, Backslash, Double quotes to format the JSON
var formattedJson = jsonString.Replace(#"\n", string.Empty)
.Replace(#"\", string.Empty)
.Replace("\"\"", string.Empty);
Console.WriteLine(formattedJson);
OUTPUT
{
"d": [
{
"foo": 15,
"bar": null
}
]
}
Convert to JArray.
var jArray = JArray.Parse(JObject.Parse(formattedJson)["d"].ToString());
Console.WriteLine($"{jArray[0]["foo"]} {jArray[0]["bar"]}");
OUTPUT
15

The problem is that the value of "d" is a string representing a string representing a string ... representing an array. You could call it JSON serialization "inception".
The way to deal with this is to deserialize the value corresponding number of times. If you're sure that the value is never going to be an actual string, you could do it like this, without having to know how many times the value was serialized:
var myObject = JObject.Parse(s);
var d = myObject["d"];
while(d.Type == JTokenType.String)
d = JToken.Parse(d.ToObject<string>());
myObject["d"] = d;
After this procedure myObject represents this data:
{
"d": [
{
"foo": 15,
"bar": null
}
]
}

Replacing escape characters in fine however I would not rely on the console.write command as the definitive output to examine. Here are a couple of other ways: -
Use Postman to make the API call so you can see the raw result. This will (hopefully) show it in an easy to read format that you can then define your class to deserialise to.
Write the raw response to a “.json” file. Open that file in a good editor (such as VS Code or VS itself) to see how the data is actually structured when it is received.
On a side note I would recommend using RestSharp to do the REST calls and Newtonsoft.Json to do the serialising/deserialising.

Unexpected character encountered while parsing value: ?. Path '', line 0, position 0

I have this JSON file:
[
{
"param1": "someURL",
"param2": "someURL2"
},
{
"param1": "someURL3",
"param2": "someURL4"
}
]
JsonLint says that this JSON is valid.
Now I read this JSON file from Azure Storage download it to a stream and then encode it:
string content = Encoding.UTF8.GetString(memoryStream.ToArray());
Next I want to deserialize this to a list of objects:
List<MyParamObject> deserialized = JsonConvert.DeserializeObject<List<MyParamObject>>(text);
MyParamObject is a POCO with two attributes named Param1 and Param2
When I try to deserialize it I get the following error:
Unexpected character encountered while parsing value: ?. Path '', line 0, position 0.
But I do give JsonConvert a string with a valid JSON what can I do?

Through a HEX Editor I checked the beginning of the file and I found out that my IDE added a BOM to the beginning of the file. So it looks like this:
[.. {.. "
As they are not recommended I chose to get rid of them by creating a new file with Explorer/Finder and adding my JSON in there.

Is "[]" valid JSON?

I'm having troubles de-serializing this JSON string using JSON.NET (note the quotes):
"[]"
Depending on which JSON validation website you go to, this is valid JSON (jsonlint for example says it is).
The JSON.NET code:
void Main()
{
string json = "\"[]\"";
var x = JsonConvert.DeserializeObject<User[]>(json);
Console.WriteLine(x);
}
// Define other methods and classes here
public class User
{
public string Id { get; set; }
public int Age { get; set; }
}
The exception
Error converting value "[]" to type 'UserQuery+User[]'. Path '', line 1, position 4.
Is there a way of forcing JSON.NET to parse this?

Part 1: Is "[]" valid JSON?
There are several documents and standards on JSON, and hundreds of parsers; and some of them suppose that JSON can only be object {} or an array [], but some allow single values like strings, numbers to be used as JSON.
Read this article, it widely describes this problem.
What is the minimum valid JSON?
This dispute on JSON validity is another question. In your case, it doesn't matter, because...
Part 2: why your code isn't working.
Even if we allow non-objects \ non-arrays to be valid JSON, then your JSON represents a single string equal to "[]". It could be anything else, not brackets, it is not an array notation, but just two symbols "[" and "]".
However, you try to parse this JSON as an array of objects, which will anyway result into error.
In other words, even if it is a valid JSON, then it is a valid JSON string, not JSON array.
var str1 = JSON.parse("\"[]\""),
str2 = JSON.parse("\"could be anything else, not brackets\""),
arr = JSON.parse("[]");
console.log(typeof str1);
console.log(typeof str2);
console.log(typeof arr);
var str1_s = JSON.stringify([]);
console.log("Valid JSON of an empty array: " + str1_s);
var arr_s = JSON.stringify("[]");
console.log("Partly valid JSON of a string '[]': " + arr_s);
Part 3: what should you do
The best idea - stop using invalid JSON as input. Tell whoever gave you this JSON that it is invalid JSON array and you cannot use it. You would be able to deserialize a JSON into your array of User if it was correct just like you use it:
string json = "[]";
var x = JsonConvert.DeserializeObject<User[]>(json);
Console.WriteLine(x);
If this JSON is provided from 3rd party services and you can do nothing about that, then you need to tidy it up and make it valid. Yeah, unfortunately, sometimes it happens.
How? It depends on what is your value when there ARE objects (users).
It may be a JSON-serialized JSON-string (double-serialized) like this, and then you need to deserialize a string, and then deserialize an array.
Or it can just have two odd quotes in the beginning and the end, and you can just remove them.

It is valid JSON, but the deserializer failes because the datatypes do not match.
"[]"
Is a string, so the deserializer wants to serialize it to a string.
[]
Is an empty array. So, in short, this should work:
string json = "[]";
var x = JsonConvert.DeserializeObject<User[]>(json);
Console.WriteLine(x);

how to validate JSON string before converting to XML in C#

I will receive an response in the form of JSON string.
We have an existing tool developed in C# which will take input in XML format.
Hence i am converting the JSON string obtained from server using Newtonsoft.JSON to XML string and passing to the tool.
Problem:
When converting JSON response to XML, I am getting an error
"Failed to process request. Reason: The ' ' character, hexadecimal
value 0x20, cannot be included in a name."
The above error indicates that the JSON Key contains a space [For Example: \"POI Items\":[{\"lat\":{\"value\":\"00\"}] which cannot be converted to XML element.
Is there any approach to identify spaces only JSON key's ["POI Items"] and remove the spaces in it?
Also suggest any alternative solution so that we needn't change the existing solution?
Regards,
Sudhir

You can use Json.Net and replace the names while loading the json..
JsonSerializer ser = new JsonSerializer();
var jObj = ser.Deserialize(new JReader(new StringReader(json))) as JObject;
var newJson = jObj.ToString(Newtonsoft.Json.Formatting.None);
.
public class JReader : Newtonsoft.Json.JsonTextReader
{
public JReader(TextReader r) : base(r)
{
}
public override bool Read()
{
bool b = base.Read();
if (base.CurrentState == State.Property && ((string)base.Value).Contains(' '))
{
base.SetToken(JsonToken.PropertyName,((string)base.Value).Replace(" ", "_"));
}
return b;
}
}
Input : {"POI Items":[{"lat":{"value":"00","ab cd":"de fg"}}]}
Output: {"POI_Items":[{"lat":{"value":"00","ab_cd":"de fg"}}]}

I recommend using some sort of Regex.Replace().
Search the input string for something like:
\"([a-zA-Z0-9]+) ([a-zA-Z0-9]+)\":
and then replace something like (mind the missing space):
\"(1)(2)\":
The 1st pair of parenthesis contain the first word in a variable name, the 2nd pair of parenthesis means the 2nd word. The : guarantees that this operation will be done in variable names only (not in string data). the JSON variable names are inside a pair of \"s.
Maybe it's not 100% correct but you can start searching by this.
For details check MSDN, and some Regex examples
http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.replace.aspx

JSON parse exception using System.Json

I get an error while parsing a json string into an object. I am using system.json to parse the json string.
The JSON file: (NOTE: I cannot change the structure of this json file because it is generated)
{
title: "My Title",
log: "",
nid: "1234",
type: "software",
language: "EN",
created: "1364480345",
revision_timestamp: "1366803957",
body: {
und: [
{
value: "abc",
summary: "def"
}
]
}
}
The C# code:
string jsonString = new WebClient().DownloadString(".......MyJson.json"); //For test purpose
var obj = JsonObject.Parse (jsonString); ///<--- At this line the exception is thrown
The Exception:
System.ArgumentException has been thrown.
Invalid JSON string literal format. At line 1, column 2
How to solve this?
Thanks in advance!

You can't. That isn't valid json. Field names must be enclosed in quotes. All json parsing tools will throw when trying to parse that.
You could process it and turn it to valid json before deserializing, but really, you need to correct it API side. No clients will work with that.

How to solve this?
(NOTE: I cannot change the structure of this json file because it is generated)
Easy, use json.Net. it works without any problem with your json
var j = JObject.Parse(jsonString);
You can even use dynamic keyword
dynamic j = JObject.Parse(jsonString);
Console.WriteLine("{0},{1}", j.title, j.body.und[0].value);