Lightweight C# Json parser and programming model

If your task is to parse json whose structure is known ahead of time, a few "quick and dirty" helper functions may do the trick. For instance

static string JsonLookupText(string json, string key) =>
    JsonFind(json, key).Split('"')[1];
static string JsonFind(string json, string key) {
    int keyIndex = json.IndexOf($"\"{key}\":");
    if (keyIndex < 0)
        throw new KeyNotFoundException($"Key \"{key}\" not found in '{json}'.");
    return json.Substring(keyIndex + 3 + key.Length).TrimStart();
}

lets you find objects within objects and look up simple text values.

Given

{
    "name": "Dbquity",
    "established": 2016,
    "primes": [ 1, 2, 3, 5, 7, 11 ],
    "engineer": { "name": "Lars", "homeTown": "Frederiksberg" }
}

you can

const string json = "{ \"name\": \"Dbquity\", <... as above ...> }"; 
Assert.AreEqual("Dbquity", JsonLookupText(json, "name"));
string engineer = JsonFind(json, "engineer");
Assert.AreEqual("Lars", JsonLookupText(engineer, "name"));
Assert.AreEqual("Frederiksberg", JsonLookupText(json, "homeTown"));

However, you'll often want to approach problems in a manner that is a little bit more structured, and that is what this project tries to do.

• It includes a C# object model for representing json, in which you find JsonObject, JsonArray, JsonText, JsonNumber, JsonBool, JsonNull types that all inherit from JsonValue.
• It supports parsing a string into this representation as well as ToStringing to a dense textual representation and Formatting with line breaks and indentation.
• Finally it allows for conversion to and from user defined C# objects - subject to certain restrictions.

Reusing the example json from above, the library lets you write

JsonObject dbquity = JsonObject.Parse(json);
Assert.AreEqual<string>("Dbquity", dbquity["name"]);
Assert.AreEqual<string>("Lars", dbquity["engineer"]["name"]);
Assert.AreEqual<int>(7, dbquity["primes"][4]);
Assert.AreEqual(6, dbquity["primes"].Array.Count);
Clipboard.SetData(DataFormats.Text, dbquity.Format());

Where the last line formats the json onto the clipboard like this:

{
    "name": "Dbquity",
    "established": 2016,
    "primes": [
        1,
        2,
        3,
        5,
        7,
        11
    ],
    "engineer": {
        "name": "Lars",
        "homeTown": "Frederiksberg"
    }
}

This json implementation is used when handling RESTful interaction with internet based storage services in the Dbquity platform.

The whole thing is kept as minimal as possible to the author who would very much welcome any input :-)

Note that the handling of escapes such as encoded unicode characters in string values is not, yet, working completely as specified at http://json.org. Please do raise an issue, if you find something specific that you need fixed.