Returning Json of byte array in web api c#

Question

Hi I have developed a Web API in which I am taking some parameters in URL and then processing them. The protocol I am using is Modbus. It returns a byte array and in return, I want to get some specific string data from it. Below is my code

  public string GetData(int slaveId, int dataAddress, int registerCount)
    {

        //string hexValue = intValue.ToString("X");
        // Convert the hex string back to the number
        int slaveHex = int.Parse(slaveId.ToString("X"), System.Globalization.NumberStyles.HexNumber);
        int addressHex = int.Parse(dataAddress.ToString("X"), System.Globalization.NumberStyles.HexNumber);
        int countHex = int.Parse(registerCount.ToString("X"), System.Globalization.NumberStyles.HexNumber);


        //serial port settings and opening it
        var serialPort = new SerialPort("COM2", 9600, Parity.Even, 8, StopBits.One);

        serialPort.Open();

        var stream = new SerialStream(serialPort);
        stream.ReadTimeout = 200;
        // send request and waiting for response
        // the request needs: slaveId, dataAddress, registerCount            
        var responseBytes = stream.RequestFunc3(slaveHex, addressHex, countHex);

        // extract the content part (the most important in the response)
        var data = responseBytes.ToResponseFunc3().Data;         

        //Convert a byte array to string
        var stringFromByteArray = System.Text.Encoding.UTF8.GetString(data);
        serialPort.Close();

        return stringFromByteArray;
    }

The data contains an array of 14 bytes

The stringFromByteArray returns the following

"\0�\0�\0�\0\u0016\0\u0017\0\u0018\0\u001a"

As you can see in above the returned string is not as expected. I want exact values as in data byte array.

The resulting output I want it to be in Json response. Like below

{
  [0] => "220",
  [1] => "230",
  [2] => "240", 
  [3] => "22",
  [4] => "23",
  [5] => "24",
  [6] => "26",
}

How can I do it? Any help would be highly appreciated.

Well then, a simple linq chain should give you the expected result: var result = data.Where(r=>r>0).Select(r=>r.ToString()).ToArray() — Eldar
– Eldar, Commented Apr 12, 2020 at 10:03
And what will you expect when the even indexed values in the array are different from 0. For example, what will you expect when you have values like [220,255,140,255]? — Eldar
– Eldar, Commented Apr 12, 2020 at 10:05
Then you something like this: var result = data.Where((r,i)=>i % 2 == 0).Select(r=>r.ToString()).ToArray() And If you want a json result just serialize result array into json. — Eldar
– Eldar, Commented Apr 12, 2020 at 10:16

Zdeněk Jelínek · Accepted Answer · 2020-04-12 10:45:30Z

2

From broad perspective, there are several options available to you.

First off, you might consider using application/octet-stream as the response type instead of application/json in the HTTP response. application/octet-stream means bytes are directly sent over HTTP. This is how you'd usually upload/download files.

Secondly, it is possible to encode binary data into text in safer manner, e.g. using encoding algorithms such as Base64, which you can achieve in .NET using Convert.ToBase64String method. Such methods are more verbose than using octet-stream but also play better when attempting to send structured data with some binary contents.

And finally, as you requested, you can use a structure to represent the data directly. There are several options, you can encode an array of numbers directly, which would yield you JSON payload as:

[220, 230, 240, 22, 23, 24, 26]

To achieve this, you simply serialize a list of numbers, e.g. byte[] directly or possibly int[] based on the behavior of your serializer (.NET Core 3.0+ System.Test.Json.JsonSerializer converts byte arrays to base64 so conversion to int[] is needed). Live sample.

The structure you requested is not directly possible in JSON, but you can achieve something similar serializing a Dictionary<string, string>, yielding a structure of { "0": "220", "1": "230", "2":"240" ... }. Note, however, that this structure is quite verbose and not very practical.

You can get the dictionary using the following snippet:

var bytes = new byte[] { 220, 230, 240, 22, 23, 24, 26 };

var dictionary = bytes
    .Select((b, i) => (value: b, index: i)) // convert bytes to sequence of (byte value, index)
    .ToDictionary(x => x.index.ToString(), x => x.value.ToString());

edited Apr 12, 2020 at 10:45

answered Apr 12, 2020 at 10:27

Zdeněk Jelínek

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6 Comments

Moeez Over a year ago

Ok finally while returning how can I return it? as I could not use return dictionary simply

Zdeněk Jelínek Over a year ago

You should just return the dictionary all the way up to your controller, either on its own or as a part of the controller's return type.

Zdeněk Jelínek Over a year ago

If you can't change the return type of the method in question, I don't see any other way than using the base-64 encoding or directly serializing into json, but I believe the second case would land you in more trouble as your controller would double-encode the response unless you're doing something special. I think changing the methods signatures would be easier but I don't have the full context of your project to cerrectly advise.

Moeez Over a year ago

I want to return a json response so I can consume it at server end

Zdeněk Jelínek Over a year ago

Yes, so what happens when you change the GetData method signature to return Dictionary<string, string>? Do you get a compiler error somewhere else? Can you change that somewhere else to also return Dictionary<string, string> and so on until you get no compiler errors?

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