C# Escape sequence introduces unwanted backslash, while returning string from Web API Controller

Question

I'm trying to do something very simple.

 string img = "sadadsasdsa";
 string res = @"<image src=""data:img/jpg;base64," + img + @"""/>";

I get the output as <image src=\"data:img/jpg;base64,sadadsasdsa\"/>

While the output that I want is <image src="data:img/jpg;base64,sadadsasdsa"/>
I don't want the unexpected '\' to be added before data and at the end.

I even tried using the backslash as the escape sequence as
string res = "<image src=\"data:img/jpg;base64," + img + "\"/>";

I still get the same output. What am I missing here?

Okay, when I print the above 'res' string using console.writeline, I'm not getting the magical slash. But when I view it in debugger, I do see it. And I still see it when I return the string from a web API values controller. I guess this has to do with parsing of the string literal

 [HttpGet]
    [Route("api/quotes/image")]
    public string ImageString()
    {
        string imgg = "sadadsasdsa" + "\"";
        string ress = @"<image src=""data:img/jpg;base64," + imgg + "/>";
        return ress;
       }  

When I try to print the string using Console.WriteLine, I don't see the unwanted backslash. But I do see it in the debugger and when returning the string from the WebAPI controller as above.

Answer 1

This is a standard debugger behaviour. You will get this:

while debugging, and this:

on the console.

See: Can the Visual Studio Debugger display strings unquoted/unescaped? for more info.

Answer 2

The string 'res' seems mangled. However, is it an option for you to use string formatting? E.g.:

string img = "sadadsasdsa";       
string actual = string.Format(
                       CultureInfo.InvariantCulture,
                       "<image src=\"data:img/jpg;base64,{0}\"/>",
                       img);

string expected = "<image src=\"data:img/jpg;base64,sadadsasdsa\"/>";

EDIT Here is a code snippet that returns the concatenated string from you initial question:

public class ValuesController : ApiController 
{
    public IEnumerable<string> Get()
    {
        // your string concat
        string img = "sadadsasdsa";
        string actual = string.Format(
                               CultureInfo.InvariantCulture,
                               "<image src=\"data:img/jpg;base64,{0}\"/>",
                               img);

        // DEBUG ONLY - for simplicity use ASCII encoding
        Encoding enc = Encoding.ASCII;
        foreach (byte b in enc.GetBytes(actual))
        {
            // write bytes and characters
            Debug.WriteLine(b.ToString("X2") + " " + enc.GetString(new byte[] {b}));
        }

        return new string[] { actual };
    }

In the debug window you will see that the string 'actual' does not contain backslashes (0x5C), as desired: 3C < 69 i 6D m 61 a 67 g 65 e 20 73 s 72 r 63 c 3D = 22 " 64 d 61 a 74 t 61 a 3A : 69 i 6D m ...

The HTTP response received contains escaped double-quotes, introduced by a JSON serializer. Since double quotes are meaningful in JSON, they will have to be escaped in JSON values. This can be observed in the Fiddler Response Raw view: Content-Type: application/json; charset=utf-8 ["<image src=\"data:img/jpg;base64,sadadsasdsa\"/>"]

After deserialization the response contains the string without backslashes. This can be observed in the Fiddler Response JSON view. (i use Fiddler 4.6.2.0)

Largely related: question 9462425

You can also look at this using Postman (Chrome extension), which is useful for changing the HTTP request 'Accept' header. 'application/json' will return you JSON, and 'application/xml' will return you XML. Both formats have quite different looks when serialized. Toying the Accept header and looking at the resulting responses illustrates the point about the need to escape meaningful characters.

If this helps, would you be so kind to remove the downvote?