.NET Core json response differences between Chrome and Firefox

Question

I wrote a Minimal Web API with this code:

app.MapGet("/api/getLogs", async (HttpContext context) =>   
{
    context.Response.Headers.ContentType = "application/json";
    data = await Data.GetLogs();  // note data is a valid json formatted string
    return context.Response.WriteAsync(data);
});

As above it shows perfectly with Firefox, the json is color highlighted numbers and strings get recognized. I feel happy how Firefox does it.

Though Chrome won't show it...

When browsing to this API endpoint, I see a developer error in Visual Studio:

System.InvalidOperationException: Headers are read-only, response has already started.

But without that context.Response line the Firefox highlighting of the json isn't shown so Firefox does receives json, despite the warning, it works perfectly ).

I tried several other ways like, just showing some below:

context.Response.WriteAsync(await Data.GetLogs() )); }

and

app.MapGet("/", (HttpContext context) => context.Response.WriteAsJsonAsync(new { Message = Data.GetLogs() }));

etc

Sometimes it worked in Chrome, and sometimes it works in Firefox, but to get it with json highlighting only works as in my first example and only for Firefox.

I like to be able to see the highlighting as in Netscape (I don't mind to have another browser for just this). But in a perfect world I rather have it so that Firefox shows it with highlighting and Chrome, however Chrome can show it (current code Chrome doesn't show it at all).

Note also that it is just this API call that should work this way, my other request are different.

No but it think it works now, I just simplified the line into return data; firefox still highlights it and now chrome shows it too — Peter
– Peter, Commented May 28, 2024 at 13:56
@Peter why can't you use return Json? What you tried is wrong, hence the error. If you receive raw JSON from another service and want to return it use return Results.Text(data,"application/json",Encoding.UTF8) — Panagiotis Kanavos
– Panagiotis Kanavos, Commented May 28, 2024 at 14:04
Are you trying to forward the results of another API? In that case you may want to look at the YARP package and more specifically the Direct Forwarding scenario — Panagiotis Kanavos
– Panagiotis Kanavos, Commented May 28, 2024 at 14:05

Panagiotis Kanavos · Accepted Answer · 2024-05-28 14:08:08Z

1

If you want to return text with a specific content type use Results.Text() with the desired application type and encoding eg :

app.MapGet("/api/getLogs", async (HttpContext context) =>   
{
    data = await Data.GetLogs();
    return Results.Text(data, "application/json", Encoding.UTF8);
});

answered May 28, 2024 at 14:08

Panagiotis Kanavos

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5 Comments

Peter Over a year ago

Okay, well i already had found a solution that worked for me (in the comments of my question), and i know there are various ways your notation i had not yet seen though, Result.Text (i guess as in plain text) and then later say application.json intriguing. My answer in the comment below the question isnt wrong runs without errors. Though in this case unsure about whats good or what is wrong, is your answer better than just my old code ending with a simple "return data ;" ?

Panagiotis Kanavos Over a year ago

Yes, because return somestring will generate a JSON response consisting of a quoted string. If you try to return {"a":123} you'll get "{\"a\":123}" instead. You'll have to deserialize this twice to get an object with a property A whose value is 123

Peter Over a year ago

Ehm this was not in my case, as i mentioined: note data is a valid json formatted string

Panagiotis Kanavos Over a year ago

You misunderstood what I said. If data is a string, returning it will re-encode it as a standalone JSON string again. If you got something that isn't surrounded by " it means data is an object and can be returned as is with return data; or return Results.OK(data)

Peter Over a year ago

Ok thanks for the clarify i upvote and mark as answer

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