reactiveui/refit · error · InvalidOperationException

The character set provided in ContentType is invalid.

Error message

The character set provided in ContentType is invalid.

What it means

The Newtonsoft.Json content serializer reads the charset from a response's Content-Type header and tries Encoding.GetEncoding(charset) after stripping one pair of surrounding quotes. When the platform cannot resolve that charset, the underlying ArgumentException is caught and rethrown as InvalidOperationException. It is a runtime, per-response error driven entirely by what the server sent.

Source

Thrown at src/Refit.Newtonsoft.Json/NewtonsoftJsonContentSerializer.cs:172

    {
        var charset = content.Headers.ContentType?.CharSet;
        if (charset is null)
        {
            return null;
        }

        try
        {
            if (charset.Length > QuotePairLength && charset[0] == '"' && charset[^1] == '"')
            {
                charset = charset.Substring(1, charset.Length - QuotePairLength);
            }

            return Encoding.GetEncoding(charset);
        }
        catch (ArgumentException e)
        {
            throw new InvalidOperationException("The character set provided in ContentType is invalid.", e);
        }
    }
}

View on GitHub (pinned to b455f65ecc)

Solutions

1. Wrap response calls in try/catch and, on this exception, re-read the content as the bytes/string and decode with a known Encoding (e.g. Encoding.UTF8) ignoring the header.
2. Intercept the response in a DelegatingHandler and rewrite/normalize Content-Type charset before deserialization.
3. If the charset is legitimate (e.g. a code-page) register the encoding provider at startup: Encoding.RegisterProvider(CodePagesEncodingProvider.Instance).
4. Switch to Refit.SystemTextJson if Newtonsoft charset handling is not required.

Example fix

// before
var result = await api.GetUserAsync(id); // throws on bad charset

// after
UserDto result;
try {
    result = await api.GetUserAsync(id);
} catch (InvalidOperationException ex) when (ex.Message.Contains("character set")) {
    // re-fetch and decode ignoring the header charset
    using var raw = await client.GetAsync($"/users/{id}");
    var body = await raw.Content.ReadAsByteArrayAsync();
    result = JsonConvert.DeserializeObject<UserDto>(Encoding.UTF8.GetString(body));
}

// Pre-validate a charset string before relying on it (if you read it yourself).
static bool IsKnownCharset(string? charset) {
    if (string.IsNullOrWhiteSpace(charset)) return true;
    try { Encoding.GetEncoding(charset.Trim('"')); return true; }
    catch { return false; }
}

try {
    return await api.GetThingAsync(id);
}
catch (InvalidOperationException ex) when (ex.InnerException is ArgumentException && ex.Message.Contains("character set")) {
    // Re-read bytes and decode with a known encoding, ignoring the bad header.
}

When it happens

Trigger: A response arrives with a Content-Type charset that is malformed or unregistered, e.g. 'charset=utf-8-sig', 'charset="utf-8' (unbalanced quote), a vendor label, or a charset absent from the running .NET runtime's registered encodings.

Common situations: A third-party/legacy server emits a non-standard charset; a CDN rewrites headers; a misconfigured reverse proxy injects charset; running on a trimmed AOT build where the encoding provider for the charset was not registered.

Related errors

• Unexpected parameter type in a Multipart request. Parameter
• Sequence contains more than one matching element
• Sequence contains no matching element
• targetInterface must be an Interface
• Method must be defined and have an HTTP Method attribute

AI-assisted analysis of reactiveui/refit@b455f65ecc (2026-08-13). Data as JSON: /api/errors/d29d9be5fc5dbb0c. Report an issue: GitHub.