DeepLClientOptions.ServerUrl don't work with base url path

[vernou]

Describe the bug

In my company, we use a reverse-proxy to access external API like the DeepL API.
So our intern URL to access the Deepl API is 'https://external-api.company.com/deepl/', next the reverse proxy forwards the query to 'https://api.deepl.com/'.

To Reproduce

I use 'DeepLClientOptions.ServerUrl' to specify our custom url :

var options = new DeepLClientOptions { ServerUrl = "https://external-api.company.com/deepl/" };
var authKey = "***";
var client = new DeepLClient(authKey, options);

var translation = await client.TranslateTextAsync(
    "Hello, world!",
    LanguageCode.English,
    LanguageCode.French
);

But the http request url is 'https://external-api.company.com/v2/translate'.

Expected behavior

I expect the http request url to be 'https://external-api.company.com/deepl/v2/translate'

Additional context

The class Uri follows the RFC 3986 - Uniform Resource Identifier (URI): Generic Syntax, so when a relative uri starts by /, then the relative path is considered to a absolute path.

See RFC 3986 - Section 5.2.2 : Transform References for more details

In this example :

Combine("https://external-api.company.com/deepl/", "/v2/translate");
Combine("https://external-api.company.com/deepl/", "v2/translate");

void Combine(string serverUrl,string relativePath)
{
    var serverUri = new Uri(serverUrl);
    var uri = new Uri(serverUri, relativePath);

    Console.WriteLine($"{serverUrl} + {relativePath}");
    Console.WriteLine(uri);
    Console.WriteLine();
}

Output :

https://external-api.company.com/deepl/ + /v2/translate
https://external-api.company.com/v2/translate

https://external-api.company.com/deepl/ + v2/translate
https://external-api.company.com/deepl/v2/translate

In the DeepL SDK, all relative uris starts by / likes in Translator.cs :

using var responseMessage = await _client
        .ApiPostAsync("/v2/translate", cancellationToken, bodyParams.Concat(textParams)).ConfigureAwait(false);

So the base path in the url reverse-proxy is ignored.

---

Can you remove the starting / in all relative uris?
So it's possible to use internal api gateway or reverse proxy.

If you agree, I can do the pull request.

[JanEbbing]

Thanks for this super detailed report! I am making a merge request, just double checking with the team if this would be considered a breaking change or not

[vernou]

This issue was fixed by b07280e.

[JanEbbing]

Thanks, our release to nuget is currently broken, it will be in 1.20.0 . Will fix today

[JanEbbing]

Released now :)

[vernou]

"DeepL.net@1.20.0" works as expected, thank you.