DiscordApi/Discord.API/Rest/RestClient.cs

using System.Text.Json;

namespace Discord.API.Rest;

internal class RestClient{

    private HttpClient httpClient;

    public RestClient(string base_url, string api_key){
        httpClient = new HttpClient(){
            BaseAddress=new Uri(base_url)
        };
        httpClient.DefaultRequestHeaders.Add("Authorization", $"Bot {api_key}");
        httpClient.DefaultRequestHeaders.Add("User-Agent", $"DiscordBot ({Discord.API.StaticProperties.LibraryWebsite}, {Discord.API.StaticProperties.LibraryVersion})");
    }

    public async Task<RestResponse<GetGatewayResponse>> GetGateway() =>
        await Get("gateway", s => JsonSerializer.Deserialize(s, SourceGenerationContext.Default.GetGatewayResponse));

    private async Task<RestResponse<T>> Get<T>(string url, Func<string, T> deserializer){
        try{
            HttpResponseMessage resp = await httpClient.GetAsync(url);
            if(resp.IsSuccessStatusCode){
                return new RestSuccessResponse<T>(
                    deserializer.Invoke(await resp.Content.ReadAsStringAsync()),
                    resp.StatusCode
                );
            }else{
                return new RestErrorResponse<T>(
                    JsonSerializer.Deserialize(await resp.Content.ReadAsStringAsync(), SourceGenerationContext.Default.RestError),
                    resp.StatusCode
                );
            }
        }catch (Exception ex){
            return new RestFailResponse<T>(ex);
        }
    }

}