initial commit; very basic REST client

Foxcord/Rest/DiscordRestClient.User.cs

@@ -0,0 +1,9 @@
+using Foxcord.Discord;
+
+namespace Foxcord.Rest;
+
+public partial class DiscordRestClient
+{
+    public Task<User> GetUserAsync(ulong id) => RequestAsync<User>(HttpMethod.Get, $"/users/{id}");
+    public Task<User> GetMeAsync() => RequestAsync<User>(HttpMethod.Get, "/users/@me");
+}

Foxcord/Rest/DiscordRestClient.cs

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+using System.Net.Http.Headers;
+using Foxcord.Serialization;
+
+namespace Foxcord.Rest;
+
+public partial class DiscordRestClient
+{
+    public string UserAgent { get; private init; } = "DiscordBot (https://codeberg.org/u1f320/Foxcord, v1)";
+
+    private readonly HttpClient _client = new();
+    private readonly string _token;
+    private readonly string _baseUrl = "https://discord.com/api/v10";
+
+    public DiscordRestClient(string token, string? userAgent = null, string? baseUrl = null)
+    {
+        _token = token;
+        if (userAgent != null) UserAgent = userAgent;
+        if (baseUrl != null) _baseUrl = baseUrl;
+    }
+
+    public async Task<TResponse> RequestAsync<TResponse>(HttpMethod method, string path,
+        IReadOnlyDictionary<string, string>? extraHeaders = null) where TResponse : class
+    {
+        var request = CreateRequest(method, path, body: null, extraHeaders);
+        var resp = await Send(request);
+        return await resp.Content.ReadAsJsonAsync<TResponse>() ??
+               throw new FoxcordException("HTTP response was unexpectedly null");
+    }
+
+    public async Task<TResponse> RequestAsync<TRequest, TResponse>(HttpMethod method, string path, TRequest body,
+        IReadOnlyDictionary<string, string>? extraHeaders = null)
+        where TRequest : class where TResponse : class
+    {
+        var request = CreateRequest(method, path, body, extraHeaders);
+        var resp = await Send(request);
+        return await resp.Content.ReadAsJsonAsync<TResponse>() ??
+               throw new FoxcordException("HTTP response was unexpectedly null");
+    }
+
+    public async Task RequestAsync<TRequest>(HttpMethod method, string path, TRequest body,
+        IReadOnlyDictionary<string, string>? extraHeaders = null) where TRequest : class =>
+        await Send(CreateRequest(method, path, body, extraHeaders));
+
+    public async Task RequestAsync(HttpMethod method, string path,
+        IReadOnlyDictionary<string, string>? extraHeaders = null) =>
+        await Send(CreateRequest(method, path, body: null, extraHeaders));
+
+    // TODO: rate limits
+    private async Task<HttpResponseMessage> Send(HttpRequestMessage request)
+    {
+        var resp = await _client.SendAsync(request);
+        if (!resp.IsSuccessStatusCode)
+        {
+            var error = await resp.Content.ReadAsJsonAsync<RestException.ErrorResponse>();
+            throw new RestException(resp.StatusCode, error!);
+        }
+
+        return resp;
+    }
+
+    private HttpRequestMessage CreateRequest(HttpMethod method, string path, object? body,
+        IReadOnlyDictionary<string, string>? extraHeaders = null)
+    {
+        var request = new HttpRequestMessage(method, _baseUrl + path);
+        request.Headers.Add("Authorization", _token);
+        if (body != null)
+        {
+            request.Content = new ReadOnlyMemoryContent(JsonSerializer.SerializeToUtf8Bytes(body));
+            request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json", "utf-8");
+        }
+
+        if (extraHeaders != null)
+            foreach (var (k, v) in extraHeaders)
+                request.Headers.Add(k, v);
+
+        return request;
+    }
+}

Foxcord/Rest/RestException.cs

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+using System.Net;
+using System.Text.Json.Nodes;
+using Foxcord.Serialization;
+
+namespace Foxcord.Rest;
+
+public class RestException : Exception
+{
+    public HttpStatusCode StatusCode { get; private init; }
+    public int Code { get; private init; }
+    public new string Message { get; private init; }
+    public string? Errors { get; private init; }
+
+    internal RestException(HttpStatusCode statusCode, ErrorResponse response)
+    {
+        StatusCode = statusCode;
+        Code = response.Code;
+        Message = response.Message;
+        Errors = response.Errors?.ToJsonString();
+    }
+    
+    public enum ErrorCode
+    {
+        GeneralError = 0
+    }
+
+    internal record ErrorResponse(int Code, string Message, JsonObject? Errors);
+}