AuthorizationFormHtmlParser: улучшить обработку ошибок

#625

VkNet/Infrastructure/Authorization/ImplicitFlow/AuthorizationFormHtmlParser.cs

@@ -6,6 +6,7 @@
 using JetBrains.Annotations;
 using VkNet.Abstractions.Utils;
 using VkNet.Exception;
+using VkNet.Model;
 using VkNet.Utils;
 
 namespace VkNet.Infrastructure.Authorization.ImplicitFlow
@@ -30,6 +31,16 @@ public async Task<VkHtmlFormResult> GetFormAsync(Uri url)
 		{
 			var response = await _restClient.PostAsync(url, Enumerable.Empty<KeyValuePair<string, string>>());
 
+			if (!response.IsSuccess)
+			{
+				throw new VkAuthorizationException(response.Message);
+			}
+
+			if (Utilities.TryDeserializeObject<VkAuthError>(response.Value, out var authError))
+			{
+				throw new VkAuthorizationException(authError.ErrorDescription);
+			}
+
 			var doc = new HtmlDocument();
 			doc.LoadHtml(response.Value);
 			var formNode = GetFormNode(doc);

VkNet/Model/VkAuthError.cs

@@ -0,0 +1,42 @@
+using System;
+using Newtonsoft.Json;
+
+namespace VkNet.Model
+{
+	/// <summary>
+	/// Authorization error.
+	/// </summary>
+	[Serializable]
+	public class VkAuthError
+	{
+		/// <summary>
+		/// Error.
+		/// </summary>
+		[JsonProperty("error")]
+		public string Error { get; set; }
+
+		/// <summary>
+		/// Error type.
+		/// </summary>
+		[JsonProperty("error_type")]
+		public string ErrorType { get; set; }
+
+		/// <summary>
+		/// Error description.
+		/// </summary>
+		[JsonProperty("error_description")]
+		public string ErrorDescription { get; set; }
+
+		/// <summary>
+		/// Captcha id.
+		/// </summary>
+		[JsonProperty("captcha_sid")]
+		public ulong? CaptchaSid { get; set; }
+
+		/// <summary>
+		/// Captcha image Uri.
+		/// </summary>
+		[JsonProperty("captcha_img")]
+		public Uri CaptchaImg { get; set; }
+	}
+}

VkNet/Utils/Utilities.cs

@@ -118,5 +118,26 @@ public static string SerializeToJson<T>(T @object)
 
 			return result == "null" ? null : result;
 		}
+
+		/// <summary>
+		/// Deserializes JSON for the specified .NET type. A return value indicates whether deserialization succeeded.
+		/// </summary>
+		/// <param name="json"> The JSON to deserialize. </param>
+		/// <param name="result"> Deserialized object. </param>
+		/// <typeparam name="T"> Type for deserialization. </typeparam>
+		/// <returns></returns>
+		public static bool TryDeserializeObject<T>(string json, out T result)
+		{
+			try
+			{
+				result = JsonConvert.DeserializeObject<T>(json);
+				return true;
+			}
+			catch
+			{
+				result = default;
+				return false;
+			}
+		}
 	}
 }