Add GetErrorMessageAsync() extensions for exception error handling.

HISTORY.md

@@ -1,3 +1,6 @@
+## v2.0.2
+* Added GetErrorMessageAsync() extension method.
+
 ## v2.0.1
 * Production ready. Models and APIs finalized.
 

README.md

@@ -93,6 +93,22 @@ The `order` object returned by the trading engine will have similar values to th
 * [`CoinbaseProWebSocket`](https://docs.pro.coinbase.com/?r=1#websocket-feed) - [Examples](https://github.com/bchavez/Coinbase.Pro/blob/master/Source/Coinbase.Tests/IntegrationTests/WebSocketTests.cs)
 
 
+### Error Handling
+When errors occur after calling an API, **Coinbase Pro** delivers error messages in the response body of an failed HTTP call. To get the error message of a failed API call, first wrap your call in a `try/catch` statement and handle the `Exception ex`. The `GetErrorMessageAsync()` extension method will read the response body of the failed HTTP call as shown below:
+```csharp
+try
+{
+   var order = await client.Orders.PlaceLimitOrderAsync(
+      OrderSide.Buy, "BTCX-USDX", size: 1, limitPrice: 5000m);
+}
+catch (Exception ex)
+{
+   var errorMsg = await ex.GetErrorMessageAsync();
+   Console.WriteLine(errorMsg);
+}
+//OUTPUT: "Product not found"
+```
+
 ### Pagination
 Some **Coinbase Pro** APIs are [paginable](https://docs.pro.coinbase.com/?r=1#pagination). However, **Coinbase Pro**'s paging can be [a little confusing](https://docs.pro.coinbase.com/?r=1#pagination) at first. So, let's review. Consider the following diagram below that illustrates the `Current Point In Time` over a paginable set of data with an item size of 5 items per page:
 ```

Source/Coinbase.Pro/CoinbaseProClient.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Globalization;
+using System.Threading;
 using System.Threading.Tasks;
+using Coinbase.Pro.Models;
 using Flurl.Http;
 using Flurl.Http.Configuration;
 
@@ -93,4 +95,28 @@ async Task SetHeaders(HttpCall http)
          settings.BeforeCallAsync = SetHeaders;
       }
    }
+
+   public static class ExtensionsForExceptions
+   {
+      /// <summary>
+      /// Parses the response body of the failed HTTP call return any error status messages.
+      /// </summary>
+      public static async Task<string> GetErrorMessageAsync(this FlurlHttpException ex)
+      {
+         if( ex is null ) return null;
+
+         var error = await ex.GetResponseJsonAsync<JsonResponse>()
+            .ConfigureAwait(false);
+
+         return error?.Message;
+      }
+
+      /// <summary>
+      /// Parses the response body of the failed HTTP call return any error status messages.
+      /// </summary>
+      public static Task<string> GetErrorMessageAsync(this Exception ex)
+      {
+         return GetErrorMessageAsync(ex as FlurlHttpException);
+      }
+   }
 }

Source/Coinbase.Tests/IntegrationTests/GeneralTests.cs

@@ -93,6 +93,24 @@ public async Task create_order4()
          o.Dump();
       }
 
+      [Test]
+      public async Task create_order5_with_error()
+      {
+         try
+         {
+            var o = await this.client.Orders.PlaceLimitOrderAsync(
+               OrderSide.Buy, "BTCX-USD", size: 1, limitPrice: 5000m);
+
+            //o.Dump();
+         }
+         catch (Exception ex)
+         {
+            var errorMsg = await ex.GetErrorMessageAsync();
+            errorMsg.Dump();
+         }
+
+      }
+
       [Test]
       public async Task get_fills1()
       {