add default User-Agent header when not set

Author: rose-a

src/GraphQL.Client/GraphQLHttpClient.cs

@@ -2,7 +2,9 @@
 using System.Collections.Concurrent;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Threading;
 using System.Threading.Tasks;
 using GraphQL.Client.Abstractions;
@@ -57,6 +59,10 @@ public GraphQLHttpClient(GraphQLHttpClientOptions options, IGraphQLWebsocketJson
             Options = options ?? throw new ArgumentNullException(nameof(options));
             JsonSerializer = serializer ?? throw new ArgumentNullException(nameof(serializer), "please configure the JSON serializer you want to use");
             HttpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
+
+            if (!HttpClient.DefaultRequestHeaders.UserAgent.Any())
+                HttpClient.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue(GetType().Assembly.GetName().Name, GetType().Assembly.GetName().Version.ToString()));
+
             _graphQlHttpWebSocket = new GraphQLHttpWebSocket(GetWebSocketUri(), this);
         }