fix: get version from X-Influxdb-Version header (#297)

Author: bednar

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## 4.0.0 [unreleased]
 
+### Bug Fixes
+1. [#297](https://github.com/influxdata/influxdb-client-csharp/pull/297): Get version from `X-Influxdb-Version` header
+
 ## 4.0.0-rc3 [2022-03-04]
 
 ### Features

Client.Core/Internal/AbstractRestClient.cs

@@ -49,7 +49,7 @@ private string GetVersion(RestResponse responseHttp)
             Arguments.CheckNotNull(responseHttp, "responseHttp");
 
             var value = responseHttp.Headers
-                .Where(header => header.Name.Equals("X-Influxdb-Version"))
+                .Where(header => header.Name.Equals("X-Influxdb-Version", StringComparison.OrdinalIgnoreCase))
                 .Select(header => header.Value.ToString())
                 .FirstOrDefault();
 

Client.Test/InfluxDbClientTest.cs

@@ -319,5 +319,15 @@ public void HttpClientIsDisposed()
 
             Assert.AreEqual(true, disposed);
         }
+
+        [Test]
+        public async Task VersionIsNotCaseSensitive()
+        {
+            MockServer.Given(Request.Create().WithPath("/ping").UsingGet())
+                .RespondWith(Response.Create().WithStatusCode(204)
+                    .WithHeader("x-influxdb-version", "2.0.0"));
+
+            Assert.AreEqual("2.0.0", await _client.VersionAsync());
+        }
     }
 }

Client/InfluxDBClient.cs

@@ -443,7 +443,7 @@ public async Task<string> VersionAsync()
         }
 
         /// <summary>
-        /// The readiness of the InfluxDB 2.0.
+        /// Check the readiness of InfluxDB Server at startup. It is not supported by InfluxDB Cloud. 
         /// </summary>
         /// <returns>return null if the InfluxDB is not ready</returns>
         public async Task<Ready> ReadyAsync()