feat: support passing HttpClient

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 1.4.0 [unreleased]
 
+### Features
+
+1. [#174](https://github.com/InfluxCommunity/influxdb3-csharp/pull/174): Support passing HttpClient to InfluxDBClient.
+
 ## 1.3.0 [2025-08-12]
 
 ### Features

Client.Test/InfluxDBClientWriteTest.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
+using System.Net.Http;
 using System.Threading.Tasks;
 using InfluxDB3.Client.Config;
 using InfluxDB3.Client.Write;
@@ -490,4 +491,57 @@ public void WriteNoSyncTrueNotSupported()
                     "Server doesn't support write with NoSync=true (supported by InfluxDB 3 Core/Enterprise servers only)."));
         });
     }
+
+    [Test]
+    public async Task TestSetHttpClient()
+    {
+        MockServer
+            .Given(Request.Create().WithPath("/api/v2/write").UsingPost())
+            .RespondWith(Response.Create().WithStatusCode(HttpStatusCode.OK));
+
+        var httpClient = new HttpClient();
+        httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("my-user-agent");
+        httpClient.DefaultRequestHeaders.Add("X-Client-ID", "123");
+
+        _client = new InfluxDBClient(new ClientConfig
+        {
+            Host = MockServerUrl,
+            Token = "my-token",
+            Database = "my-database",
+            HttpClient = httpClient
+        });
+
+        await _client.WriteRecordAsync("mem,tag=a field=1");
+        var requests = MockServer.LogEntries.ToList();
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(requests[0].RequestMessage.Headers?["User-Agent"].First(), Is.EqualTo("my-user-agent"));
+            Assert.That(requests[0].RequestMessage.Headers["X-Client-ID"].First(), Is.EqualTo("123"));
+        }
+        Assert.Pass();
+    }
+
+    [Test]
+    public void TestCheckHttpClientStillOpen()
+    {
+        MockServer
+            .Given(Request.Create().WithPath("/test").UsingGet())
+            .RespondWith(
+                Response.Create()
+                    .WithStatusCode(HttpStatusCode.OK)
+                    .WithBody("Still ok"));
+
+        var httpClient = new HttpClient(new HttpClientHandler());
+        _client = new InfluxDBClient(new ClientConfig
+        {
+            Host = MockServerUrl,
+            Token = "my-token",
+            Database = "my-database",
+            HttpClient = httpClient
+        });
+        _client.Dispose();
+
+        var httpResponseMessage = httpClient.Send(new HttpRequestMessage(HttpMethod.Get, "test"));
+        Assert.That(httpResponseMessage.Content.ReadAsStringAsync().Result, Is.EqualTo("Still ok"));
+    }
 }

Client.Test/Internal/FlightSqlClientTest.cs

@@ -22,7 +22,7 @@ public void SetUp()
             Timeout = TimeSpan.FromSeconds(45)
         };
 
-        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateAndConfigureHttpClient(config));
+        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateOrGetHttpClient(config));
     }
 
     [TearDown]
@@ -108,7 +108,7 @@ public void HeadersMetadataFromConfig()
             }
         };
 
-        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateAndConfigureHttpClient(config));
+        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateOrGetHttpClient(config));
 
         var prepareHeadersMetadata =
             _flightSqlClient.PrepareHeadersMetadata(new Dictionary<string, string>());
@@ -139,7 +139,7 @@ public void HeadersMetadataFromRequestArePreferred()
             }
         };
 
-        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateAndConfigureHttpClient(config));
+        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateOrGetHttpClient(config));
 
         var prepareHeadersMetadata =
             _flightSqlClient.PrepareHeadersMetadata(new Dictionary<string, string> { { "X-Tracing-Id", "258" } });
@@ -170,7 +170,7 @@ public void UserAgentHeaderNotChanged()
             }
         };
 
-        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateAndConfigureHttpClient(config));
+        _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateOrGetHttpClient(config));
 
         var prepareHeadersMetadata =
             _flightSqlClient.PrepareHeadersMetadata(new Dictionary<string, string> { { "user-agent", "another/user-agent" } });
@@ -199,7 +199,7 @@ public void TestGrpcCallOptions()
         };
 
         Assert.DoesNotThrow(() =>
-            _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateAndConfigureHttpClient(config)));
+            _flightSqlClient = new FlightSqlClient(config, InfluxDBClient.CreateOrGetHttpClient(config)));
     }
 
 }

Client.Test/Internal/RestClientTest.cs

@@ -294,7 +294,7 @@ public void Timeout()
 
     private void CreateAndConfigureRestClient(ClientConfig config)
     {
-        _httpClient = InfluxDBClient.CreateAndConfigureHttpClient(config);
+        _httpClient = InfluxDBClient.CreateOrGetHttpClient(config);
         _client = new RestClient(config, _httpClient);
     }
 

Client.Test/MockHttpsServerTest.cs

@@ -4,7 +4,7 @@
 
 namespace InfluxDB3.Client.Test;
 
-public class MockHttpsServerTest
+public abstract class MockHttpsServerTest
 {
     internal WireMockServer MockHttpsServer;
     internal string MockHttpsServerUrl;

Client.Test/MockServerTest.cs

@@ -3,7 +3,7 @@
 
 namespace InfluxDB3.Client.Test;
 
-public class MockServerTest
+public abstract class MockServerTest
 {
     internal WireMockServer MockServer, MockProxy;
     internal string MockServerUrl, MockProxyUrl;

Client/Config/ClientConfig.cs

@@ -2,6 +2,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Net;
+using System.Net.Http;
 using System.Web;
 using InfluxDB3.Client.Write;
 
@@ -26,6 +27,7 @@ namespace InfluxDB3.Client.Config;
 /// <item>- Proxy: The HTTP proxy URL. Default is not set.</item>
 /// <item>- WriteOptions: Write options.</item>
 /// <item>- QueryOptions Query options.</item>
+/// <item>- HttpClient: The HttpClient will be used for Write and Query apis.</item>
 /// </list>
 ///
 /// <para>If you want create client with custom options, you can use the following code:</para>
@@ -200,6 +202,13 @@ public string Host
     /// </summary>
     public QueryOptions QueryOptions { get; set; }
 
+    /// <summary>
+    /// User-defined HttpClient.
+    /// Influxdb client will add an authentication header and base url to HttpClient. The rest is up to the users.
+    /// Users will be responsible for closing the HttpClient.
+    /// </summary>
+    public HttpClient? HttpClient { get; set; }
+
     internal void Validate()
     {
         if (string.IsNullOrEmpty(Host))

Client/InfluxDBClient.cs

@@ -343,7 +343,7 @@ public InfluxDBClient(ClientConfig config)
             config.Validate();
 
             _config = config;
-            _httpClient = CreateAndConfigureHttpClient(_config);
+            _httpClient = CreateOrGetHttpClient(_config);
             FlightSqlClient = new FlightSqlClient(config: _config, httpClient: _httpClient);
             _restClient = new RestClient(config: _config, httpClient: _httpClient);
             _gzipHandler = new GzipHandler(config.WriteOptions != null ? config.WriteOptions.GzipThreshold : 0);
@@ -840,7 +840,12 @@ await _restClient
 
         public void Dispose()
         {
-            _httpClient.Dispose();
+            // _config.HttpClient == null means HttpClient is created by the library, not from the user.
+            // so the client will be responsible for disposing of the HttpClient.
+            if (_config.HttpClient == null)
+            {
+                _httpClient.Dispose();
+            }
             FlightSqlClient.Dispose();
             _disposed = true;
         }
@@ -876,7 +881,28 @@ private static StringBuilder ToLineProtocolBody(IEnumerable<object?> data, Write
             return sb;
         }
 
-        internal static HttpClient CreateAndConfigureHttpClient(ClientConfig config)
+        internal static HttpClient CreateOrGetHttpClient(ClientConfig config)
+        {
+            var httpClient = config.HttpClient;
+            if (httpClient == null)
+            {
+                httpClient = CreateHttpClient(config);
+            }
+
+            if (httpClient.BaseAddress == null)
+            {
+                httpClient.BaseAddress = new Uri(config.Host);
+            }
+
+            if (!string.IsNullOrEmpty(config.Token))
+            {
+                _setAuthenticationHeader(httpClient, config);
+            }
+
+            return httpClient;
+        }
+
+        private static HttpClient CreateHttpClient(ClientConfig config)
         {
             var handler = new HttpClientHandler();
             if (handler.SupportsRedirectConfiguration)
@@ -916,17 +942,17 @@ internal static HttpClient CreateAndConfigureHttpClient(ClientConfig config)
             {
                 Timeout = config.Timeout
             };
-
             client.DefaultRequestHeaders.UserAgent.ParseAdd(AssemblyHelper.GetUserAgent());
-            if (!string.IsNullOrEmpty(config.Token))
-            {
-                string authScheme = string.IsNullOrEmpty(config.AuthScheme) ? "Token" : config.AuthScheme!;
-                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(authScheme, config.Token);
-            }
 
             return client;
         }
 
+        private static void _setAuthenticationHeader(HttpClient httpClient, ClientConfig config)
+        {
+            var authScheme = string.IsNullOrEmpty(config.AuthScheme) ? "Token" : config.AuthScheme!;
+            httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(authScheme, config.Token);
+        }
+
         private static string OptionMessage(string property)
         {
             return $"Please specify the '{property}' as a method parameter or use default configuration " +