feat: Add default HTTP custom header

Author: HofmeisterAn

src/Docker.DotNet/DockerClient.cs

@@ -393,12 +393,13 @@ internal HttpRequestMessage PrepareRequest(HttpMethod method, string path, IQuer
             request.Version = new Version(1, 1);
             request.Headers.Add("User-Agent", UserAgent);
 
-            if (headers != null)
+            var customHeaders = headers == null
+                ? Configuration.DefaultHttpRequestHeaders
+                : Configuration.DefaultHttpRequestHeaders.Concat(headers);
+
+            foreach (var header in customHeaders)
             {
-                foreach (var header in headers)
-                {
-                    request.Headers.Add(header.Key, header.Value);
-                }
+                request.Headers.Add(header.Key, header.Value);
             }
 
             if (data != null)

src/Docker.DotNet/DockerClientConfiguration.cs

@@ -1,17 +1,27 @@
 using System;
+using System.Collections.Generic;
 using System.Runtime.InteropServices;
 using System.Threading;
 
 namespace Docker.DotNet
 {
     public class DockerClientConfiguration : IDisposable
     {
-        public DockerClientConfiguration(Credentials credentials = null, TimeSpan defaultTimeout = default)
-            : this(GetLocalDockerEndpoint(), credentials, defaultTimeout)
+        public DockerClientConfiguration(
+            Credentials credentials = null,
+            TimeSpan defaultTimeout = default,
+            TimeSpan namedPipeConnectTimeout = default,
+            IReadOnlyDictionary<string, string> defaultHttpRequestHeaders = null)
+            : this(GetLocalDockerEndpoint(), credentials, defaultTimeout, namedPipeConnectTimeout, defaultHttpRequestHeaders)
         {
         }
 
-        public DockerClientConfiguration(Uri endpoint, Credentials credentials = null, TimeSpan defaultTimeout = default)
+        public DockerClientConfiguration(
+            Uri endpoint,
+            Credentials credentials = null,
+            TimeSpan defaultTimeout = default,
+            TimeSpan namedPipeConnectTimeout = default,
+            IReadOnlyDictionary<string, string> defaultHttpRequestHeaders = null)
         {
             if (endpoint == null)
             {
@@ -23,29 +33,25 @@ public DockerClientConfiguration(Uri endpoint, Credentials credentials = null, T
                 throw new ArgumentException("Default timeout must be greater than -1", nameof(defaultTimeout));
             }
 
-            if (credentials == null)
-            {
-                credentials = new AnonymousCredentials();
-            }
-
-            if (defaultTimeout == default)
-            {
-                defaultTimeout = TimeSpan.FromSeconds(100);
-            }
-
             EndpointBaseUri = endpoint;
-            Credentials = credentials;
-            DefaultTimeout = defaultTimeout;
-            NamedPipeConnectTimeout = TimeSpan.FromMilliseconds(100);
+            Credentials = credentials ?? new AnonymousCredentials();
+            DefaultTimeout = TimeSpan.Equals(default, defaultTimeout) ? TimeSpan.FromSeconds(100) : defaultTimeout;
+            NamedPipeConnectTimeout = TimeSpan.Equals(default, namedPipeConnectTimeout) ? TimeSpan.FromMilliseconds(100) : namedPipeConnectTimeout;
+            DefaultHttpRequestHeaders = defaultHttpRequestHeaders ?? new Dictionary<string, string>();
         }
 
+        /// <summary>
+        /// Gets the collection of default HTTP request headers.
+        /// </summary>
+        public IReadOnlyDictionary<string, string> DefaultHttpRequestHeaders { get; }
+
         public Uri EndpointBaseUri { get; }
 
         public Credentials Credentials { get; }
 
         public TimeSpan DefaultTimeout { get; }
 
-        public TimeSpan NamedPipeConnectTimeout { get; set; }
+        public TimeSpan NamedPipeConnectTimeout { get; }
 
         public DockerClient CreateClient(Version requestedApiVersion = null)
         {