.NET Core 3.0之Configuration原始碼探究(一)

艾心❤發表於2019-05-13

Configuration總體介紹

微軟在.NET Core裡設計出了全新的配置體系,並以非常靈活、可擴充套件的方式實現。從其原始碼來看,其執行機制大致是,根據其Source,建立一個Builder例項,並會向其新增Provider,在我們使用配置資訊的時候,會從記憶體中獲取相應的Provider例項。

.NET Core採用了統一的呼叫方式來載入不同型別的配置資訊,並通過統一的抽象介面IConfigurationSource對配置源進行管理,這也是剛剛所說的靈活。而其擴充套件性就是我們可以自己自定義新的Provider例項,而不會改變其原來的呼叫方式。接下來的文章將會基於Consul,擴充套件一個新的Provider例項。

在ASP.NET Core 中,我們的應用配置是基於IConfigurationProvider的鍵值對。 我們先看一下思維導圖:

image

基於上圖,我們可以看到主要有鍵值對有多種,分別是:

 

環境變數

命令列引數

各種形式的配置檔案

記憶體物件

使用者自定義擴充套件源

 

核心物件

在介紹.NET Core配置功能之前,先簡要說明一下Microsoft.Extensions.Configuration.Abstractions,該元件抽象了.NET Core的配置功能,並對自定義擴充套件制定了新的標準。以下介紹的四個核心物件全部來自於該元件。

IConfiguration

該介面表示一組鍵/值應用程式配置屬性,應用程式使用配置時的入口物件,.NET Core對其有多種擴充套件,其派生類包括位於統一類庫的IConfigurationSection,以及Microsoft.Extensions.Configuration類庫中的ConfigurationRoot、ConfigurationSection、IConfigurationRoot。我們可以通過DI獲取IConfiguration例項。

它主要有以下三個方法:

  • GetChildren():獲取直接子配置子節
  • GetReloadToken():返回一個IChangeToken,可用於確定何時重新載入配置
  • GetSection(String):獲取指定鍵的子節點

我們來看一下原始碼:

   1:  /// <summary>
   2:      /// Represents a set of key/value application configuration properties.
   3:      /// </summary>
   4:      public interface IConfiguration
   5:      {
   6:          /// <summary>
   7:          /// Gets or sets a configuration value.
   8:          /// </summary>
   9:          /// <param name="key">The configuration key.</param>
  10:          /// <returns>The configuration value.</returns>
  11:          string this[string key] { get; set; }
  12:   
  13:          /// <summary>
  14:          /// Gets a configuration sub-section with the specified key.
  15:          /// </summary>
  16:          /// <param name="key">The key of the configuration section.</param>
  17:          /// <returns>The <see cref="IConfigurationSection"/>.</returns>
  18:          /// <remarks>
  19:          ///     This method will never return <c>null</c>. If no matching sub-section is found with the specified key,
  20:          ///     an empty <see cref="IConfigurationSection"/> will be returned.
  21:          /// </remarks>
  22:          IConfigurationSection GetSection(string key);
  23:   
  24:          /// <summary>
  25:          /// Gets the immediate descendant configuration sub-sections.
  26:          /// </summary>
  27:          /// <returns>The configuration sub-sections.</returns>
  28:          IEnumerable<IConfigurationSection> GetChildren();
  29:   
  30:          /// <summary>
  31:          /// Returns a <see cref="IChangeToken"/> that can be used to observe when this configuration is reloaded.
  32:          /// </summary>
  33:          /// <returns>A <see cref="IChangeToken"/>.</returns>
  34:          IChangeToken GetReloadToken();
  35:      }

通常我們要求配置檔案要有足夠的靈活性,尤其是我們所擴充套件的配置資訊存放在了其他伺服器,當修改的時候我們很需要一套監控功能,以及時靈活的應對配置資訊的修改。現在.NET Core為我們提供了這樣一個功能,我們只需要自定義少量程式碼即可完成配置資訊的同步。這個方法就是GetReloadToken(),其返回值是IChangeToken。此處對配置資訊的同步只做一個引子,後面的文章會詳細說明。

由於ConfigurationRoot、ConfigurationSection聚集於IConfiguration介面,此處也對這兩個類進行討論,方便我們對.NET Core的配置功能有個更加形象的印象。這兩個介面,本質上就是.NET Core關於配置資訊的讀取方式。

XML是使用比較廣泛的一種資料結構,我們在配置XML時,一般會使用根節點、父節點、子節點之類的術語,此處也一樣。

ConfigurationRoot是配置的根節點,也實現了IConfigurationRoot,此介面只有一個方法,其主要功能就是實現對配置資訊的重新載入,另外還包括一個IConfigurationProvider型別的集合屬性。其原始碼如下

   1:  /// <summary>
   2:  /// Represents the root of an <see cref="IConfiguration"/> hierarchy.
   3:  /// </summary>
   4:  public interface IConfigurationRoot : IConfiguration
   5:  {
   6:      /// <summary>
   7:      /// Force the configuration values to be reloaded from the underlying <see cref="IConfigurationProvider"/>s.
   8:      /// </summary>
   9:      void Reload();
  10:   
  11:      /// <summary>
  12:      /// The <see cref="IConfigurationProvider"/>s for this configuration.
  13:      /// </summary>
  14:      IEnumerable<IConfigurationProvider> Providers { get; }
  15:  }

下面是ConfigurationRoot關於Reload()方法的實現

   1:  /// <summary>
   2:  /// Force the configuration values to be reloaded from the underlying sources.
   3:  /// </summary>
   4:  public void Reload()
   5:  {
   6:      foreach (var provider in _providers)
   7:      {
   8:          provider.Load();
   9:      }
  10:   
  11:      RaiseChanged();
  12:  }

通過原始碼我們知道,如果呼叫了Reload()方法,所有型別的Provider都會重新載入。

前面有ConfigurationRoot表示配置的根節點,那麼ConfigurationSection則表示非跟節點,畢竟父節點、子節點都是相對,所以此處使用非根節點。ConfigurationSection繼承於IConfigurationSection,該介面只有三個只讀屬性,分別表示配置資訊的Key、Value以及路徑資訊,需要指出的是,此處的路徑資訊主要指從根節點到當前節點的路徑,以表示當前節點的位置,類似於A:B:C可以表示節點C的位置,其中A、B、C都是ConfigurationSection的Key。以下是ConfigurationSection的原始碼

   1:  /// <summary>
   2:  /// Represents a section of application configuration values.
   3:  /// </summary>
   4:  public interface IConfigurationSection : IConfiguration
   5:  {
   6:      /// <summary>
   7:      /// Gets the key this section occupies in its parent.
   8:      /// </summary>
   9:      string Key { get; }
  10:   
  11:      /// <summary>
  12:      /// Gets the full path to this section within the <see cref="IConfiguration"/>.
  13:      /// </summary>
  14:      string Path { get; }
  15:   
  16:      /// <summary>
  17:      /// Gets or sets the section value.
  18:      /// </summary>
  19:      string Value { get; set; }
  20:  }

IConfigurationBuilder

該介面主要用於建立IConfigurationProvider,其派生類包括Microsoft.Extensions.Configuration.ConfigurationBuilder。其成員包括

兩個只讀屬性:

  • Properties:獲取可用於在IConfigurationBuilder之間共享資料的鍵/值集合
  • Sources:該屬性用於快取不同的配置源,以用於相對應的Provider的建立

兩個方法:

  • Add(IConfigurationSource source):新增IConfigurationSource,並新增到屬性中Sources中
  • Build():該方法遍歷Sources屬性,並呼叫IConfigurationSource的Build()方法,通過獲取Provider集合,最終建立IConfigurationRoot物件

ConfigurationBuilder原始碼如下

   1:  /// <summary>
   2:      /// Used to build key/value based configuration settings for use in an application.
   3:      /// </summary>
   4:      public class ConfigurationBuilder : IConfigurationBuilder
   5:      {
   6:          /// <summary>
   7:          /// Returns the sources used to obtain configuration values.
   8:          /// </summary>
   9:          public IList<IConfigurationSource> Sources { get; } = new List<IConfigurationSource>();
  10:   
  11:          /// <summary>
  12:          /// Gets a key/value collection that can be used to share data between the <see cref="IConfigurationBuilder"/>
  13:          /// and the registered <see cref="IConfigurationProvider"/>s.
  14:          /// </summary>
  15:          public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
  16:   
  17:          /// <summary>
  18:          /// Adds a new configuration source.
  19:          /// </summary>
  20:          /// <param name="source">The configuration source to add.</param>
  21:          /// <returns>The same <see cref="IConfigurationBuilder"/>.</returns>
  22:          public IConfigurationBuilder Add(IConfigurationSource source)
  23:          {
  24:              if (source == null)
  25:              {
  26:                  throw new ArgumentNullException(nameof(source));
  27:              }
  28:   
  29:              Sources.Add(source);
  30:              return this;
  31:          }
  32:   
  33:          /// <summary>
  34:          /// Builds an <see cref="IConfiguration"/> with keys and values from the set of providers registered in
  35:          /// <see cref="Sources"/>.
  36:          /// </summary>
  37:          /// <returns>An <see cref="IConfigurationRoot"/> with keys and values from the registered providers.</returns>
  38:          public IConfigurationRoot Build()
  39:          {
  40:              var providers = new List<IConfigurationProvider>();
  41:              foreach (var source in Sources)
  42:              {
  43:                  var provider = source.Build(this);
  44:                  providers.Add(provider);
  45:              }
  46:              return new ConfigurationRoot(providers);
  47:          }
  48:      }

此處令人感慨頗多,我們最終呼叫 ConfigurationRoot 的建構函式,究其原因是Provider提供了統一的資料訪問方式,不管是基於何種型別的Provider,我們都可以呼叫其Load()方法載入配置項。此外,IConfigurationBuilder本身有很多的擴充套件方法來註冊資料來源,比如AddJsonFile()擴充套件方法。我們來看一下,我們常見的寫法,

   1:  var builder = new ConfigurationBuilder()
   2:   
   3:              .SetBasePath(env.ContentRootPath)
   4:   
   5:              .AddJsonFile("appsettings1.json", false, true)
   6:   
   7:              .AddJsonFile("appsettings2.json", false, true);
   8:   
   9:  Configuration = builder.Build();

IConfigurationSource

該介面表示應用程式配置的鍵值對。其派生類包括Microsoft.Extensions.Configuration.ChainedConfigurationSource、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationSource。另外該派生類還會在檔案類配置場景下依賴Microsoft.Extensions.Configuration.FileExtensions元件。

它是所有配置源的抽象表示,包括JSON、XML、INI、環境變數等等。通過上文我們也知道了,IConfigurationBuilder會註冊多個IConfigurationSource例項。它只有一個方法,就是Build()方法,並返回IConfigurationProvider,由此可見,IConfigurationProvider的建立依賴於IConfigurationSource,這也是一一對應的關係。所有不同的源最終都會轉化成統一的鍵值對錶示。

以下為

   1:  /// <summary>
   2:  /// Represents a source of configuration key/values for an application.
   3:  /// </summary>
   4:  public interface IConfigurationSource
   5:  {
   6:      /// <summary>
   7:      /// Builds the <see cref="IConfigurationProvider"/> for this source.
   8:      /// </summary>
   9:      /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
  10:      /// <returns>An <see cref="IConfigurationProvider"/></returns>
  11:      IConfigurationProvider Build(IConfigurationBuilder builder);
  12:  }

以下是MemoryConfigurationSource的原始碼

   1:  /// <summary>
   2:  /// Represents in-memory data as an <see cref="IConfigurationSource"/>.
   3:  /// </summary>
   4:  public class MemoryConfigurationSource : IConfigurationSource
   5:  {
   6:      /// <summary>
   7:      /// The initial key value configuration pairs.
   8:      /// </summary>
   9:      public IEnumerable<KeyValuePair<string, string>> InitialData { get; set; }
  10:   
  11:      /// <summary>
  12:      /// Builds the <see cref="MemoryConfigurationProvider"/> for this source.
  13:      /// </summary>
  14:      /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
  15:      /// <returns>A <see cref="MemoryConfigurationProvider"/></returns>
  16:      public IConfigurationProvider Build(IConfigurationBuilder builder)
  17:      {
  18:          return new MemoryConfigurationProvider(this);
  19:      }
  20:  }

IConfigurationProvider

通過上文的介紹,我們可以知道IConfigurationProvider是統一的對外介面,對使用者提供配置的查詢、重新載入等功能。其派生類包括Microsoft.Extensions.Configuration.ConfigurationProvider、Microsoft.Extensions.Configuration.ChainedConfigurationProvider、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationProvider。另外該派生類還會在檔案類配置場景下依賴Microsoft.Extensions.Configuration.FileExtensions元件。

以下是Microsoft.Extensions.Configuration.ConfigurationProvider的原始碼:

   1:  /// <summary>
   2:  /// Base helper class for implementing an <see cref="IConfigurationProvider"/>
   3:  /// </summary>
   4:  public abstract class ConfigurationProvider : IConfigurationProvider
   5:  {
   6:      private ConfigurationReloadToken _reloadToken = new ConfigurationReloadToken();
   7:   
   8:      /// <summary>
   9:      /// Initializes a new <see cref="IConfigurationProvider"/>
  10:      /// </summary>
  11:      protected ConfigurationProvider()
  12:      {
  13:          Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
  14:      }
  15:   
  16:      /// <summary>
  17:      /// The configuration key value pairs for this provider.
  18:      /// </summary>
  19:      protected IDictionary<string, string> Data { get; set; }
  20:   
  21:      /// <summary>
  22:      /// Attempts to find a value with the given key, returns true if one is found, false otherwise.
  23:      /// </summary>
  24:      /// <param name="key">The key to lookup.</param>
  25:      /// <param name="value">The value found at key if one is found.</param>
  26:      /// <returns>True if key has a value, false otherwise.</returns>
  27:      public virtual bool TryGet(string key, out string value)
  28:          => Data.TryGetValue(key, out value);
  29:   
  30:      /// <summary>
  31:      /// Sets a value for a given key.
  32:      /// </summary>
  33:      /// <param name="key">The configuration key to set.</param>
  34:      /// <param name="value">The value to set.</param>
  35:      public virtual void Set(string key, string value)
  36:          => Data[key] = value;
  37:   
  38:      /// <summary>
  39:      /// Loads (or reloads) the data for this provider.
  40:      /// </summary>
  41:      public virtual void Load()
  42:      { }
  43:     
  44:      /// <summary>
  45:      /// Returns the list of keys that this provider has.
  46:      /// </summary>
  47:      /// <param name="earlierKeys">The earlier keys that other providers contain.</param>
  48:      /// <param name="parentPath">The path for the parent IConfiguration.</param>
  49:      /// <returns>The list of keys for this provider.</returns>
  50:      public virtual IEnumerable<string> GetChildKeys(
  51:          IEnumerable<string> earlierKeys,
  52:          string parentPath)
  53:      {
  54:          var prefix = parentPath == null ? string.Empty : parentPath + ConfigurationPath.KeyDelimiter;
  55:   
  56:          return Data
  57:              .Where(kv => kv.Key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
  58:              .Select(kv => Segment(kv.Key, prefix.Length))
  59:              .Concat(earlierKeys)
  60:              .OrderBy(k => k, ConfigurationKeyComparer.Instance);
  61:      }
  62:   
  63:      private static string Segment(string key, int prefixLength)
  64:      {
  65:          var indexOf = key.IndexOf(ConfigurationPath.KeyDelimiter, prefixLength, StringComparison.OrdinalIgnoreCase);
  66:          return indexOf < 0 ? key.Substring(prefixLength) : key.Substring(prefixLength, indexOf - prefixLength);
  67:      }
  68:   
  69:      /// <summary>
  70:      /// Returns a <see cref="IChangeToken"/> that can be used to listen when this provider is reloaded.
  71:      /// </summary>
  72:      /// <returns></returns>
  73:      public IChangeToken GetReloadToken()
  74:      {
  75:          return _reloadToken;
  76:      }
  77:   
  78:      /// <summary>
  79:      /// Triggers the reload change token and creates a new one.
  80:      /// </summary>
  81:      protected void OnReload()
  82:      {
  83:          var previousToken = Interlocked.Exchange(ref _reloadToken, new ConfigurationReloadToken());
  84:          previousToken.OnReload();
  85:      }
  86:   
  87:      /// <summary>
  88:      /// Generates a string representing this provider name and relevant details.
  89:      /// </summary>
  90:      /// <returns> The configuration name. </returns>
  91:      public override string ToString() => $"{GetType().Name}";
  92:  }

通過原始碼,我們可以知道ConfigurationProvider以字典型別快取了多個Provider物件,有需要的時候,從記憶體中獲取即可,配置的載入通過Load()方法實現,在ConfigurationRoot裡我們介紹了其Reload,並且說明其方法是在迴圈呼叫ConfigurationProvider的Load方法,但是此處只提供了一個虛方法,其目的是要交給其他具體的Provider,比如環境變數、JSON、XML等,這些具體的Provider可以從相應的配置源中獲取配置資訊。所有的子節點KEY通過GetChildKeys方法實現,其重新載入方式通過ConfigurationReloadToken例項完成。

另外需要說明一下,在ConfigurationProvider建構函式裡,對字典進行了初始化,並同時設定了字典Key不受大小寫限制,這是一個需要注意的細節。

Configuration元件結構

通過檢視.NET配置功能的原始碼,所有依賴均基於Microsoft.Extensions.Configuration.Abstractions,在其上有一層實現,即Microsoft.Extensions.Configuration,其內部也多數是抽象實現,並提供了多個虛方法交給其派生元件,比如環境變數、命令列引數、各種檔案型配置等,當然各種檔案型配置還要依賴Microsoft.Extensions.Configuration.FileExtensions元件。

以下是.NET Core 3.0預覽版裡的Configuration各個元件的結構圖:

peizhi1

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