Blazor Server中ILoggerProvider配置注入异常求助

我遇到了一个诡异的问题：自定义的BlobLoggerProvider接收的BlobLoggerOptions所有属性均为null，但另一个FileLoggerProvider却能正常读取配置。更奇怪的是，如果把BlobLoggerProvider的参数换成FileLoggerOptions，哪怕它带有[ProviderAlias("Blob")]特性，居然会读取到appSettings.json里"File"节点的配置。

以下是相关代码：

临时硬编码的BlobLoggerProvider构造函数（为保证运行） #

public BlobLoggerProvider(BlobLoggerOptions options)
{
    Options = options;
    // 传入的options所有属性都是null，临时硬编码赋值
    Options = new BlobLoggerOptions
    {
        Path = "log/{yyyy-MM-dd}.txt",
        Interval = "day",
        AzureStorage = "UseDevelopmentStorage=true"
    };
    Interval = GetInterval(Options.Interval);

    Start();
}

正常运行的FileLoggerProvider #

[ProviderAlias("File")]
public class FileLoggerProvider : LoggerProviderBase
{
    protected FileLoggerOptions? Options;

    public FileLoggerProvider(IOptionsMonitor<FileLoggerOptions> options) : this(options.CurrentValue)
    {
        SettingsChangeToken = options.OnChange(opt => { Options = opt; });
    }

    public FileLoggerProvider(FileLoggerOptions options)
    {
        Options = options;
        Interval = GetInterval(options.Interval);

        Start();
    }
}

异常的BlobLoggerProvider #

[ProviderAlias("Blob")]
public class BlobLoggerProvider : LoggerProviderBase
{
    protected BlobLoggerOptions Options;

    public BlobLoggerProvider(IOptionsMonitor<BlobLoggerOptions> options) : this(options.CurrentValue)
    {
        SettingsChangeToken = options.OnChange(opt => { Options = opt; });
    }

    public BlobLoggerProvider(BlobLoggerOptions options)
    {
        Options = options;

        Start();
    }
}

appSettings.json配置节点 #

"Blob": {
    "Path": "logs/{yyyy-MM-dd}.txt",
    "Interval": "Day",
    "AzureStorage": "UseDevelopmentStorage=true"
},

"File": {
    "Path": "C:/temp/{yyyy-MM-dd}.txt",
    "Interval": "day"
},

配置类与Setup实现 #

public class FileLoggerOptions
{
    public string? Path { get; set; }
    public string? Interval { get; set; }
}

internal class FileLoggerOptionsSetup : ConfigureFromConfigurationOptions<FileLoggerOptions>
{
    public FileLoggerOptionsSetup(ILoggerProviderConfiguration<FileLoggerProvider> providerConfiguration)
        : base(providerConfiguration.Configuration)
    {
    }
}

public class BlobLoggerOptions
{
    public string? Path { get; set; }
    public string? Interval { get; set; }
    public string? AzureStorage { get; set; }
}

internal class BlobLoggerOptionsSetup : ConfigureFromConfigurationOptions<BlobLoggerOptions>
{
    // 此处为问题核心
    public BlobLoggerOptionsSetup(ILoggerProviderConfiguration<BlobLoggerOptions> providerConfiguration)
        : base(providerConfiguration.Configuration)
    {
    }
}

服务注册代码 #

public static class LoggingBuilderExtensions
{
    public static ILoggingBuilder AddFileLogger(this ILoggingBuilder builder)
    {
        builder.AddConfiguration();

        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<ILoggerProvider,
            FileLoggerProvider>());
        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<FileLoggerOptions>,
            FileLoggerOptionsSetup>());
        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IOptionsChangeTokenSource<FileLoggerOptions>,
            LoggerProviderOptionsChangeTokenSource<FileLoggerOptions, FileLoggerProvider>>());
        return builder;
    }

    public static ILoggingBuilder AddAzureBlobLogger(this ILoggingBuilder builder)
    {
        builder.AddConfiguration();

        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<ILoggerProvider,
            BlobLoggerProvider>());

        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<BlobLoggerOptions>,
            BlobLoggerOptionsSetup>());
        builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IOptionsChangeTokenSource<BlobLoggerOptions>,
            LoggerProviderOptionsChangeTokenSource<BlobLoggerOptions, BlobLoggerProvider>>());

        return builder;
    }
}

问题原因与修复方案 #

核心问题 #

BlobLoggerOptionsSetup的构造函数泛型参数使用错误：ILoggerProviderConfiguration<T>中的T必须是LoggerProvider类型，而非Options类型。该接口的作用是通过LoggerProvider上的[ProviderAlias]特性匹配appSettings中的配置节点，你错误地传入了Options类型，导致框架无法找到对应的配置节点，返回null。

对比正常的FileLoggerOptionsSetup，它使用ILoggerProviderConfiguration<FileLoggerProvider>，才能正确匹配"File"节点的配置。

修复步骤 #

修改BlobLoggerOptionsSetup的构造函数，将泛型参数从BlobLoggerOptions改为BlobLoggerProvider：

internal class BlobLoggerOptionsSetup : ConfigureFromConfigurationOptions<BlobLoggerOptions>
{
    // 替换泛型参数为BlobLoggerProvider
    public BlobLoggerOptionsSetup(ILoggerProviderConfiguration<BlobLoggerProvider> providerConfiguration)
        : base(providerConfiguration.Configuration)
    {
    }
}

修改后，框架会通过BlobLoggerProvider上的[ProviderAlias("Blob")]特性，正确匹配appSettings中的"Blob"节点，BlobLoggerOptions就能正常绑定配置值。

额外说明 #

为什么换成FileLoggerOptions能读取到"File"的配置？因为FileLoggerOptionsSetup的构造参数是ILoggerProviderConfiguration<FileLoggerProvider>，会固定匹配"File"节点，和注册时关联的LoggerProvider无关，才会出现这种交叉读取的诡异情况。

内容的提问来源于stack exchange，提问作者David Thielen