在开发中，将系统日志集中管理并支持实时搜索是提升运维效率的重要手段。本文将介绍如何在 ASP.NET Core 项目中通过 HttpClient 与 Elasticsearch 进行集成，实现日志的自动记录、索引和查询功能。

技术架构概览

• o ASP.NET Core：构建 Web API 服务
• o HttpClient：与 Elasticsearch REST 接口通信
• o Elasticsearch：用于日志数据的存储与检索
• o 中间件（Middleware）：拦截请求并记录日志
• o Basic Auth：保障 Elasticsearch 安全访问

一、配置文件设置

首先，在 appsettings.json 中配置 Elasticsearch 的地址和认证信息：

{
  "Elasticsearch": {
    "Url": "https://es-host:9200",
    "Username": "username",
    "Password": "password"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information"
    }
  },
  "AllowedHosts": "*"
}

二、创建 Elasticsearch 服务类

创建 ElasticsearchService.cs 类，封装对 Elasticsearch 的基本操作，如写入文档和查询数据：

public class ElasticsearchService
{
    private readonly HttpClient _client;
    private readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);

    public ElasticsearchService(HttpClient client, IConfiguration config)
    {
        var uri = config["Elasticsearch:Url"];
        var username = config["Elasticsearch:Username"];
        var password = config["Elasticsearch:Password"];

        client.BaseAddress = new Uri(uri);
        var byteArray = Encoding.ASCII.GetBytes(#34;{username}:{password}");
        client.DefaultRequestHeaders.Authorization =
            new AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));

        _client = client;
    }

    public async Task<bool> IndexAsync<T>(T document, string indexName, string? id = null)
    {
        var url = id != null ? #34;/{indexName}/_doc/{id}" : #34;/{indexName}/_doc";
        var content = new StringContent(JsonSerializer.Serialize(document, _jsonOptions), Encoding.UTF8, "application/json");

        var response = await _client.PostAsync(url, content);
        return response.IsSuccessStatusCode;
    }

    public async Task<List<T>> SearchAsync<T>(object query, string indexName)
    {
        var content = new StringContent(JsonSerializer.Serialize(query, _jsonOptions), Encoding.UTF8, "application/json");

        var response = await _client.PostAsync(#34;/{indexName}/_search", content);
        response.EnsureSuccessStatusCode();

        var json = await response.Content.ReadAsStringAsync();
        using var doc = JsonDocument.Parse(json);

        var hits = doc.RootElement.GetProperty("hits").GetProperty("hits");
        var result = new List<T>();

        foreach (var hit in hits.EnumerateArray())
        {
            var source = hit.GetProperty("_source").GetRawText();
            var obj = JsonSerializer.Deserialize<T>(source, _jsonOptions);
            if (obj != null) result.Add(obj);
        }

        return result;
    }
}

三、注册服务

在 Program.cs 中注册 HttpClient 和 ElasticsearchService：

builder.Services.AddHttpClient<ElasticsearchService>();

四、定义日志实体类

创建一个用于记录请求日志的实体类 ApiLogEntity：

public class ApiLogEntity
{
    public string Name { get; set; }
    public string Ip { get; set; }
    public string Url { get; set; }
    public string ReqMethod { get; set; }
    public DateTime OpTime { get; set; }
    public string Account { get; set; }
    public int StatusCode { get; set; }
    public string ResponseBody { get; set; }
}

五、编写日志记录中间件

通过自定义中间件拦截请求，并将日志写入 Elasticsearch：

public class RequestLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestLoggingMiddleware> _logger;
    private readonly ElasticsearchService _esService;

    public RequestLoggingMiddleware(RequestDelegate next, ILogger<RequestLoggingMiddleware> logger, ElasticsearchService esService)
    {
        _next = next;
        _logger = logger;
        _esService = esService;
    }

    public async Task Invoke(HttpContext context)
    {
        // 判断是否启用日志记录
        if (!App.Configuration["AppLogEntity"].ToBool())
        {
            await _next(context);
            return;
        }

        var request = context.Request;

        if (!request.Path.Value.Contains("api"))
        {
            await _next(context);
            return;
        }

        request.EnableBuffering();
        var originalBodyStream = context.Response.Body;
        await using var responseBody = new MemoryStream();
        context.Response.Body = responseBody;

        try
        {
            await _next(context);

            context.Response.Body.Seek(0, SeekOrigin.Begin);
            var responseText = await new StreamReader(context.Response.Body).ReadToEndAsync();
            context.Response.Body.Seek(0, SeekOrigin.Begin);

            var entity = new ApiLogEntity
            {
                Name = Environment.MachineName,
                Ip = context.Connection.RemoteIpAddress?.ToString(),
                Url = request.Path + request.QueryString,
                ReqMethod = request.Method,
                OpTime = DateTime.Now,
                Account = "wx-" + App.User.FindFirst("UserID")?.Value,
                StatusCode = context.Response.StatusCode,
                ResponseBody = responseText
            };

            await _esService.IndexAsync(entity, "jltlogs");
        }
        finally
        {
            await responseBody.CopyToAsync(originalBodyStream);
            context.Response.Body = originalBodyStream;
        }
    }
}

注册中间件：

app.UseMiddleware<RequestLoggingMiddleware>();

六、测试接口

1. 写入日志文档

• o 请求路径：POST /search/index
• o Body 示例：

{
  "title": "Test Document",
  "description": "Elasticsearch integration with HttpClient"
}