C# 实现Http请求-优快云博客

在现代应用中，HTTP 请求是与 API 服务交互的核心方式。本文将系统讲解 C# 实现 HTTP 请求的多种方案，涵盖从基础用法到企业级高性能实践（支持 .NET 5+）。

一、基础 HTTP 请求方法

1. HttpClient 基础用法

// GET 请求示例
async Task<string> GetDataAsync(string url)
{
    using var httpClient = new HttpClient();
    HttpResponseMessage response = await httpClient.GetAsync(url);
    response.EnsureSuccessStatusCode();
    return await response.Content.ReadAsStringAsync();
}

// POST 请求示例
async Task PostDataAsync(string url, object data)
{
    using var httpClient = new HttpClient();
    var json = JsonSerializer.Serialize(data);
    var content = new StringContent(json, Encoding.UTF8, "application/json");
    var response = await httpClient.PostAsync(url, content);
    response.EnsureSuccessStatusCode();
}

⚠️ 警告：不要每次请求创建新 HttpClient！这会导致：

端口耗尽 (TIME_WAIT 状态)
DNS 更新延迟
连接池无法复用

二、高性能 HTTP 客户端实践

1. IHttpClientFactory 最佳实践

// 1. Startup 注册服务
services.AddHttpClient("FinanceAPI", client => {
    client.BaseAddress = new Uri("https://api.finance.com");
    client.Timeout = TimeSpan.FromSeconds(15);
    client.DefaultRequestHeaders.Add("Accept", "application/json");
});

// 2. 控制器中使用
public class DataController : Controller
{
    private readonly IHttpClientFactory _factory;
    
    public DataController(IHttpClientFactory factory) => _factory = factory;

    public async Task<IActionResult> GetStockData()
    {
        var client = _factory.CreateClient("FinanceAPI");
        var response = await client.GetAsync("/stocks/MSFT");
        // ...
    }
}

2. HTTP/2 连接复用

var handler = new SocketsHttpHandler
{
    PooledConnectionLifetime = TimeSpan.FromMinutes(5),
    EnableMultipleHttp2Connections = true
};

var client = new HttpClient(handler)
{
    DefaultRequestVersion = HttpVersion.Version20,
    DefaultVersionPolicy = HttpVersionPolicy.RequestVersionExact
};

3. 流式处理大响应

// 避免大响应阻塞内存
async Task ProcessLargeResponse(string url)
{
    using var client = new HttpClient();
    using var response = await client.GetAsync(url, HttpCompletionOption.ResponseHeadersRead);
    using var stream = await response.Content.ReadAsStreamAsync();
    
    await using var buffer = new BufferedStream(stream);
    using var reader = new StreamReader(buffer);
    
    while (!reader.EndOfStream)
    {
        var line = await reader.ReadLineAsync();
        ProcessLine(line);  // 逐行处理
    }
}

三、高级场景实现

1. 自定义重试策略

// 指数退避重试器
async Task<T> ExecuteWithRetry<T>(Func<Task<T>> action, int maxRetries = 3)
{
    int retryCount = 0;
    while (true)
    {
        try
        {
            return await action();
        }
        catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.TooManyRequests)
        {
            if (retryCount++ >= maxRetries) throw;
            var delay = TimeSpan.FromSeconds(Math.Pow(2, retryCount));
            await Task.Delay(delay);
        }
    }
}

// 使用示例
var data = await ExecuteWithRetry(() => GetDataAsync("https://unstable-api.com/data"));

2. 动态请求头签名

// 安全 API 调用签名
async Task SendSignedRequest(string url)
{
    var handler = new CustomSignatureHandler();
    var client = new HttpClient(handler);
    // ... 正常调用
}

class CustomSignatureHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancelToken)
    {
        // 1. 获取时间戳
        var timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
        
        // 2. 生成签名
        var signData = $"{request.Method}{request.RequestUri}{timestamp}{API_SECRET}";
        var signature = HMACSHA256.Hash(signData);
        
        // 3. 添加安全头
        request.Headers.Add("X-Timestamp", timestamp.ToString());
        request.Headers.Add("X-Signature", Convert.ToBase64String(signature));
        
        return await base.SendAsync(request, cancelToken);
    }
}

四、性能优化策略

1. 连接管理优化

参数	推荐值	作用
`MaxConnectionsPerServer`	50-100	控制单个主机最大连接数
`PooledConnectionIdleTimeout`	1-2 分钟	空闲连接保持时间
`PooledConnectionLifetime`	5-10 分钟	连接最大存活时间

2. 响应处理优化技巧

// 高效 JSON 反序列化
async Task<T> ParseJsonResponse<T>(HttpResponseMessage response)
{
    // 使用流式 API 避免大对象分配
    await using var stream = await response.Content.ReadAsStreamAsync();
    return await JsonSerializer.DeserializeAsync<T>(stream, new JsonSerializerOptions
    {
        PropertyNameCaseInsensitive = true,
        DefaultBufferSize = 8192  // 8KB 缓冲区
    });
}

// 使用 ArrayPool 处理二进制响应
async Task ProcessBinaryResponse(string url)
{
    var response = await _httpClient.GetAsync(url);
    var buffer = ArrayPool<byte>.Shared.Rent(1024 * 64);
    
    try
    {
        await using var stream = await response.Content.ReadAsStreamAsync();
        int bytesRead;
        while ((bytesRead = await stream.ReadAsync(buffer)) > 0)
        {
            ProcessChunk(new ReadOnlySpan<byte>(buffer, 0, bytesRead));
        }
    }
    finally
    {
        ArrayPool<byte>.Shared.Return(buffer);
    }
}

五、常见问题解决方案

1. DNS 更新问题

// 强制刷新 DNS 缓存
var handler = new SocketsHttpHandler
{
    PooledConnectionLifetime = TimeSpan.FromMinutes(5),  // 设置连接生命周期
    PooledConnectionIdleTimeout = TimeSpan.FromSeconds(30)
};

2. 证书验证处理

// 开发环境忽略证书错误（生产环境禁用！）
var handler = new HttpClientHandler
{
    ServerCertificateCustomValidationCallback = (_, _, _, _) => true
};

3. 多部分表单上传

async Task UploadFile(string url, string filePath)
{
    using var content = new MultipartFormDataContent();
    using var fileStream = File.OpenRead(filePath);
    
    content.Add(new StreamContent(fileStream), "file", "data.zip");
    content.Add(new StringContent("2024-report"), "description");
    
    var response = await _httpClient.PostAsync(url, content);
    response.EnsureSuccessStatusCode();
}

六、性能监控与诊断

1. HttpClient 指标监控

# 查看连接池状态
dotnet-counters monitor -n MyApp System.Net.Http

2. 请求跟踪

// 添加日志记录器
services.AddHttpClient("LoggingClient")
    .ConfigurePrimaryHttpMessageHandler(() => new LoggingHandler(new SocketsHttpHandler()));

class LoggingHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var stopwatch = Stopwatch.StartNew();
        try 
        {
            return await base.SendAsync(request, cancellationToken);
        }
        finally
        {
            _logger.LogInformation($"{request.Method} {request.RequestUri} took {stopwatch.ElapsedMilliseconds}ms");
        }
    }
}

最佳实践总结：