.NET Core 6异步流式API消费异常：结果批量返回而非实时输出

我正在构建一个可实时返回就绪结果的API，目标如下：

• 实现一个可在结果就绪时立即输出的API端点
• 构建一个消费应用，可在结果就绪时立即处理数据

我的API调用另一个服务的代码如下：

[HttpGet]
[Route("stream")]
public async IAsyncEnumerable<ReturnModel> GetStream()
{        
    // 单独声明请求消息变量，因为后续Post请求也要用
    var request = new HttpRequestMessage
    {
        Method = HttpMethod.Get,
        RequestUri = new Uri(the_url_that_allowed_streaming_of_data)
    };
                
    var client = new HttpClient();
    client.DefaultRequestHeaders.Add("Accept", "application/json"); // Post请求需要这个头
    
    var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
    
    var stream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);
    using var reader = new StreamReader(stream);
    while (!reader.EndOfStream)
    {                
        var message = await reader.ReadLineAsync();
        Console.WriteLine(message); // 用于检查是否能快速获取数据
        
        // 在这里处理message
        
        yield return new ReturnModel { ... };
    }
}

在浏览器访问该URL（stream）时，响应是批量输出的（多个yield结果一起返回而非逐个返回）。我在控制台应用中使用以下代码消费该API，也出现了同样的批量返回问题：

static async Task ConsumeStream(string url)
{
    var client = new HttpClient();
        
    var request = new HttpRequestMessage
    {
        Method = HttpMethod.Get,
        RequestUri = new Uri(url),
    };

    var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
    var stream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);
    IAsyncEnumerable<ReturnModel> items = System.Text.Json.JsonSerializer
        .DeserializeAsyncEnumerable<ReturnModel>(
            stream,
            new JsonSerializerOptions
            {
                PropertyNameCaseInsensitive = true,
                DefaultBufferSize = 10 // 不管设什么值，结果都一样
            });

    var lineCtr = 0;
    await foreach (var item in items)
    {
        lineCtr++;
        Console.WriteLine($"Line: {lineCtr} ---- Time: {DateTime.Now.ToLongTimeString()} ---- Content: {item.Content}"); // 不会立即输出
    }   
}

我尝试了另一种方法，但情况更糟，似乎要等待所有数据加载完成后才会处理并输出到控制台：

// 所有Console.WriteLine会一次性显示在窗口中
static async Task ConsumeStreamV2(string url)
{
    var client = new HttpClient();
        
    var request = new HttpRequestMessage
    {
        Method = HttpMethod.Get,
        RequestUri = new Uri(url),
    };

    var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
    var stream = await response.Content.ReadAsStreamAsync();
    
    using var reader = new StreamReader(stream);
    while (!reader.EndOfStream)
    {
        var message = await reader.ReadLineAsync();
        Console.WriteLine($"Time: {DateTime.Now.ToLongTimeString()} ---- Content: {message}");
    }

}

我遗漏了什么？

内容的提问来源于stack exchange，提问作者von v.