C# 如何轮询 GetStreamAsync api 调用

Question

我有以下代码调用银行 api，并将响应转换为 object。

public static async Task<ExchangeModel> LoadExchange(string currency, string date)
{
    string url = "here is the bank's api url";

    var streamTask = await _clientPolicy.LinearHttpRetry.ExecuteAsync(
        () => _client.GetStreamAsync(url));
    var deserialized = await JsonSerializer.DeserializeAsync<Root>(await streamTask);
    var rate = deserialized.ExchangeModel.FirstOrDefault(r => r.Currency == currency);
    return rate;
}

我想添加 polly 以便在失败时重试 api 调用。 为此，我创建了一个策略客户端，但我不知道如何检查GetStreamAsync是否成功，因为它是System.IO.Stream并且它没有成功状态或其他东西。

public AsyncRetryPolicy<System.IO.Stream> LinearHttpRetry { get; }

public ClientPolicy()
{
    LinearHttpRetry = Policy.HandleResult<System.IO.Stream>(
        res => !res.IsSuccessStatusCode).
        WaitAndRetryAsync(5, retryAttempts => TimeSpan.FromSeconds(3));
}

在这个例子中，我保留了它.res.IsSuccessStatusCode但在我的例子中没有这样的参数。

Answer 1

您可以执行以下“技巧” ，而不是直接调用GetStreamAsync ：

var response = await _client.GetAsync(url, HttpCompletionOption.ResponseHeadersRead);
//TODO: Check response status code then
using var stream = await response.Content.ReadAsStreamAsync();

---

首先，您需要像这样更改您的策略定义：

public IAsyncPolicy<HttpResponseMessage> LinearHttpRetry { get; }

public ClientPolicy()
{
    LinearHttpRetry = Policy
        .HandleResult<HttpResponseMessage>(res => !res.IsSuccessStatusCode)
        .WaitAndRetryAsync(5, _ => TimeSpan.FromSeconds(3));
}

然后您还需要调整使用情况

public static async Task<ExchangeModel> LoadExchange(string currency, string date)
{
    string url = "here is the bank's api url";

    var response = await _clientPolicy.LinearHttpRetry.ExecuteAsync(
        async () => await _client.GetAsync(url, HttpCompletionOption.ResponseHeadersRead));

    using var stream = await response.Content.ReadAsStreamAsync();
    var deserialized = await JsonSerializer.DeserializeAsync<Root>(stream);
    var rate = deserialized.ExchangeModel.FirstOrDefault(r => r.Currency == currency);
    return rate;
}