使用 HttpClient 处理响应值

Question

I'm implementing a service that makes API calls to an external service using HttpClient . One of these calls in particular does not always return the same answer that is expected. Pratically:

this is my call:

using (HttpClientHandler handler = new HttpClientHandler { Credentials = new NetworkCredential(key, "") })
using (HttpClient client = new HttpClient(handler))
{
    client.Timeout = TimeSpan.FromMilliseconds(Timeout.Infinite);
    HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, url);
    using (HttpResponseMessage response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead))
    {
        using (Stream body = await response.Content.ReadAsStreamAsync())
        {
            using (StreamReader reader = new StreamReader(body))
            {
                string read = string.Empty;
                while (!reader.EndOfStream)
                {
                    read += reader.ReadLine();
                }

                return JsonObject.Parse(read);
            }
        }
    }

this is the aspected response body object:

{
    "id" : 15,
    "key" : "API_KEY",
    "status" : "successful",
    "sandbox" : true,
    "created_at" : "2013-10-27T13:41:00Z",
    "finished_at" : "2013-10-27T13:41:13Z",
    "source_file" : {"id":2,"name":"testfile.pdf","size":90571},
    "target_files" : [{"id":3,"name":"testfile.pptx","size":15311}],
    "target_format" : "png",
    "credit_cost" : 1
}

where the status parameter is successful and the target_files parameter is an array of objects .

Sometimes however, the answer basically comes back saying that it hasn't finished converting yet (this API is a files conversion service), with this type of body:

{
    "id" : 15,
    "key" : "API_KEY",
    "status" : "converting",
    "sandbox" : true,
    "created_at" : "2013-10-27T13:41:00Z",
    "finished_at" : "2013-10-27T13:41:13Z",
    "source_file" : {"id":2,"name":"testfile.pdf","size":90571},
    "target_files" : [{}],
    "target_format" : "png",
    "credit_cost" : 0
}

where the status parameter is converting and the target_files parameter is empty.

There is a way to manage the call in order to return the object of the response but only when the status parameter is successfull ? Thanks

Answer 1

Some apis take a wait=1 parameter or something similar to wait. Otherwise, you'd have to poll (likely a different url).

Details should be available from your API documentation.

Answer 2

As suggested, solved polling the request: (the client is instantiated at the scope level)

for (int attempt = 0; attempt < maxAttempts; attempt++)
{
    using (HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, url))
    {
        TimeSpan delay = default;
        using (HttpResponseMessage response = await _client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false))
        {
            if (response.IsSuccessStatusCode)
            {
                using (HttpContent content = response.Content)
                {
                    string data = await content.ReadAsStringAsync().ConfigureAwait(false);
                    JsonValue value = JsonObject.Parse(data);
                    JsonValue status = value["status"] ?? string.Empty;
                    string statusString = status != null ? (string)status : string.Empty;

                    if (!string.IsNullOrEmpty(status) && statusString.Equals("successful", StringComparison.InvariantCultureIgnoreCase))
                        return value;
                }
            }

            delay = response.Headers.RetryAfter?.Delta ?? TimeSpan.FromSeconds(3);
        }

        await Task.Delay(delay);
    }
}