C#•2y ago

Generic api base client

I'm trying to implement a generic api base client using Polly and System.Net.Http.Formatting. I have this GetAsync<T>(string url) function here

public async Task<RestResponse<T>> GetAsync<T>(string url)
{
    var response = await _retryPolicy.ExecuteAsync(async () => await _httpClient.GetAsync(url));
    
    if (!response.IsSuccessStatusCode)
    {
        throw new Exception($"Failed to call API endpoint. Status code: {response.StatusCode}");
    }

    //var content = await response.Content.ReadAsByteArrayAsync();
    var content2 = await response.Content.ReadAsAsync<T>();
    return new RestResponse<T>(response.StatusCode, content2);
}

public async Task<RestResponse<T>> GetAsync<T>(string url)
{
    var response = await _retryPolicy.ExecuteAsync(async () => await _httpClient.GetAsync(url));
    
    if (!response.IsSuccessStatusCode)
    {
        throw new Exception($"Failed to call API endpoint. Status code: {response.StatusCode}");
    }

    //var content = await response.Content.ReadAsByteArrayAsync();
    var content2 = await response.Content.ReadAsAsync<T>();
    return new RestResponse<T>(response.StatusCode, content2);
}

RestResponse just encapsulates the data and the statuscode and _retryPolicy is an IAsyncPolicy from Polly.

public class RestResponse<T>
{
    public RestResponse(HttpStatusCode statusCode, T data)
    {
        StatusCode = statusCode;
        Data = data;
    }

    public HttpStatusCode StatusCode { get; set; }

    public T Data { get; set; }
}

public class RestResponse<T>
{
    public RestResponse(HttpStatusCode statusCode, T data)
    {
        StatusCode = statusCode;
        Data = data;
    }

    public HttpStatusCode StatusCode { get; set; }

    public T Data { get; set; }
}

Now the question is: Could I somehow use this function when T is byte[]? If I do that in the current state, then I get an error, that the media type of the response data is application/pdf and no MediaTypeFormatter exists for that.

1 Reply

HimmDawgOP•2y ago

Ok, I stumbled upon a solution. ReadAsAsync<T> has an overload that accepts an IEnumerable<MediaTypeFormatters> and an IFormatterLogger. Then I wrote a custom media type formatter for byte[]

public class ByteArrayMediaTypeFormatter : MediaTypeFormatter
{
    public ByteArrayMediaTypeFormatter()
    {
        base.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/pdf"));
    }

    public override bool CanReadType(Type type)
    {
        if (type == typeof(byte[]))
        {
            return true;
        }

        return false;
    }

    public override bool CanWriteType(Type type)
    {
        if (type == typeof(byte[]))
        {
            return true;
        }

        return false;
    }

    public async override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
    {
        if (value is byte[] bytes)
        {
            await writeStream.WriteAsync(bytes, 0, bytes.Length);
        }
        else
        {
            throw new ArgumentException($"Cannot serialize type for {nameof(value)}");
        }
    }

    public async override Task<object> ReadFromStreamAsync(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)
    {
        return await content.ReadAsByteArrayAsync();
    }
}

public class ByteArrayMediaTypeFormatter : MediaTypeFormatter
{
    public ByteArrayMediaTypeFormatter()
    {
        base.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/pdf"));
    }

    public override bool CanReadType(Type type)
    {
        if (type == typeof(byte[]))
        {
            return true;
        }

        return false;
    }

    public override bool CanWriteType(Type type)
    {
        if (type == typeof(byte[]))
        {
            return true;
        }

        return false;
    }

    public async override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
    {
        if (value is byte[] bytes)
        {
            await writeStream.WriteAsync(bytes, 0, bytes.Length);
        }
        else
        {
            throw new ArgumentException($"Cannot serialize type for {nameof(value)}");
        }
    }

    public async override Task<object> ReadFromStreamAsync(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)
    {
        return await content.ReadAsByteArrayAsync();
    }
}

And that gives me the exact bytes as with ReadAsByteArrayAsync()

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Generic api base client