Send image with HttpClient to POST WebApi and consume the data

Question

My HttpClient sends the image with PostAsync. I am not really sure what to do now since this is my first REST Api and I can't really adapt the things I sorted out in other posts yet. Hopefully you guys can help me out and can give me a direction.

public async Task SendImage(string fullFileName, string fileName)
    {            
        var client = new HttpClient();
        client.BaseAddress = new Uri("http://x.x.x.x");

        var content = new StringContent(fullFileName, Encoding.UTF8, "image/jpg");
        HttpResponseMessage response = await client.PostAsync($"/values/file/{fileName}", content);
    }

I have several questions about the POST function. First of all I can successfully access it with PostMan and the fileName is correct.

How do I read the image data and write it to a file?

[HttpPost("file/{fileName}")]
public void Upload(string fileName)
{        
    Debug.Write(fileName);
}

EDIT:

I setup my environment and I can now send a post via the internet to my published Web Api. On my app just nothing happens. For now I just tried to get something of a message to work on but I dont getting one.

[HttpPost("file/{fileName}")]
public HttpResponseMessage Upload(UploadedFile fileName)
{
    Debug.Write(fileName);
    if (!ModelState.IsValid)
    {

    }
    if (fileName == null)
    {

    }

    string destinationPath = Path.Combine(@"C:\", fileName.FileFullName);
    System.IO.File.WriteAllBytes(destinationPath, fileName.Data);
    HttpResponseMessage rm = new HttpResponseMessage();
    rm.StatusCode = HttpStatusCode.OK;
    return rm;
}

Aman B · Accepted Answer · 2018-12-12 11:30:14Z

1

1.Your controller should look like this:

//For .net core 2.1
[HttpPost]
public IActionResult Index(List<IFormFile> files)
{
    //Do something with the files here. 
    return Ok();
}

//For previous versions

[HttpPost]
public IActionResult Index()
{
    var files = Request.Form.Files;
    //Do something with the files here. 
    return Ok();
}

2.To upload a file you can also use Multipart content:

        public async Task UploadImageAsync(Stream image, string fileName)
        {
            HttpContent fileStreamContent = new StreamContent(image);
            fileStreamContent.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("form-data") { Name = "file", FileName = fileName };
            fileStreamContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/octet-stream");
            using (var client = new HttpClient())
            using (var formData = new MultipartFormDataContent())
            {
                formData.Add(fileStreamContent);
                var response = await client.PostAsync(url, formData);
                return response.IsSuccessStatusCode;
            }
         }

3.If you are uploading large files you should consider streaming the files instead, you can read about it here

edited Dec 12, 2018 at 11:30

answered Dec 12, 2018 at 11:05

Aman B

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1 Comment

Judah Gabriel Himango Over a year ago

Adding the ContentDisposition and ContentType, as you describe, finally helped solve my issue. Thank you!

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

You're going fine until you're trying to retrieve the image data, I'm afraid.

According to your question:

How do I read the image data and write it to a file?

All you want to do is getting the file's data and its file name and sending it to your service.

I would personally create an UploadedFile class on both sides (client and service side), having the file's name and its data, so:

public class UploadedFile
{
    public string FileFullName { get; set; }
    public byte[] Data { get; set; }

    public UploadedFile(string filePath)
    {
        FileFullName = Path.GetFileName(Normalize(filePath));
        Data = File.ReadAllBytes(filePath);
    }

    private string Normalize(string input)
    {
        return new string(input
                .Normalize(System.Text.NormalizationForm.FormD)
                .Replace(" ", string.Empty)
                .ToCharArray()
                .Where(c => CharUnicodeInfo.GetUnicodeCategory(c) != UnicodeCategory.NonSpacingMark)
                .ToArray());
    }
}

Then you will need, for example, the NewtonSoft's JsonConvert in order to serialize the object and send it through.

So now you would be able to send your data async:

public async Task SendDataAsync(string fullFilePath)
{
    if (!File.Exists(fullFilePath))
        throw new FileNotFoundException();
    var data = JsonConvert.SerializeObject(new UploadedFile(fullFilePath));
    using (var client = new WebClient())
    {
        client.Headers.Add(HttpRequestHeader.ContentType, "application/json");
        await client.UploadStringTaskAsync(new Uri("http://localhost:64204/api/upload/"), "POST", data);
    }
}

Now, make sure you correctly handle the request on the server side. If for whatever reason the parameters doesn't match it won't enter into the method (remember having the same model/class - UploadedFile on the service as well).

On the service, just change the arguments of your method and perform something "like this":

[HttpPost]
public HttpResponseMessage Upload(UploadedFile file)
{
    if (!ModelState.IsValid)
        ...
        
    if (file == null)
        ...
    string destinationPath = Path.Combine(_whateverPath, file.FileFullName);
    File.WriteAllBytes(destinationPath, file.Data);
}

Hope it helped you having an idea about what to do and what you're actually doing wrong. I've exposed something similar based in my experience.

EDIT: I've actually uploaded an example with both sides working: a simple .NET Core console app which retrieves a file and sends it through POST and a basic WebAPI2 service with a simple controller to retrieve the data. Both ready to go and tested working! Download it here.

Enjoy.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 12, 2018 at 11:23

Gonzo345

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10 Comments

user8393563 Over a year ago

I'll give it a shot right now. Thanks for your effort!

user8393563 Over a year ago

Now I have an FileNotFoundException. Thats interesting.

Gonzo345 Over a year ago

@paulvoelker Where are you getting the FileNotFoundException? If you're getting it on client side, review you're passing the full file path to the constructor, or try performing a File.Exists(path) . Debugging will tell, probably.

user8393563 Over a year ago

Well, I do check this. I've removed the referenced from Normalize and now I am getting a DirectoryNotFoundException. Debugging is kind of hart since I only can test it on my physical iPhone.

Gonzo345 Over a year ago

@paulvoelker Keep going! I've updated my solution to check if file doesn't exist in first instance. Good luck and I know it could seem more complex than your original example but it will allow you to upload "anything". If you finally get it and found my solution helpful, I would appreciate you marking it as solution.

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