Question 86664 in ASP.NET Question posted in
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File format validation – Asp.net

How can I write a code in the Asp.net Core project to get the format of the photo file and accept only the jpg format and not any other format?
The code I wrote was this, but it didn’t work

        pro.ItemId = pro.Id;
     

        if (Product.Picture?.Length > 0)
        {
            string filepath = Path.Combine(Directory.GetCurrentDirectory(),
                "wwwroot",
                "image",
                pro.Id + Path.GetExtension(Product.Picture.FileName));
            // string Image = @"filepath";
            string Format = Path.GetExtension(filepath);
            if (Format == "jpg")
            {
                using (var stream = new FileStream(filepath, FileMode.Create))
                {
                    Product.Picture.CopyTo(stream);
                }
            }
            else
            {
                ModelState.AddModelError("Picture", "لطفا تصویر را با فرمت jpg انتخاب کنید.");
            }
        }
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3

Answers


  1. 0

    I think you misunderstood string interpolation. Instead of string Image = @"filepath"; you probably wanted to do string Image = $"{filepath}"; but that would just be the same as string Image = filepath; and you’d be creating a second variable that would be holding the same value as filepath.

    Instead, try removing that line and just do string Format = Path.GetExtension(filepath);

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  2. 0

    You can retrieve uploaded Content Type (MIME) in controller and check corresponding format

     HttpFileCollection MyFileCollection = Request.Files;

 for (int Loop1 = 0; Loop1 < MyFileCollection.Count; Loop1++)
 {
    if (MyFileCollection[Loop1].ContentType == "image/jpeg")
    {
       //...
    }
 }

    Source: Microsoft Docs

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  3. 0

    You can actually check the byte signatures to verify if it’s jpg or any other image file by reading their byte stream, they begin with a unique byte header ex. jpg files begin with "FFD8".

    I do actually have a method that covers 4 different image extensions and checks if the image is either jpg/png/bmp/gif;

        public static bool ExtensionVerifier(string expectedExtension, IFormFile file)
{
    
    var fileName = file.FileName.Split('.')[0];
        var fileExtension = file.FileName.Split('.')[file.FileName.Split('.').Length-1];
    var pExtension = expectedExtension.ToString().ToLower();
    

    #region Byte_Signatures_of_ImageTypes

    var ImageTypes = new Dictionary<string, string>();
    ImageTypes.Add("FFD8", "jpg");
    ImageTypes.Add("424D", "bmp");
    ImageTypes.Add("474946", "gif");
    ImageTypes.Add("89504E470D0A1A0A", "png");

    #endregion


    using (var signatureChecker = file.OpenReadStream())
    {
        signatureChecker.Seek(0, SeekOrigin.Begin);
        var builder = new StringBuilder();
        int byteHeader = ImageTypes.FirstOrDefault(img => img.Value == fileExtension).Key.Length;

        for (int i = 0; i < byteHeader; i += 2)
        {
            string bit = signatureChecker.ReadByte().ToString("X2");
            builder.Append(bit);
            string builtHex = builder.ToString();
            if (ImageTypes.ContainsKey(key: builtHex))
            {
                if (fileExtension == pExtension)
                {
                    signatureChecker.Dispose();
                    return true;
                }

            }

        }
        return false;
    }

}
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