将文件保存到计算机之前检查MD5

Question

I want to check MD5 hash without saving it,

to check if it exists already i have tried this code below but it just wont compute the MD5 of the file if its not saved already.

so i was thinking about filling the file in a byte array then get that byte array MD5 but that will leave me with no bytes in the file.

Any suggestions ? this is my code

public void ProcessRequest(HttpContext context)
{
    if (context.Request.Files.Count > 0)
    {
        HttpFileCollection files = context.Request.Files;
        for (int i = 0; i < files.Count; i++)
        {
            HttpPostedFile file = files[i];
            string ServerPath = context.Server.MapPath("~/uploads/" + file.FileName);
            string Name = file.FileName;
            string MD5 = GetMD5(ServerPath);
            int Size = file.ContentLength;
            string type = file.ContentType;
            file.SaveAs(ServerPath);   
        }
    }
}

This is getMD5 Method

public string GetMD5(string fileName)
{
    try
    {
        using (var md5 = MD5.Create())
        {
            using (var stream = File.OpenRead(fileName))
            {
                string Hash = BitConverter.ToString(md5.ComputeHash(stream)).Replace("-", "");
                     return Hash;
            }
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

Answer 1

Since the bottleneck here is the download, you don't have any real advantage in not saving the file before checking the hash. What you may want to do is to download into your temp folder and then eventually delete it yourself or let the OS clean it if not needed.

Check this answer for information about how to use the temp folder and temporary files: Writing File to Temp Folder

One more complex option is to host a page on the same server where files are stored and let it calculate the MD5: this way you can check the MD5 before downloading. Otherwise, since the hash is a function of the physical bytes composing your file you need the whole file (downloaded or memory stored) to compute it.

Answer 2

You can use the InputStream property in the HttpPostedFile class. And to compute a hash, use the ComputeHash method of the HashAlgorithm class.

public void ProcessRequest(HttpContext context)
{
    if (context.Request.Files.Count > 0)
    {
        HttpFileCollection files = context.Request.Files;
        for (int i = 0; i < files.Count; i++)
        {
            HttpPostedFile file = files[i];
            var hasAlg=HashAlgorithm.Create("MD5");
            var MD5= hasAlg.ComputeHash(file.InputStream);

        }

    }
}