CODEWITHSUNDEEP
c#httpfilewebclientexists
Mats
Mats

Reputation: 14817

How to check if a file exists on a server using c# and the WebClient class

In my application I use the WebClient class to download files from a Webserver by simply calling the DownloadFile method. Now I need to check whether a certain file exists prior to downloading it (or in case I just want to make sure that it exists). I've got two questions with that:

  1. What is the best way to check whether a file exists on a server without transfering to much data across the wire? (It's quite a huge number of files I need to check)
  2. Is there a way to get the size of a given remote file without downloading it?

Thanks in advance!

Upvotes: 23

Views: 36198

Answers (4)

Arun Prasad E S
Arun Prasad E S

Reputation: 10115

In case anyone stuck with ssl certificate issue

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback
                                                                            (
                                                                               delegate { return true; }
                                                                            );
            WebRequest request = WebRequest.Create(new Uri("http://.com/flower.zip"));
            request.Method = "HEAD";

            using (WebResponse response = request.GetResponse())
            {
                Console.WriteLine("{0} {1}", response.ContentLength, response.ContentType);
            }

Upvotes: 0

SNag
SNag

Reputation: 18141

What is the best way to check whether a file exists on a server without transfering to much data across the wire?

You can test with WebClient.OpenRead to open the file stream without reading all the file bytes:

using (var client = new WebClient()) 
{
    Stream stream = client.OpenRead(url); 
    // ^ throws System.Net.WebException: 'Could not find file...' if file is not present
    stream.Close(); 
}

This will indicate if the file exists at the remote location or not.

To fully read the file stream, you would do:

using (var client = new WebClient()) 
{
    Stream stream = client.OpenRead(url); 
    StreamReader sr = new StreamReader(stream);
    Console.WriteLine(sr.ReadToEnd());
    stream.Close(); 
}

Upvotes: 0

Code
Code

Reputation: 99

When you request file using the WebClient Class, the 404 Error (File Not Found) will lead to an exception. Best way is to handle that exception and use a flag which can be set to see if the file exists or not.

The example code goes as follows:

System.Net.HttpWebRequest request = null;
System.Net.HttpWebResponse response = null;
request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create("www.example.com/somepath");
request.Timeout = 30000;
try
{
    response = (System.Net.HttpWebResponse)request.GetResponse();
    flag = 1;
}
catch 
{
    flag = -1;
}

if (flag==1)
{
    Console.WriteLine("File Found!!!");
}
else
{
    Console.WriteLine("File Not Found!!!");
}

You can put your code in respective if blocks. Hope it helps!

Upvotes: 5

Tim Robinson
Tim Robinson

Reputation: 54724

WebClient is fairly limited; if you switch to using WebRequest, then you gain the ability to send an HTTP HEAD request. When you issue the request, you should either get an error (if the file is missing), or a WebResponse with a valid ContentLength property.

Edit: Example code:

WebRequest request = WebRequest.Create(new Uri("http://www.example.com/"));
request.Method = "HEAD";

using(WebResponse response = request.GetResponse()) {
   Console.WriteLine("{0} {1}", response.ContentLength, response.ContentType);
}

Upvotes: 45

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