how to read a csv file from a url?

// Download the file to a specified path. Using the WebClient class we can download 
// files directly from a provided url, like in this case.

System.Net.WebClient client = new WebClient();
client.DownloadFile(url, csvPath);

Where the url is your site with the csv file and the csvPath is where you want the actual file to go.

You could use:

public string GetCSV(string url)
{
    HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
    HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

    StreamReader sr = new StreamReader(resp.GetResponseStream());
    string results = sr.ReadToEnd();
    sr.Close();

    return results;
} 

And then to split it:

public static void SplitCSV()
{
    List<string> splitted = new List<string>();
    string fileList = getCSV("http://www.google.com");
    string[] tempStr;

    tempStr = fileList.Split(',');

    foreach (string item in tempStr)
    {
        if (!string.IsNullOrWhiteSpace(item))
        {
            splitted.Add(item);
        }
    }
}

Though there are plenty of CSV parsers out there and i would advise against rolling your own. FileHelpers is a good one.

Sebastien Lorion's CSV Reader has a constructor that takes a Stream.

If you decided to use this, your example would become:

void GetCSVFromRemoteUrl(string url)
{
    HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
    HttpWebResponse response = request.GetResponse() as HttpWebResponse;

    using (CsvReader csvReader = new CsvReader(response.GetResponseStream(), true))
    {
        int fieldCount = csvReader.FieldCount;
        string[] headers = csvReader.GetFieldHeaders();

        while (csvReader.ReadNextRecord())
        {
            //Do work with CSV file data here
        }
    }

}

The ever popular FileHelpers also allows you to read directly from a stream.

In your Web Service you could use the WebClient class to download the file, something like this ( I have not put any exception handling, not any using or Close/Dispose calls, just wanted to give the idea you can use and refine/improve... )

using System.Net;

WebClient webClient = new WebClient();
webClient.DownloadFile("http://www.domain.co.uk/prices.csv");

then you can do anything you like with it once the file content is available in the execution flow of your service.

if you have to return it to the client as return value of the web service call you can either return a DataSet or any other data structure you prefer.