Question

I found the following example to download web page(string) asynchounously:

let getImage (imageUrl:string) =
    async {
        try 
            let req = WebRequest.Create(imageUrl) :?> HttpWebRequest
            req.UserAgent <- "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)";
            req.Method <- "GET";
            req.AllowAutoRedirect <- true;
            req.MaximumAutomaticRedirections <- 4;
            let! response1 = req.AsyncGetResponse()
            let response = response1 :?> HttpWebResponse
            use stream = response.GetResponseStream()
            use streamreader = new System.IO.StreamReader(stream)
            return! streamreader.AsyncReadToEnd() // .ReadToEnd()
        with
            _ -> return "" // if there's any exception, just return an empty string

    }

It returns a string. However, I need to download an online image(an array of bytes) asynchournously.

Anyone could give me some hint?

Answer 1

Maybe you can use my answer to another question (here). It asks the google chart API for an image (an URL) and converts the bytes to a Bitmap.

The relevant code:

async {
    let req = HttpWebRequest.Create(..URI HERE..)
    let! response = req.AsyncGetResponse()
    return new Bitmap(response.GetResponseStream())
} |> Async.RunSynchronously