datamatrix net documentation BUILDING SMART WEB APPLICATIONS in VB.NET


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Listing 14-1. A Simple Web Server open open open open open System.Net System.Net.Sockets System.IO System.Text.RegularExpressions System.Text
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/// A table of MIME content types let mimeTypes = dict [".html", "text/html"; ".htm", "text/html"; ".txt", "text/plain"; ".gif", "image/gif"; ".jpg", "image/jpeg"; ".png", "image/png"] /// Compute a MIME type from a file extension let getMimeType(ext) = if mimeTypes.ContainsKey(ext) then mimeTypes.[ext] else "binary/octet" /// The pattern Regex1 uses a regular expression to match /// one element let (|Regex1|_|) (patt: string) (inp: string) = try Some(Regex.Match(inp, patt).Groups.Item(1).Captures.Item(0).Value) with _ -> None /// The root for the data we serve let root = @"c:\inetpub\wwwroot" /// /// /// let Handle a TCP connection for an HTTP GET. We use an asynchronous task in case any future actions in handling a request need to be asynchronous. handleRequest(client: TcpClient) = async { use stream = client.GetStream() let out = new StreamWriter(stream) let inp = new StreamReader(stream) match inp.ReadLine() with | Regex1 "GET (.* ) HTTP/1\\.[01]$" fileName -> let fname = root + @"\" + fileName.Replace("/", @"\") let mimeType = getMimeType(Path.GetExtension(fname)) let content = File.ReadAllBytes fname fprintfn out "HTTP/1.0 200 OK" fprintfn out "Content-Length: %d" content.Length fprintfn out "Content-Type: %s" mimeType fprintfn out "" out.Flush() stream.Write(content, 0, content.Length) | line -> () }
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/// The server as an asynchronous process. We handle requests /// sequentially. let server = async { let socket = new TcpListener(IPAddress.Parse(""), 8090) socket.Start() while true do use client = socket.AcceptTcpClient() try Async.Start (handleRequest client) with _ -> () } You can use this code as follows, where http is the function defined in 2 for requesting web pages and where you assume the directory c:\inetpub\wwwroot contains the file iisstart.htm: > Async.Start server;; val it : unit = () > http "";; val it : string = "..." // the text of the iisstart.htm file will be shown here This HTTP request (you can also open the previous URL in a browser) ultimately sends the following text down the TCP socket connection: GET iisstart.htm HTTP/1.1 When started, the server in Listing 14-1 attaches itself to a given port (8090) on the local machine (which has IP and listens for incoming requests. These requests are line-based, so when one comes in, you read the full input line and attempt to parse a valid GET request using regular expression matching. Other commands and error recovery aren t dealt with. The server s actions in response are simple: it locates the requested file relative to a root web directory, determines the MIME type from a fixed table, and sends the necessary response header and the content of the file through the client TCP connection. When all this is done, the connection is disposed, and the session ends. The main loop of the server task is a busy waiting loop you wait for requests indefinitely and handle them one by one. Listing 14-1 uses two techniques not directly related to web programming: Regex1 is a very simple and common active pattern for regular expression pattern matching. You learned about active patterns in 9. This example is particularly interesting because it also shows how to use a parameterized active pattern. The value server is an asynchronous task, as is the handleRequest function. You learned about asynchronous tasks in 13. Many web servers handle multiple requests simultaneously, and high-performance web servers use asynchronous techniques extensively. In this example, the server task serves requests sequentially using a single thread, but you can just as well start a dedicated thread for the server using more explicit threading techniques from System.Threading.
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While the above example may look simple, many common server-side applications are primarily TCP-based, and you can use the pattern shown above to implement many of these. For example, the following encapsulates an arbitrary TCP server: type AsyncTcpServer(addr,port,handleServerRequest) = let socket = new TcpListener(addr, port) member x.Start() = async { do x.Run() } |> Async.Start member x.Run() = socket.Start() while true do let client = socket.AcceptTcpClient() Async.Start (async { try // Client has lifetime equal to the async request use _holder = client do! handleServerRequest client with e -> () }) This class can now be instantiated and developed in many ways, including more interesting applications than simple HTTP servers. For example, the code below is a simulation of a quote server that serves quotes (represented here as a blob of bytes) to a TCP client every 1 second. Because serving each quote is very simple (simply writing a few bytes to the socket), you can serve many thousands of clients simultaneously using this technique. let quoteSize = 512 // one quote let quote = Array.init<byte> quoteSize (fun i -> 1uy) let handleRequest (client: TcpClient) = async { // Cleanup the client at the end of the request let stream = client.GetStream() do! stream.AsyncWrite(quote, 0, 1) // write header while true do do! stream.AsyncWrite(quote, 0, quote.Length) // Mock an I/O wait for the next quote do! Async.Sleep 1000 stream.Close() } let server() = AsyncTcpServer(IPAddress.Loopback, 10003, handleRequest) Additionally, you should consider using secure sockets (https) for your application. Secure network programming is a big topic, beyond the scope of this book, but the code below indicates the basic shape of an SSL server, built compositionally using a non-secure one, and indicates the .NET types you can use to implement authentication-related functionality: type AsyncTcpServerSecure(addr,port,handleServerRequest) = let getCertficate() = // Instantiate the x509Store object to represent the Certificate Store // that contains the certificate to use for server authentication. let store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
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