(I am writing a processor that handles requests in a queue (console app).
I would like to use the .NET Core DI.
So far my code looks like this:
...
var connectionString = exportConfiguration.ConnectionString;
using (var scope = _serviceProvider.CreateScope())
{
var provider = scope.ServiceProvider;
var service = provider.GetRequiredService<MyContext>();
service.SqlConnectionString = sqlConnectionString; // I don't think property injection on a dbcontext will work, it takes its connection string in via the constructor
}
I have read how to assign parameters to the object as shown above, but how do I create a new context based on the connection string that is used in all the objects that the service uses (using constructor injection because thats why dbcontexts take - connection string in constructor)?
(I am not storing my connection string in the queue by the way, a code comes down the queue and my app then chooses the connection string to use).
I have managed to work this out. The key was that when you use CreateScope(), then GetRequiredService(), the DI system will provide new objects. So I just had to provide the correct information. This is now what my code looks like:
// Prior code gets information from a queue, which could be different every time.
// This needs passing as a constructor to the DbContext and possibly other information from the queue to other methods constructors
// (constructor injection not property injection)
var connectionString = queueItem.ConnectionString;
// save the connection string so the DI system (startup.cs) can pick it up
Startup.ConnectionString = connectionString;
using (var scope = _serviceProvider.CreateScope())
{
var provider = scope.ServiceProvider;
var service = provider.GetRequiredService<IMyService>();
// go off and get data from the correct dbcontext / connection string
var data = service.GetData();
// more processing
}
/// The Service has the DbContext in its constructor:
public class MyService : IMyService {
private DbContext _dbContext;
public MyService(DbContext dbContext) {
_dbContext = dbContext;
}
// more stuff that uses dbcontext
}
/// In startup.cs:
public static string ConnectionString {get;set;}
...
builder.Services.AddScoped<IMyService, MyService>();
builder.Services.AddScoped<DbContext>(options => options.UseSqlServer(Startup.ConnectionString));
// Also the following code will work if needed:
// Parameter1 is something that comes from the queue and could be different for each
// CreateScope()
build.Services.AddScoped<IMyOtherService>((_) =>
new MyOtherService(Startup.Parameter1));
I hope this helps somebody, because when I was googling around I couldn't find out how to do this.
Unlike normal, I have code that actually works, but I'm wondering if it's the only (or best approach).
The basic Idea is I have an existing application that's handmade data layer is being ported to Entity Framework. As a compromise to minimize code changes, I'm working with existing methods, which tend to take a more disconnected approach. For example I have a lot of things like this:
UpdateNote(int noteId, string note)
I seem to have a method that works for this type of update without requiring a re-fetch:
var context = new MyEntities();
context.Configuration.ValidateOnSaveEnabled = false;
var note = new Model.Note{ Id = noteId, Note = ""};
context.Notes.Attach(note);
note.Note = "Some Note";
context.SaveChanges();
It's a little ugly (though concise enough), so I would like to know if there is there a better approach to use with EF? Any downsides to this method, other than loosing built-in validation?
This is a pattern that will be used all over my app.
The following extension method for DbContext is an approach which would avoid to initialize your entities with some values different to the values you want to change it to.
public static class EFExtensions
{
public static void MarkAsModified(this DbContext context, object entity,
params string[] properties)
{
foreach (var property in properties)
context.Entry(entity).Property(property).IsModified = true;
}
}
You could then use it this way:
var context = new MyEntities();
context.Configuration.ValidateOnSaveEnabled = false;
var note = new Model.Note { Id = noteId }; // only key properties required to set
note.Note = "Some Note";
note.SomeOtherProperty = 1234;
note.AndAnotherProperty = "XYZ";
context.Notes.Attach(note);
context.MarkAsModified(note, "Note", "SomeOtherProperty" , "AndAnotherProperty");
context.SaveChanges();
Note: This only works for scalar properties, not navigation properties.
Besides validation I could imagine that this approach is problematic for a proper concurrency checking.
Edit
According to #Adam Tuliper's comment below concurrency is likely not a problem because the concurrency check is skipped when an entity is attached manually to the context (without reading it from the database) and marked as modified to send an UPDATE command to the database. It just overwrites the lastest version in the DB. Thanks to Adam for pointing this out!
See the following code I use to easily attach a disconnected object back to the graph, assuming we're now going to save it.
public static class EntityFrameworkExtensions
{
/// <summary>
/// This class allows you to attach an entity.
/// For instance, a controller method Edit(Customer customer)
/// using ctx.AttachAsModified(customer);
/// ctx.SaveChanges();
/// allows you to easily reattach this item for udpating.
/// Credit goes to: http://geekswithblogs.net/michelotti/archive/2009/11/27/attaching-modified-entities-in-ef-4.aspx
/// </summary>
public static void AttachAsModified<T>(this ObjectSet<T> objectSet, T entity) where T : class
{
objectSet.Attach(entity);
objectSet.Context.ObjectStateManager.ChangeObjectState(entity, EntityState.Modified);
}
/// <summary>
/// This marks an item for deletion, but does not currently mark child objects (relationships).
/// For those cases you must query the object, include the relationships, and then delete.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="objectSet"></param>
/// <param name="entity"></param>
public static void AttachAsDeleted<T>(this ObjectSet<T> objectSet, T entity) where T : class
{
objectSet.Attach(entity);
objectSet.Context.ObjectStateManager.ChangeObjectState(entity, EntityState.Deleted);
}
public static void AttachAllAsModified<T>(this ObjectSet<T> objectSet, IEnumerable<T> entities) where T : class
{
foreach (var item in entities)
{
objectSet.Attach(item);
objectSet.Context.ObjectStateManager.ChangeObjectState(item, EntityState.Modified);
}
}
}
I have a COM object that I am trying to wrap in a C# class in order to make it more readily available for other applications that wish to consume it.
I have the following code that creates an instance of the COM object, and then using reflection makes a call to a method to retrieve user data. This code works fine when it is located in an aspx page.
object jdObj = Server.CreateObject("jd_api.UserCookie");
string username = jdObj.GetType().InvokeMember("GetUserName", System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();
However, when I move the code to a class file (JD_API.cs) in order to abstract it from the actual website, I can no longer get it to work. For example, I have the following static method that is declared like such:
public static string GetUserName() {
object jdObj = Server.CreateObject("jd_api.UserCookie");
string username = jdObj.GetType().InvokeMember("GetUserName",
System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();
return username;
}
Unfortunately, the Server object is restricted to some ASP.NET libraries that are included by default in web applications, and so the above code was a no-go. So at this point I decided to try to create an instance of the COM object like such:
public static string GetUserName() {
Type type = Type.GetTypeFromProgID("jd_api.UserCookie");
object jdObj = Activator.CreateInstance(type);
string username = jdObj.GetType().InvokeMember("GetUserName", System.Reflection.BindingFlags.InvokeMethod, null, jdObj , null).ToString();
return username;
}
However at runtime I get an error that says, "Attempted to read or write protected memory. This is often an indication that other memory is corrupt.".
I'm not sure where to go from here. Any help on how to abstract creating an instance of this COM object to a layer that is not within the web application itself would greatly appreciated. Thanks!!
Declare DLL functions within a class. Then define a static method for each DLL function you want to call.
The following code sample creates a wrapper named Win32MessageBox that calls the MessageBox function in User32.dll each time a .NET app calls the object Show method.
It requeres the System.Runtime.InteropServices namespace.
using System;
using System.Runtime.InteropServices;
class Win32MessageBox
{
[DllImport("user32.dll")]
private static extern int MessageBox(IntPtr hWnd, String text,
String caption, uint type);
public static void Show(string message, string caption)
{
MessageBox(new IntPtr(0), message, caption, 0);
}
}
To call it, just type:
Win32MessageBox.Show("StackOverflow!", "my stack box");
The method where you call the above line doesn't need to be aware that it's a actually calling a function in an unmanaged DLL.
Resources: the MCTS Self-Paced Training Kit (Exam 70-536) by Tony Northrup.
Hove you tried usinsing interoperating
I've done the following in the past (working from memory so you might need to fiddle with this a bit):
Right Click "References" in your project
Select "Add Reference"
Selelct the "Com" Tab
Find and add your Com Instnace
In your class file
using yourComName;
public static string GetUserName()
{
yourComName.yourComClass jdObj = new yourComClass();
string username = jdObj.GetUserName(someParameters);
return username;
}
Hope this a) works and b) helps!
I have some REST services using plain old IHttpHandlers. I'd like to generate cleaner URLs, so that I don't have the .ashx in the path. Is there a way to use ASP.NET routing to create routes that map to ashx handlers? I've seen these types of routes previously:
// Route to an aspx page
RouteTable.Routes.MapPageRoute("route-name",
"some/path/{arg}",
"~/Pages/SomePage.aspx");
// Route for a WCF service
RouteTable.Routes.Add(new ServiceRoute("Services/SomeService",
new WebServiceHostFactory(),
typeof(SomeService)));
Trying to use RouteTable.Routes.MapPageRoute() generates an error (that the handler does not derive from Page). System.Web.Routing.RouteBase only seems to have 2 derived classes: ServiceRoute for services, and DynamicDataRoute for MVC. I'm not sure what MapPageRoute() does (Reflector doesn't show the method body, it just shows "Performance critical to inline this type of method across NGen image boundaries").
I see that RouteBase is not sealed, and has a relatively simple interface:
public abstract RouteData GetRouteData(HttpContextBase httpContext);
public abstract VirtualPathData GetVirtualPath(RequestContext requestContext,
RouteValueDictionary values);
So perhaps I can make my own HttpHandlerRoute. I'll give that a shot, but if anyone knows of an existing or built-in way of mapping routes to IHttpHandlers, that would be great.
Ok, I've been figuring this out since I originally asked the question, and I finally have a solution that does just what I want. A bit of up front explanation is due, however. IHttpHandler is a very basic interface:
bool IsReusable { get; }
void ProcessRequest(HttpContext context)
There is no built in property for accessing the route data, and the route data also can't be found in the context or the request. A System.Web.UI.Page object has a RouteData property , ServiceRoutes do all the work of interpreting your UriTemplates and passing the values to the correct method internally, and ASP.NET MVC provides its own way of accessing the route data. Even if you had a RouteBase that (a) determined if the incoming url was a match for your route and (b) parsed the url to extract all of the individual values to be used from within your IHttpHandler, there's no easy way to pass that route data to your IHttpHandler. If you want to keep your IHttpHandler "pure", so to speak, it takes responsibility for dealing with the url, and how to extract any values from it. The RouteBase implementation in this case is only used to determine if your IHttpHandler should be used at all.
One problem remains, however. Once the RouteBase determines that the incoming url is a match for your route, it passes off to an IRouteHandler, which creates the instances of the IHttpHandler you want to handle your request. But, once you're in your IHttpHandler, the value of context.Request.CurrentExecutionFilePath is misleading. It's the url that came from the client, minus the query string. So it's not the path to your .ashx file. And, any parts of your route that are constant (such as the name of the method) will be part of that execution file path value. This can be a problem if you use UriTemplates within your IHttpHandler to determine which specific method within your IHttpHandler should handing the request.
Example: If you had a .ashx handler at /myApp/services/myHelloWorldHandler.ashx
And you had this route that mapped to the handler: "services/hello/{name}"
And you navigated to this url, trying to call the SayHello(string name) method of your handler:
http://localhost/myApp/services/hello/SayHello/Sam
Then your CurrentExecutionFilePath would be: /myApp/services/hello/Sam. It includes parts of the route url, which is a problem. You want the execution file path to match your route url. The below implementations of RouteBase and IRouteHandler deal with this problem.
Before I paste the 2 classes, here's a very simple usage example. Note that these implementations of RouteBase and IRouteHandler will actually work for IHttpHandlers that don't even have a .ashx file, which is pretty convenient.
// A "headless" IHttpHandler route (no .ashx file required)
RouteTable.Routes.Add(new GenericHandlerRoute<HeadlessService>("services/headless"));
That will cause all incoming urls that match the "services/headless" route to be handed off to a new instance of the HeadlessService IHttpHandler (HeadlessService is just an example in this case. It would be whatever IHttpHandler implementation you wanted to pass off to).
Ok, so here are the routing class implementations, comments and all:
/// <summary>
/// For info on subclassing RouteBase, check Pro Asp.NET MVC Framework, page 252.
/// Google books link: http://books.google.com/books?id=tD3FfFcnJxYC&pg=PA251&lpg=PA251&dq=.net+RouteBase&source=bl&ots=IQhFwmGOVw&sig=0TgcFFgWyFRVpXgfGY1dIUc0VX4&hl=en&ei=z61UTMKwF4aWsgPHs7XbAg&sa=X&oi=book_result&ct=result&resnum=6&ved=0CC4Q6AEwBQ#v=onepage&q=.net%20RouteBase&f=false
///
/// It explains how the asp.net runtime will call GetRouteData() for every route in the route table.
/// GetRouteData() is used for inbound url matching, and should return null for a negative match (the current requests url doesn't match the route).
/// If it does match, it returns a RouteData object describing the handler that should be used for that request, along with any data values (stored in RouteData.Values) that
/// that handler might be interested in.
///
/// The book also explains that GetVirtualPath() (used for outbound url generation) is called for each route in the route table, but that is not my experience,
/// as mine used to simply throw a NotImplementedException, and that never caused a problem for me. In my case, I don't need to do outbound url generation,
/// so I don't have to worry about it in any case.
/// </summary>
/// <typeparam name="T"></typeparam>
public class GenericHandlerRoute<T> : RouteBase where T : IHttpHandler, new()
{
public string RouteUrl { get; set; }
public GenericHandlerRoute(string routeUrl)
{
RouteUrl = routeUrl;
}
public override RouteData GetRouteData(HttpContextBase httpContext)
{
// See if the current request matches this route's url
string baseUrl = httpContext.Request.CurrentExecutionFilePath;
int ix = baseUrl.IndexOf(RouteUrl);
if (ix == -1)
// Doesn't match this route. Returning null indicates to the asp.net runtime that this route doesn't apply for the current request.
return null;
baseUrl = baseUrl.Substring(0, ix + RouteUrl.Length);
// This is kind of a hack. There's no way to access the route data (or even the route url) from an IHttpHandler (which has a very basic interface).
// We need to store the "base" url somewhere, including parts of the route url that are constant, like maybe the name of a method, etc.
// For instance, if the route url "myService/myMethod/{myArg}", and the request url were "http://localhost/myApp/myService/myMethod/argValue",
// the "current execution path" would include the "myServer/myMethod" as part of the url, which is incorrect (and it will prevent your UriTemplates from matching).
// Since at this point in the exectuion, we know the route url, we can calculate the true base url (excluding all parts of the route url).
// This means that any IHttpHandlers that use this routing mechanism will have to look for the "__baseUrl" item in the HttpContext.Current.Items bag.
// TODO: Another way to solve this would be to create a subclass of IHttpHandler that has a BaseUrl property that can be set, and only let this route handler
// work with instances of the subclass. Perhaps I can just have RestHttpHandler have that property. My reticence is that it would be nice to have a generic
// route handler that works for any "plain ol" IHttpHandler (even though in this case, you have to use the "global" base url that's stored in HttpContext.Current.Items...)
// Oh well. At least this works for now.
httpContext.Items["__baseUrl"] = baseUrl;
GenericHandlerRouteHandler<T> routeHandler = new GenericHandlerRouteHandler<T>();
RouteData rdata = new RouteData(this, routeHandler);
return rdata;
}
public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values)
{
// This route entry doesn't generate outbound Urls.
return null;
}
}
public class GenericHandlerRouteHandler<T> : IRouteHandler where T : IHttpHandler, new()
{
public IHttpHandler GetHttpHandler(RequestContext requestContext)
{
return new T();
}
}
I know this answer has been quite long winded, but it was not an easy problem to solve. The core logic was easy enough, the trick was to somehow make your IHttpHandler aware of the "base url", so that it could properly determine what parts of the url belong to the route, and what parts are actual arguments for the service call.
These classes will be used in my upcoming C# REST library, RestCake. I hope that my path down the routing rabbit hole will help anyone else who decides to RouteBase, and do cool stuff with IHttpHandlers.
I actually like Joel's solution better, as it doesn't require you to know the type of handler while you're trying to setup your routes. I'd upvote it, but alas, I haven't the reputation required.
I actually found a solution which I feel is better than both mentioned. The original source code I derived my example from can be found linked here http://weblogs.asp.net/leftslipper/archive/2009/10/07/introducing-smartyroute-a-smarty-ier-way-to-do-routing-in-asp-net-applications.aspx.
This is less code, type agnostic, and fast.
public class HttpHandlerRoute : IRouteHandler {
private String _VirtualPath = null;
public HttpHandlerRoute(String virtualPath) {
_VirtualPath = virtualPath;
}
public IHttpHandler GetHttpHandler(RequestContext requestContext) {
IHttpHandler httpHandler = (IHttpHandler)BuildManager.CreateInstanceFromVirtualPath(_VirtualPath, typeof(IHttpHandler));
return httpHandler;
}
}
And a rough example of use
String handlerPath = "~/UploadHandler.ashx";
RouteTable.Routes.Add(new Route("files/upload", new HttpHandlerRoute(handlerPath)));
EDIT: I just edited this code because I had some issues with the old one. If you're using the old version please update.
This thread is a bit old but I just re-wrote some of the code here to do the same thing but on a more elegant way, using an extension method.
I'm using this on ASP.net Webforms, and I like to have the ashx files on a folder and being able to call them either using routing or a normal request.
So I pretty much grabbed shellscape's code and made an extension method that does the trick. At the end I felt that I should also support passing the IHttpHandler object instead of its Url, so I wrote and overload of the MapHttpHandlerRoute method for that.
namespace System.Web.Routing
{
public class HttpHandlerRoute<T> : IRouteHandler where T: IHttpHandler
{
private String _virtualPath = null;
public HttpHandlerRoute(String virtualPath)
{
_virtualPath = virtualPath;
}
public HttpHandlerRoute() { }
public IHttpHandler GetHttpHandler(RequestContext requestContext)
{
return Activator.CreateInstance<T>();
}
}
public class HttpHandlerRoute : IRouteHandler
{
private String _virtualPath = null;
public HttpHandlerRoute(String virtualPath)
{
_virtualPath = virtualPath;
}
public IHttpHandler GetHttpHandler(RequestContext requestContext)
{
if (!string.IsNullOrEmpty(_virtualPath))
{
return (IHttpHandler)System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(_virtualPath, typeof(IHttpHandler));
}
else
{
throw new InvalidOperationException("HttpHandlerRoute threw an error because the virtual path to the HttpHandler is null or empty.");
}
}
}
public static class RoutingExtension
{
public static void MapHttpHandlerRoute(this RouteCollection routes, string routeName, string routeUrl, string physicalFile, RouteValueDictionary defaults = null, RouteValueDictionary constraints = null)
{
var route = new Route(routeUrl, defaults, constraints, new HttpHandlerRoute(physicalFile));
routes.Add(routeName, route);
}
public static void MapHttpHandlerRoute<T>(this RouteCollection routes, string routeName, string routeUrl, RouteValueDictionary defaults = null, RouteValueDictionary constraints = null) where T : IHttpHandler
{
var route = new Route(routeUrl, defaults, constraints, new HttpHandlerRoute<T>());
routes.Add(routeName, route);
}
}
}
I'm putting it inside the same namespace of all the native routing objects so it will be automatically available.
So to use this you just have to call:
// using the handler url
routes.MapHttpHandlerRoute("DoSomething", "Handlers/DoSomething", "~/DoSomething.ashx");
Or
// using the type of the handler
routes.MapHttpHandlerRoute<MyHttpHanler>("DoSomething", "Handlers/DoSomething");
Enjoy,
Alex
Yeah, I noticed that, too. Perhaps there is a built-in ASP.NET way to do this, but the trick for me was to create a new class derived from IRouteHandler:
using System;
using System.IO;
using System.Reflection;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.Routing;
namespace MyNamespace
{
class GenericHandlerRouteHandler : IRouteHandler
{
private string _virtualPath;
private Type _handlerType;
private static object s_lock = new object();
public GenericHandlerRouteHandler(string virtualPath)
{
_virtualPath = virtualPath;
}
#region IRouteHandler Members
public System.Web.IHttpHandler GetHttpHandler(RequestContext requestContext)
{
ResolveHandler();
IHttpHandler handler = (IHttpHandler)Activator.CreateInstance(_handlerType);
return handler;
}
#endregion
private void ResolveHandler()
{
if (_handlerType != null)
return;
lock (s_lock)
{
// determine physical path of ashx
string path = _virtualPath.Replace("~/", HttpRuntime.AppDomainAppPath);
if (!File.Exists(path))
throw new FileNotFoundException("Generic handler " + _virtualPath + " could not be found.");
// parse the class name out of the .ashx file
// unescaped reg-ex: (?<=Class=")[a-zA-Z\.]*
string className;
Regex regex = new Regex("(?<=Class=\")[a-zA-Z\\.]*");
using (var sr = new StreamReader(path))
{
string str = sr.ReadToEnd();
Match match = regex.Match(str);
if (match == null)
throw new InvalidDataException("Could not determine class name for generic handler " + _virtualPath);
className = match.Value;
}
// get the class type from the name
Assembly[] asms = AppDomain.CurrentDomain.GetAssemblies();
foreach (Assembly asm in asms)
{
_handlerType = asm.GetType(className);
if (_handlerType != null)
break;
}
if (_handlerType == null)
throw new InvalidDataException("Could not find type " + className + " in any loaded assemblies.");
}
}
}
}
To create a route for an .ashx:
IRouteHandler routeHandler = new GenericHandlerRouteHandler("~/somehandler.ashx");
Route route = new Route("myroute", null, null, null, routeHandler);
RouteTable.Routes.Add(route);
The code above may need to be enhanced to work with your route arguments, but it's starting point. Comments welcome.
All of these answers are very good. I love the simplicity of Mr. Meacham's GenericHandlerRouteHandler<T> class. It is a great idea to eliminate an unnecessary reference to a virtual path if you know the specific HttpHandler class. The GenericHandlerRoute<T> class is not needed, however. The existing Route class which derives from RouteBase already handles all of the complexity of route matching, parameters, etc., so we can just use it along with GenericHandlerRouteHandler<T>.
Below is a combined version with a real-life usage example that includes route parameters.
First are the route handlers. There are two included, here -- both with the same class name, but one that is generic and uses type information to create an instance of the specific HttpHandler as in Mr. Meacham's usage, and one that uses a virtual path and BuildManager to create an instance of the appropriate HttpHandler as in shellscape's usage. The good news is that .NET allows both to live side by side just fine, so we can just use whichever we want and can switch between them as we wish.
using System.Web;
using System.Web.Compilation;
using System.Web.Routing;
public class HttpHandlerRouteHandler<T> : IRouteHandler where T : IHttpHandler, new() {
public HttpHandlerRouteHandler() { }
public IHttpHandler GetHttpHandler(RequestContext requestContext) {
return new T();
}
}
public class HttpHandlerRouteHandler : IRouteHandler {
private string _VirtualPath;
public HttpHandlerRouteHandler(string virtualPath) {
this._VirtualPath = virtualPath;
}
public IHttpHandler GetHttpHandler(RequestContext requestContext) {
return (IHttpHandler) BuildManager.CreateInstanceFromVirtualPath(this._VirtualPath, typeof(IHttpHandler));
}
}
Let's assume that we created an HttpHandler that streams documents to users from a resource outside our virtual folder, maybe even from a database, and that we want to fool the user's browser into believing that we are directly serving a specific file rather than simply providing a download (i.e., allow the browser's plug-ins to handle the file rather than forcing the user to save the file). The HttpHandler may expect a document id with which to locate the document to provide, and may expect a file name to provide to the browser -- one that may differ from the file name used on the server.
The following shows the registration of the route used to accomplish this with a DocumentHandler HttpHandler:
routes.Add("Document", new Route("document/{documentId}/{*fileName}", new HttpHandlerRouteHandler<DocumentHandler>()));
I used {*fileName} rather than just {fileName} to allow the fileName parameter to act as an optional catch-all parameter.
To create a URL for a file served by this HttpHandler, we can add the following static method to a class where such a method would be appropriate, such as in the HttpHandler class, itself:
public static string GetFileUrl(int documentId, string fileName) {
string mimeType = null;
try { mimeType = MimeMap.GetMimeType(Path.GetExtension(fileName)); }
catch { }
RouteValueDictionary documentRouteParameters = new RouteValueDictionary { { "documentId", documentId.ToString(CultureInfo.InvariantCulture) }
, { "fileName", DocumentHandler.IsPassThruMimeType(mimeType) ? fileName : string.Empty } };
return RouteTable.Routes.GetVirtualPath(null, "Document", documentRouteParameters).VirtualPath;
}
I omitted the definitions of MimeMap and and IsPassThruMimeType to keep this example simple. But these are intended to determine whether or not specific file types should provide their file names directly in the URL, or rather in a Content-Disposition HTTP header. Some file extensions could be blocked by IIS or URL Scan, or could cause code to execute that might cause problems for users -- especially if the source of the file is another user who is malicious. You could replace this logic with some other filtering logic, or omit such logic entirely if you are not exposed to this type of risk.
Since in this particular example the file name may be omitted from the URL, then, obviously, we must retrieve the file name from somewhere. In this particular example, the file name can be retrieved by performing a look-up using document id, and including a file name in the URL is intended solely to improve the user's experience. So, the DocumentHandler HttpHandler can determine if a file name was provided in the URL, and if it was not, then it can simply add a Content-Disposition HTTP header to the response.
Staying on topic, the important part of the above code block is the usage of RouteTable.Routes.GetVirtualPath() and the routing parameters to generate a URL from the Route object that we created during the route registration process.
Here's a watered-down version of the DocumentHandler HttpHandler class (much omitted for the sake of clarity). You can see that this class uses route parameters to retrieve the document id and the file name when it can; otherwise, it will attempt to retrieve the document id from a query string parameter (i.e., assuming that routing was not used).
public void ProcessRequest(HttpContext context) {
try {
context.Response.Clear();
// Get the requested document ID from routing data, if routed. Otherwise, use the query string.
bool isRouted = false;
int? documentId = null;
string fileName = null;
RequestContext requestContext = context.Request.RequestContext;
if (requestContext != null && requestContext.RouteData != null) {
documentId = Utility.ParseInt32(requestContext.RouteData.Values["documentId"] as string);
fileName = Utility.Trim(requestContext.RouteData.Values["fileName"] as string);
isRouted = documentId.HasValue;
}
// Try the query string if no documentId obtained from route parameters.
if (!isRouted) {
documentId = Utility.ParseInt32(context.Request.QueryString["id"]);
fileName = null;
}
if (!documentId.HasValue) { // Bad request
// Response logic for bad request omitted for sake of simplicity
return;
}
DocumentDetails documentInfo = ... // Details of loading this information omitted
if (context.Response.IsClientConnected) {
string fileExtension = string.Empty;
try { fileExtension = Path.GetExtension(fileName ?? documentInfo.FileName); } // Use file name provided in URL, if provided, to get the extension.
catch { }
// Transmit the file to the client.
FileInfo file = new FileInfo(documentInfo.StoragePath);
using (FileStream fileStream = file.OpenRead()) {
// If the file size exceeds the threshold specified in the system settings, then we will send the file to the client in chunks.
bool mustChunk = fileStream.Length > Math.Max(SystemSettings.Default.MaxBufferedDownloadSize * 1024, DocumentHandler.SecondaryBufferSize);
// WARNING! Do not ever set the following property to false!
// Doing so causes each chunk sent by IIS to be of the same size,
// even if a chunk you are writing, such as the final chunk, may
// be shorter than the rest, causing extra bytes to be written to
// the stream.
context.Response.BufferOutput = true;
context.Response.ContentType = MimeMap.GetMimeType(fileExtension);
context.Response.AddHeader("Content-Length", fileStream.Length.ToString(CultureInfo.InvariantCulture));
if ( !isRouted
|| string.IsNullOrWhiteSpace(fileName)
|| string.IsNullOrWhiteSpace(fileExtension)) { // If routed and a file name was provided in the route, then the URL will appear to point directly to a file, and no file name header is needed; otherwise, add the header.
context.Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", HttpUtility.UrlEncode(documentInfo.FileName)));
}
int bufferSize = DocumentHandler.SecondaryBufferSize;
byte[] buffer = new byte[bufferSize];
int bytesRead = 0;
while ((bytesRead = fileStream.Read(buffer, 0, bufferSize)) > 0 && context.Response.IsClientConnected) {
context.Response.OutputStream.Write(buffer, 0, bytesRead);
if (mustChunk) {
context.Response.Flush();
}
}
}
}
}
catch (Exception e) {
// Error handling omitted from this example.
}
}
This example uses some additional custom classes, such as a Utility class to simplify some trivial tasks. But hopefully you can weed through that. The only really important part in this class with regard to the current topic, of course, is the retrieval of the route parameters from context.Request.RequestContext.RouteData. But I've seen several posts elsewhere asking how to stream large files using an HttpHandler without chewing up server memory, so it seemed like a good idea to combine examples.