ASP.NET 4 Unleased - p 22 pdf

ptg 184 CHAPTER 4 Using the Rich Controls The page includes a method named CheckFileType(), which prevents users from uploading a file that does not have the .gif, .jpeg, .jpg, or .png extension. The method restricts the type of file that can be uploaded based on the file extension. NOTE The HTML 4.01 specifications define an accept attribute that you can use to filter the files that can be uploaded. Unfortunately, no browser supports the accept attribute, so you must perform filtering on the server (or use some JavaScript to check the filename extension on the client). To save a file to the file system, the Windows account associated with the ASP.NET page must have sufficient permissions to save the file. For Windows 2003 and Windows 2008 servers, an ASP.NET page executes in the security context of the NETWORK SERVICE account. In the case of every other operating system, an ASP.NET page executes in the security context of the ASPNET account. To enable ASP.NET Framework to save an uploaded file to a particular folder, you need to right-click the folder within Windows Explorer, select the Security tab, and provide either the NETWORK SERVICE or ASPNET account Write permissions for the folder (see Figure 4.2). FIGURE 4.2 Adding Write permissions for the ASPNET account. From the Library of Wow! eBook ptg 185 Accepting File Uploads Saving Files to a Database You also can use the FileUpload control to save files to a database table. Saving and retrieving files from a database can place more stress on your server. However, it does have certain advantages. First, you can avoid file system permissions issues. Second, saving files to a database enables you to more easily back up your information. The page in Listing 4.2 enables you to save Microsoft Word documents to a database table (see Figure 4.3). LISTING 4.2 FileUploadDatabase.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.IO” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> protected void btnAdd_Click(object sender, EventArgs e) { if (upFile.HasFile) { if (CheckFileType(upFile.FileName)) srcFiles.Insert(); } } bool CheckFileType(string fileName) { return (Path.GetExtension(fileName).ToLower() == “.doc” || Path.GetExtension(fileName).ToLower() == “.docx”); } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <style type=”text/css”> .fileList li { margin-bottom:5px; } </style> <title>FileUpload Database</title> </head> <body> <form id=”form1” runat=”server”> <div> 4 From the Library of Wow! eBook ptg 186 <asp:Label id=”lblFile” Text=”Word Document:” AssociatedControlID=”upFile” Runat=”server” /> <asp:FileUpload id=”upFile” Runat=”server” /> <asp:Button id=”btnAdd” Text=”Add Document” OnClick=”btnAdd_Click” Runat=”server” /> <hr /> <asp:Repeater id=”rptFiles” DataSourceID=”srcFiles” Runat=”server”> <HeaderTemplate> <ul class=”fileList”> </HeaderTemplate> <ItemTemplate> <li> <asp:HyperLink id=”lnkFile” Text=’<%#Eval(“FileName”)%>’ NavigateUrl=’<%#Eval(“Id”, “~/FileHandler.ashx?id={0}”)%>’ Runat=”server” /> </li> </ItemTemplate> <FooterTemplate> </ul> </FooterTemplate> </asp:Repeater> <asp:SqlDataSource id=”srcFiles” ConnectionString=”Server=.\SQLExpress;Integrated Security=True; AttachDbFileName=|DataDirectory|FilesDB.mdf;User Instance=True” SelectCommand=”SELECT Id,FileName FROM Files” InsertCommand=”INSERT Files (FileName,FileBytes) VALUES ➥ (@FileName,@FileBytes)” CHAPTER 4 Using the Rich Controls From the Library of Wow! eBook ptg 187 Accepting File Uploads 4 FIGURE 4.3 Uploading Microsoft Word documents. Runat=”server”> <InsertParameters> <asp:ControlParameter Name=”FileName” ControlID=”upFile” PropertyName=”FileName” /> <asp:ControlParameter Name=”FileBytes” ControlID=”upFile” PropertyName=”FileBytes” /> </InsertParameters> </asp:SqlDataSource> </div> </form> </body> </html> When you submit the form in Listing 4.2, the btnAdd_Click() method executes. This method checks the file extension to verify that the file is a Microsoft Word document. Next, the SqlDataSource control’s Insert() method is called to insert the values of the FileUpload control’s FileName and FileBytes properties into a local SQL Express database table. The SQL Express database table, named Files, looks like this: From the Library of Wow! eBook ptg 188 The page also displays a list of the current Microsoft Word documents in the database. You can click any file and view the contents of the file. Exactly what happens when you click a file is browser (and browser settings) dependent. With Microsoft Internet Explorer, for example, the document opens directly in the browser. Clicking the name of a document links you to a page named FileHandler.ashx. The FileHandler.ashx file is a generic HTTP Handler file. Chapter 25, “Using the ASP.NET URL Routing Engine,” discusses HTTP Handlers in detail. An HTTP Handler enables you to execute code when someone makes a request for a file with a certain path. The FileHandler.ashx file is contained in Listing 4.3. LISTING 4.3 FileHandler.ashx <%@ WebHandler Language=”C#” Class=”FileHandler” %> using System; using System.Web; using System.Data; using System.Data.SqlClient; public class FileHandler : IHttpHandler { const string conString = @”Server=.\SQLExpress;Integrated Security=True; AttachDbFileName=|DataDirectory|FilesDB.mdf;User Instance=True”; public void ProcessRequest (HttpContext context) { context.Response.ContentType = “application/msword”; SqlConnection con = new SqlConnection(conString); SqlCommand cmd = new SqlCommand(“SELECT FileBytes FROM Files WHERE ➥ Id=@Id”, con); cmd.Parameters.AddWithValue(“@Id”, context.Request[“Id”]); using (con) { con.Open(); byte[] file = (byte[])cmd.ExecuteScalar(); context.Response.BinaryWrite(file); } CHAPTER 4 Using the Rich Controls Column Name Data Type Id Int (IDENTITY) FileName NVarchar(50) FileBytes Varbinary(max) From the Library of Wow! eBook ptg 189 Accepting File Uploads 4 } public bool IsReusable { get { return false; } } } When the FileHandler.aspx page is requested, the ProcessRequest() method executes. This method grabs a query string item named Id and retrieves the matching record from the Files database table. The record contains the contents of a Microsoft Word document as a byte array. The byte array is sent to the browser with the Response.BinaryWrite() method. Uploading Large Files You must do extra work when uploading large files. You don’t want to consume your entire server’s memory by placing the entire file in memory. When working with a large file, you need to work with the file in more manageable chunks. First, you need to configure your application to handle large files. Two configuration settings have an effect on posting large files to the server: the httpRuntime maxRequestLength and httpRuntime requestLengthDiskThreshold settings. The maxRequestLength setting places a limit on the largest form post that the server can accept. By default, you cannot post a form that contains more than 4MB of data—if you try, you get an exception. If you need to upload a file that contains more than four megabytes of data, you need to change this setting. The requestLengthDiskThreshold setting determines how a form post is buffered to the file system. In an older version of ASP.NET (ASP.NET 1.1), uploading a large file could do horrible things to your server. The entire file was uploaded into the server memory. While a 10-megabyte video file was uploaded, for example, 10 megabytes of server memory was consumed. The ASP.NET 4 Framework enables you to buffer large files onto the file system. When the size of the file passes the requestLengthDiskThreshold setting, the remainder of the file is buffered to the file system (in the Temporary ASP.NET Files folder). By default, the ASP.NET framework is configured to buffer any post larger than 80KB to a file buffer. If you are not happy with this setting, you can modify the requestLengthDiskThreshold to configure a new threshold (The requestLengthDiskThreshold setting must be less than the maxRequestLength setting.) The web configuration file in Listing 4.4 enables files up to 10MB to be posted. It also changes the buffering threshold to 100KB. Changing the buffering threshold controls the amount of information stored in memory before it is flushed to disk. From the Library of Wow! eBook ptg 190 CHAPTER 4 Using the Rich Controls LISTING 4.4 Web.Config <?xml version=”1.0”?> <configuration> <system.web> <httpRuntime maxRequestLength=”10240” requestLengthDiskThreshold=”100” /> </system.web> </configuration> When working with large files, you must be careful about the way that you handle the file when storing or retrieving the file from a data store. For example, when saving or retrieving a file from a database table, you should never load the entire file into memory. The page in Listing 4.5 demonstrates how you can save a large file to a database table efficiently. LISTING 4.5 FileUploadLarge.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.IO” %> <%@ Import Namespace=”System.Data” %> <%@ Import Namespace=”System.Data.SqlClient” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> const string conString = @”Server=.\SQLExpress;Integrated Security=True; AttachDbFileName=|DataDirectory|FilesDB.mdf;User Instance=True”; void btnAdd_Click(Object s, EventArgs e) { if (upFile.HasFile) { if (CheckFileType(upFile.FileName)) { AddFile(upFile.FileName, upFile.FileContent); rptFiles.DataBind(); } } } bool CheckFileType(string fileName) { From the Library of Wow! eBook ptg 191 Accepting File Uploads 4 return Path.GetExtension(fileName).ToLower() == “.doc”; } void AddFile(string fileName, Stream upload) { SqlConnection con = new SqlConnection(conString); SqlCommand cmd = new SqlCommand(“INSERT Files (FileName) Values ➥ (@FileName);” + “SELECT @Identity = SCOPE_IDENTITY()”, con); cmd.Parameters.AddWithValue(“@FileName”, fileName); SqlParameter idParm = cmd.Parameters.Add(“@Identity”, SqlDbType.Int); idParm.Direction = ParameterDirection.Output; using (con) { con.Open(); cmd.ExecuteNonQuery(); int newFileId = (int)idParm.Value; StoreFile(newFileId, upload, con); } } void StoreFile(int fileId, Stream upload, SqlConnection connection) { int bufferLen = 8040; BinaryReader br = new BinaryReader(upload); byte[] chunk = br.ReadBytes(bufferLen); SqlCommand cmd = new SqlCommand(“UPDATE Files SET FileBytes=@Buffer WHERE Id=@FileId”, connection); cmd.Parameters.AddWithValue(“@FileId”, fileId); cmd.Parameters.Add(“@Buffer”, SqlDbType.VarBinary, bufferLen).Value = chunk; cmd.ExecuteNonQuery(); SqlCommand cmdAppend = new SqlCommand(“UPDATE Files SET FileBytes ➥ .WRITE(@Buffer,NULL, 0) WHERE Id=@FileId”, connection); cmdAppend.Parameters.AddWithValue(“@FileId”, fileId); cmdAppend.Parameters.Add(“@Buffer”, SqlDbType.VarBinary, bufferLen); chunk = br.ReadBytes(bufferLen); while (chunk.Length > 0) { cmdAppend.Parameters[“@Buffer”].Value = chunk; cmdAppend.ExecuteNonQuery(); From the Library of Wow! eBook ptg 192 CHAPTER 4 Using the Rich Controls chunk = br.ReadBytes(bufferLen); } br.Close(); } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>FileUpload Large</title> </head> <body> <form id=”form1” runat=”server”> <div> <asp:Label id=”lblFile” Text=”Word Document:” AssociatedControlID=”upFile” Runat=”server” /> <asp:FileUpload id=”upFile” Runat=”server” /> <asp:Button id=”btnAdd” Text=”Add Document” OnClick=”btnAdd_Click” Runat=”server” /> <hr /> <asp:Repeater id=”rptFiles” DataSourceID=”srcFiles” Runat=”server”> <HeaderTemplate> <ul class=”fileList”> </HeaderTemplate> <ItemTemplate> <li> <asp:HyperLink id=”lnkFile” From the Library of Wow! eBook ptg 193 Accepting File Uploads 4 Text=’<%#Eval(“FileName”)%>’ NavigateUrl=’<%#Eval(“Id”, “~/FileHandlerLarge.ashx?id={0}”)%>’ Runat=”server” /> </li> </ItemTemplate> <FooterTemplate> </ul> </FooterTemplate> </asp:Repeater> <asp:SqlDataSource id=”srcFiles” ConnectionString=”Server=.\SQLExpress;Integrated Security=True; AttachDbFileName=|DataDirectory|FilesDB.mdf;User Instance=True” SelectCommand=”SELECT Id,FileName FROM Files” Runat=”server” /> </div> </form> </body> </html> In Listing 4.5, the AddFile() method is called. This method adds a new row to the Files database table that contains the filename. Next, the StoreFile() method is called. This method adds the actual bytes of the uploaded file to the database. The file contents are divided into 8040-byte chunks. The SQL UPDATE statement includes a .WRITE clause used when the FileBytes database column is updated. NOTE Microsoft recommends that you set the buffer size to multiples of 8,040 when using the .WRITE clause to update database data. The page in Listing 4.5 never represents the entire uploaded file in memory. The file is yanked into memory from the file system in 8,040-byte chunks and fed to SQL Server in chunks. When you click a filename, the FileHandlerLarge.ashx HTTP Handler executes. This handler retrieves the selected file from the database and sends it to the browser. The handler is contained in Listing 4.6. From the Library of Wow! eBook . other operating system, an ASP. NET page executes in the security context of the ASPNET account. To enable ASP. NET Framework to save an uploaded file to a particular folder, you need to right-click. Explorer, select the Security tab, and provide either the NETWORK SERVICE or ASPNET account Write permissions for the folder (see Figure 4. 2). FIGURE 4. 2 Adding Write permissions for the ASPNET. ptg 1 84 CHAPTER 4 Using the Rich Controls The page includes a method named CheckFileType(), which prevents users from uploading a file that does not have the .gif, .jpeg, .jpg, or .png