ASP.NET provides intrinsic objects to enable low-level access to the Web application framework. These objects allow you to work directly with the underlying HTTP streams and server, session, and application objects. The intrinsic objects can be accessed in a Web form through the properties of the Page class. Table 4.1 lists the important intrinsic objects and the properties of the Page class to which they are mapped. Table 4.1. Intrinsic Objects and Their Mappings to the Page Class Properties Intrinsic Object | Property of the Page Class | HttpRequest | Request | HttpResponse | Response | HttpServerUtility | Server | HttpApplicationState | Application | HttpSessionState | Session | The HttpRequest Object The HttpRequest object represents the incoming request from the client to the Web server. The request from the client can come in two ways GET or POST . GET attaches the data with the URL, whereas POST embeds the data within the HTTP request body. The HttpRequest intrinsic object can be accessed by the Request property of the Page class. Tables 4.2 and 4.3 list the properties and methods of the HttpRequest class, respectively. Note that all the properties except the Filter property of the HttpRequest class are read-only. Table 4.2. Properties of the HttpRequest Class Property | Description | AcceptTypes | Specifies the MIME types that the client browser accepts | ApplicationPath | Represents the application's virtual application root path on the server | Browser | Provides access to the capabilities and characteristics of the requesting browser | ClientCertificate | Represents the certificate, if any, sent by the client for secure communications | ContentEncoding | Represents the character encoding (such as UTF7, ASCII , and so on) for the entity body | ContentLength | Specifies the length in bytes of the request | ContentType | Specifies the MIME type of the incoming request | Cookies | Represents the cookies collection that is sent by the client to the server | CurrentExecutionFilePath | Specifies the virtual path of the current executing page on the Web server | FilePath | Specifies the virtual path of the file on the Web server | Files | Represents the file collection that is posted by the client to the Web server | Filter | Represents a stream that is applied as a filter on the incoming request | Form | Specifies the contents of a form posted to the server | Headers | Represents the HTTP headers included with the incoming request | HttpMethod | Represents the method of the HTTP request (for example, GET, POST , or HEAD ) | InputStream | Represents the stream that contains the incoming HTTP request body | IsAuthenticated | Indicates whether the client has been authenticated to the Web site | IsSecureConnection | Indicates whether the client connection is over a secure HTTPS connection | Params | Represents the form, query string, cookies, and server variables collection of the current request | Path | Specifies the virtual path of the current request, along with additional path information | PathInfo | Specifies the additional path information of the current request | PhysicalApplicationPath | Specifies the physical file system path of the application's root directory | PhysicalPath | Specifies the physical file system path of the current request on the Web server | QueryString | Represents the query string collection sent by the client to the Web server through the URL | RawUrl | Specifies the URL portion of the current request, excluding the domain information | RequestType | Represents the type of request ( GET or POST ) made by the client | ServerVariables | Represents the collection of Web server variables | TotalBytes | Represents the total number of bytes posted to the server in the current request | Url | Specifies information about the current URL request | UrlReferrer | Specifies the URL of the client's previous request that linked to the current URL request | UserAgent | Represents the browser being used by the client | UserHostAddress | Represents the IP address of the requesting client's machine | UserHostName | Represents the domain name system (DNS) name of the requesting client's machine | UserLanguages | Specifies the languages preferred by the client's browser | Table 4.3. Methods of the HttpRequest Class Method | Description | Method | Description | BinaryRead() | Reads the specified number of bytes from the request stream. This method is provided for backward compatibility; you should use the InputStream property instead. | MapImageCoordinates() | Returns the coordinates of a form image that is sent to the server in the current request. | MapPath() | Returns the physical file system path of the file for a specified virtual path of a Web server. | SaveAs() | Saves the current HTTP request into a disk file, with an option to include or exclude headers. | The following code segment displays the header information sent by the client to the server: // Display the request header System.Collections.Specialized.NameValueCollection nvcHeaders = Request.Headers; String[] astrKeys = nvcHeaders.AllKeys; // Iterate through all header keys and display their values foreach (String strKey in astrKeys) { Response.Write(strKey + ": " + nvcHeaders[strKey].ToString()); Response.Write("<br>"); } Some properties of the HttpRequest objectsuch as Form , QueryString , Headers , and so onreturn a NameValueCollection containing a collection of key-value pairs of their contents. The previous code segment demonstrates how to iterate through this collection by iterating through the keys of the Headers collection and displaying the key and value of each header sent by the client. The HttpResponse Object The HttpResponse object represents the response sent back to the client from the Web server. It contains properties and methods that provide direct access to the response stream and enable you to set its behavior and operations. The Response property of the Page class provides access to the HttpResponse object. Tables 4.4 and 4.5 list the properties and methods of the HttpResponse class, respectively. Table 4.4. Properties of the HttpResponse Class Property | Description | Buffer | Indicates whether output to the response stream needs to be buffered and sent to the client after the entire page is processed . This property is provided for backward compatibility; the BufferOutput property should be used instead. | BufferOutput | Indicates whether the output to the response stream needs to be buffered and then sent to the client after the entire page is processed. The default is true . | Cache | Represents the caching policy of the page. The policy controls where caching can be done, the expiration time, and so on. | CacheControl | Specifies where the caching should be done. The possible values are Public and Private . | Charset | Represents the character set of the output stream. If set to null , the content-type header is suppressed. | ContentEncoding | Represents the character set of the response output stream. | ContentType | Represents the MIME type for the outgoing response stream, such as text/html, text/xml , and so on. | Cookies | Represents the cookies collection that is sent by the server to the client. | Expires | Indicates the number of minutes until the page is cached by the client browser. | ExpiresAbsolute | Indicates the specific date and time until the page is cached by the client browser. | Filter | Represents a stream that is applied as a filter to the outgoing response. | IsClientConnected | Indicates whether the client is connected to the server. This property is very helpful when running a lengthy request. | Output | Returns a TextWriter object that enables writing custom output to the outgoing response. | OutputStream | Allows writing binary output to the outgoing response. | Status | Specifies the status of the HTTP output that is sent to the client. This property returns both the status code and the text description of the status (for example, 200 OK ). | StatusCode | Specifies the numeric representation of the status of the HTTP output sent to the client (for example, 200, 302 , and so on). | StatusDescription | Specifies the text representation of the status of the HTTP output sent to the client. (for example, OK, Redirect , and so on). | SupressContent | Indicates whether the content in the page should be suppressed and not sent to the client. | Table 4.5. Methods of the HttpResponse Class Method | Description | AddCacheItemDependencies() | Specifies that the current cached response is dependent on the items specified in a given ArrayList object. | AddCacheItemDependency() | Specifies that the current cached response is dependant on the item specified in the given String object. | AddFileDependencies() | Adds a group of files to the collection on which the current response depends. | AddFileDependency() | Adds a file to the collection on which the current response depends. | AddHeader() | Adds an HTTP header to the outgoing response stream. This method is provided for backward compatibility with ASP. | AppendHeader() | Adds an HTTP header to the outgoing response stream. | AppendToLog() | Adds information to the IIS Web log file. | ApplyAppPathModifier() | In case of a cookieless session, it adds a session ID to the given virtual path. | BinaryWrite() | Allows writing binary data such as an image file or a PDF file to the response stream. | Clear() | Clears the entire response stream buffer, including its contents and headers. | ClearContent() | Clears the entire content portion of the response stream buffer. | ClearHeaders() | Clears the headers portion of the response stream buffer. | Close() | Closes the response object and the socket connection to the client. | End() | Stops the execution of the page after flushing the output buffer to the client. | Flush() | Flushes the currently buffered content out to the client. | Pics() | Adds a PICS-label HTTP header to the outgoing response. | Redirect() | Redirects the client browser to any URL. This method requires an additional round trip to the browser. | RemoveOutputCacheItem() | Removes all cache items for the path specified. | Write() | Writes output to the outgoing response. | WriteFile() | Writes a file to the outgoing response. | The following example shows the use of the HttpResponse object methods and properties to create a response that displays the File Download dialog box and allows the user to download a text file from the Web server to the client's machine: -
Add a new Visual C# ASP.NET Web Application project to the solution, and name it Example4_2 . Change the pageLayout property of the DOCUMENT element of the Web form to FlowLayout . -
Add a text file to the project that contains some data that needs to be downloaded. Name it Summary.txt . -
Add a LinkButton control ( lbtnDownload ) to the Web form with its Text property set to Download Summary.txt . -
Double-click the lbtnDownload control and add the following code to the Click event handler: private void lbtnDownload_Click(object sender, System.EventArgs e) { // Force a download of Summary.txt as an attachment Response.AppendHeader("Content-Disposition", "Attachment;FileName=" + "Summary.txt"); // The download file is a TXT file Response.ContentType = "text/plain"; // Write the file to the Response Response.WriteFile("Summary.txt"); // Stop further execution of the page Response.End(); } -
Run the project. Click the link button; you should see a File Download dialog box that enables you to save the file locally. The HttpServerUtility Object The HttpServerUtility object contains utility methods and properties to work with the Web server. It also contains methods to enable HTML/URL encoding and decoding, execute or transfer to an ASPX page, create COM components , and so on. The Server property of the Page class provides access to the HttpServerUtility object. Tables 4.6 and 4.7 list the properties and methods of this class, respectively. Table 4.6. Properties of the HttpServerUtility Class Property | Description | MachineName | Returns the name of the server that hosts the Web application | ScriptTimeout | Indicates the number of seconds that are allowed to elapse when processing the request before a timeout error is sent to the client | Table 4.7. Methods of the HttpServerUtility Class Method | Description | ClearError() | Clears the last exception from memory | CreateObject() | Creates a COM object on the server | CreateObjectFromClsid() | Creates a COM object on the server identified by a specified class identifier (CLSID) | Execute() | Executes an ASPX page within the current requested page | GetLastError() | Returns the last exception that occurred on the Web server | HtmlDecode() | Decodes a string that has been previously encoded to eliminate invalid HTML characters | HtmlEncode() | Encodes a string converting any characters that are illegal in HTML for transmission over HTTP | MapPath() | Returns the physical path for a specified virtual path on a Web server | Transfer() | Allows the transfer of ASPX page execution from the current page to another ASPX page on the same Web server | UrlDecode() | Decodes a string that has been previously encoded to eliminate invalid characters for transmission over HTTP in a URL | UrlEncode() | Encodes a given string for safe transmission over HTTP | UrlPathEncode() | Encodes the path portion of the URL string for safe transmission over HTTP | |