Interception of ASP. NET output Stream processing

The title of this article refers to the processing of a page that has generated HTML before it is output to the client.

The principle of the method is: Redirect the output of response to the custom container, that is, our StringBuilder object, in the HTML all the page output to the StringBuilder output, Then we finish the StringBuilder processing, then redirect the output of response to the original page, and then output the StringBuilder content to the page by Response.Write method.

Reflection is used here because the output property of the response object is read-only, and by deserializing the assembly of the class, it is actually the internal private member _writer to implement the outputs. Therefore, the value of the member is overwritten by reflection to implement the redirection of the output stream.

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2. Using System;
4. Using System.Collections.Generic;
6. Using System.Linq;
8. Using System.Web;
10. Using System.Web.UI;
12. Using System.Web.UI.WebControls;
14. Using System.Text;
16. Using System.IO;
18. Using System.Reflection;
22. Public partial class _default:system.web.ui.page
24. {
26. StringBuilder content = new StringBuilder ();
28. TextWriter Tw_old, tw_new;
30. FieldInfo Tw_field;
34. protected void Page_Load (object sender, EventArgs e)
36. {
38. var context = HttpContext.Current;
42. Tw_old = context. Response.Output; //response the original output
44. Tw_new = New StringWriter (content); A stringwriter to get the page content
46. var TYPE_RP = context. Response.gettype ();
48. //Get the private field of an object by reflection
50. Tw_field = Type_rp. GetField ("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic |  System.Reflection.BindingFlags.Instance);
52. Tw_field. SetValue (context. Response, tw_new);
54. }
58. protected override void Render (HtmlTextWriter writer)
60. {
62. base.  Render (writer);
64. //Replace output of response back
66. Tw_field. SetValue (HttpContext.Current.Response, tw_old);
68. //Do your own processing
70. Content.  Appendline ("<!--Lake----");
72. HttpContext.Current.Response.Write (content. ToString ());
74. }
76. }
80. Method two, using Httpmodul to achieve:
84. Using System;
86. Using System.Collections.Generic;
88. Using System.Linq;
90. Using System.Web;
92. Using System.Web.UI;
94. Using System.IO;
96. Using System.Text;
98. Using System.Reflection;
102. <summary>
104. Summary description of HttpModule
106. </summary>
108. Public class Httpmodule:ihttpmodule
110. {
112. private HttpApplication _contextapplication;
114. private TextWriter tw_new, Tw_old;
116. private StringBuilder _content;
118. private FieldInfo Tw_field;
122. public void Init (HttpApplication context)
124. {
126. _contextapplication = context;
128. _contextapplication.prerequesthandlerexecute + = new EventHandler (_contextapplication_prerequesthandlerexecute  );
130. }
134. public void Dispose ()
136. {
138. _contextapplication = null;
140. _contextapplication.dispose ();
142. }
146. public void _contextapplication_prerequesthandlerexecute (object sender, EventArgs e)
148. {
150. HttpContext context = _contextapplication.context;
154. var _page = context.  Handler as System.Web.UI.Page;
156. _page.  Unload + = new EventHandler (_page_unload);
160. _content = new StringBuilder ();
162. Tw_old = context. Response.Output; //response the original output
164. Tw_new = new StringWriter (_content); A stringwriter to get the page content
166. var TYPE_RP = context. Response.gettype ();
168. Tw_field = Type_rp. GetField ("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic |  System.Reflection.BindingFlags.Instance);
170. Tw_field. SetValue (context. Response, tw_new);
172. }
178. void _page_unload (object sender, EventArgs e)
180. {
182. //Replace output of response back
184. Tw_field. SetValue (HttpContext.Current.Response, tw_old);
186. //Do your own processing
188. _content.  Appendline ("<!--Lake----");
190. HttpContext.Current.Response.Write (_content. ToString ());
192. }
196. }
200. Method Three:
202. Public class Httpmodule:ihttpmodule
204. {
206. private HttpApplication _contextapplication;
208. private TextWriter tw_new, Tw_old;
210. private StringBuilder _content;
212. private FieldInfo Tw_field;
216. public void Init (HttpApplication application)
218. {
220. _contextapplication = Application;
222. _contextapplication.beginrequest + = new EventHandler (_contextapplication_beginrequest);
224. _contextapplication.endrequest + =new EventHandler (_contextapplication_endrequest);
226. }
230. void _contextapplication_beginrequest (object sender, EventArgs e)
232. {
234. _content = new StringBuilder ();
236. Tw_old = _contextapplication.response.output;
238. Tw_new = new StringWriter (_content);
240. var type_rp = _contextapplication.response.gettype ();
242. Tw_field = Type_rp. GetField ("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic |  System.Reflection.BindingFlags.Instance);
244. Tw_field. SetValue (_contextapplication.response, tw_new);
246. }
250. void _contextapplication_endrequest (object sender, EventArgs e)
252. {
254. Tw_field. SetValue (_contextapplication.response, tw_old);
256. //Do your own processing
258. _content.  Appendline ("<!--jhxz-->");
260. _contextapplication.response.write (_content. ToString ());
262. }
266. public void Dispose ()
268. {
270. _contextapplication = null;
272. _contextapplication.dispose ();
274. }
276. }

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Interception of ASP. NET output Stream processing