網頁程式不像視窗程式可以直接由單一的 process 執行。 它通常必須掛載在 Web Server 上，等待用戶端的 Web Browser 提出要求。 這二者之間的通訊就是使用 HTTP 協定。

網頁通訊

Web Server

  • The first Web servers were responsible for receiving and processing simple user requests from browsers via HTTP.
  • The Web server handled its request and sent a response back to the Web browser.
  • The Web server then closed any connection between it and the browser and released all resources that were involved with the request.

A simple request and response between browser and server in a stateless environment

Web Browser

  • The Web browser provides a platform-independent means of displaying Web pages that were written in HTML.
  • Although the Web browser’s role is simply to present information and collect data from users, many new client-side technologies enable today’s Web browsers to execute code such as JavaScript and to support plug-ins that improve the user’s experience, such as JavaScript and AJAX.

HTTP (Hypertext Transfer Protocol)

HTTP

  • 一種以文字為基礎的通訊協定，用來向 WebServer 提出需求，或者發送回應給 Browser 。
  • WebServer 和 Browser 之間的訊息傳送通常使用 80 port ，若是安全性HTTP (HTTPS) 則使用 443 port。

Request

當 Browser 向 WebServer 提出需求時，這個訊息內容會長的像底下這個樣子：
<span style=”color:red”>GET</span> <span style=”color:blue”>/default.aspx</span> <span style=”color:green”>HTTP/1.1</span> Host: www.corpname.com
上面需求內容，說明如下：

  1. 第一行第一個字稱為 Command ( 或 Verb 或 Method ) ，此例為 GET
  2. 接著是 URI ，此例為 /default.aspx
  3. 接著是 HTTP Version ，此例為 HTTP/1.1
  4. 第二行是網站的識別名稱，通常會對應到一組 IP 。

HTTP/1.1 支援的 Methods

  • GET：Gets a URL from the server
  • POST：Sends data to the Web server for processing.
  • PUT：Allows a client to directly create a resource at the indicated URL on the server.
  • DELETE：Used to delete a resource at the Web server.
  • HEAD：Retrieves the meta information for a resource.
  • OPTIONS：
  • CONNECT：
  • TRACE：
  • DEBUG：

當 IIS 收到 Browser 所提出的需求時， 它會先以一個 Requtst 物件來 wrap 這個需求內容再交由 ASP.NET 處理，以便日後可於程式碼中存取需求內容。 例如：cookies, query string parameters, request path 等資訊。

Response

當 ASP.NET 處理完需求，要送給 Browser 回應時，會將訊息 wrap 成 Response 物件。 你可以透過這個物件設定 cookies, caching, page expiration 等資訊。

而 IIS 則會根據 Response 物件中內容，回應如下的訊息內容：
HTTP/1.1 200 OK Server: Microsoft-IIS/6.0 Content-Type: text/html Content-Length: 38 <html><body>Hello, world.</body><html>
上面回應內容，說明如下：

  1. communication protoco, status code
  2. the type of Web server
  3. 回應給 Browser 的內容型態 (a MIME type)
  4. the content length
  5. the response message

狀態碼說明 (Status Codes)

簡單說，HTTP是一種請求／回應(Request/Response)的網路傳輸協定，當用戶端應用程式(瀏覽器)要求一網頁資訊或資源(Document)時，網站伺服器端就會回傳狀態碼(Status Code)，這些狀態碼通常是以數據化顯示。 使用者最常見到應該是404，其它包括200、301、302、304、403、410、500等等，都是3碼數字組成，第1碼是不同屬性的分類，以下依照數字小到大個別說明。
<!–#include file=”status-code.htm” –>
PS. IIS7 還有另外擴充一些狀態碼，可參考 MSDN : The HTTP status codes in IIS 7.0

多用途網際網路郵件延伸標準 (Multipurpose Internet Mail Extensions , MIME)

MIME 類型是用來識別從 WebServer 提供給瀏覽器或郵件用戶端的內容類型。 瀏覽器要求 WebServer 提供內容時，瀏覽器也同時要求該內容的 MIME 類型。 在傳回內容之前，IIS 會將此 MIME 類型隨著 HTTP 標頭中的 Content_Type 欄位傳回，這樣瀏覽器就可以知道如何處理或顯示該內容。

MIME type 都是由二部份組成 type/subtype 。底下為一些常見的 MIME Types.

  • Text：Textual information
  • Image：Image data..
  • Audio：Audio data.
  • Video：Video data.
  • Application：Other kinds of data, typically either uninterpreted binary data or information to be processed by an application.

Submit Data to the Web Server

The HTML <form> tag can be used to create a Web page that collects data from the user and sends the collected data back to the Web server. There are two HTTP methods that can be used to submit the form data back to the Web server: GET and POST.

<form method="POST" action="getCustomer.aspx">
Enter Customer ID:
<input type="text" name="Id">
<input type="submit" value="Get Customer">
</form>

Using GET verb

When the GET verb is used, the form data is appended to the URL as part of the query string. The following provides an example:
GET /getCustomer.aspx?Id=123&color=blue HTTP/1.1 Host: www.xxx.com
Note： When using Microsoft Internet Explorer and IIS, the limit for a given query string is 1,024 characters.

Using POST verb

When the POST verb is used, the form data is placed into the message body of the request as follows:
POST /getCustomer.aspx HTTP/1.1 Host: www.northwindtraders.com

Id=123&color=blue

MISC

Request 屬性

屬性GET RequestPOST Request
RequestContextSystem.Web.Routing.RequestContext 
IsLocalTrue 
HttpMethodGETPOST
RequestTypeGETPOST
ContentType  
ContentLength022
ContentEncodingSystem.Text.UTF8Encoding 
AcceptTypesSystem.String[] 
IsAuthenticatedTrue 
IsSecureConnectionFalse 
Path/C01_ASPNET_WebSite/Understanding.aspx 
AnonymousID  
FilePath/C01_ASPNET_WebSite/Understanding.aspx 
CurrentExecutionFilePath/C01_ASPNET_WebSite/Understanding.aspx 
CurrentExecutionFilePathExtension.aspx 
AppRelativeCurrentExecutionFilePath~/C01_ASPNET_WebSite/Understanding.aspx 
PathInfo  
PhysicalPathD:\myMCTS\VitoPractice\70-528\Practice70515\C01_ASPNET_WebSite\Understanding.aspx 
ApplicationPath/ 
PhysicalApplicationPathD:\myMCTS\VitoPractice\70-528\Practice70515\ 
UserAgentMozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP06) 
UserLanguagesSystem.String[] 
BrowserSystem.Web.Mobile.MobileCapabilities 
UserHostName::1 
UserHostAddress::1 
RawUrl/C01_ASPNET_WebSite/Understanding.aspx 
Urlhttp://localhost:14081/C01_ASPNET_WebSite/Understanding.aspx 
UrlReferrer  
Params…… 
QueryStringEmpNo=001&EmpName=Vito 
Form EmpNo=001&EmpName=vito
Headers…… 
ServerVariables…… 
CookiesSystem.Web.HttpCookieCollection 
FilesSystem.Web.HttpFileCollection 
InputStreamSystem.Web.HttpInputStream 
TotalBytes022
FilterSystem.Web.HttpInputStreamFilterSource 
ClientCertificateSystem.Web.HttpClientCertificate 
LogonUserIdentitySystem.Security.Principal.WindowsIdentity 

Request.ServerVariables 變數

變數資料
ALL_HTTPHTTP_CACHE_CONTROL:no-cache <br> HTTP_CONNECTION:Keep-Alive <br> HTTP_CONTENT_LENGTH:211 <br> HTTP_CONTENT_TYPE:application/x-www-form-urlencoded <br> HTTP_ACCEPT:text/html, application/xhtml+xml, */* <br> HTTP_ACCEPT_ENCODING:gzip, deflate <br> HTTP_ACCEPT_LANGUAGE:zh-TW <br> HTTP_COOKIE:ASP.NET_SessionId=kd4egzz12bn2frgf2yvmbnjj <br> HTTP_HOST:localhost:60755 <br> HTTP_REFERER:http://localhost:60755/C01_ASPNET_WebSite/Understanding.aspx <br> HTTP_USER_AGENT:Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP06)
ALL_RAWCache-Control: no-cache <br> Connection: Keep-Alive <br> Content-Length: 211 <br> Content-Type: application/x-www-form-urlencoded <br> Accept: text/html, application/xhtml+xml, */* <br> Accept-Encoding: gzip, deflate <br> Accept-Language: zh-TW <br> Cookie: ASP.NET_SessionId=kd4egzz12bn2frgf2yvmbnjj <br> Host: localhost:60755 <br> Referer: http://localhost:60755/C01_ASPNET_WebSite/Understanding.aspx <br> User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP06)
APPL_MD_PATH 
APPL_PHYSICAL_PATHD:\myMCTS\VitoPractice\70-528\Practice70515\
AUTH_TYPENTLM
AUTH_USERVITO-2011W7\Administrator
AUTH_PASSWORD 
LOGON_USERVITO-2011W7\Administrator
REMOTE_USERVITO-2011W7\Administrator
CERT_COOKIE 
CERT_FLAGS 
CERT_ISSUER 
CERT_KEYSIZE 
CERT_SECRETKEYSIZE 
CERT_SERIALNUMBER 
CERT_SERVER_ISSUER 
CERT_SERVER_SUBJECT 
CERT_SUBJECT 
CONTENT_LENGTH211
CONTENT_TYPEapplication/x-www-form-urlencoded
GATEWAY_INTERFACE 
HTTPS 
HTTPS_KEYSIZE 
HTTPS_SECRETKEYSIZE 
HTTPS_SERVER_ISSUER 
HTTPS_SERVER_SUBJECT 
INSTANCE_ID 
INSTANCE_META_PATH 
LOCAL_ADDR::1
PATH_INFO/C01_ASPNET_WebSite/Understanding.aspx
PATH_TRANSLATEDD:\myMCTS\VitoPractice\70-528\Practice70515\C01_ASPNET_WebSite\Understanding.aspx
QUERY_STRING 
REMOTE_ADDR::1
REMOTE_HOST::1
REMOTE_PORT 
REQUEST_METHODPOST
SCRIPT_NAME/C01_ASPNET_WebSite/Understanding.aspx
SERVER_NAMElocalhost
SERVER_PORT60755
SERVER_PORT_SECURE0
SERVER_PROTOCOLHTTP/1.1
SERVER_SOFTWARE 
URL/C01_ASPNET_WebSite/Understanding.aspx
HTTP_CACHE_CONTROLno-cache
HTTP_CONNECTIONKeep-Alive
HTTP_CONTENT_LENGTH211
HTTP_CONTENT_TYPEapplication/x-www-form-urlencoded
HTTP_ACCEPTtext/html, application/xhtml+xml, */*
HTTP_ACCEPT_ENCODINGgzip, deflate
HTTP_ACCEPT_LANGUAGEzh-TW
HTTP_COOKIEASP.NET_SessionId=kd4egzz12bn2frgf2yvmbnjj
HTTP_HOSTlocalhost:60755
HTTP_REFERERhttp://localhost:60755/C01_ASPNET_WebSite/Understanding.aspx
HTTP_USER_AGENTMozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP06)

ASP.NET 頁面事件的執行順序

<!–#include file=”page-life-cycle.htm” –>