{"id":143,"date":"2011-10-27T13:13:01","date_gmt":"2011-10-27T05:13:01","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=143"},"modified":"2018-09-03T21:10:08","modified_gmt":"2018-09-03T13:10:08","slug":"the-http-request-and-how-it-relates-to-system-net-httplistener","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/the-http-request-and-how-it-relates-to-system-net-httplistener\/","title":{"rendered":"The HTTP request and how it relates to System.Net.HttpListener"},"content":{"rendered":"

This is part 2 of the sequel to \"How to build a web based user interaction layer in C#<\/a>\". In this post, I will discuss how we can examine HTTP requests received from clients.<\/p>\n

In part 1, we learn how we can get an instance of the System.Net.HttpListenerContext<\/code> class whenever a client sends a HTTP request<\/a>.<\/p>\n

Continuing the sequel<\/h3>\n

The HTTP request received from the client will be represented as an instance of the System.Net.HttpListenerRequest<\/code><\/a> class and is available via the Request<\/code><\/a> property of the System.Net.HttpListenerContext<\/code><\/a> instance. <\/p>\n

\r\nHttpListenerRequest clientRequest = context.Request;\r\n<\/pre>\n
From the HttpListenerRequest<\/code> instance, your C# program can examine the HTTP request received from the client.<\/p>\n
The Url requested by the client<\/h3>\n
\r\nUri requestUrl = clientRequest.Url;\r\n<\/pre>\n
The Url<\/code> property contains an instance of the System.Uri<\/a> class that represents the HTTP resource requested by the client. With the Uri<\/code> instance, we can know which resource that a client wants to interact with, via the Uri.AbsolutePath<\/code><\/a> property.<\/p>\n
\r\nstring requestAbsolutePath \r\n    = clientRequest.Uri.AbsolutePath;\r\n<\/pre>\n
The AbsolutePath property will contain the part of the url that is after the hostname and\/or port and the first ?<\/strong> that denotes the first query string variable. For example, <\/p>\n
\/GetPersonName<\/strong> will be returned for<\/p>\n
http:\/\/localhost:12345\/GetPersonName?id=1<\/strong> <\/p>\n
and <\/p>\n
\/GetPersonName&id=1<\/strong> will be returned for<\/p>\n
http:\/\/localhost:12345\/GetPersonName&id=1<\/strong>.<\/p>\n
If the second case occurs, your C# program can consider the case as a 404 immediately.<\/p>\n
Query strings<\/h3>\n
Although we can get the query string via the Url<\/code> property of our HttpListenerRequest<\/code> instance, the QueryString<\/code><\/a> property of the HttpListenerRequest<\/code> instance provides better programmatic access to the query string values submitted by the client. The QueryString<\/code> property is an instance of the System.Collections.Specialized.NameValueCollection<\/code><\/a> class. <\/p>\n
\r\nNameValueCollection queryStringCollection \r\n    = clientRequest.QueryString;\r\n\/\/ Get the value of the variable named as "id"\r\n\/\/ id will be null when client does not send \r\n\/\/ any query string variable named as "id"\r\nstring id = queryStringCollection["id"];\r\n<\/pre>\n
The HTTP method<\/h3>\n
\r\nstring requestHttpMethod = clientRequest.HttpMethod;\r\n<\/pre>\n
With this information, your C# program can decide how to process input information from the client. For instance, if the client had indicated a HTTP Get, your C# program can take it that if there are any input from the client, it will be supplied as query strings. The System.Net.WebRequestMethods.Http<\/code><\/a> class supplies the possible values that may be contained in the HttpMethod<\/code><\/a> property of the HttpListenerRequest<\/code> instance.  <\/p>\n
The content type<\/h3>\n
The content type denotes the type of content that is contained in the HTTP request. <\/p>\n
\r\nstring requestContentType = clientRequest.ContentType;\r\n<\/pre>\n
This value is used in conjunction with the HTTP method. <\/p>\n
For HTTP Get, the browser typically don't fill up the content type field. <\/p>\n
For HTTP post, two possible values are: <\/p>\n