Tài liệu Module 11: Internet Access pptx

Use the System.Net classes to communicate with other applications by using the HTTP, Transmission Control Protocol TCP, User Datagram Protocol UDP, and Socket Internet protocols!. Inter

Contents

Overview 1

Internet Application Scenarios 2

The WebRequest and WebResponse Model 3

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Instructor Notes

After completing this module, students will be able to:

! Use the basic request/response model to send and receive data over the Internet

! Use the System.Net classes to communicate with other applications by

using the HTTP, Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Socket Internet protocols

Materials and Preparation

This section provides the materials and preparation tasks that you need to teach this module

Required Materials

To teach this module, you need the Microsoft® PowerPoint® file 2349B_11.ppt

Preparation Tasks

To prepare for this module, you should:

! Read all of the materials for this module

! Complete the lab

Presentation:

60 Minutes

Lab:

45 Minutes

Module Strategy

Use the following strategy to present this module:

! Internet Application Scenarios

Briefly introduce examples of Internet applications that use the System.Net

classes, including server-side ASP.NET applications, peer-to-peer Microsoft Windows® Forms applications that act as servers and clients to send and receive data, and client applications that periodically access the network for updates

! The WebRequest and WebResponse Model Introduce the WebRequest and WebResponse model Explain how the Microsoft NET Framework uses the Uniform Resource Identifier (URI) to identify the desired communication protocol and Internet resource Discuss network streams as the means of obtaining and receiving Web data

Explain how to use the WebRequest class to request data from a server,

invoke the request for the Internet resource, and send data through a

network stream Discuss how the WebResponse.GetResponseStream

method serves as the means of obtaining a stream that contains response data from a network resource

! Application Protocols Discuss the HTTP, TCP, and UDP protocol support that is provided in the NET Framework, as well as information about using the Windows Sockets interface to implement custom protocols

! Best Practices Briefly outline the list of recommendations that will help students use the

classes that are contained in System.Net more effectively

Overview

! Internet Application Scenarios

! The WebRequest and WebResponse Model

! Application Protocols

! Handling Errors

! Security

! Best Practices

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The Microsoft® .NET Framework System.Net and System.Net.Sockets

namespaces provide a layered, extensible, and managed implementation of Internet protocols that applications can use to send or receive data over the

Internet The System.Net classes provide functionality that is similar to the

Microsoft WinInet API These classes provide varying levels of detail, from a generic request/response model to control over application protocols and

sockets In particular, the System.Net classes are designed for writing

scaleable, high-performance applications

An application can use the System.Net classes to communicate with any other

application that supports the basic Internet protocols However, that other application need not be a NET application The NET Framework provides alternative mechanisms for inter-application communication

For example, NET Framework remoting implements a generic mechanism for NET Framework objects to interact with one another across application

domains In addition, the System.Web.Services namespace contains classes for

applications to build and use XML Web services that are based on the standard Simple Object Access Protocol (SOAP)

For more information about the remoting and XML Web services approaches to inter-application communication, see Module 12, “Serialization,” in Course

2349B, Programming with the Microsoft NET Framework (Microsoft Visual C#™ NET)

After completing this module, you will be able to:

! Use the basic request/response model to send and receive data over the Internet

! Use the System.Net classes to communicate with other applications by

using the Hypertext Transfer Protocol (HTTP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Socket Internet protocols

In this module, you will learn

about the basic

request/response model that

is used to send and receive

data over the Internet, the

System.Net classes that

are used to communicate

with other applications, and

various techniques to

enhance application security

and performance

Internet Application Scenarios

! Server-Side ASP.NET Applications

" Obtain data from back-end sources for a browser request

! Peer-to-Peer Applications

" Send and receive data by acting as servers and clients

! Client Applications That Periodically Access the Network

" A robust implementation of HTTP 1.1, including:

Pipelining, chunking, authentication, pre-authentication, encryption, proxy support, server certificate validation, and connection management

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Several types of applications use the System.Net classes to send or receive data

over the Internet The following three Internet application scenarios are

examples of Internet applications that use the System.Net classes:

! Server-side ASP.NET applications that request data from server resources in response to a browser request

The System.Net classes are designed for writing scalable, high-performance

ASP.NET middle-tier applications The server-side ASP.NET scenario requires a robust middle-tier networking stack that can tolerate a high load

The System.Net classes specifically fulfill this important customer

requirement Such features as connection management, pipelining, Keep-alive, and asynchronous operations ensure strong support for the middle tier

In addition, because the System.Net classes are part of an overall

framework, integration with ASP.NET features, such as impersonation and caching, is seamless

! Peer-to-peer Windows Forms applications that act as servers and clients to send and receive data

! Client applications that periodically access the network for updates

The System.Net classes expose a robust implementation of the HTTP

protocol Because a large share of Internet traffic travels over the HTTP protocol, the protocol’s importance as an application protocol is significant

The System.Net classes support most of the HTTP 1.1 protocol features

The advanced features of HTTP 1.1 include pipelining, chunking, authentication, pre-authentication, encryption, proxy support, server certificate validation, connection management, and HTTP extensions

Topic Objective

To introduce Internet

application scenarios that

use the System.Net

classes

Lead-in

Several types of

applications use the

System.Net classes to send

or receive data over the

Internet

# The WebRequest and WebResponse Model

! Uniform Resource Identifier

! Using the WebRequest and WebResponse Model

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Internet applications can be classed broadly into two types: client applications that request information, and server applications that respond to information requests from clients The classic Internet client/server application is the World Wide Web, where people use browsers to access documents and other data that

is stored on Web servers worldwide

Applications are not limited to playing either the client or server role; the familiar middle-tier application server responds to requests from clients by requesting data from another server In this case, it is acting as both a server and

a client

The client application makes a request by identifying the desired Internet resource and the communication protocol that will be used to exchange the request and response If necessary, the client application also specifies any additional data that is required to complete the request, such as proxy location

or authentication information Authentication information includes such information as user name and password When the request is formed, it can be sent to the server

After the server has received the request and processed the response, the response is returned to the client application The response includes information that supplements the contents of the response, such as the type of content, which may include raw text or XML data

Topic Objective

To introduce the topics in

the section

Lead-in

Internet applications can be

classed broadly into two

types: client applications

that request information,

and server applications that

respond to information

requests from clients

The NET Framework provides classes that can be used to implement a request/response model to access Internet resources The two principal classes

are the WebRequest class, which contains a request for the resource; and the WebResponse class, which provides a container for the incoming response In addition, the Uri class is used to contain a Uniform Resource Identifier (URI),

which identifies the Internet resource that you are seeking The

NetworkStream class is used to write and read the data

A Uniform Resource Identifier URI is a compact representation of a resource that is available to your application through the Internet You may be more familiar with the term, URL, which stands for Uniform Resource Locator URLs form a subset of the more general URI naming scheme A URL identifies

an Internet resource that has a Web page address

For applications that need to make simple requests for Internet resources, the

WebClient class provides common methods for uploading data to or downloading data from an Internet server WebClient relies on the WebRequest class to provide access to Internet resources; therefore, the WebClient class can use any registered pluggable protocol

Note

Uniform Resource Identifier

! URI Contains:

! Example: http://www.contoso.com/whatsnew.aspx?date=today

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The NET Framework uses the URI to identify the desired communication protocol and Internet resource

The URI consists of at least three, and possibly four, parts:

! The scheme identifier, which identifies the communications protocol that is used by the request and response

! The server identifier, which consists of a Domain Name System (DNS) host name or TCP address that uniquely identifies the server on the Internet

! The path identifier, which locates the requested information on the server

! An optional query string, which passes information from the client to the server

For example, the URI http://www.contoso.com/whatsnew.aspx?date=today

consists of the scheme identifier http, the server identifier www.contoso.com, the path identifier /whatsnew.aspx, and the query string ?date=today

Topic Objective

To introduce the four parts

of the URI

Lead-in

The NET Framework uses

the URI to identify the

desired communication

protocol and Internet

resource

NetworkStream Class

! A NetworkStream Object Provides:

! System.Text.Encoding – Characters from and to Bytes

! Sequential Blocks Use StreamReader and StreamWriter

// reading ASCII stream to string Byte[] read = new Byte[32];

int bytes = anASCIIStream1.Read(read, 0, read.Length);

string stringData = Encoding.ASCII.GetString(read);

// writing string to ASCII stream Byte[] asciiBytes = Encoding.ASCII.GetBytes(stringData); anASCIIStream2.Write(asciiBytes, 0, asciiBytes.Length);

// reading ASCII stream to string Byte[] read = new Byte[32];

int bytes = anASCIIStream1.Read(read, 0, read.Length);

string stringData = Encoding.ASCII.GetString(read);

// writing string to ASCII stream Byte[] asciiBytes = Encoding.ASCII.GetBytes(stringData);

anASCIIStream2.Write(asciiBytes, 0, asciiBytes.Length);

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When resources on the Internet are obtained by using the System.Net classes, a Stream object represents the data that is being sent and received

Streams provide:

! A common way to send and receive Web data

Whether the actual contents of the file are HTML, XML, or another format,

an application uses Stream.Write and Stream.Read to send and receive

byte data

! Compatibility with streams across the NET Framework

Streams are used throughout the NET Framework, which provides a rich infrastructure for handling them For example, by changing only the few lines of code that initialize the stream, you can modify an application that reads XML data from a file stream to read data from a network stream instead

The major differences between the NetworkStream class and other streams are that the NetworkStream class is not seekable, the CanSeek property always returns false, and the Seek and Position methods throw a

NotSupportedException

! Processing of data as it arrives

Streams provide access to data as it arrives from the Internet, rather than forcing your application to wait for an entire data set to be downloaded

Topic Objective

To explain the function of

Network streams in the

.NET Framework

Lead-in

When resources on the

Internet are obtained by

using the System.Net

classes, the data that is

being sent and received is

represented through a

Stream object

Conversion Between Characters and Bytes The System.Text namespace contains classes for converting blocks of characters to and from blocks of bytes In particular, the Encoding class has

methods to convert arrays and strings of Unicode characters to and from arrays

of bytes, as in the following example:

// variable named anASCIIStream1 of type Stream // has been previously assigned to a Stream // containing bytes representing 7 bit ASCII character //

// reading ASCII stream and converting to string Byte[] read = new Byte[32];

int bytes = anASCIIStream1.Read(read, 0, read.Length);

string stringData = Encoding.ASCII.GetString(read);

//

// variable named anASCIIStream2 of type Stream // has been previously assigned to a writable Stream //

// converting string and writing 7 bit ASCII characters Byte[] asciiBytes =

Encoding.ASCII.GetBytes(stringData);

anASCIIStream2.Write(asciiBytes, 0, asciiBytes.Length);

Converting Data from Sequential Blocks

When the data that must be converted is only available in sequential blocks, such as data that is read from a long stream, an application may choose to use a decoder or an encoder to perform the conversion However, you can use the

StreamReader and StreamWriter classes to facilitate decoding and encoding

characters, as in the following example:

// variable anASCIIStream has been previously assigned // to a Stream of ASCII bytes

StreamReader sr = new StreamReader(

bytesread = sr.Read( Buffer, 0, length);

} //Close the stream when finished sr.Close();

Creating a WebRequest

! The WebRequest Encapsulates Details of Request

" Created by calling WebRequest.Create method

" Set any property values that are required

" Cast to access protocol-specific features

WebRequest req = WebRequest.Create("http://www.contoso.com/");

WebRequest req = WebRequest.Create("http://www.contoso.com/");

HttpWebRequest httpReq = (HttpWebRequest)WebRequest.Create("http://www.contoso.com/");

// Turn off connection keep-alives

req.Credentials = new NetworkCredential("username","password");

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Client applications request data from servers by using the WebRequest class and its descendents The WebRequest class encapsulates the details of the

process of connecting to the server, sending the request, and receiving the response

Calling WebRequest.Create Applications create WebRequest instances through the static WebRequest.Create method WebRequest.Create is a static method that creates a descendent WebRequest instance that is based on the URI scheme

that is passed

For example, the following code creates an HTTP request to www.contoso.com:

WebRequest req = WebRequest.Create("http://www.contoso.com/");

Setting Required Property Values Clients set required property values in the WebRequest instance For example,

to support authentication, you can set the Credentials property to an instance of the NetworkCredential class, as shown in the following code:

req.Credentials = new NetworkCredential("username","password");

Topic Objective

To describe how client

applications use the

WebRequest

Lead-in

Client applications request

data from servers by using

the WebRequest class and

its descendents

Casting WebRequest Objects to HttpWebRequest

To handle HTTP protocol requests to the Internet, the NET Framework

provides an HttpWebRequest class that is derived from the WebRequest class In most cases, the WebRequest class provides all of the properties that

you need to make a request However, if you need to access the HTTP

protocol-specific properties of the request, you can typecast WebRequest objects that are created by the WebRequest.Create to HttpWebRequest, as in

the following example:

HttpWebRequest httpReq = (HttpWebRequest) WebRequest.Create("http://www.contoso.com/");

// Turn off connection keep-alives

httpReq.KeepAlive = false;

Supporting Additional Protocols

The NET Framework provides protocol-specific WebRequest and WebResponse descendants for URIs that begin with http:, https:, and file: The programmable pluggable protocols of System.Net allow applications to

provide access through other protocols To support additional protocols, you

should implement protocol-specific descendants of WebRequest and WebResponse and register the descendant’s constructor with the WebRequest.RegisterPrefix method

For more information about supporting additional protocols, see the NET Framework Software Development Kit (SDK) documentation

Invoking a WebRequest

! Request Is Made by Calling the GetResponse Method

" Cast to access HTTP-specific features

WebResponse resp = req.GetResponse();

HttpWebResponse httpResp =(HttpWebResponse)httpReq.GetResponse();

//Get the HTTP content length returned by the server.String contentLength =

httpResp.ContentLength.ToString();

HttpWebResponse httpResp =(HttpWebResponse)httpReq.GetResponse();

//Get the HTTP content length returned by the server.String contentLength =

httpResp.ContentLength.ToString();

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After creating the WebRequest, you invoke the request for the Internet resource by calling the GetResponse method on the WebRequest instance The GetResponse method is responsible for:

! Constructing the protocol-specific request from the properties of the

WebRequest instance

! Making the TCP or UDP socket connection to the server

! Sending the request

The GetResponse method returns an instance that is derived from WebResponse that matches the instance that is derived from WebRequest, as

in the following example:

WebResponse resp = req.GetResponse();

The WebResponse class is also an abstract class that defines properties and

methods that are available to all applications that use pluggable protocols

WebResponse descendents are responsible for implementing these properties

and methods for the underlying protocol

For example, the HttpWebResponse class implements the WebResponse class

for the HTTP protocol If you need to access the HTTP protocol-specific

properties of the response, you can typecast WebResponse objects to HttpWebResponse, as in the following example:

HttpWebResponse httpResp = (HttpWebResponse)httpReq.GetResponse();

//Get the HTTP content length returned by the server

String contentLength = httpResp.ContentLength.ToString();

Topic Objective

To explain how to invoke the

request for an Internet

resource by calling the

GetResponse method on

the WebRequest instance

Lead-in

After creating the

WebRequest, you invoke

the request for the Internet

resource by calling the

GetResponse method on

the WebRequest instance

Sending Data

! For Requests That Send Data to the Server

//

try {

byte[] sendData =

Encoding.ASCII.GetBytes("some data");

int sendLength = sendData.Length;

HttpWebRequest httpReq = (HttpWebRequest) WebRequest.Create(

//

try {

byte[] sendData =

Encoding.ASCII.GetBytes("some data");

int sendLength = sendData.Length;

HttpWebRequest httpReq = (HttpWebRequest) WebRequest.Create(

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For requests that send data to the server, such as HTTP-POST or FTP-PUT requests, the data is sent through a network stream that is provided by the

WebRequest.GetRequestStream method You use the resulting Stream

object to write the data When you have finished uploading, you must close the

request stream with the Stream.Close method

The following example shows how to create a request that uses HTTP-POST to send data to the server:

//

try { byte[] sendData = Encoding.ASCII.GetBytes("some data"); int sendLength = sendData.Length;

HttpWebRequest httpReq = (HttpWebRequest) WebRequest.Create(

} //

After closing the stream, you can call GetResponse to ensure that the server

received the data correctly

Topic Objective

To describe how requests

that send data to the server

are created

Lead-in

For requests that send data

to the server, such as

HTTP-POST or FTP-PUT

requests, the data is sent

through a network stream

that is provided by the

WebRequest.GetRequest

Stream method

Receiving Data

! Reading Response Data

// Get the response stream

Stream respstrm = resp.GetResponseStream();

// Create a buffer to hold the response data

int BufferSize = 512;

Byte[] Buffer = new Byte[BufferSize];

// Read the stream to access the data

int bytesRead = respstrm.Read(Buffer, 0, BufferSize);while (bytesRead > 0) {

Console.Write(

Encoding.ASCII.GetString(Buffer, 0, bytesRead));bytesRead = respstrm.Read(Buffer, 0, BufferSize);}

respstrm.Close();

// Get the response stream

Stream respstrm = resp.GetResponseStream();

// Create a buffer to hold the response data

int BufferSize = 512;

Byte[] Buffer = new Byte[BufferSize];

// Read the stream to access the data

int bytesRead = respstrm.Read(Buffer, 0, BufferSize);while (bytesRead > 0) {

Console.Write(

Encoding.ASCII.GetString(Buffer, 0, bytesRead));bytesRead = respstrm.Read(Buffer, 0, BufferSize);}

respstrm.Close();

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To obtain the stream that contains response data from the network resource, use

the GetResponseStream method of the WebResponse instance, as in the

following example:

// Get the response stream

Stream respstrm = resp.GetResponseStream();

// Create a buffer to hold the response data

int BufferSize = 512;

Byte[] Buffer = new Byte[BufferSize];

// Read the stream to access the data

int bytesRead = respstrm.Read(Buffer, 0, BufferSize);

while (bytesRead > 0) { Console.Write(

Encoding.ASCII.GetString(Buffer, 0, bytesRead));

bytesRead = respstrm.Read(Buffer, 0, BufferSize);

} respstrm.Close();

If your application requires only the header information that is returned in the

WebResponse and ignores any returned data, then you do not need to get the

response stream

Closing Responses

After reading the data from the response, you must close any opened stream by

using the Stream.Close method or close the response by using the WebResponse.Close method, as in the following example:

resp.Close();

Topic Objective

To explain how to obtain the

stream that contains

response data from the

network

Lead-in

To obtain the stream that

contains response data from

the network resource, use

the GetResponseStream

method of the

WebResponse instance

You do not have to call the Close method on both the response stream and the WebResponse instance, but it is recommended WebResponse.Close calls Stream.Close when it closes the response If you do not close each response,

your application will run out of connections to the server and be unable to process additional requests

Considerations for Working with NetworkStreams

When using streams from network resources, remember the following:

! Because the NetworkStream class cannot change position in the stream, the CanSeek property always returns false The Seek and Position methods throw a NotSupportedException

! When you use WebRequest and WebResponse, stream instances that are created by calling GetResponseStream are read-only, and stream instances that are created by calling GetRequestStream are write-only

! The call to GetResponse may block if network resources are not available

You should consider using an asynchronous request with the

BeginGetResponse and EndGetResponse methods

! The call to GetRequestStream may block while the connection to the

server is created

You should consider using an asynchronous request for the stream with the

BeginGetRequestStream and EndGetRequestStream methods

Asynchronous operations are beyond the scope of this course

! You can use the StreamReader class to make the task of encoding easier The following code example uses a StreamReader to read an ASCII- encoded stream from a WebResponse instance The creation of the request

is not shown

// Create a response object

WebResponse response = request.GetResponse();

// Get a readable stream from the server

StreamReader sr = new StreamReader(

response.GetResponseStream(), Encoding.ASCII); // Use the stream Remember when you are through // with the stream to close it

//

sr.Close();

Using the WebRequest and WebResponse Model

//

WebRequest wReq = WebRequest.Create ("http://localhost/postinfo.html");

WebResponse wResp = wReq.GetResponse();

// Get a readable stream from the server StreamReader sr = new StreamReader(

bytesread = sr.Read( Buffer, 0, length);

} //Close the stream when finished sr.Close();

//

//

WebRequest wReq = WebRequest.Create ("http://localhost/postinfo.html");

WebResponse wResp = wReq.GetResponse();

// Get a readable stream from the server StreamReader sr = new StreamReader(

bytesread = sr.Read( Buffer, 0, length);

} //Close the stream when finished sr.Close();

//

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The following code example fully demonstrates the use of the WebRequest and WebResponse model as discussed in this section:

public static void Main(string[] args) {

try { WebRequest wReq = WebRequest.Create ("http://localhost/postinfo.html");

WebResponse wResp = wReq.GetResponse();

// Get a readable stream from the server StreamReader sr = new StreamReader(

wResp.GetResponseStream(),Encoding.ASCII); int length = 1024;

char[] Buffer = new char[1024];

You will now see an

example of the use of the

WebRequest and

WebResponse model as

discussed in this section

//Read from the stream and write data to console bytesread = sr.Read( Buffer, 0, length);

while( bytesread > 0 )

Console.Write( Buffer,0, bytesread);

bytesread = sr.Read( Buffer, 0, length);

//Close the stream when finished sr.Close();

} catch(Exception e) {

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The NET Framework supports application protocols that are currently in common use on the Internet

This section provides information about using the HTTP, TCP, and UDP protocol support that is provided in the NET Framework, in addition to

information about using the Windows Sockets interface to implement custom

protocols that are currently

in common use on the

Internet

HTTP

! Classes That Provide HTTP and HTTPS Protocols

" HttpWebRequest and HttpWebResponse

! Support Most HTTP 1.1 features

! HTTP Redirects Automatically if AllowAutoRedirect Property Is true (the Default)

! Use ServicePoint, ServicePointManager, and ConnectionGroupName Classes to Manage Connections

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With the HttpWebRequest and HttpWebResponse classes, the NET

Framework provides comprehensive support for the HTTP protocol, which makes up the majority of all Internet traffic

Classes for the HTTP and HTTPS Protocols The HttpWebRequest and HttpWebResponse classes are derived from the WebRequest and WebResponse classes, as was described in Creating a WebRequest in this module HttpWebRequest and HttpWebResponse are returned by default whenever the static method WebRequest.Create

encounters a URI that begins with http or https

In most cases, the WebRequest and WebResponse classes provide all that is

necessary to make the request, but if you need access to the HTTP-specific features that are exposed as properties, you can typecast these classes to

HttpWebRequest or HttpWebResponse, as demonstrated in Creating a

WebRequest in this module

Do not use the HttpWebRequest constructor Use the WebRequest.Create method to initialize new HttpWebRequest instances If

the scheme for the URI is http:// or https://, Create returns an HttpWebRequest instance

Support for HTTP 1.1 Features The HttpWebRequest and HttpWebResponse classes encapsulate a standard

HTTP request/response transaction and provide access to common HTTP headers These classes also support most HTTP 1.1 features, including pipelining, chunking, authentication, pre-authentication, encryption, proxy support, server certificate validation, and connection management Custom headers and headers that are not provided through properties can be stored in

and accessed through the Headers property

Topic Objective

To describe the support that

the NET Framework

provides for the HTTP

comprehensive support for

the HTTP protocol, which

makes up the majority of all

Internet traffic

Note

Support for HTTP Redirects

You can make your application follow HTTP redirects automatically by setting

the AllowAutoRedirect property to true, which is the default value The application redirects requests, and the ResponseURI property of

HttpWebResponse contains the actual Internet resource that responds to the request If you set AllowAutoRedirect to false, your application must be able

to handle redirects as HTTP protocol errors

Applications receive HTTP protocol errors by catching a WebException with the value of the Status property set to WebExceptionStatus.ProtocolError The Response property contains the WebResponse that is sent by the server

and indicates the actual HTTP error that is encountered

Managing Internet Connections

Applications that use HTTP to connect to data resources can use the NET

Framework ServicePoint and ServicePointManager classes to manage the

number of connections to the Internet and to optimize scale and performance The number of connections between a client and server can have a dramatic effect on application throughput

You can use ConnectionGroupName to form connection grouping that

associates specific requests within a single application to a defined connection pool You may have to use this technique with a middle-tier application that connects to a back-end server on behalf of a user and uses an authentication protocol that supports delegation, such as Kerberos, or by a middle-tier application that supplies its own credentials

For more information about classes that are used to manage connections and their methods, see the NET Framework SDK documentation

Internet Domain Name System

! Dns Class Retrieves Data About a Host from DNS

" GetHostByName query for www.contoso.com

" Resolve query for www.contoso.com

IPHostEntry hostInfo = Dns.GetHostByName("www.contoso.com");

IPHostEntry hostInfo = Dns.GetHostByName("www.contoso.com");

IPHostEntry hostInfo = Dns.Resolve("www.contoso.com");

IPHostEntry hostInfo = Dns.Resolve("www.contoso.com");

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The Dns class is a static class that retrieves information about a specific host

from the Internet Domain Name System (DNS)

The host information from a GetHostByName query is returned in an instance

of the IPHostEntry class If the specified host has more than one entry in the DNS database, IPHostEntry contains multiple Internet Protocol (IP) addresses

and aliases

The following example queries the DNS database for information about a host that is called www.contoso.com:

IPHostEntry hostInfo = Dns.GetHostByName("www.contoso.com");

The Resolve method queries a DNS server for the IP address that is associated

with a host name, such as www.contoso.com, or for an IP address in dotted-quad notation, such as 192.168.1.2

When the host name is a DNS-style host name that is associated with multiple

IP addresses, only the first IP address that resolves to that host name is returned,

as in the following example:

IPHostEntry hostInfo = Dns.Resolve("www.contoso.com");

The Dns class is a static

class that retrieves

information about a specific

host from the Internet

Domain Name System

TCP and UDP

! TCP Client Connecting to a Server/Listener

! TCP Server/Listener Monitors Port for Clients

TcpClient tcpc = new TcpClient(serverURI, 14);

Stream s = tcpc.GetStream();

Byte[] read = new Byte[32];

int bytes = s.Read(read, 0, read.Length);

String strInData = Encoding.ASCII.GetString(read);

TcpClient tcpc = new TcpClient(serverURI, 14);

Stream s = tcpc.GetStream();

Byte[] read = new Byte[32];

int bytes = s.Read(read, 0, read.Length);

String strInData = Encoding.ASCII.GetString(read);

TcpListener tcpl = new TcpListener(14);

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

Applications can use TCP and UDP services with the TcpClient, TcpListener, and UdpClient classes These classes, which are built on top of the Socket

class, represent the data that is sent and received from the network as streams These classes also take care of the details of creating a connection

Using the TcpClient Class You use the TcpClient class to request data from an Internet resource that uses TCP The methods and properties of TcpClient abstract the details for creating

a Socket instance that requests and receives data through TCP The connection

to the Internet is represented as a stream; therefore data can be read and written

Byte[] read = new Byte[32];

int bytes = s.Read(read, 0, read.Length);

String strInData = Encoding.ASCII.GetString(read);

Topic Objective

To explain how to use the

TcpClient and TcpListener

classes to request data from

an Internet resource and to

monitor TCP ports

Lead-in

Applications can use TCP

and UDP services with the

TcpClient, TcpListener,

and UdpClient classes