PDN-C11-PPT.ppt

Chapter 11Web Services

(Code Reuse over the Internet)Yingcai Xiao

What is it?What it is for?

ExamplesHow to write one?

What’s inside?How does it work?

Web Services

Proxy of Interface 2

Client 2

Application 1

UDDI Registry 1

WSDL Interface 1

UDDI Registry 2

Application 2 WSDL Interface 2

SOAP

SOAP

WEB


Client 1

A Web service is an application that exposes Web methods over the Web.

Sharing Objects over the Internet: How? Transmitting => HTTP Sharing => Standard:

SOAP (Simple Object Access Protocol) for objects

WSDL (Web Service Definition Language) for services Defining => XML for both

.

Web Services (XML Web Services) (Outside) A Web service is a different kind of Web application. It’s not designed to serve end users. It’s designed to provide services to other applications

through a highly programmable Internet. It doesn’t have a user interface. It exposes callable API functions, known as Web

methods, over the Internet. .NET Framework makes writing Web services and Web

service clients easy. Web services are not the property of Microsoft. They’re an

industry standard built on open protocols such as HTTP and the Simple Object Access Protocol (SOAP).

You don’t need the .NET Framework to write Web services or Web service clients.

Web Services (Inside) A Web service is an application that:

Runs on a Web server Exposes Web methods to interested callers Listens for HTTP requests representing commands to

invoke Web methods Executes Web methods and returns the results Most Web services expect SOAP messages. SOAP is an XML-based vocabulary for performing

remote procedure calls using HTTP and other protocols. (http://www.w3.org/TR/SOAP).

http://www.w3.org/TR/SOAP

Professional Web Service Examples

Microsoft TerraService: http://terraservice.net/terraservice.asmx

http://winserv1.cs.uakron.edu/xiaotest/CityView.aspx

Ubid:

https://www.ubid.com/app/mypage/Login.aspx

http://login.live.com/login.srf

http://terraservice.net/terraservice.asmx



http://login.live.com/login.srf

Professional Web Service ExamplesWeb Service started to evolve into Cloud Computing, where the

software is in the “cloud”. One of the main techniques for Cloud Computing is software as a service (SaaS).

Amazon E-Commerce Service (ECS) / Amazon Web Services (AWS): http://aws.amazon.com/ (Cloud Computing)Discussion Forums: http://developer.amazonwebservices.com/connect/forumindex.jspa

Google Apps: (Cloud Computing)http://www.google.com/appshttp://code.google.com/intl/en/http://www.google.com/apis/maps/http://maps.google.com/300 E Buchtel Ave, Akron, Ohio 44325

Ways to Write WS

There are many ways to write Web services write Web services by hand; use SOAP toolkits from Microsoft, IBM, and other companies; use the .NET Framework (easy, managed). (need to install IIS and

ASP.NET, http://www.cs.uakron.edu/~xiao/windows/IISUpdateProcedure.html)

Our First Web Service Using ASP.NET

Calc.asmx<%@ WebService Language="C#" Class="CalcService" %>

using System;using System.Web.Services;

[WebService (Name="Calculator Web Service", Description="Performs simple math over the Web")]class CalcService{[WebMethod (Description="Computes the sum of two integers")] public int Add (int a, int b) { return a + b; }


[WebMethod

(Description="Computes the difference between two integers")]

public int Subtract (int a, int b)

{

return a - b;

}

}


The ASMX file (calc.asmx) is a complete Web service. It implements two Web methods: Add and Subtract. Both take two integers as input and return an integer as well. Calc.asmx implements two Web methods: Add and

Subtract. Deploying: copying it to a directory on your Web server

that is URL-addressable (in C:\inetpub\wwwroot). Accessing:

http://winserv1.cs.uakron.edu/xiaotest/calc.asmx. Or map the examples directory as virtual directory

Examples, http://winserv1.cs.uakron.edu/WP/c11/calc/calc.asmx

(Need to be on the server to test locally.)


Important principles of Web service programming using the .NET Framework: ASMX is a file name extension registered to ASP.NET in

Machine.config. ASMX files begin with @ WebService directives. At a minimum, the directive must contain a Class attribute

identifying the class that makes up the Web service. Web service classes can be attributed with optional

WebService attributes. Web methods are declared by tagging public methods with

WebMethod attributes. Helper methods are not exposed by omitting the attribute. HTTP, XML, and SOAP are hidden under the hood. The Web methods can be invoked with SOAP, HTTP GET,

and HTTP POST. They can return output in SOAP responses or simple XML

wrappers.

How a Web Service can be tested

ASP.NET can generate forms to test web services on the fly from ASMX files.

Therefore, we don’t have to write special clients and GUI to test web services.

Example: Calc.asmx Users call http://winserv1.cs.uakron.edu/xiaotest/Calc.asmx up in a

browser. IIS sends the request to ASP.NET on winserv1.cs.uakron.edu. ASP.NET compiles Calc.asmx into a DLL. ASP.NET displays a page that users can test the Add method. Users Interact with it by clicking the “Add” button. ASP.NET finds the method name and signature by reading them from

the metadata in the DLL. It generates an HTML form that users can use to call the Add method

with choice of inputs. When the users type 2 and 2 into the “a” and “b” boxes and click

Invoke, the XML returned by the Web method appears in a separate browser window.

Inside Web Services

The WebService Base Class class CalcService : WebService

WebService belongs to the System.Web.Services namespace.

It contributes properties named Application, Session, Context, Server, and User to derived classes.

The WebMethod Attribute

The WebMethod attribute tags a method as a Web method and supports the following parameters:

Parameter Name Description

BufferResponse Enables and disables response buffering

CacheDuration Caches responses, in seconds

Description Adds a textual description to a Web method

EnableSession Enables and disables session state for this Web method (default: disabled)

MessageName Specifies the Web method’s name

TransactionOption Specifies the transactional behavior of a Web method

The WebMethod Attribute [WebMethod (EnableSession="true",

Description="Adds an item to a shopping cart")]

public void AddToCart (Item item)

{ ShoppingCart cart = (ShoppingCart) Session["MyShoppingCart"];

cart.Add (item); }

Web methods cannot be overloaded. (Why?)

[WebMethod (MessageName="AddInts")]

public int Add (int a, int b)

{ return a + b; }

[WebMethod (MessageName="AddFloats")]

public float Add (float a, float b)

{ return a + b; }

The Web Services Description Language (WSDL)

A new standard for describing web services. An XML vocabulary. For machines to read. Documented at http://www.w3.org/TR/wsdl. Need to publish a WSDL contract when publishing a Web service. Other developers can use the contract to write clients for your Web

service. Wsdl.exe generates a wrapper class containing all the elements needed to talk to a Web service.

To generate a WSDL contract :

http://winserv1.cs.uakron.edu/xiaotest/Calc.asmx?wsdl

http://www.w3.org/TR/wsdl

WSDL Contract

A WSDL contract which contains: service element that describes the Web service; operation elements that document the “operations,” or Web

methods, that the service supports; binding elements that document the protocols that the Web

methods support; other descriptive information.

Web Services and Complex Data Types

Complex types are supported. Represented in XML using SOAP. A client obtains an XML schema describing

the data type from the service’s WSDL contract.

Note: WSDL is for describing web services (special web applications) while SOAP is for describing web objects. Both use XML vocabulary. (books, chapters, paragraphs, English).

Web Services and Complex Data TypesC# Classpublic class Bookstore{ public string Name; public string Address; public string City; public string State;

…}

SOAP in XML<s:complexType name="Bookstore"> <s:sequence> <s:element minOccurs="1" maxOccurs="1" name="Name" nillable="true" type="s:string" /> <s:element minOccurs="1" maxOccurs="1" name="Address" nillable="true" type="s:string" /> <s:element minOccurs="1" maxOccurs="1" name="City" nillable="true" type="s:string" /> <s:element minOccurs="1" maxOccurs="1" name="State" nillable="true" type="s:string" /> </s:sequence></s:complexType>

Web Services and Complex Data Types

You can’t pass complex types to a Web method using HTTP GET and POST. That’s not a limitation if you use SOAP to invoke Web methods. (ASP.NET generates test pages using HTTP GET).

Any fields or properties declared in a class or struct that’s passed to or from a Web method must be public if they’re to be serialized (transmitted or saved) when instances of the class or struct are serialized. That’s because the .NET Framework’s XML serializer will not serialize nonpublic members.

Examine a WSDL contract:

http://winserv1.cs.uakron.edu/xiaotest/calc2.asmx?wsdl

How to Use/Consume Web Services (WS) Internal (low-level) code for using web services. HTTP commands for using web services through a

web browser. How to write a WS client using proxies. A console-based WS client. An ASP.NET-based WS client. For-fee WSs. Searching for WSs.

WS Low-level Code

Example: a Web service that publishes Web methods named Add and Subtract at www.wintellect.com/calc.asmx.

• Before sending a request to the web service, the client needs to know the services provided by the web service by reading its WSDL contract.

• http://tempuri.org/ provides namespaces for XML Web Services under development.

http://tempuri.org/

http://tempuri.org/

http://tempuri.org/

WS Low-level CodeA client sent a request to add 2 and 2 to the “Add” Web method using SOAP.

POST /calc.asmx HTTP/1.1Host: www.wintellect.comContent-Type: text/xml; charset=utf-8Content-Length: 338SOAPAction: "http://tempuri.org/Add"<?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <Add xmlns="http://tempuri.org/"> <a>2</a> <b>2</b> </Add> </soap:Body></soap:Envelope>

WS Low-level Code• And here’s how the Web service would respond using SOAP:

HTTP/1.1 200 OKContent-Type: text/xml; charset=utf-8Content Length: 353<?xml version="1.0" encoding="utf8"?><soap:Envelope xmlns:xsi=http://www.w3.org/2001/XMLSchemainstance xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body>

<AddResponse xmlns="http://tempuri.org/"> <AddResult>4</AddResult> </AddResponse>

</soap:Body></soap:Envelope>

WS Low-level Code The Web service’s job for responding to each request is to

receive input from client, parse the SOAP envelope containing the inputs, compute, formulate a SOAP envelope containing the result, return it to the client in the body of the HTTP response.

The WSDL contract is published just once for each web service, not for each request.

• .NET Framework insulates developers from the low-level details of SOAP, HTTP, and XML and provides a high-level framework for writing Web services and Web service clients.

.NET Framework also allows Web methods to be invoked using ordinary HTTP GET and POST commands instead of SOAP. This is a non-OO approach and can’t take care of ComplexType objects.

Using Get:GET /calc.asmx/Add?a=2&b=2 HTTP/1.1 Host: www.wintellect.com

The Web service responds as follows:HTTP/1.1 200 OKContent-Type: text/xml; charset=utf-8Content-Length: 80

<?xml version="1.0" encoding="utf-8"?><int xmlns="http://tempuri.org/">4</int>

WS Using HTTP GET

Here’s a POST command that adds 2 and 2:POST /calc.asmx/Add HTTP/1.1Host: www.wintellect.comContent-Type: application/x-www-form-urlencodedContent-Length: 7

a=2&b=2

And here’s the Web service’s response:HTTP/1.1 200 OKContent-Type: text/xml; charset=utf-8Content-Length: 80

<?xml version="1.0" encoding="utf-8"?><int xmlns="http://tempuri.org/">4</int>

WS Using HTTP POST

Web Services


Client 2

Application 1

UDDI Registry 1

WSDL Interface 1

UDDI Registry 2


SOAP

SOAP

WEB


Client 1


Writing Clients to Consume

Web Services

Web Service Clients & Proxies

Web service clients—applications that use, or consume, Web methods.

Web Service Proxies A Web service proxy is an object that

provides a local representation of a remote Web service.

A proxy is instantiated in the client’s own application domain, but calls to the proxy flow through the proxy and out to the Web service that the proxy represents.

Web Service Clients & Proxies

Calling the corresponding Web service is a simple matter of calling methods on the proxy.CalculatorWebService calc = new CalculatorWebService ();int sum = calc.Add (2, 2);

When you call one of these methods, the proxy packages up the input parameters and invokes the Web method using the protocol encapsulated in the proxy (typically SOAP).

The proxy insulates you from the low-level details of the Web service and of the protocols that it uses. It even parses the XML that comes back and makes the result available as managed types.

Generation of a Web Service Proxy The wsdl.exe utility that comes with the .NET Framework SDK

generates Web service proxy classes from WSDL contracts.

For Web services written with .NET: All Programs->…-> Visual Studio Command Promptcd to the directory you are going to write your clientwsdl http://winserv1.cs.uakron.edu/xiaotest/calc.asmx

In the lab:Z:mkdir wscd wswsdl http://lwinserv1.cs.uakron.edu/calc.asmx

For Web services not written with .NET:find the WSDL contract and wsdl calc.wsdl

Generation of a Web service proxy Wsdl.exe generates a CS file containing a class that

represents the Web service proxy. Use the class to invoke the Web service’s methods. The proxy class’s name comes from the service name.Example:[WebService (Name="Calculator Web Service")]

The resulting <service> tag in the WSDL contract looks like this:Name=Calculator_x0020_Web_x0020_Service

The resulting proxy class is named CalculatorWebService.

Wsdl.exe switches:/out:Calc.cs /language:vb /namespace:Calc /protocol:httpget /protocol:httppost /proxy:http://myproxy

A Simple Web Service ClientWrite a console client (not a web client) for web service Calc.asmx.

1. Use Wsdl.exe to create a proxy class for Calc.asmx. wsdl http://winserv1.cs.uakron.edu/xiaotest/calc.asmx

or wsdl http://winserv1.cs.uakron.edu/WP/c11/calc/calc.asmx

wsdl.exe responds by creating a file named CalculatorWebService.cs which contains the proxy class.

2. Create a new text file named CalcConsoleClient.cs to use the proxy class.using System;class MyApp{ public static void Main () { CalculatorWebService calc = new CalculatorWebService (); int sum = calc.Add (2, 2); Console.WriteLine ("2 + 2 = " + sum);} }

A Simple Web Service Client

3. Compile the CS files into a console application:

csc CalcConsoleClient.cs CalculatorWebService.cs

4. Run CalcConsoleClient.exe.

5. The WS client program instantiates a Web service proxy, calls the service’s Add method, and displays the result.

Write an ASP client for Calc.asmx

1. Create a proxy class for Calc.asmx the same way as above.

2. Create a new CS file named CalcASPClient.cs to use the proxy class.

using System; using System.Web.UI;

using System.Web.UI.WebControls;

public class CalcASPClient : Page

{ protected Label Sum;

protected TextBox op1, op2;

public void OnAdd (Object sender, EventArgs e)

{ int a = Convert.ToInt32 (op1.Text);

int b = Convert.ToInt32 (op2.Text);

CalculatorWebService calc = new CalculatorWebService ();

int c = calc.Add (a, b); Sum.Text = c.ToString ();

}


3. Compile the CS files into a dll for code behind:csc /target:library /out:bin\CalcASPClient.dll CalcASPClient.cs CalculatorWebService.cs

4. Create a new ASP file named CalcASPClient.aspx file to use the code behind.

<%@ Page Inherits="CalcASPClient" %><html> <body> <form runat="server"> <asp:TextBox ID="op1" RunAt="server" /> + <asp:TextBox ID="op2" RunAt="server" /> <asp:Button Text="=" OnClick="OnAdd" RunAt="server" /> <asp:Label ID="Sum" RunAt="server" /></form> </body> </html>


5. Create a virtual directory: CalcASPClient. 6. Access the “client” through a browser.

http://winserv1.cs.uakron.edu/xiaotest/CalcASPClient.aspx

The event flow when the user clicks to add:

User->Web Client (a browser)->Web Server (IIS) where Web app CalcASPClient.aspx is ->ASP.NET->ASP Application (CalcASPClient.aspx and

CalcASPClient::OnAdd)->Web Service Proxy (CalculatorWebService::Add) -> Web Server (IIS) where Calc.asmx is->ASP.NET->Web Service (CalcService::Add)->Web Service Client (Web Server (IIS) where CalcASPClient.aspx is) ->Web Client of Web Application CalcASPClient.aspx ->User.

The CityView Application A real Web application as a Web service client.

The Web service is the Microsoft TerraService (http://terraservice.net/terraservice.asmx).

It is a Web service front end to the Microsoft TerraServer database.

TerraServer (http://terraservice.net) is one of the world’s largest online databases of photographs and maps of the Earth’s surface.

TerraService exposes TerraServer’s content via Web methods. Its WSDL contract is available at http://terraservice.net/terraservice.asmx?wsdl.



http://terraservice.net/

http://terraservice.net/

http://terraservice.net/terraservice.asmx?wsdl

http://terraservice.net/terraservice.asmx?wsdl

The CityView Application

Installing the client:

CityView.aspx: a Web form that defines CityView’s user interface.

CityView.ashx: an HTTP handler that returns the requested image.

TerraService.dll contains a TerraService proxy class named TerraService.

http://winserv1.cs.uakron.edu/xiaotest/CityView.aspx

Web Services and More

• Code-Behind • Asynchronous• For-fee

Web Services and Code-Behind

Coding: Calc2.asmx: <%@ WebService Class="CalcService" %>

Calc.cs: contains the class codbe and needs to be compiled into bin\Calc.dll.

Deploying: Root must be a virtual directory (WS-Calc). http://localhost/calc2.asmx

Benefits: (a) Catches compilation errors before the service is deployed. (b) Enables to write Web services in languages that ASP.NET doesn’t natively support.

Asynchronous Method Calls

An asynchronous call returns immediately, no matter how long the Web service requires to process the call.

To retrieve the results from an asynchronous call, you make a separate call later on by setting up a callback function.

AsyncCallback cb = new AsyncCallback (AddCompleted);

IAsyncResult res = calc.BeginAdd (2, 2, cb, null);

public void AddCompleted (IAsyncResult res)

{ int sum = calc.EndAdd (res); }

For-Fee Web Services

Authenticate Web Service Callers: Assign authorized callers an authentication key and

require them to pass the key in each method call. Transmit user credentials in HTTP Authorization headers. Transmit user credentials in SOAP headers.

System.Web.Services.Protocols.SoapHeader


Server Side:

public class AuthHeader : SoapHeader{ public string UserName; public string Password; }class SafeService{ public AuthHeader header; [WebMethod] [SoapHeader ("header", Required="true")] public int Add (int a, int b) { if (header.UserName == "jeffpro" && header.Password == "imbatman") return a + b; else throw new HttpException (401, "Not authorized");}}


Client Side:

SafeService calc = new SafeService ();

AuthHeader header = new AuthHeader ();

header.UserName = "jeffpro";

header.Password = "imbatman";

calc.AuthHeaderValue = header;

int sum = calc.Add (2, 2);

For-Fee Web ServicesThe outgoing SOAP envelope (generated by .NET): <?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Header> <AuthHeader xmlns="http://tempuri.org/"> <UserName>jeffpro</UserName> <Password>imbatman</Password> </AuthHeader> </soap:Header> <soap:Body> <Add xmlns="http://tempuri.org/"> <a>2</a> <b>2</b> </Add> </soap:Body></soap:Envelope>

Web Services


Client 2

Application 1

UDDI Registry 1

WSDL Interface 1

UDDI Registry 2


SOAP

SOAP

WEB


Client 1


Finding Web ServicesOn a Server (DISCO)

On the Internet (UDDI)

Web Service Discovery—DISCO

How do clients know that a Web service exists? DISCO (short for “discovery”) is a file-based protocol for

local Web service discovery—that is, for getting a list of available Web services from DISCO files deployed on Web servers.

Publish a DISCO file on your Web server that describes the Web services.

Clients interrogate the DISCO file to find out what Web services are available and where the services’ WSDL contracts can be found.

DISCO’s chief disadvantage is that you can’t read a DISCO file if you don’t have its URL.


As an example, to publish two Web services:

http://www.wintellect.com/calc.asmx

http://www.wintellect.com/locator.asmx

Deploy the following DISCO file at a well-known URL on your server. The contractRef elements identify the URLs of the Web services’ WSDL contracts.

<?xml version="1.0" ?>

<discovery xmlns="http://schemas.xmlsoap.org/disco/"

xmlns:scl="http://schemas.xmlsoap.org/disco/scl/">

<scl:contractRef ref="http://www.wintellect.com/calc.asmx?wsdl"

docRef="http://www.wintellect.com/calc.asmx" />

<scl:contractRef ref="http://www.wintellect.com/locator.asmx?wsdl"

docRef="http://www.wintellect.com/locator.asmx" />

</discovery>


Or deploy a VSDISCO file to enable dynamic discovery. The following VSDISCO file automatically exposes all ASMX and DISCO files in a host directory and its subdirectories, with the exception of those subdirectories noted with exclude elements:

<?xml version="1.0" ?><dynamicDiscovery xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17"> <exclude path="_vti_cnf" /> <exclude path="_vti_pvt" /></dynamicDiscovery>

Web Service Discovery—UDDI UDDI (Universal Description,

Discovery, and Integration) is a global (Internet) Web service directory that is itself implemented as a Web service.

Developed by IBM, Microsoft, and Ariba. A specification for building distributed

databases that enable interested parties to “discover” each other’s Web services.

No one company owns the databases; anyone is free to publish a UDDI-based business registry.

Operator sites have already been established by IBM and Microsoft.

Web Service Discovery—UDDI UDDI sites are themselves Web service sites. They publish a pair of SOAP-based APIs:

an inquiry API for inquiring about companies and their Web services

a publisher API for advertising a company’s Web services (operator sites typically limit the publisher API to registered members).

Most developers will use high-level tools to query UDDI business registries and generate wrapper classes that allow them to place calls to the Web services.

Dawn of a New Era

True cross-platform distributed computing based on HTTP, XML, and SOAP.

Summary: Web Services (Architecture), Web Methods, WSDL,

SOAP, XML, DISCO, UDDI, Web Service Clients (Stand Alone, Web Based), Web Service Proxies, For-Fee Web Services.

Technology

PDN-C11-PPT.ppt