Exposing and Consuming Web Services with.NET Tutorial 33

Exposing and Consuming Web Services with .NET

Tutorial 33

XML Web Servicesin .NET

casey# (pronounced kc-sharp) chesnut

brains-N-brawn.com

OOPSLAOctober 15, 2001

Presentation Style

• Informal• Interrupt for topical questions

– Notice agenda• Save off topic questions until end• Fun

Agenda

• Introduction• Standards• Exposing• Consuming• Non functional• Case Study• Questions

• 3rd generation of the Internet– Distributed communication

• Government and Academic• No revenue model

– HTML presentation of backend DBMS• Dot Com• Advertising crash

– Web Services …• Most compelling reason to .NET

Where They Fit In .NET

Base Class LibraryBase Class Library

Common Language SpecificationCommon Language Specification

Common Language RuntimeCommon Language Runtime

ADO.NET: Data and XMLADO.NET: Data and XML

VBVB C++C++ C#C#V

isual S

al Stu

ASP.NET: Web ServicesASP.NET: Web Servicesand Web Formsand Web Forms

JScriptJScript ……

WindowsWindowsFormsForms

What Are They?

• Application logic exposed programmatically over the internet

• Based on standards that are neither platform, vendor, language dependent

• Data and functions, NOT user interface• COTS on the web

DEMO – Hello World

• Build from scratch (Without VS.NET)• Minimal client

– Send/Receive HTTP– Process XML

Why Do We Need Them?

• Current distributed computing paradigms are lacking

• Make business logic accessible everywhere– Internal and external systems– Variety of clients

Current Distributed Computing Paradigms

• DCOM, RMI, IIOP– Heavyweight– Not interoperable

• Screen-scraping– Brittle

Business Logic Accessibility (Systems)

WebService

BusinessPartner

HTMLFront-End

IntranetApp

Business Logic Accessibility (Clients)

WebService

GenericBrowser

WirelessCell Phone

WirelessPocket PC

DedicatedClient

Who Is Involved?• Microsoft• DevelopMentor• UserLand• IBM• Lotus• Ariba• HP• Sun• W3C• BEA• …

How Do They Work?

ConsumerWeb Service

Provider

Description

Discovery

Communication

Web Service Standards

• Discovery (XML)– UDDI– DISCO

• Description (XML)– WSDL

• Communication (XML, HTTP …)– SOAP, XSD

• OTHER– SOAP-RP, DIME, XLANG, WSFL, XSL(T) …

Discovery

• UDDI (Universal Discovery and Description Interface)– Directory

• DISCO– Static– Dynamic

• Word of Mouth, …

• Centralized directory of Business and Web Services

• Has an API which is exposed as a Web Service

• Replicated among uddi.microsoft.com, IBM, Ariba is back in! … HP soon

• uddi.org/specification.html

• XML file for discovering a service contract, and related resources.

• Web crawlers can be used to auto discover services

• Least solid of the specs• msdn.microsoft.com/xml/general/

disco.asp

DISCO Examples

• Static:<disco:discovery>

<scl:contractRef ref=‘service.wsdl' docRef=‘documentation.htm'>

</disco:discovery>• Dynamic:

<?xml version="1.0" ?><dynamicDiscovery xmlns="urn:schemas-

dynamicdiscovery:disco.2000-03-17"></dynamicDiscovery>

DEMO - DISCO

• http://localhost/default.vsdisco

Description

• WSDL (Web Service Description Language)

• Describes protocols, operations, parameters, return values, …

• Used to generate proxy objects so clients can easily consume the service

• msdn.microsoft.com/xml/general/wsdl.asp

XML Schema

• Define content, structure, semantics of XML documents

• Like a DTD, but written as XML• Replaces DTDs• W3C Recommendation in May• Schema repositories

DEMO – WSDL

• Show auto-generated WSDL file

Communication• HTTP GET

– Parameters in query string (limited)• HTTP POST

– Name/value pairs in body (ad hoc)• SOAP

– Predominantly HTTP POST w/ XML– SMTP for asynchronous calls …– Complex data types

Marshal Types

• HTTP GET/POST– Primitives– Enums– Arrays of above

• SOAP– Primitives, Enums– Classes, Structs– DataSets– XmlDoc, XmlNodes– Arrays of above

• SOAP (Simple Object Access Protocol)– SOAP == HTTP + XML [de facto]– SOAP != HTTP + XML[SOAP <> HTTP + XML … for VB’ers ]

• Message Format• SMTP …

• msdn.microsoft.com/xml/general/soapspec.asp

SOAP/XML/HTTP

• HTTP is the transport protocol– Other protocols can be used as well

• SOAP is the wire protocol (XML)– What the message should look like on

the wire• XML is used to describe the SOAP

message and the data being passed and returned to the service

SOAP Message

• HTTP Request/Response– HTTP Headers

• SOAPAction Header

– HTTP Body• SOAP Envelope

– Optional SOAP Headers– Mandatory SOAP Body

» Boxcar Method calls

– Referenced XML Data

Entire SOAP Message

POST /news/groups.asmx HTTP/1.1Content-Length: 504Content-Type: text/xmlHost: localhostUser-Agent: MS Web Services Client Protocol

1.0.2204.21SOAPAction:

"http://tempuri.org/GetNewMessageHeaders“// comment // followed by CRLF’s before HTTP body

Entire SOAP Message …<?xml version="1.0"?><soap:Envelope xmlns=“”> <soap:Body> <GetNewMessageHeaders

xmlns="http://tempuri.org/"> <DateYYMMDD>010618</DateYYMMDD> <TimeHHMMSS>164431</TimeHHMMSS> <GroupName>dnug.test</GroupName> </GetNewMessageHeaders> </soap:Body></soap:Envelope>

SOAP Request<?xml version="1.0"?><soap:Envelope xmlns:soap=“…”

xmlns:soapenc=“…” xmlns:xsi=“…" xmlns:xsd=“…">

<soap:Body> <HelloTo xmlns="http://tempuri.org/"> <Name>casey</Name> </HelloTo> </soap:Body></soap:Envelope>

SOAP Response

<?xml version="1.0"?><soap:Envelope xmlns:soap=“…”

xmlns:soapenc=“…" xmlns:xsi=“…" xmlns:xsd=“…">

<soap:Body> <HelloToResult xmlns="http://tempuri.org/"> <result>Hello casey</result> </HelloToResult> </soap:Body></soap:Envelope>

SOAP Fault<?xml version="1.0"?><soap:Envelope xmlns:soap=“…"> <soap:Body> <soap:Fault> <soap:faultcode>Server</soap:faultcode>

<soap:faultstring>BAD</soap:faultstring> <soap:faultactor>URL</soap:faultactor>

<soap:detail/> </soap:Fault> </soap:Body></soap:Envelope>

SOAP Process• Client calls method on proxy object• Proxy object serializes parameters, and sends

SOAP request• Server receives SOAP request, and deserializes

parameters• Method is run on server• Results are serialized and send as a SOAP

response or fault• Proxy object receives SOAP, and deserializes

the results to return to client

Coding .NET Web Services

• Plumbing is automatically taken care of:– UDDI does not have to be done– DISCO is auto– WSDL is auto– SOAP de/serialization is auto

• Concentrate on business logic• Concentrate on non-func. requirements

Demo – VS.NET

• Create simple Web Service• Consume with auto-generated client

Passing Parameters

• Primitives for the auto-generated help page

• out parameters are SOAP only• SOAP Headers

– SoapHeader Class– SoapHeader Attribute

• in/out direction• required bool

Return Value(s)

• You have 1 return value … use it wisely• Throw exception, not HRESULT style• SOAP can manage multiple returnspublic string RetTwoStrings(out string b)Returned as <b>value</b> following

Mandatory Soap BodyDoes not work for HTTP Get/PostReturn null for empty sets

DEMO - DataSet

• In-memory Database– tables, rows, relations, constraints

• Can strongly-type with XSD– schema compiler

• Built-in support for errors– Tables – bool HasErrors()– Rows – Rows[] GetErrors()

Exceptions

• Exceptions are promoted to SoapExceptions

• SoapExceptions are serialized to SOAP faults

• Also the possibility for standard HTTP exceptions before SOAP processing occurs

• Set errors within DataSets/XmlDocs

State(less)

• Should design stateless, or pass state in method calls/headers … unless state is too large to keep passing back and forth

– Session State– Application State

• Shared among all instances of service

Caching

• SOAP response payloads can be cached on the server

• Beta 1 Hack– Write off to XmlDocument on server,

and then return that XmlDoc based on time

Asynchronous

• Automatically get Begin/End methods

Services s = new Service();IAsyncResult ar = s.BeginLongTime(null);//waitif(ar.IsCompleted == true){string result = s.EndLongTime(ar);}

AsynchronousBeginMethod()

IsComplete()

EndMethod ()

result

WebService Attributes

[WebService…(Description=“blah”)](Description=“<a href>docs<a>”)](Namespace=“http://dnug.net/service”)](Name=“ServiceName”)]

WebMethod Attributes[WebMethod…(Description=“blah”)](Transaction=Transaction.Required)](EnableSessionState=False)](CacheDuration=20)](BufferResponse=“true”)](MessageName=“MethodName”)]

Help Page

• Modify ASP.NET web configuration• Modify default ASP.NET web help page

– Documentation– Branding– GET/POST– …

XML Attributes

[XmlInclude(typeof(foo))]

[XmlAttribute()] [SoapAttribute()][XmlElement()] [SoapElement()][XmlArray()] [SoapArray()]

Entry Points• Global.asax

– Application_Begin/EndRequest()– Session_Start/End()– HTTP Request/Response

• SOAP Extensions– SOAP Message before request

deserialization and after response serialization

– Roll your own SOAP implementation

DEMO – SOAP Extension

• Request / Response• Before / After (De)serialization• Client / Server

Service Design Tips

• Don’t change interface; additional data can be returned without harm

• Make flexible to support all possible clients

• Validate on server, you do not control the client

• Provide test instance for people to code against

Service Design Tips

• Provide client examples for different consumers

• Provide simple type example for testing• Find a standard schema to use• Ping()• Beware denial of service• Make chunky calls, reduce network trips• …

Service Design

WebService

Component

Consumer

chunkychatty

DEMO – Consuming Services

• Create client• Add Web Reference• Call method• Display DataSet

Discovering

• Can discover at design or run time– Web based registry– Exposed as web services

UDDI tModel

ClientUDDI

Repository

MyWeb Service

Competitor’sWeb Service

tModel

• Can occur at design or run time• SOAP by default• Store URL in XML config file• Firewall authentication• Timeout• Cookie support

Exceptions

• HTTP• SOAP

Try{//make web service call}Catch(SoapException){ //SOAP }Catch(Exception){ //HTTP }Finally {}

DEMO - Exceptions

• Parsing parameters• SOAP Fault• HTTP Error

Client Design Tips

• Cache data if disconnected• Have fail-over if a service is down• Dynamically discover services based on

a schema• Don’t code to ith-index, reference Xml

nodes explicitly in case schema changes

Non-Functional

• Security• Auditing• Deployment• Reliability• Performance• Maintainability• Usability• Scalability

Security

• IIS (Basic, Digest, Kerberos, …)• User/Pass as Service parameters• Login method which returns a session,

make session a parameter of other calls• User/Pass in Soap Header• Certificates / SSL / HTTPS• Passport Service• Public/Private encrypt at client, server

DEMO - Encryption

• Encryption algorithms are platform/language independent

• Symmetric• PGP

What Else Is There?

• .NET Remoting• XML-RPC• ebXML• BXXP• BizTalk• ATL Server

When Do We Start?

• Beta 2• SOAP Toolkit is for DNA projects• .NET supercedes SOAP Toolkit• More wireless clients all the time• More specs. coming all the time

3rd Party Services

• HailStorm / My Services• UDDI• eBay• XMethods• SalCentral• …

Case Study - Problem

• ListServs– Fills up email box and harddrive– Moderated vs Unmoderated lists

• Newsgroups– Lacks notification feature– Port 119 might be blocked

Case Study – Architecture

NewsServer

NNTPWeb

Service

DedicatedClient

Firewall

OutlookExpress

Case Study – Future

MS NewsServer

NNTPWeb

Service

DedicatedClient

@HomeNewsServerWeb

Client

MobileClient

OutlookExpress

SOAP over NNTP

• True Asynchronous• Messaging is almost identical to SMTP• WSDL?

Other Demos

• XSLT• User Objects• Typed DataSet• XML Server Control

Summary

• Web Services allow heterogeneous distributed systems to communicate

• Standard adoption and support is growing

• Powerful new model for application development

• .NET Framework makes developing Web Services easy

• Likely to live-up to the hype

Online Resources

• msdn.microsoft.com/webservices• msdn.microsoft.com/theshow• W3C.org• soap-wrc.com• xmethods.com• sys-con.com/webservices

Questions

• ???

Exposing and Consuming Web Services with.NET Tutorial 33

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