ASP Web Services

1
ASP Web Services Rob Howard Microsoft
Corporation
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Agenda

• Web service overview
• Building web services with .NET technologies
• Description and discovery
• Building the proxy
• Tips and tricks
• Resources and QA

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What is a Web Service?

• A web service is programmatically available
  application logic exposed over the Internet
• Available to a variety of clients (platform
  independent)
• E.g. stock quote, weather, and authentication
  services
• Makes building distributed applications less
  difficult
• Most common metaphor for accessing information is
  through a web browser
• Traditional web applications don't expose any
  application logic (Microsoft's Money Central)

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What is a Web Service?
A web service is programmable application logic
accessible via standard Web protocols
HTML
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Common Questions/Issues

• How do you publish the location of a web service?
• How do you describe a web service?
• What protocols does it support?
• What data types does it use?
• Challenges
• Simple and fast programming model
• Understanding of transport protocols,
  serialization, discovery, etc. are challenges
  most developers don't have time to deal with
• Solutions today still have complexities
• Microsoft SOAP Toolkit
• IBM (SOAP Toolkit)
• Etc.

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Microsoft Web Services

• Built on standard web protocols
• HTTP and XML
• Technology innovations for web services
• SOAP (Simple Object Access Protocol)
• Explicit serialization protocol (HTTP XML
  description) used in service exchanges
• SCL (SOAP Contract Language)
• XML document describing the location and
  interfaces a particular service supports the
  client's contract
• DISCO (Discovery)
• XML document describing (URI) of service

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Using ASP

• ASP is a simple, consistent, and powerful web
  application development paradigm
• Build web pages (microsoft.com)
• Traditionally browser targeted (.aspx)
• Build web services (credit card authorization)
• Programmable application logic (.asmx)
• Uses SOAP, SCL, and DISCO
• ASP makes building web services easy!

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ASP .NET Web Services

• File extension is .asmx (subject to change)
• Source file (text and notepad accessible) is
  compiled at run-time
• .asmx file can either contain application logic
  or point to .NET assembly/class
• You programmatically determine what is web
  service accessible

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ASP .NET Web Services

• Part of the ASP application model
• Must be URL accessible via Internet Information
  Server
• IIS is host for the ASP HTTP runtime
• Access to ASP object model (Request, Session,
  Application, etc.)
• The web service emits no UI
• The web browser is not the intended client
• Supports multiple protocols
• Including SOAP

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Demo

• Creating the Fibonacci Web Service

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.asmx Deconstructed (1 of 5)

• Modeled after component based application logic
  development
• You simply author a component and mark the method
  as being a web service
• Processing Directives
• Language Supports JScript, VB7, C, and other
  .NET common language runtime languages
• Class Allows for the definition of the
  application logic in a component, rather than
  within the .asmx file itself

lt_at_ directivevaluegt
lt_at_ language"C" gt lt_at_ language"VB7" gt
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.asmx Deconstructed (2 of 5)

• WebMethod attribute
• C WebMethod
• VB7 ltWebMethod()gt
• JScript WebMethodAttribute
• Declares a particular method of a class as
  publicly accessible as a service

WebMethodpublic method Add(int a, int b)...
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.asmx Deconstructed (3 of 5)

• WebMethod attribute
• The modifier public is orthogonal to the web
  service modifier WebMethod - otherwise, all
  public methods and properties would be accessible
• Such as ToString()
• Enables access to session state and transactions

WebMethod(EnableSessionStatetrue) WebMethod(Tr
ansactionTransaction.Required)
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.asmx Deconstructed (4 of 5)

• Access to ASP application services
• Session, application state, server variables,
  etc.

WebMethodpublic int HitCounter get
return (int) Application"HitCounter"
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.asmx Deconstructed (5 of 5)

• You develop one application model (ASP) and
  expose your application logic through either web
  pages or web services
• Both share
• Common application logic
• application logic developed to display stock
  quote values is the same
• Consistency
• programming framework is identical (leverage your
  existing skill ASP pages web services)

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Testing a Web Service

• Web service itself emits no UI
• ASP provides .aspx page template for web service
  for testing purposes
• Accessible through HTML 3.2 browser
• Uses HTML forms to allow interaction with web
  service

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Testing a Web Service

• Template page is named
• DefaultSDLHelpGenerator.aspx
• Accessible at (directory to change)
• system drive\WinNT\ComPlus\v2000.14.1812\
• Alternate template page can be named via
  config.web entry
• ltsdlHelpGenerator href"DefaultSdlHelpGenerator.as
  px"/gt

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Demo

• Accessing a service through the browser

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Supported Protocols (HTTP-Get/Post)

• HTTP-GET and HTTP-POST
• Encodes data with URL via either HTTP
• GET Data sent as part of URL
• POST Data sent in HTTP message body
• Support simple types (int, string, enum, arrays)
• Returns data as a simple XML document

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Supported Protocols (SOAP)

• SOAP (Simple Object Access Protocol)
• Serialization format for request/response
  semantics using XML and HTTP as transport
• Data is sent via POST (or M-POST)
• Extensible XML document (Envelope, Encoding
  Rules, RPC)
• Supports complex and simple types (structs,
  datasets, classes)

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SOAP Contract Language (SCL)

• Clients need a contract to understand what the
  service is providing
• COM used IDL (Interface Definition Language)
• Web Services use SCL
• SCL is an XML document that describes
• Supported service transports SOAP, HTTP-GET,
  HTTP-POST
• Invocation Semantics How requests are made and
  how responses are sent

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SOAP Contract Language (SCL)

• SCL and service do not have to exist on the same
  server
• Allows clients to build strongly typed proxies
• Programmatically describes interfaces, methods,
  and properties that are exposed as web services
• .NET SDK PDC builds (including MSDN pre-release)
  refer to SDL
• SDL (Service Description Language) is predecessor
  to SCL

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DISCO (Discovery)

• How do we find (or discover) web services?
• DISCO XML document that contains references to
  the SCL location for web services
• Typically lives at the root of a web application
• Not limited to web services
• Outlines a "discovery algorithm"
• HTTP request to URL
• Application responds with document (either XML or
  HTML)
• Response is either the DISCO document or an HTML
  document with a pointer to the DISCO document

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DISCO (Discovery)

• Place a link in the default site document
• ltlink type'text/xml' rel'alternate'
  href'some.disco'/gt

ltdiscodiscoverygt ltsclcontractRef
ref'myl.sdl'gt ltsclcontractRef ref'my2.sdl'
docRef'my.htm'gt lt/discodiscoverygt
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Demo

• Discovering IBuySpy.com
• Viewing the SCL

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Consuming a Web Service

• Several options for clients to consume web
  services
• .NET clients can use Visual Studio.NET
• .NET (SDK) clients can use WebServiceUtil.exe
• Other platforms can simply interpret XML

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WebServiceUtil.exe

• Command line tool that comes with the .NET SDK
• Used to build client .NET proxy class from the
  SCL document of a web service
• Classes
• are strongly typed
• can be asynchronous
• can be created in Jscript, C, or VB7 simply by
  specifying a command line setting
• The tool can also generate
• SCL file from a given .NET class
• Defined server .NET class from an SCL

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Demo

• Build and use proxy class

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Web Services (In Practice)
Design-Time or Dynamic
Runtime
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Tips and Tricks

• Know and understand the supported data types
• Don't send unnecessary data (such as an image)
  when you can send a URL
• Eliminate latency in the server first
• Use the ASP Cache API where possible
• Build the service to be asynchronous if the
  potential exists to block other work

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Tips and Tricks

• Handle client errors when the server is
  unavailable
• Cache data from the service where possible,
  rather than requesting the same data 100 times
• Be efficient about the number of requests for
  dynamic data
• collapse multiple web service methods into one
• Read the SOAP, DISCO, and SCL specs
• Stay tuned for more books from Wrox!

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Summary
A programmable application component accessible
via standard Web protocols
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Summary

• Microsoft provides the leading platform for
  building web applications and services today
• Great support for XML, HTTP, HTML
• Full extensibility enables developers to support
  the latest protocols
• The new .NET platform makes building and using
  web services automatic just part of
  the framework

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Resources

• Wrox Press "A Preview of ASP"
• Chapter 5 covers ASP Web Services
• Web sites
• http//msdn.microsoft.com/net/
• http//www.asptoday.com
• http//www.develop.com/dm/default.asp
• http//www.aspng.com/aspng/index.aspx

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Terminology

• .asmx
• ASP application file for web services
• Assembly
• A unit of deployment in .NET
• Assemblies contain classes (application logic)
• DISCO
• Resource file that provides a discovery mechanism
  for web services
• SCL (SOAP Contract Language)
• Contract that describes a web service
• SDL (Service Description Language) was
  predecessor to SCL
• SOAP (Simple Object Access Protocol)
• RPC serialization through XML and HTTP

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Questions? Rob Howard Microsoft Corporation