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complete web service1.ppt

  1. 1. WEB SERVICES – SERVICE ORIENTED ARCHITECTURE Dr.Saranya K G, Assistant Professor (S.Gr), Dept.of CSE, PSG College of Technology, Coimbatore.
  2. 2. What is a Web Service • A web service is a network accessible interface to application functionality, built using standard Internet technologies. • Clients of web services do NOT need to know how it is implemented. Application client Application code Network Web Service
  3. 3. Web Service Technology Stack Discovery Description Packaging Transport Network shopping web service? WSDL URIs Web Service Client Web Service UDDI Proxy WSDL SOAP pkg request WSDL SOAP pkg response
  4. 4. Step1. Write Web Service Method Discovery Description Packaging Transport Network shopping web service? WSDL URIs Web Service Client Web Service UDDI Proxy WSDL SOAP pkg request WSDL SOAP pkg response
  5. 5. Step2. Describe Web Service using WSDL Discovery Description Packaging Transport Network shopping web service? WSDL URIs Web Service Client Web Service UDDI Proxy WSDL SOAP pkg request WSDL SOAP pkg response
  6. 6. Step3. Write Proxy to Access Web Service Discovery Description Packaging Transport Network shopping web service? WSDL URIs Web Service Client Web Service UDDI Proxy WSDL SOAP pkg request WSDL SOAP pkg response
  7. 7. Step4. Write Client to Invoke Proxy Discovery Description Packaging Transport Network shopping web service? WSDL URIs Web Service Client Web Service UDDI Proxy WSDL SOAP pkg request WSDL SOAP pkg response
  8. 8. Web Services - Definition from W3C “ A Web service is a software system identified by a URI, whose public interfaces and bindings are defined and described using XML. Its definition can be discovered by other software systems. These systems may then interact with the Web service in a manner prescribed by its definition, using XML based messages conveyed by internet protocols.”
  9. 9. Service Oriented Architectures Technologies capable of: •Exchanging messages •Describing Web services •Publishing and discovering Web service descriptions Component Role Operation service requestor retrieves a service description A service publishes its description One-way, conversational, many-to-many
  10. 10. Web Services – Architectural Extensions • Incorporates additional features and functionality by extending technologies and components defined within the basic architecture, such as: • Asynchronous messaging • Attachment – typical usage : associating binary data with SOAP messages. • Caching • Message exchange pattern (MEP) - Describes a generalized pattern of message exchange between two services. e.g. : one-way, request/response, publish/subscribe, and broadcast. • Reliable message - implementation of Reliable Messaging one MEP is a series of requests between two nodes with an acknowledgement SOAP Module. • Message confidentiality – Can transmit the message via SSL or TLS, or have a SOAP Module provides for encryption and decryption. • Message integrity – Can have a SOAP Module use digital signature. • Session
  11. 11. The Complete Web Services "Stack" More mature technologies
  12. 12. The Wire Stack •Transport: HTTP is the de facto, other may be supported. •Packaging: SOAP is the de facto standard for XML messaging. •Extensions : Additional information attached to web services messages.
  13. 13. The Description Stack It is actually a stack of description documents defined using XML Schema. Satisfied by WSDL minimum service description necessary to support interoperable Web services. facts, or assertions, and rules that apply to a particular Web service Input/ Output rendering Not fully specified
  14. 14. The Discovery Stack  Service can be published using a variety of mechanisms:  Direct publish: description sent directly to requestor;  WSIL : HTTP GET retrieves descriptions from URL;  Universal Description, Discovery and Integration (UDDI) registries: a Web-based distributed directory.  Service requestors can retrieve a service description at design time (search by interface) or runtime (by communication and QoS) from a Web page (URL), a service description repository, a simple service registry or a UDDI registry. Discovery depends on how services are published; WSIL : de-centralized service discovery method
  15. 15. The technology so far The WS technology is completely based on XML. Therefore, both the data format and the interaction protocols are XML-based:  customized XML -> data format  SOAP -> communication protocol  WSDL -> the Interface definition language  WSIL/UDDI -> standards for services discovery The lowest-level layers (the transport layer) should exploit some existing Internet protocols, like HTTP or SMTP
  16. 16. What is XML XML is a simple tag-based language for describing information in a structured way. Basic elements:  Tags  Attributes  Text <xhtml:table><xhtml:tr> <xhtml:td width="40%">LastName</xhtml:td> <xhtml:td width="60%">Allen</xhtml:td> </xhtml:tr></xhtml:table> StartTag Text EndTag Attributes LastName Allen
  17. 17. How to work on XML The tree-like structure of XML makes developers life hard. In practice there is not a standard way for editing and analyzing, but the best method depends on your need. Just choose among:  SAX -> callback-based parser  DOM -> tree representation  XSLT -> “XML to XML” conversion  XPATH -> queries  XML Binding -> transparent conversion to objects
  18. 18. Simple Object Access Protocol SOAP is a technology to support the exchange of XML-coded messages over a transport protocol, such as HTTP and SMTP. (wire stack) HTTP server Skeleton Server HTTP client Stub Client   XML XML   POST… HTTP 1.1 200 OK   SOAP SOAP   HTTP SOAP XML Protocols Folding SOAP basic mechanism
  19. 19. SOAP • Actually used to communicate with the Web Service • Both the request and the response are SOAP messages • The body of the message (whose grammar is defined by the WSDL) is contained within a SOAP “envelope” • “Binds” the client to the web service
  20. 20. WSDL • Describes the Web Service and defines the functions that are exposed in the Web Service • Defines the XML grammar to be used in the messages • Uses the W3C Schema language
  21. 21. UDDI • UDDI is used to register and look up services with a central registry • Service Providers can publish information about their business and the services that they offer • Service consumers can look up services that are available by • Business • Service category • Specific service
  22. 22. SOAP
  23. 23. SOAP I: Intro and Message Formats
  24. 24. SOAP and Web Services • The actual communications are encoded with SOAP. • Transported by HTTP Client Service WSDL WSDL SOAP Request SOAP Response
  25. 25. Beyond Client-Server • SOAP assumes messages have an originator, one or more ultimate receivers, and zero or more intermediaries. • The reason is to support distributed message processing. • Implementing this message routing is out of scope for SOAP. • Assume each node is a Tomcat server or JMS broker. • That is, we can go beyond client- server messaging. Originator Recipient Intermediary Intermediary Intermediary
  26. 26. SOAP • SOAP is just a message format. • Must transport with HTTP, TCP, etc. • SOAP is independent of but can be connected to WSDL. • SOAP provides rules for processing the message as it passes through multiple steps. • SOAP payloads • SOAP carries arbitrary XML payloads as a body. • SOAP headers contain any additional information • These are encoded using optional conventions
  27. 27. Web Service Messaging Infrastructure Requirements? • Define a message format • Define a messaging XML schema • Allow the message to contain arbitrary XML from other schemas. • Keep It Simple and Extensible • Messages may require advanced features like security, reliability, conversational state, etc. • KISS, so don’t design these but do design a place where this sort of advanced information can go. • Add these capabilities in further specifications: WS-Security, WS-ReliableMessaging, etc. • Tell the message originator is something goes wrong. • Define data encodings • That is, you need to tell the message recipient the types of each piece of data. • Define some RPC conventions that match WSDL • Your service will need to process the message, so you need to provide some simple conventions for matching the message content to the WSDL service. • Decide how to transport the message. • Generalize it, since messages may pass through many entities. • Decide what to do about non-XML payloads (movies, images, arbitrary documents).
  28. 28. SOAP • SOAP Messages: • Headers and body elements with examples. • SOAP Encoding: • Rules for encoding data. • Focus on SOAP for RPC • SOAP Routing and Processing • SOAP Over HTTP: • How SOAP gets sent over the wire.
  29. 29. SOAP Messaging
  30. 30. SOAP Basics • SOAP is often thought of as a protocol extension for doing Remote Procedure Calls (RPC) over HTTP. • This is how it is often used. • This is not accurate: SOAP is an XML message format for exchanging structured, typed data. • It may be used for RPC in client-server applications • May be used to send XML documents • Also suitable for messaging systems (like JMS) that follow one-to-many (or publish-subscribe) models. • SOAP is not a transport protocol. You must attach your message to a transport mechanism like HTTP.
  31. 31. What Does SOAP Look Like? • The next two slides shows examples of SOAP message from our Echo service. • It’s just XML • First slide is an example message that might be sent from a client to the echo service. • Second slide is an example response. • I have highlighted the actual message payload.
  32. 32. <?xml version=‘1.0’ ?> <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <soapenv:Body> <ns1:echo soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:ns1="http://.../axis/services/EchoService"> <in0 xsi:type="xsd:string">Hollow World</in0> </ns1:echo> </soapenv:Body> </soapenv:Envelope> SOAP Request
  33. 33. <?xml version=‘1.0’ ?> <soapenv:Envelope xmlns:soapenv=http://schemas.xmlsoap.org/soap/envelope/ xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <soapenv:Body> <ns1:echoResponse soapenv:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/ xmlns:ns1="http://../axis/services/echoService"> <echoReturn xsi:type=“String“> Hollow World </echoReturn> </ns1:echoResponse> </soapenv:Body> </soapenv:Envelope> SOAP Response
  34. 34. SOAP Structure • SOAP structure is very simple. • 0 or 1 header elements • 1 body element • Envelop that wraps it all. • Body contains XML payload. • Headers are structured the same way. • Can contain additional payloads of “metadata” • Security information, quality of service, etc. Envelope Body Message Payload Header
  35. 35. SOAP Schema Notes • All of this is expressed formally in the SOAP schema. • Which in turn derives from the SOAP Infoset • XML on the right is taken directly from the SOAP schema. • This just encodes the previously stated rules. • Also, note that the SOAP envelope can contain other attributes. • <anyAttribute> tag is the wildcard <xs:complexType name="Envelope"> <xs:sequence> <xs:element ref="tns:Header" minOccurs="0" /> <xs:element ref="tns:Body" minOccurs="1" /> </xs:sequence> <xs:anyAttribute namespace="##other" processContents="lax" /> </xs:complexType>
  36. 36. SOAP Envelop • The envelop is the root container of the SOAP message. • Things to put in the envelop: • Namespaces you will need. • http://schemas.xmlsoap.org/soap/envelope is required, so that the recipient knows it has gotten a SOAP message. • Others as necessary • Encoding rules (optional) • Specific rules for deserializing the encoded SOAP data. • More later on this. • Header and body elements. • Headers are optional, body is mandatory. • Headers come first in the message, but we will look at the body first.
  37. 37. Brief Aside:WS-* is WS-<any> • We’ll next look at the structure of the header and body. • SOAP and many other web services use the <any> tag for extensibility. • And they use “lax” processing assertions. • Allows for skipping over the SOAP payload. • Needed in distributed messaging environments
  38. 38. Options on <xsd:any/> • The <xsd:any/> element takes the usual optional maxOccurs, minOccurs attributes. • Allows a namespace attribute taking one of the values: • ##any (the default), • ##other (any namespace except the target namespace), • List of namespace names, optionally including either ##targetNamespace or ##local. Controls what elements the wildcard matches, according to namespace. • It also allows a processContents attribute taking one of the values strict, skip, lax (default strict), controlling the extent to which the contents of the matched element are validated. • SOAP is lax.
  39. 39. Lax • “If the item, or any items among its children if it's an element information item, has a uniquely determined declaration available, it must be ·valid· with respect to that definition.” • That is, ·validate· message payloads when you can, don't worry when you can't.
  40. 40. SOAP Headers • SOAP Body elements contain the primary message contents. • Headers are really just extension points where you can include elements from other namespaces. • i.e., headers can contain arbitrary XML. • Headers may be processed independently of the body. • Headers may optionally define encodingStyle. • Headers may optionally have a “role” attribute • Header entries may optionally have a “mustUnderstand” attribute. • mustUnderstand=1 means the message recipient must process the header element. • If mustUnderstand=0 or is missing, the header element is optional. • Headers may also have a “relay” attribute.
  41. 41. Header Definition From SOAP Schema <xs:element name="Header" type="tns:Header" /> <xs:complexType name="Header"> <xs:annotation> <xs:documentation>Elements replacing the wildcard MUST be namespace qualified, but can be in the targetNamespace</xs:documentation> </xs:annotation> <xs:sequence> <xs:any namespace="##any" processContents="lax" minOccurs="0" maxOccurs="unbounded" /> </xs:sequence> <xs:anyAttribute namespace="##other" processContents="lax" /> </xs:complexType>
  42. 42. Example Uses of Headers • Security: WS-Security and SAML place additional security information (like digital signatures and public keys) in the header. • Quality of Service: SOAP headers can be used if we want to negotiate particular qualities of service such as reliable message delivery and transactions. • Session State Support: Many services require several steps and so will require maintenance of session state. • Equivalent to cookies in HTTP. • Put session identifier in the header.
  43. 43. Example Header from SOAP Primer <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> <env:Header> <m:reservation xmlns:m=“http://my.example.com/" env:role="http://www.w3.org/2003/05/soap-envelope/role/next" env:mustUnderstand="true"> <m:reference>uuid:093a2da1-q345-739r-ba5d-pqff98fe8j7d </m:reference> <m:dateAndTime>2001-11-29T13:20:00.000-05:00 </m:dateAndTime> </m:reservation> <n:passenger xmlns:n=“…" env:role="http://www.w3.org/2003/05/soap-envelope/role/next" env:mustUnderstand="true"> <n:name>Åke Jógvan Øyvind</n:name> </n:passenger> </env:Header>
  44. 44. Explanation of Header Example • In general, we can import tags into the header from name spaces outside of soap. • <reservation/>, <reference/>, <dataAndTime/>,<passenger/> • SOAP doesn’t need to worry to much about these. • It is the node’s job to process these things. • In this particular case, we may imagine an ongoing transaction for making an airline reservation. • Involves several steps and messages, so client must remind the server of this state information when sending a message. • The actual header content all comes from other namespaces. • The role and mustUnderstand attributes are from SOAP.
  45. 45. Header Processing • SOAP messages are allowed to pass through many intermediaries before reaching their destination. • Intermediary=some unspecified routing application. • Imagine SOAP messages being passed through many distinct nodes. • The final destination processes the body of the message. • Headers are allowed to be processed independently of the body. • May be processed by intermediaries. • This allows an intermediary application to determine if it can process the body, provide the required security, session, or reliability requirements, etc.
  46. 46. Roles, Understanding, and Relays Role? must Understand Relay? Forward Header No Yes Process Header Yes No Yes No Remove Header
  47. 47. Header Roles • SOAP nodes may be assigned role designations. • SOAP headers then specify which role or roles should process. • Standard SOAP roles: • None: SOAP nodes MUST NOT act in this role. • Next: Each SOAP intermediary and the ultimate SOAP receiver MUST act in this role. • UltimateReceiver: The ultimate receiver MUST act in this role. • In our example, all nodes must process the header entries.
  48. 48. SOAP Body • Body entries are really just placeholders for XML from some other namespace. • The body contains the XML message that you are transmitting. • It may also define encodingStyle, just as the envelop. • The message format is not specified by SOAP. • The <Body></Body> tag pairs are just a way to notify the recipient that the actual XML message is contained therein. • The recipient decides what to do with the message.
  49. 49. SOAP Body Element Definition <xs:element name="Body" type="tns:Body" /> <xs:complexType name="Body"> <xs:sequence> <xs:any namespace="##any" processContents="lax" minOccurs="0“ maxOccurs="unbounded" /> </xs:sequence> <xs:anyAttribute namespace="##other" processContents="lax" /> </xs:complexType>
  50. 50. SOAP Body Example <soapenv:Body> <ns1:echo soapenv:encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/" xmlns:ns1= "http://.../axis/services/EchoService"> <in0 xsi:type="xsd:string">Hollow World</in0> </ns1:echo> </soapenv:Body.
  51. 51. Example SOAP Body Details • The <Body> tag is extended to include elements defined in our Echo Service WSDL schema. • This particular style is called RPC. • Maps WSDL bindings to SOAP body elements. • Guidelines will be given in next lecture. • xsi-type is used to specify that the <in0> element takes a string value. • This is data encoding • Data encoding rules will also be examined in next lectures.
  52. 52. When Things Go Wrong • One of the precepts of distributed computing is that things will go wrong in any operational system. • Servers will fail, networks will go down, services will change or go away. • Need a way to communicate failures back to message originators. • Consider HTTP faults • SOAP provides its own fault communication mechanism. • These may be in addition to HTTP errors when we use SOAP over HTTP. • HTTP Error Messages 403 Forbidden 404 Not Found 405 Method Not Allowed 406 Not Acceptable 407 Proxy Authentication Required 408 Request Time-Out 409 Conflict 410 Gone 411 Length Required 412 Precondition Failed 413 Request Entity Too Large 414 Request-URL Too Large 415 Unsupported Media Type 500 Server Error 501 Not Implemented 502 Bad Gateway 503 Out of Resources 504 Gateway Time-Out 505 HTTP Version not supported
  53. 53. SOAP Fault Scenarios • HTTP errors will take precedence. • Involve message transmission problems. • SOAP errors occur during the processing of the message. • Faults can occur when • You sent an improperly formatted message that the service can’t process (an integer instead of a string, for example). • There is a SOAP version mismatch • You sent SOAP 1.2 and I understand SOAP 1.0 • You have a “must understand” header that can’t be understood. • You failed to meet some required quality of service specified by a header. • The server fails to correctly process the message. • Each of these corresponds to a named fault value. • It’s env:Sender on the next page.
  54. 54. Sample SOAP Fault From SOAP Primer <env:Body> <env:Fault> <env:Code> <env:Value>env:Sender</env:Value> <env:Subcode> <env:Value>rpc:BadArguments</env:Value> </env:Subcode> </env:Code> <env:Reason> <env:Text xml:lang="en-US">Processing error</env:Text> </env:Reason> <env:Detail> <e:myFaultDetails> ...</e:myFaultDetails> </env:Detail> </env:Fault> </env:Body>
  55. 55. Fault Structure from SOAP Schema • Fault messages are included in the <body>. • <Code> and <Reason> are required. • <Node>,<Role>, and <Detail> are optional. <xs:element name="Fault" type="tns:Fault" /> <xs:complexType name="Fault“ final="extension"> <xs:sequence> <xs:element name="Code“ type="tns:faultcode" /> <xs:element name="Reason" type="tns:faultreason" /> <xs:element name="Node" type="xs:anyURI“ minOccurs="0" /> <xs:element name="Role" type="xs:anyURI" minOccurs="0" /> <xs:element name="Detail“ type="tns:detail" minOccurs="0" /> </xs:sequence> </xs:complexType>
  56. 56. SOAP Fault Codes • These are one of the required subelements of Faults. • They must contain one of the standard fault code enumerations (next slide). • They may also contain subcodes. • For more detailed error messages. <xs:complexType name="faultcode"> <xs:sequence> <xs:element name="Value" type="tns:faultcodeEnum" /> <xs:element name="Subcode" type="tns:subcode" minOccurs="0" /> </xs:sequence> </xs:complexType>
  57. 57. Enumerating Faults • Fault codes must contain one of the standard fault messages. • DataEncodingUnknown: you sent data encoded in some format that I don’t understand. • MustUnderstand: I don’t support this header. • Receiver: message was correct, but receiver could not process for some reason. • Sender: message was incorrectly formatted, or lacked required additional information • Couldn’t authenticate you • VersionMismatch: I don’t support your version of SOAP. <xs:simpleType name="faultcodeEnum"> <xs:restriction base="xs:QName"> <xs:enumeration value="tns:DataEncoding Unknown" /> <xs:enumeration value="tns:MustUndersta nd" /> <xs:enumeration value="tns:Receiver" /> <xs:enumeration value="tns:Sender" /> <xs:enumeration value="tns:VersionMisma tch" /> </xs:restriction> </xs:simpleType>
  58. 58. Fault Subcodes • Fault codes may contain subcodes that refine the message. • Unlike Codes, subcodes don’t have standard values. • Instead, they can take any QName value. • This is an extensibility mechanism. • Subcodes may contain other subcodes. <env:Code> <env:Value>env:Sender </env:Value> <env:Subcode> <env:Value>rpc:Bad Arguments </env:Value> </env:Subcode> </env:Code>
  59. 59. Fault Reasons • This is intended to provide human readable reasons for the fault. • The reason is just a simple string determined by the implementer. • For Axis, this is the Java exception name. • At least, for my version of Axis. • We must also provide at least one language. <xs:complexType name="faultreason"> <xs:sequence> <xs:element name="Text" type="tns:reasontext" minOccurs="1" maxOccurs="unbounded" /> </xs:sequence> </xs:complexType> <xs:complexType name="reasontext"> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute ref="xml:lang" use="required" /> </xs:extension> </xs:simpleContent> </xs:complexType>
  60. 60. Optional Fault Elements • Code and Reason are required. • Node, Role, and Detail are optional • Node and Role are used in SOAP processing steps that we have lightly covered. • SOAP messages may go through several intermediaries. • Nodes and roles are needed in case a fault occurs in an intermediary. • Return the URI of the node and role • Details will be described. Source Dest. Node 1 Node 2 “I Check AuthN” “I Check AuthZ”
  61. 61. Fault Detail • A fault detail is just an extension element. • Carries application specific information • It can contain any number of elements of any type. • This is intended for the SOAP implementer to put in specific information. • You can define your own SOAP fault detail schemas specific to your application. • Axis, for example, includes Java exception stack traces. <xs:complexType name="detail"> <xs:sequence> <xs:any namespace="##any" processContents="lax" minOccurs="0" maxOccurs="unbounded" /> </xs:sequence> <xs:anyAttribute namespace="##other" processContents="lax" /> </xs:complexType>