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JXTA Messages

JXTA Messages. Learning Objectives. This module will help you... Develop applications and services which exchange messages either through JXTA Pipes or directly with other peers. Message Components. Ordered Sequence of Message Elements Messages can have multiple parts

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JXTA Messages

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  1. JXTA Messages

  2. Learning Objectives • This module will help you... • Develop applications and services which exchange messages either through JXTA Pipes or directly with other peers

  3. Message Components • Ordered Sequence of Message Elements • Messages can have multiple parts • Ordered so you can do streaming • Each element belongs to a namespace • Namespaces provide protocol segregation • Two Default Namespaces • “”(empty) • The default namespace • “jxta” • For the JXTA Core Protocols

  4. Message Element Components • Name • UTF8 Character String • Need not be unique • MIME Type • UTF8 Character String • Same as for web content or email • Data • Bytes is bytes ... almost • Signature/Hash • Another Message Element

  5. Message Element Data • We said: • Has a MIME-type • “application/octet-stream” default • Uninterpreted Bytes Content • Bindings may add Interpretation to Content • Streams, Files, XML Documents • Strings, Objects, Complex Data • MIME-type is used as key • MIME parameters help the helper

  6. Message Element Signature • We said: • It is also a Message Element • So.... • Element Name can be used • MIME-type can be used to describe format • Signature can contain arbitrary data • Helper can present signature as an Object • JXTA does not validate signatures automatically

  7. Message Serialization • JXTA Bindings deal with messages in an abstract way • To send a message it must be serialized • Message Transports choose Wire Formats for efficiency, everyone else shouldn't care • Wire formats follow rough requirements of RFC 1521:MIME • XML, DIME, MIME, Java Serialization have all been used; default is “JXTA Binary Message Wire Format”

  8. Messages Within JXTA • Transport Layer • Messages are sent to a transport defined address • Simple point-to-point messaging • Only valid while the transport is valid • Endpoint • Messages are sent to an abstract “Peer” address • Peer may move within the network, change transports, physical addresses, etc. • Pipes • Messages are sent to an abstract “Pipe” address • May be served by a single peer, redundantly by any one of a number of peers or cooperatively by a federation of peers. This may also change over time.

  9. Summary Thus Far... • Messages are abstract containers • Messages contain elements in namespaces • Elements have a name, a type, data and a signature • Messages are serialized for sending • Bindings provide functionality for manipulating messages • Messages are sent to Pipes, Peers, Transports

  10. Using Messages with JXTA-C • Message and Message Element API • Building a message • Sending a message • Receiving a message

  11. JXTA-C : Message API Jxta_message* jxta_message_new(void); • Create a new Message Jxta_message* jxta_message_clone(Jxta_message* msg); • Clone a Message, all elements are shared Jxta_status jxta_message_read(Jxta_message* msg, char const * mime_type, ReadFunc read_func, void *stream ); • Read a Message from a stream Jxta_status jxta_message_write(Jxta_message* msg, char const * mime_type, WriteFunc write_func, void *stream); • Write a Message to a stream Jxta_endpoint_address* jxta_message_get_{source|destination}( Jxta_message* msg); • Get the source or destination Endpoint Address of a Message Jxta_status jxta_message_set_{source|destination}( Jxta_message* msg, Jxta_endpoint_address *src); • Set the source or destination of a Message Jxta_status jxta_message_to_jstring(Jxta_message* msg, char const * mime_type, JString* string ); • Serialize a message in wire format to a JString

  12. JXTA-C : Message API (cont.) Jxta_status jxta_message_add_element(Jxta_message* msg, Jxta_message_element* el); • Add a Message Element to a Message Jxta_status jxta_message_get_element_*(Jxta_message* msg, char const * qname, Jxta_message_element** el ); • Get a Message Element from a Message Jxta_vector* jxta_message_get_elements(Jxta_message* msg ); • Get a Vector of all the elements of a Message Jxta_vector* jxta_message_get_elements_of_namespace( Jxta_message* msg, char const *Namespace ); • Get a Vector of all the elements of a single namespace Jxta_status jxta_message_remove_element_*(Jxta_message* msg, char const * ns, char const * name ); • Remove a Message Element from a Message

  13. JXTA-C : Message Element API Jxta_message_element* jxta_message_element_new_*( char const *ns, char const *ncname, char const *mime_type, char const *value, size_t length, Jxta_message_element* sig ); • Create a new Message Element from bytes Jxta_message_element* jxta_message_element_new_3( char const *ns, char const *ncname, char const *mime_type, Jxta_bytevector* value, Jxta_message_element* sig ); • Create a new Message Element from a share byte vector\ char const* jxta_message_element_get_namespace(el ); • Get namespace of an element char const* jxta_message_element_get_name(Jxta_message_element* el); • Get name of an element char const* jxta_message_element_get_mime_type( el ); • Get mime type of an element Jxta_bytevector* jxta_message_element_get_value( el ); • Get value an element as a shared byte vector Jxta_message_element* jxta_message_element_get_signature( el ); • Get signature element of element

  14. JXTA-C : Building a Message const char * HELLO = “Hello World!”; const char * MIME = “text/plain; charset='UTF8'”; Jxta_bytevector* bytes = jxta_bytevector_new_1 ( 50 ); jxta_bytevector_add_bytes_at( bytes, HELLO, 0, strlen(HELLO) ); Jxta_message* msg = jxta_message_new(); Jxta_message_element* el1 = jxta_message_element_new_2( “jxta”, “hello”, MIME, HELLO, strlen(HELLO), null ); jxta_message_add_element(msg, el1); Jxta_message_element* el2 = jxta_message_element_new_3( “”, “hello”, MIME, bytes, null ); jxta_message_add_element(msg, el2);

  15. JXTA-C : Sending A Message jxta_message_set_source( msg, localPeerAddr ); jxta_message_set_destination( msg, destAddr ); Jxta_status res = jxta_message_write( msg, “application/x-jxta-msg”, HTTP_SendFunc, httpStream );

  16. JXTA-C : Receiving A Message msg = jxta_message_new(); res = jxta_message_read( msg, NULL, HTTP_ReadFunc, httpStream ); jxta_message_get_element_2( msg, “jxta”, “hello”, el1 ); Jxta_bytevector bytes = jxta_message_element_get_value(el1); char const * data = (char const *) malloc( jxta_bytevector_size( bytes ) + 1); jxta_bytevector_get_bytes_at( bytes, data, 0, jxta_bytevector_size( bytes ) ); data[jxta_bytevector_size( bytes )] = 0; printf( “Someone says : %s”, data );

  17. Using Messages with JXTA-J2SE • Message and Message Element APIs • Building a message • Sending a message • Receiving a message

  18. JXTAJ2SE : Message API Message(); • Construct a new message Object clone(); • Clone a message, elements are not copied boolean equals( Object target ); • Compare two messages String toString(); • Show message number and lineage void addMessageElement( MessageElement add ); • Add an element to default namespace void addMessageElement( String namespace, MessageElement add ); • Add an element to specified namespace MessageElement replaceMessageElement( String namespace, MessageElement replacement ); • Replace first occurrence of an element in specified namespace Iterator getMessageNamespaces( ); • Get list of namespaces in message MessageElement getMessageElement( String namespace, String name ); • Get a message element by name ElementIterator getMessageElements( ); • Get all elements of message ElementIterator getMessageElements( String namespace, String name ); • Get all elements matching name from namespace

  19. JXTAJ2SE : Message API (cont.) ElementIterator getMessageElementsOfNamespace( String namespace ); • Get all elements of specified namespace ElementIterator getMessageElements( String namespace, MimeMediaType type ); • Get all elements of specified type from namespace boolean removeMessageElement( MessageElement remove ); • Remove specified element from any namespace boolean removeMessageElement( String namespace, MessageElement remove ); • Remove first occurrence of element from specified namespace void clear(); • Clear all elements from message synchronized long getByteLength(); • Get cumulative length of all elements int getMessageModCount(); • Number of times a message has been modified int getMessageNumber( ); • Get message number which was assigned at creation Iterator getMessageLineage( ); • Get list message numbers of ancestors of this message Object setMessageProperty( Object key, Object value ); • Associate a transient property with message Object getMessageProperty( Object key ); • Retrieve a transient property with message

  20. JXTAJ2SE : Message Element API String toString( ); • Get String representation of element data String getElementName(); • Get name of the element MimeMediaType getMimeType(); • Get MIME type of message long getByteLength(); • Get length of element data in bytes byte[] getBytes( boolean copy ); • Get element data as byte array, optionally copied InputStream getStream() throws IOException; • Get element data as byte stream void sendToStream( OutputStream sendTo ) throws IOException; • Send element data to stream MessageElement getSignature(); • Get element signature as another element Object setElementProperty( Object key, Object value ); • Set transient property for element

  21. J2SE: Building a Message Message msg = new Message(); MessageElement el1 = new StringMessageElement( “hello”, “Hello World!”, null ); msg.addMessageElement( el1 ); msg.addMessageElement( “jxta”, el1 );

  22. J2SE: Sending a Message EndpointService endp = group.getEndpointService(); EndpointAddress destAddr = new EndpointAddress( dest, “welcome”, null ); Messenger messenger = endp.getMessenger( destAddr, null ); messenger.sendMessage( msg );

  23. J2SE: Receiving A Message EndpointService endp = group.getEndpointService(); endp.addIncomingMessageListener( new EndpointListener() { void processIncomingMessage( Message msg, srcAddr, destAddr ) { MessageElement el1 = msg.getMessageElement( “jxta”, “hello” ); System.out.println( srcAddr + “ says: “ + el1 ); } }, “welcome”, null ); // wait for messages...

  24. Summary • Messages form the basis for JXTA and application protocols • The same messages work for physical destinations, peers and pipes • JXTA Bindings let you work with messages without worrying about wire representation

  25. End – JXTA Messages

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