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This program illustrates how to implement a simple client and server
using CORBA, IIOP, and asynchronous method invocations (AMI). Client
applications can use this service to download and display files from a
CORBA server on the network. The core functionality of this program
is as follows:
* Client applications will use an iterator in conjunction with AMI
to download and display files from multiple CORBA server one
``chunk'' at a time simultaneously, without requiring
multiple threads. This design will help improve the memory
management overhead on the client and server.
* Operations in the IDL interface will use exceptions to propagate
problems back to clients.
* The CORBA Naming Service is used to bind and resolve object
references, rather than using a file.
The client program performs the following activities:
1. From the command-line, it reads the name of the pathname
you want to download. It then initializes the client-side
ORB and uses resolve_initial_references() to obtain a
reference to a Naming Service (which must be running). This
object reference is then downcast via _narrow() to an
object reference for a CosNaming::NamingContext interface,
which is then used to resolve the object reference that the
server bound earlier. After narrowing this to the Server
interface, the get_iterator() operation is called via the
object reference to obtain the Chunk_Iterator, which is
used to download the file.
2. The client invokes the sendc_next_chunk() method on the
iterator, passing in the offset and the object reference to
the client's reply handler. Only one pending call at a
time per-server. To relax this constraint would require
some type of offset parameter to the next_chunk() callback
to perform reassembly if chunks for the same file arrived
out of order.
3. When next_chunk() returns a chunk of the file, the contents
are written into a temporary file created in your a cache
(e.g., /tmp/yourloginname) on the local host. Then, an
external viewer is spawned to display the file. The type
of viewer to spawn is determined by examining the the
content_type_ metadata returned by the server.
The example can be run as follows:
1. Start the Name Service:
$ NameService -o /tmp/ns.ior
2. Start the SMI Content Server:
$ server -ORBInitRef NameService=file:///tmp/ns.ior
3. Request a file using the client:
$ client -ORBInitRef NameService=file:///tmp/ns.ior \
~/foo.jpg ~/bar.jpg
This example can service multiple file requests.
----------------------------------------
The server output should look like the following:
$ ./server -ORBInitRef NameService=file:///tmp/ns.ior
Bound <Iterator_Factory> to <IOR:010000002400000049444c3a57653625f5365727665722f4974657261746f725f466163746f72793a312e300001000000000000007c000000010102001400000076616c696e6f12722e6563652e7563692e65647500f39600001b00000014010f00525354bd9d4e39a6ac03000000000001000000010000000003000000000000000800000001000000004f4154010000001400000001ad85e4001000100000000000901010000000000004f41540400000001ac0000> in Name Service.
Accepting requests.
Received request for file: </home/myhome/foo.jpg>
Sending chunk 1 at offset <0> of size <8192>
Received request for file: </home/myhome/bar.jpg>
Sending chunk 2 at offset <8192> of size <8192>
Sending chunk 1 at offset <0> of size <8192>
Sending chunk 3 at offset <16384> of size <8192>
Sending chunk 4 at offset <24576> of size <8192>
Sending chunk 2 at offset <8192> of size <8192>
Sending chunk 5 at offset <32768> of size <4573>
Sending chunk 3 at offset <16384> of size <8192>
Sending chunk 4 at offset <24576> of size <8192>
Sending chunk 5 at offset <32768> of size <6997>
Notice that requests for chunks of data from two separate files occur
in the above run.
----------------------------------------
The client output should look similar to:
$ ./client -ORBInitRef NameService=file:///tmp/ns.ior ~/foo.jpg ~/bar.jpg
Wrote retrieved data to file </tmp/ace-file-nBqLM2>
Spawned viewer <xv> with PID <11134>.
Wrote retrieved data to file </tmp/ace-file-MKURUU>
Spawned viewer <xv> with PID <11135>.
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