Re: Socket program problem -- MIDRANGE-L

John Allen wrote:

The iSeries is acting as the Server and it sits and waits for the PC Clients
to connect.
The PC sends a request for a file to the iSeries and then waits for a
response back (Event message).
The iSeries builds the file and sends it back to the PC one record at a time
(in XML format) The building of the file and sending all of the records in
XML format takes about 2 seconds.
While the iSeries is sending the records, the PC client starts receiving the
records in groups (number of records it receives with each receive varies
from 1-5 records at a time) Before the PC receives all the records it
receives a 10053  WSAECONNABORTED and transmission is terminated.

I read somewhere that after sending data I should wait for an ack before
proceeding. Does this mean when the iSeries send a single record it should
wait til the PC receives it and the PC send an ack back to the iSeries, then
the iSeries should send another record etc. etc. ?

Unless I'm really misunderstanding something here, I think you are confused. The TCP protocol itself sends the ACK. Your application is a higher layer so it doesn't. TCP takes care of SYN, ACK, etc. without you having to do anything.

In this application when the iSeries receives a request (ie PC wants file x) The iSeries spawns off a separate job that builds the file and send the data to the PC. The iSeries never acknowledges to the PC that it got the request. It just builds the file and starts sending records to the PC. When the iSeries program (spawned program) is done sending the records it ends. The PC (client) starts receiving the records and when done receiving the records it displays them.

Sounds very reasonable.

At all 10 remote locations, if the file requested is small (about 10
records) all 10 locations work fine, they receive all data just fine.

But when the file requested is larger (about 20 or so records)
Two of our 10 remote locations never receive all the data They both
consistently get the 10053  WSAECONNABORTED before all records are received.

We were going to re-write the application tonight and write it so that
whenever the PC or the iSeries sends data (even after each individual( they
are going to wait until the other side ack that they received the data and
is waiting for the next

Is this a waste of my time? The programmers here are just guessing at what
it could be, but we are out of ideas except for this rewrite.

New program would
1) iSeries waiting for request
2) PC send req to iSeries for file X, then waits for ack from iSeries
3) iSeries receives request for file x, sends ack to the PC that the request
was received and spawns Job A to build the file and transmit to PC
4) PC get ack from iseries and waits for data
5) iSeries Job A build file and sends record 1 (with X'FF' at end of record)
then waits for ack from PC that the record was received
PC receives record 1 and knows it is complete because of x'FF' and send ack
to the iSeries
6) iSeries receives ack from PC and the two go back and forth til all
records are sent and received.

Is there any chance this might fix my problem?

While you certainly can communicate between the hosts when data is received (and that is probably a good idea), TCP does ACK, not your application. You can send your own custom acknowlege if you want in addition, but TCP is still going to ACK.

Try something like this:

1. Start the server program on the iSeries. 2. Use telnet to connect to the server program. For example: telnet myas400 4543 (this assumes that your server program runs on port 4543) 3. In telnet, send to the iSeries the command the PC would normally send to initiate the file transfer. 4. Watch what happens.

If in step 4 things don't work like you expect, let us know what happened.

James Rich