CONNECTED() function raises errors if it detects TCP connection is lost

If calling CONNECTED() function is the point where AVM detects TCP connection is lost, that raises errors "Error reading socket, ret=10053, errno=2. (778)" and "** Incomplete write when writing to the server. (735)" instead of just returning "NO".

Sep 21, 2017
Knowledge

Title

URL Name

CONNECTED-function-raises-errors-if-it-detects-TCP-connection-is-lost

Article Number

000188458

Environment

Product: OpenEdge Version: 11.6.x OS: Windows

Question/Problem Description

CONNECTED() function doesn't gracefully handle situation where calling the function itself causes client to detect a TCP connection to database was lost.
It triggers errors "Error reading socket, ret=10053, errno=2. (778)" and "** Incomplete write when writing to the server. (735)" instead of just returning "NO".

Depending on how the errors are handled, unexpected behaviors can occur. For example, application code may end up ignoring them, only to raise "<program name> Database <dbname> not connected. (1006)" later on.

Steps to Reproduce

Clarifying Information

Following examples assume an instance of sports2000 database is running, with broker listening on port 5123.
In all cases, connection loss is simulated/forced by disconnecting the session with proshut.

This code:

/* traditional error handling */
message num-dbs.
pause. /* disconnect session using proshut while pausing */
message connected("sports2000").
message "after".
connect sports2000 -S 5123.
message num-dbs.

will raise the errors but will continue and reconnect.

But this version:

/* structured error handling */
routine-level on error undo, throw.
message num-dbs.
pause. /* disconnect session using proshut while pausing */
message connected("sports2000").
message "after".
connect sports2000 -S 51234.
message num-dbs.

will abort without reconnecting.
The difference is in how the error condition is handled.

Error Message

Error reading socket, ret=10053, errno=2. (778) ** Incomplete write when writing to the server. (735)

Defect Number

Defect PSC00357144

Enhancement Number

Cause

The exact cause is not known at this time.

Resolution

Until the fix is available, use the workaround below.

Workaround

The following workaround has been tested and works on classic AppServer, however fails on PAS for OpenEdge.

/* Ensure errors are caught and handled immediately after calling CONNECTED(), for example: */
def var lconnected as logical no-undo.

pause. /* use proshut to disconnect session from database while pausing */

do on error undo, throw:
   lconnected = false.
   lconnected = connected("sports2000").

   catch e as progress.lang.syserror:
   /* catch & ignore errore 778 & 735 pair, rethrow other errors */
   if not e:getmessagenum(1) = 778 then undo, throw e.
      else message e:getmessage(1).
   end catch.
end.

message lconnected. 
message "after".

/* Reconnect */ 
if not lconnected then do:
  connect sports2000 -S 5123.
  if not connected("sports2000") then message "Connection to database lost, could not be restored".
    else message "Connection to database restored".
end.

For a comprehensive solution that works in both Classic and PAS for OE AppServer environments, refer to Article How to reconnect to a database after an error in the AppServer or WebSpeed agent

Notes

Keyword Phrase

Last Modified Date

11/20/2020 7:13 AM

CONNECTED() function raises errors if it detects TCP connection is lost

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