WebAPI connection exception Error Subset Found: Server error-00150-No response returned from the server

When writing a Colleague custom WebAPI, I encountered a connection error while executing a transaction:

[Ellucian.Data.Colleague.Exceptions.ColleagueTransactionException] = {"Error Subset Found: Server error-00150-No response returned from the server."}

I made sure my credential was correct and the connection was established before calling the transaction. After much debugging, I found out that the string that was passed to the transaction exceeded the size limit of a field in Colleague. I passed in a 15 character long string and tried to write it to a 10 character long field in Colleague through the transaction, and it resulted in a truncation error which ended the Colleague session. This also returned the error above. They do not look like they're related, so it was hard to track down. Make sure you check the size of the arguments of the transaction when you get these error.

Check if a record is locked

It is useful to check to see if the record is lock before beginning any processing. This eliminates the process to spin and wait for the record to be unlocked. When you work withe the WebAPI, it is more important to return a status of "resource is unavailable please try again" than to wait and risk the process timing out. To check to see if a record is locked, follow the below template:

XKV.FILE = V.BPV.DOC.IDS
XR.FILE = ""
CALL @MIO.READ.RECORD(MIO.READU.EXIT.ON.LOCKED,XFV.FILE,XKV.FILE,XR.FILE)
IF MIO.STATUS = MIO.STAT.LOCKED THEN ;* file is locked
   X.ERROR = 1
   * Output your message, set the status, or do some other process
END ELSE ;* record is not lock, proceed like normal
   * normal record read/write
END

The following give you different statuses of the lock check:

To read a record from a previously opened file.
@MIO.READ.RECORD(read_option, FV.FILE, KV.FILE, R.FILE)

Where FV.FILE is the previously opened file, KV.FILE is the key of the
record to be read, and R.FILE is the array into which the record will be
read.

Read_option is one of the following. These are equates so they should not
be surrounded by quotes.

MIO.READ - Reads the record without locking

MIO.READU - Reads the record and locks. If the record is already locked by
someone else, the user will get a message and will have the opportunity to
cancel the command.

MIO.READU.NO.CANCEL - Same as READU but without the option to cancel if the
record is locked.

MIO.READ.VERIFY - Checks to see if the record exists. R.FILE will be set to
1 if the record exists and 0 if the record does not exist. The entire
record is not read into the R.FILE variable if this option is used.

MIO.READ.ORIG - Will read the record from disk instead of from the MIO
memory buffers.