OpenLogFile.aplf

 (tn msg)←OpenLogFile LOGFILE;logdir;NL
⍝ Return tie number and empty msg on success, else (0 message)
 (tn msg)←0 ''
 NL←⎕UCS 10

 :If ⎕NEXISTS LOGFILE
     :Trap 0
         tn←LOGFILE ⎕FTIE 0
     :Else
         msg←'ERROR: error attempting to ⎕ftie LOGFILE ',LOGFILE,NL
         msg,←⎕JSON ⎕DMX
     :EndTrap
 :Else
     :Trap (~SSGDEBUG)/0
         logdir←⊃1 ⎕NPARTS LOGFILE
         ⍝ ROS points out that ⎕nexists⋄12⎕ninfo has a timing hole, so safer to trap error if logdir doesn't exist
         :If ~12 ⎕NINFO logdir ⍝ 12: Is file/folder writable?
             msg←'ERROR: Unable to write to existant log directory ',logdir
         :EndIf
     :Else
         msg←'ERROR: log directory',logdir,' does not exist'
     :EndTrap

     tn←LOGFILE ⎕FCREATE 0
     (1 3⍴0 ¯1 0)⎕FSTAC tn
     ⎕←'Created log file "',LOGFILE,'"'
     'Security Monitor Log File v1.0'⎕FAPPEND tn
     (9⍴⊂'reserved')⎕FAPPEND¨tn
 :EndIf