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IPC: Connecting

Kdb+ uses tcp/ip connection to talk between two kdb+ processes or when using http browser

All messages in kdb+ connection goes via message handler functions

  • to declare port number inside a q process we use /p [port_number], we can also assign port number when starting the process using -p [port_number]

  • when inside a process we can use \p to see the port number, by default if port number is not declared it 0i

user@host:~ $ q
q)\p 1234
q)\p 
1234i

user@host:~ $ q -p 1234
q)\p 
1234i

user@host:~ $ q
q)\p
0i
  • let's create 2 q processes:
  • server - one which is serving queries

  • client - one which is making queries

  • we can open a connection from client to server using function hopen

  • we can also see which socket this handle is assigned to by checking value of h 
    q)// server
q)\p 
1234i

q)// client
q)h:hopen 1234
q)h
3i
  • we can use another version of hopen command by specifyign host and port number - hopen ``:host:port 
    q)// client 
q)h1: `:localhost:1234
q)h1
3i
q)h1:`::1234 // if we dont provide host, it defaults to localhost
q)h1
4i
  • we can see all the handles open on client process by checking dictionary .z.W
q)//client
q).z.W
q).z.W
3|
4|
  • to close a connection we use function hclose
  • we can also give handle number as an argument to hclose function to close a handle - handle number can be checked from .z.W command
q)//client
q)hclose h1
q)hclose 4i

Message Handler Functions

  • we can reset any of the message handler function to their original definition by using \x function_name or \x .z.pw

.z.pw

  • used to check password of user while opening connection
  • arguments to .z.pw function are username and password
  • can be reset to default using \x .z.pw
// server
q)permittedusers:`abc`xyz`pqr
q).z.pw:{[u;p] (u in permittedusers) and (p~"pass")}

//client
q)h:hopen `::1234
'access
  [0]  h:hopen `::1234
         ^
q)h:hopen `::1234:abc:pass
q).z.W
7|

.z.po

  • this is executed whenever a handle is opened and after .z.pw has executed successfully
  • we can print details of just opened handle in this function, like: ip address, username, date time and handle number
  • argument passed to function .z.po is handle number
  • .z.a - show ip address
  • .z.p - current timestamp
  • .z.u - user opening handle
// server
q).z.po:{[x] show(.z.a;.z.p;.z.u;x)}
{[x] show(.z.a;.z.p;.z.u;x)}
q)2130706433i
2022.02.21D03:38:51.578467000
`abc
10i

//client
q)h2:hopen `::1234:abc:pass

.z.pc

  • we can use .z.pc to be executed whenever a handle is closed to server
//server
q).z.pc:{[x] show(.z.h;.z.p;x)}
q)`ykr-mbam1.local
2022.02.21D03:42:57.717442000
10i

//client
q)hclose h2

Timeout

  • we can also define timeout in millisecods when opening a handle
// server
q)system "sleep 60"

// client
q)h2:hopen (`::1234:abc:pass;10)
'timeout
  [0]  h2:hopen (`::1234:abc:pass;10)

Restricting user access on start-up

  • we can define username and password combination in a file and specify it using -u filepath when strating q session
  • Only username password combination in the file will be allowed when opening handle
// server

ranayk@ykr-mbam1: $ cat users.txt
abc:pass1
xyz:pass2
qwe:pass3

ranayk@ykr-mbam1: $ q -p 1234 -u users.txt
KDB+ 4.0 2021.04.26 Copyright (C) 1993-2021 Kx Systems
m64/ 8(16)core 8192MB ranayk ykr-mbam1.local 127.0.0.1 EXPIRE 2022.05.30 yankeekiloromeo@gmail.com KOD #4176402

q)

//client
q)h2:hopen `::1234:abc:pass
'access
  [0]  h2:hopen `::1234:abc:pass
          ^
q)h2:hopen `::1234:abc:pass1
q)h2:hopen `::1234:xyz:pass1
'access
  [0]  h2:hopen `::1234:xyz:pass1
          ^
q)h2:hopen `::1234:xyz:pass2
q)
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