msg:context_exists_and_get
Name
msg:context_exists_and_get — Check if a context variable exists and get it
Synopsis
msg:context_exists_and_get(type, key);
type: numeric key: string
Description
Check if a context variable exists and get it. Legal values for type are:
-
msys.core.ECMESS_CTX_MESS -
msys.core.ECMESS_CTX_CONN
local e, str = msg:context_exists_and_get(msys.core.ECMESS_CTX_MESS, 'key')
If the context variable key was found, e will be 1 and str will be a string value. If the context variable key was not found, e will be 0 and str will be nil.
This function is similar to msg:context_get(); however, msg:context_get() returns an empty string if the key does not exist. msg:context_exists_and_get() is more useful in the general case because policy scripts generally take a different path when the key does not exist and in those cases a default of empty string is not helpful.
The return value of this function should always be compared explicitly. For example:
local e, str = msg:context_exists_and_get(msys.core.ECMESS_CTX_MESS, 'key')
if e == 1 then
-- do something here that depends on the key existing
end
Note that Lua treats the numeric value 0 as true, which can be confusing.
Because this function is in the msys.core namespace, an explicit require('msys.core') is not necessary.