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Last updated March 2020


msg:context_exists_and_get — Check if a context variable exists and get it


msg:context_exists_and_get(type, key);

type: numeric
key: string


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

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.

See Also

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