GCM and Lua
Support for GCM includes new Lua functionality and Lua callouts. This chapter covers these topics.
Note
GCM-related changes to the C API and to C hook points are documented in Hooks in the gcm Scope.
In addition to the callouts documented here, you can also use the callouts documented at Callouts and Push Notifications .
For a description of how to use Lua scripts see The scriptlet Module and Implementing Policy Using Scriptlets.
The basic Lua callouts are defined at Implementing Policy Using Scriptlets. When scripting GCM push notifications you can also use the hook points described here.
The gcm_request_eval(req, msg) hook will be called immediately before sending to GCM. Use this hook to inspect or modify the request before delivery to Google. The request has been built from the MCMT by extracting the headers and JSON message payload from the MIME part and encoding them into a JSON string suitable for injection. At this hook point, feedback from Google GCM Servers can be handled, including maintenance related to the Registration ID. Feedback is provided for messages that were rejected as well as messages that were accepted. The callout parameters are userdata of the types, gcm_request and ec_message.
An example that shows the elements of a gcm_request and changes the Registration ID follows.
require("msys.gcm")
require("json")
local mod = {}
function mod:gcm_request_eval(req, msg)
print("registration id =", req.json.registration_ids[1])
print("package = ", req.json.restricted_package_name)
print("time to live = ", req.json.time_to_live)
print("data = ", tostring(req.json.data))
print("message = ", req.json.data.message)
-- assign registration id
req.json.registration_ids[1] = "APA91bHAUcDAJP-cQJuwQaHYGK6hGU4G4NTUPJT4zI6f2 »
o4sl1S0-zOlPlqJUFTSvHBmudvhMLrkGR1sQMc5qYBVjcNIpzyXoC2CIEj_1FeFKmNBDYX2LBp_zG-rj2hVA2 »
-t7Fm40tQY2DzyjAI8maYIogujSPtq-jSUG0WybCQ0mT1eGOZsgy0"
-- modify message
req.json.data.message = "We are changing the message to this!"
end
msys.registerModule("gcm_hooks", mod);
In order to reference a gcm_request you must include the line, require("msys.gcm"). For more information about the Lua functions used in “gcm_request_eval example” see Lua Functions List.
The gcm_response_eval(resp, msg) hook will be called when there is a response from GCM. It can be used to inspect this response before delivery to GCM. The request has been built from the MCMT by extracting the headers and JSON message payload from the MIME part and encoding into a JSON string suitable for injection.
Note
This hook is only called if the HTTP status code is 200. You should not modify the gcm_message_response at this hook point.
require("msys.core")
require("msys.gcm")
require("json")
local mod = {}
function mod:gcm_response_eval(message_response, msg)
-- get original message id
local reg_id = msg:context_get(msys.core.ECMESS_CTX_MESS, "DLV_Dest_ID")
if(reg_id != "") then
print("Registration ID = ", reg_id)
end
-- check response for registration id update info
if message_response.canonical_ids > 0 then
-- Add test entry to log for receipt of canonical response
print ("canonical_ids = ", message_response.canonical_ids)
if message_response.results.registration_id then
-- The customer would want to use this updated Registration Feedback and would
-- insert appropriate logic here.
print("GCM: Found canonical registration id feedback:", »
message_response.results.registration_id)
else
print("GCM: Missing canonical registration id value")
end
else
print("GCM: No canonical registration id feedback indicated")
end
end
msys.registerModule("gcm_hooks", mod);
In order to reference a gcm_request you must include the line, require("msys.gcm"). For more information about the Lua functions used in “gcm_response_eval example” see Lua Functions List.