Prevent multiple parallel connections

http_client.connect() is async and imposes a race condition if we set
the gobal connection variable *after* this async call returns.
We now set connection = true to prevent further calls to
http_client.connect() and write the correct value to the connection
global once the async call returns.

mod_push_appserver_apns/mod_push_appserver_apns.lua

@@ -12,7 +12,6 @@ local cq = require "net.cqueues".cq;
 local http_client = require "http.client";
 local new_headers = require "http.headers".new;
 local ce = require "cqueues.errno";
-local new_tls_context = require "http.tls".new_client_context;
 local openssl_ctx = require "openssl.ssl.context";
 local x509 = require "openssl.x509";
 local pkey = require "openssl.pkey";
@@ -108,6 +107,7 @@ local function apns_handler(event)
 
 			-- create new connection
 			local err, errno;
+			connection = true;		-- prevent multiple parallel connections (http_client.connect() is async)
 			connection, err, errno = http_client.connect({
 				host = push_host;
 				port = push_port;