Handle throttle return codes from send APIs

Patch 4.4.0 and 10.2.7 are "improving" SendAddonMessage and its logged
cousin by making it return a bit more information on failure in the form
of an enum, rather than a boolean.

This means that we can now deal with cases where the client is actively
throttling comms on a specific prefix. The problem however, is that with
this implementation comes a separate change that now means that *all*
traffic is subject to the 10-message-slots-per-prefix system that had
been applied to party and raid comms in recent patches.

This means that in cases where there's few addons actually sending data,
the default tuning of Chomp's BPS and BURST values is stratospherically
high and will result in messages being dropped by the API - so we need
to handle the throttling.

Using the result, we'll check if the client has blocked a message due to
the per-prefix or per-channel throttle, and if it is we'll requeue it
and redistribute bandwidth to the remainder of the messages in the same
priority.

There is a bit of gnarly logic here though - the function that sends
data out relies only terminates its loop if there's no data left to
send, or if there's not enough bytes left in the pool for us to send the
remaining data with. This fights with the whole process of requeueing.

As such - when requeueing messages we put them back into the queue,
redistribute the bandwidth, but we don't requeue the queue itself until
we're outside of the loop, instead deferring that operation by placing
it into a 'blocked queues' table.

We also now don't destroy queues before sending data, but wait until
afterwards - this is required because we only want to clean up the
'priority.byName' queue reference only if a queue is in an empty and
unblocked state post-send.

These changes should hopefully keep much of the logic in the
successful-send and unrecoverable-failure cases the same.

.luacheckrc

@@ -51,6 +51,7 @@ read_globals = {
 	"CreateFrame",
 	"CreateFromMixins",
 	"DoublyLinkedListMixin",
+	"Enum.SendAddonMessageResult",
 	"ERR_CHAT_PLAYER_NOT_FOUND_S",
 	"FULL_PLAYER_NAME",
 	"GetAutoCompleteRealms",

Internal.lua

@@ -14,7 +14,7 @@
 	CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 ]]
 
-local VERSION = 24
+local VERSION = 25
 
 if IsLoggedIn() then
 	error(("Chomp Message Library (embedded: %s) cannot be loaded after login."):format((...)))
@@ -278,11 +278,45 @@ end
 	INTERNAL BANDWIDTH POOL
 ]]
 
+local SendAddonMessageResult = Mixin({
+    Success = 0,
+    InvalidPrefix = 1,
+    InvalidMessage = 2,
+    AddonMessageThrottle = 3,
+    InvalidChatType = 4,
+    NotInGroup = 5,
+    TargetRequired = 6,
+    InvalidChannel = 7,
+    ChannelThrottle = 8,
+    GeneralError = 9,  -- Reporting for duty, sir!
+}, Enum.SendAddonMessageResult or {})
+
+local function MapToSendAddonMessageResult(result)
+	if result == true then
+		result = SendAddonMessageResult.Success
+	elseif result == false then
+		result = SendAddonMessageResult.GeneralError
+	end
+
+	return result
+end
+
+local function IsRecoverableDeliveryError(result)
+	if result == SendAddonMessageResult.AddonMessageThrottle then
+		return true
+	elseif result == SendAddonMessageResult.ChannelThrottle then
+		return true
+	else
+		return false
+	end
+end
+
 function Internal:RunQueue()
 	if self:UpdateBytes() <= 0 then
 		return
 	end
 	local active = {}
+	local blockedQueues = {}
 	for i, priority in ipairs(PRIORITIES) do
 		if self[priority].front then -- Priority has queues.
 			active[#active + 1] = self[priority]
@@ -296,20 +330,28 @@ function Internal:RunQueue()
 		while priority.front and priority.bytes >= priority.front.front.length do
 			local queue = priority:PopFront()
 			local message = queue:PopFront()
-			if queue.front then -- More messages in this queue.
-				priority:PushBack(queue)
-			else -- No more messages in this queue.
-				priority.byName[queue.name] = nil
-			end
-			local didSend = false
+			local sendResult = SendAddonMessageResult.GeneralError
 			if (message.kind ~= "RAID" and message.kind ~= "PARTY" or IsInGroup(LE_PARTY_CATEGORY_HOME)) and (message.kind ~= "INSTANCE_CHAT" or IsInGroup(LE_PARTY_CATEGORY_INSTANCE)) then
 				priority.bytes = priority.bytes - message.length
 				self.isSending = true
-				didSend = message.f(unpack(message, 1, 4)) ~= false
+				sendResult = MapToSendAddonMessageResult(select(-1, message.f(unpack(message, 1, 4))))
 				self.isSending = false
 			end
-			if message.callback then
-				xpcall(message.callback, CallErrorHandler, message.callbackArg, didSend)
+			if IsRecoverableDeliveryError(sendResult) then
+				-- Requeue the message, but don't requeue the queue.
+				queue:PushFront(message)
+				priority.bytes = priority.bytes + message.length
+				blockedQueues[#blockedQueues + 1] = { priority, queue }
+			else
+				if queue.front then -- More messages in this queue.
+					priority:PushBack(queue)
+				else -- No more messages in this queue.
+					priority.byName[queue.name] = nil
+				end
+				if message.callback then
+					local didSend = (sendResult == SendAddonMessageResult.Success)
+					xpcall(message.callback, CallErrorHandler, message.callbackArg, didSend)
+				end
 			end
 		end
 		if not priority.front then
@@ -318,8 +360,10 @@ function Internal:RunQueue()
 			priority.bytes = 0
 		end
 	end
-	if remaining == 0 then
-		self.hasQueue = nil
+	for _, blockedQueueInfo in ipairs(blockedQueues) do
+		local priority = blockedQueueInfo.priority
+		local queue = blockedQueueInfo.queue
+		priority:PushBack(queue)
 	end
 end
 
@@ -362,20 +406,12 @@ for i, priority in ipairs(PRIORITIES) do
 end
 
 function Internal:StartQueue()
-	if not self.hasQueue then
-		self.hasQueue = true
-		C_Timer.After(POOL_TICK, self.OnTick)
-	end
-end
+	if not self.queueTicker then
+		local function OnTick()
+			self:RunQueue()
+		end
 
-function Internal.OnTick()
-	local self = Internal
-	if not self.hasQueue then
-		return
-	end
-	self:RunQueue()
-	if self.hasQueue then
-		C_Timer.After(POOL_TICK, self.OnTick)
+		self.queueTicker = C_Timer.NewTicker(POOL_TICK, OnTick)
 	end
 end