Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/platform/services/remotecluster/send.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package remotecluster
+
+import (
+	"context"
+	"hash/fnv"
+)
+
+// enqueueTask adds a task to one of the send channels based on remoteId.
+//
+// There are a number  of send channels (`MaxConcurrentSends`) to allow for sending to multiple
+// remotes concurrently, while preserving message order for each remote.
+func (rcs *Service) enqueueTask(ctx context.Context, remoteId string, task any) error {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
+	h := hash(remoteId)
+	idx := h % uint32(len(rcs.send))
+
+	select {
+	case rcs.send[idx] <- task:
+		return nil
+	case <-ctx.Done():
+		return NewBufferFullError(cap(rcs.send))
+	}
+}
+
+func hash(s string) uint32 {
+	h := fnv.New32a()
+	h.Write([]byte(s))
+	return h.Sum32()
+}
+
+// sendLoop is called by each goroutine created for the send pool and waits for sendTask's until the
+// done channel is signalled.
+//
+// Each goroutine in the pool is assigned a specific channel, and tasks are placed in the
+// channel corresponding to the remoteId.
+func (rcs *Service) sendLoop(idx int, done chan struct{}) {
+	for {
+		select {
+		case t := <-rcs.send[idx]:
+			switch task := t.(type) {
+			case sendMsgTask:
+				rcs.sendMsg(task)
+			case sendFileTask:
+				rcs.sendFile(task)
+			case sendProfileImageTask:
+				rcs.sendProfileImage(task)
+			}
+		case <-done:
+			return
+		}
+	}
+}