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memory_broker.go
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memory_broker.go
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// Copyright 2023 Harness, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package stream
import (
"fmt"
"sync"
"sync/atomic"
"github.com/hashicorp/go-multierror"
gonanoid "github.com/matoous/go-nanoid"
)
const (
idPrefixUIDAlphabet = "abcdefghijklmnopqrstuvwxyz0123456789"
idPrefixUIDLength = 8
)
// MemoryBroker is a very basic in memory broker implementation that supports multiple streams and consumer groups.
type MemoryBroker struct {
// idPrefix is a random prefix the memory broker is seeded with to avoid overlaps with previous runs!
idPrefix string
// latestID is used to generate unique, sequentially increasing message IDs
latestID uint64
// queueSize is the max size of the queues before enqueing is blocking
queueSize int64
mx sync.RWMutex
// messageQueues contains all streams requested for a specific group
// messageQueues[streamID][groupName]: queue of messages for a specific stream and group
messageQueues map[string]map[string]chan message
}
func NewMemoryBroker(queueSize int64) (*MemoryBroker, error) {
idPrefix, err := gonanoid.Generate(idPrefixUIDAlphabet, idPrefixUIDLength)
if err != nil {
return nil, fmt.Errorf("failed to generate random prefix for in-memory event IDs: %w", err)
}
return &MemoryBroker{
idPrefix: idPrefix,
latestID: 0,
queueSize: queueSize,
mx: sync.RWMutex{},
messageQueues: make(map[string]map[string]chan message),
}, err
}
// enqueue enqueues a message to a stream.
// NOTE: messages are only send to existing groups - groups created after completion won't get the message.
// NOTE: if any of the groups' message queues is full, an aggregated error is returned.
// However, the error is only returned after attempting to send the message to all groups.
func (b *MemoryBroker) enqueue(streamID string, m message) (string, error) {
// similar to redis, only populate the ID if's empty or requested explicitly
if m.id == "" || m.id == "*" {
id := atomic.AddUint64(&b.latestID, 1)
m.id = fmt.Sprintf("%s-%d", b.idPrefix, id)
}
// the lock is for reading from the messageQueues map
// NOTE: this method isn't blocking anywhere so we should be safe from deadlocking
// NOTE: might be possible to optimize (potentially not even required), but okay for initial local solution.
b.mx.RLock()
defer b.mx.RUnlock()
// get all group queues for the stream - no lock needed as it's read-only
queues, ok := b.messageQueues[streamID]
if !ok {
// if there are no groups - discard message
return "", nil
}
// we have to queue up the message to ALL EXISTING groups of a stream
var errs error
for groupName, queue := range queues {
select {
case queue <- m:
continue
default:
errs = multierror.Append(errs, fmt.Errorf("queue for group '%s' is full", groupName))
}
}
return m.id, errs
}
// messages returns a read-only stream that can be used to receive messages of a stream under a specific group.
// If no such stream exists yet, a new one is created, otherwise, the existing one is returned.
func (b *MemoryBroker) messages(streamID string, groupName string) <-chan message {
// the lock is for writing in the messageQueues map
b.mx.Lock()
defer b.mx.Unlock()
groups, ok := b.messageQueues[streamID]
if !ok {
groups = make(map[string]chan message)
b.messageQueues[streamID] = groups
}
groupQueue, ok := groups[groupName]
if !ok {
groupQueue = make(chan message, b.queueSize)
groups[groupName] = groupQueue
}
return groupQueue
}