Fix the issue with message dispatcher and channels

Resolved a previous error where each subscription would create a new
channel with the fixed buffer size. This caused blocking when the
channel buffer was full, preventing the client from handling additional messages.

Now, there is a `subscriptions` struct that holds a queue for receiving
notifications, ensuring the notify function does not block.

1 files changed, 83 insertions, 0 deletions

diff --git a/jsonrpc/client/subscription.go b/jsonrpc/client/subscription.go
new file mode 100644
index 0000000..a9a94e7
--- /dev/null
+++ b/jsonrpc/client/subscription.go
@@ -0,0 +1,83 @@
+package client
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sync/atomic"
+
+	log "github.com/sirupsen/logrus"
+)
+
+var (
+	subscriptionIsClosedErr = errors.New("Subscription is closed")
+)
+
+// Subscription A subscription established when the client's subscribe to a method
+type Subscription struct {
+	ch         chan json.RawMessage
+	ID         int
+	queue      *queue[json.RawMessage]
+	stopSignal chan struct{}
+	isClosed   atomic.Bool
+}
+
+// newSubscription Creates a new Subscription
+func newSubscription(subID int, bufferSize int) *Subscription {
+	sub := &Subscription{
+		ch:         make(chan json.RawMessage),
+		ID:         subID,
+		queue:      newQueue[json.RawMessage](bufferSize),
+		stopSignal: make(chan struct{}),
+	}
+	sub.startBackgroundJob()
+
+	return sub
+}
+
+// Recv Receives a new notification.
+func (s *Subscription) Recv() <-chan json.RawMessage {
+	return s.ch
+}
+
+// startBackgroundJob starts waiting for the queue to receive new items.
+// It stops when it receives a stop signal.
+func (s *Subscription) startBackgroundJob() {
+	go func() {
+		logger := log.WithField("Subscription", s.ID)
+		for {
+			msg, ok := s.queue.pop()
+			if !ok {
+				logger.Debug("Background job stopped")
+				return
+			}
+			select {
+			case <-s.stopSignal:
+				logger.Debug("Background job stopped: %w", receivedStopSignalErr)
+				return
+			case s.ch <- msg:
+			}
+		}
+	}()
+}
+
+// notify adds a new notification to the queue.
+func (s *Subscription) notify(nt json.RawMessage) error {
+	if s.isClosed.Load() {
+		return subscriptionIsClosedErr
+	}
+	if err := s.queue.push(nt); err != nil {
+		return fmt.Errorf("Unable to push new notification: %w", err)
+	}
+	return nil
+}
+
+// stop Terminates the subscription, clears the queue, and closes channels.
+func (s *Subscription) stop() {
+	if !s.isClosed.CompareAndSwap(false, true) {
+		return
+	}
+	close(s.stopSignal)
+	close(s.ch)
+	s.queue.clear()
+}