I could not share my code link because this is my client project.

But I share you some code here.

// Receive messages

componentDidUpdate(prevProps) {
    if (this.props.chatMessages !== prevProps.chatMessages) {
      const { chatMessages } = this.props;
      this.setState(
        () => {
          return {
            messages: GiftedChat.append([], chatMessages)
          };
        },
        () => this.setMessage()
      );
    }
  }

Here is used subscribe method so it returns all messages when any updations happen in firebase.