搜索retain标记消息的内容，订阅端上线后如何收到被retain标记消息

lib/net_mosq.c

@@ -713,7 +713,7 @@ int _mosquitto_packet_write(struct mosquitto *mosq)
  while(mosq->current_out_packet){
  packet = mosq->current_out_packet;
 
- while(packet->to_process > 0){
+ while(packet->to_process > 0){//发送一个包，可能包很长，一次没有发完
  write_length = _mosquitto_net_write(mosq, &(packet->payload[packet->pos]), packet->to_process);
  if(write_length > 0){
 #if defined(WITH_BROKER) && defined(WITH_SYS_TREE)

src/read_handle_server.c

@@ -665,7 +665,7 @@ int mqtt3_handle_subscribe(struct mosquitto_db *db, struct mosquitto *context)
  // printf("it's crutial to subclient%s\n", sub);
  rc2 = mqtt3_sub_add(db, context, sub, qos, &db->subs);
  if(rc2 == MOSQ_ERR_SUCCESS){
- if(mqtt3_retain_queue(db, context, sub, qos)) rc = 1;
+ if(mqtt3_retain_queue(db, context, sub, qos)) rc = 1; //调用该函数保证刚上线的订阅端可以收到服务端储存的retain的消息
  }else if(rc2 != -1){
  rc = rc2;
  }

src/subs.c

@@ -92,11 +92,11 @@ static int _subs_process(struct mosquitto_db *db, struct _mosquitto_subhier *hie
  db->persistence_changes++;
  }
 #endif
- if(hier->retained){
+ if(hier->retained){ //如果非空，证明这里有上次存储的retain的消息，现在有新的消息需要retain,则替换旧的消息，故要做下面的减法
  hier->retained->ref_count--;
  /* FIXME - it would be nice to be able to remove the message from the store at this point if ref_count == 0 */
  db->retained_count--;
- // printf("hier->retained is not null,hier->retained->ref_count:%d,db->retained_count:%d\n", hier->retained->ref_count, db->retained_count);
+ //printf("hier->retained is not null,hier->retained->ref_count:%d,db->retained_count:%d\n", hier->retained->ref_count, db->retained_count);
  }
  if(stored->msg.payloadlen){
  hier->retained = stored;