解决两个问题：

1）大文件修改后，不能成功编译，解决编译问题
2）订阅系统消息“\$SYS/broker/heap/current”时发现会自动断开，前面也有一个Log，但不是导致断开的真正原因，真正原因是本Log中对于Client/sub_client.c的修改。
当时忘了添加一句初始化。现在不会出现断开现象。前面那个Log的说法也是有问题的。

client/sub_client.c

@@ -103,9 +103,11 @@ void my_message_callback(struct mosquitto *mosq, void *obj, const struct mosquit
  }
 
  printf("printf finished!\n");
+
 #else
 
  clientMsg = (struct mosquitto_message_all *)malloc(sizeof(struct mosquitto_message_all) );
+ clientMsg = mosq->in_messages;
  while(clientMsg)
  {
  printf("timestamp:%d, state:%d, dup:%d\n",clientMsg->timestamp, (int)clientMsg->state, clientMsg->dup);
@@ -115,7 +117,6 @@ void my_message_callback(struct mosquitto *mosq, void *obj, const struct mosquit
  }
 
 
-
 #endif 
 
  if(ud->filter_outs){

src/subs.c

@@ -67,6 +67,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <mosquitto_broker.h>
 #include <memory_mosq.h>
 #include <util_mosq.h>
+#include <errno.h>
+#include "mqtt3_protocol.h"
 
 struct _sub_token {
  struct _sub_token *next;
@@ -84,6 +86,7 @@ static int _subs_process(struct mosquitto_db *db, struct _mosquitto_subhier *hie
  // if BigFile is true, it make sense, else useless
  int packetlen; 
  struct _mosquitto_packet *packet = NULL;
+ ssize_t write_length;
 
  leaf = hier->subs;
  if(retain && set_retain){
@@ -133,7 +136,7 @@ static int _subs_process(struct mosquitto_db *db, struct _mosquitto_subhier *hie
  }
  _mosquitto_write_string(packet, stored->msg.topic, strlen(stored->msg.topic));
  /* Payload */
- if(payloadlen){
+ if( stored->msg.payloadlen){
  _mosquitto_write_bytes(packet, stored->msg.payload, stored->msg.payloadlen);
  }
  packet->pos = 0;
@@ -193,7 +196,7 @@ static int _subs_process(struct mosquitto_db *db, struct _mosquitto_subhier *hie
  //发送packet
  // pthread_mutex_lock(&mosq->current_out_packet_mutex); 这里差一个锁机制，不知道可不可以用这个
  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);
+ write_length = _mosquitto_net_write(leaf->context, &(packet->payload[packet->pos]), packet->to_process);
  if(write_length > 0){
  packet->to_process -= write_length;
  packet->pos += write_length;
@@ -744,23 +747,23 @@ static int _retain_search(struct mosquitto_db *db, struct _mosquitto_subhier *su
  /* Subscriptions with wildcards in aren't really valid topics to publish to
  * so they can't have retained messages.
  */
- if(!strcmp(tokens->topic, "#") && !tokens->next){
+ if(!strcmp(tokens->topic, "#") && !tokens->next){ //遇到通配符“#”
  /* Set flag to indicate that we should check for retained messages
  * on "foo" when we are subscribing to e.g. "foo/#" and then exit
  * this function and return to an earlier _retain_search().
  */
  flag = -1;
- if(branch->retained){
+ if(branch->retained){ //处理当前topic对应的retained
  _retain_process(db, branch->retained, context, sub, sub_qos);
  }
- if(branch->children){
+ if(branch->children){ //递归处理子topic对应的retained
  _retain_search(db, branch, tokens, context, sub, sub_qos, level+1);
  }
  }else if(strcmp(branch->topic, "+") && (!strcmp(branch->topic, tokens->topic) || !strcmp(tokens->topic, "+"))){
- if(tokens->next){
+ if(tokens->next){ //tokens还没有比较完
  if(_retain_search(db, branch, tokens->next, context, sub, sub_qos, level+1) == -1
  || (!branch->next && tokens->next && !strcmp(tokens->next->topic, "#") && level>0)){
-
+ //如果遇到了通配符“#”,或者遇到了当前树中topic已比较完，而仍遇到通配符“#”
  if(branch->retained){
  _retain_process(db, branch->retained, context, sub, sub_qos);
  }