Protect "delete this" with a stack refcounter

(to fix use-after-free, too, but "delete this" was a time bomb anyway)

http_client.cpp

@@ -50,7 +50,13 @@ struct http_co_t
 
     websocket_t ws;
 
+    int onstack = 0;
+    bool ended = false;
+
     ~http_co_t();
+    inline void stackin() { onstack++; }
+    inline void stackout() { onstack--; if (!onstack && ended) end(); }
+    inline void end() { ended = true; if (!onstack) { delete this; } }
     void start_connection();
     void handle_events();
     void handle_connect_result();
@@ -138,12 +144,11 @@ void websocket_t::post_message(int type, const std::string & msg)
 
 void websocket_t::close()
 {
-    delete co;
+    co->end();
 }
 
 http_co_t::~http_co_t()
 {
-    epoll_events = 0;
     if (timeout_id >= 0)
     {
         tfd->clear_timer(timeout_id);
@@ -175,14 +180,15 @@ http_co_t::~http_co_t()
 
 void http_co_t::start_connection()
 {
+    stackin();
     int port = extract_port(host);
     struct sockaddr_in addr;
     int r;
     if ((r = inet_pton(AF_INET, host.c_str(), &addr.sin_addr)) != 1)
     {
         parsed.error_code = ENXIO;
-        // FIXME 'delete this' is ugly...
-        delete this;
+        stackout();
+        end();
         return;
     }
     addr.sin_family = AF_INET;
@@ -191,7 +197,8 @@ void http_co_t::start_connection()
     if (peer_fd < 0)
     {
         parsed.error_code = errno;
-        delete this;
+        stackout();
+        end();
         return;
     }
     fcntl(peer_fd, F_SETFL, fcntl(peer_fd, F_GETFL, 0) | O_NONBLOCK);
@@ -203,7 +210,7 @@ void http_co_t::start_connection()
             {
                 parsed.error_code = ETIME;
             }
-            delete this;
+            end();
         });
     }
     epoll_events = 0;
@@ -212,7 +219,8 @@ void http_co_t::start_connection()
     if (r < 0 && errno != EINPROGRESS)
     {
         parsed.error_code = errno;
-        delete this;
+        stackout();
+        end();
         return;
     }
     tfd->set_fd_handler(peer_fd, [this](int peer_fd, int epoll_events)
@@ -221,10 +229,12 @@ void http_co_t::start_connection()
         handle_events();
     });
     state = HTTP_CO_CONNECTING;
+    stackout();
 }
 
 void http_co_t::handle_events()
 {
+    stackin();
     while (epoll_events)
     {
         if (state == HTTP_CO_CONNECTING)
@@ -240,15 +250,17 @@ void http_co_t::handle_events()
             }
             else if (epoll_events & (EPOLLRDHUP|EPOLLERR))
             {
-                delete this;
-                return;
+                end();
+                break;
             }
         }
     }
+    stackout();
 }
 
 void http_co_t::handle_connect_result()
 {
+    stackin();
     int result = 0;
     socklen_t result_len = sizeof(result);
     if (getsockopt(peer_fd, SOL_SOCKET, SO_ERROR, &result, &result_len) < 0)
@@ -258,17 +270,20 @@ void http_co_t::handle_connect_result()
     if (result != 0)
     {
         parsed.error_code = result;
-        delete this;
+        stackout();
+        end();
         return;
     }
     int one = 1;
     setsockopt(peer_fd, SOL_TCP, TCP_NODELAY, &one, sizeof(one));
     state = HTTP_CO_SENDING_REQUEST;
     submit_send();
+    stackout();
 }
 
 void http_co_t::submit_read()
 {
+    stackin();
     int res;
     if (rbuf.size() != READ_BUFFER_SIZE)
     {
@@ -288,18 +303,19 @@ void http_co_t::submit_read()
     }
     else if (res < 0)
     {
-        delete this;
-        return;
+        end();
     }
     else if (res > 0)
     {
         response += std::string(rbuf.data(), res);
         handle_read();
     }
+    stackout();
 }
 
 void http_co_t::submit_send()
 {
+    stackin();
     int res;
 again:
     if (sent < request.size())
@@ -318,7 +334,8 @@ again:
         }
         else if (res < 0)
         {
-            delete this;
+            stackout();
+            end();
             return;
         }
         sent += res;
@@ -338,10 +355,12 @@ again:
             goto again;
         }
     }
+    stackout();
 }
 
 bool http_co_t::handle_read()
 {
+    stackin();
     if (state == HTTP_CO_REQUEST_SENT)
     {
         int pos = response.find("\r\n\r\n");
@@ -376,7 +395,8 @@ bool http_co_t::handle_read()
                 if (!target_response_size)
                 {
                     // Sorry, unsupported response
-                    delete this;
+                    stackout();
+                    end();
                     return false;
                 }
             }
@@ -384,7 +404,8 @@ bool http_co_t::handle_read()
     }
     if (state == HTTP_CO_HEADERS_RECEIVED && target_response_size > 0 && response.size() >= target_response_size)
     {
-        delete this;
+        stackout();
+        end();
         return false;
     }
     if (state == HTTP_CO_CHUNKED && response.size() > 0)
@@ -412,7 +433,8 @@ bool http_co_t::handle_read()
         }
         if (parsed.eof)
         {
-            delete this;
+            stackout();
+            end();
             return false;
         }
         if (want_streaming && parsed.body.size() > 0)
@@ -429,11 +451,13 @@ bool http_co_t::handle_read()
             parsed.body = "";
         }
     }
+    stackout();
     return true;
 }
 
 void http_co_t::post_message(int type, const std::string & msg)
 {
+    stackin();
     if (state == HTTP_CO_WEBSOCKET)
     {
         request += ws_format_frame(type, msg.size());
@@ -445,6 +469,7 @@ void http_co_t::post_message(int type, const std::string & msg)
         ws_outbox += ws_format_frame(type, msg.size());
         ws_outbox += msg;
     }
+    stackout();
 }
 
 uint64_t stoull_full(const std::string & str, int base)