Fixed: #1645 Impossible to shut down server before it has started

httplib.h

@@ -827,9 +827,15 @@ class Server {
   bool listen(const std::string &host, int port, int socket_flags = 0);
 
   bool is_running() const;
+
+  // True when the server should never start again.
+  bool is_decommissioned() const;
   void wait_until_ready() const;
   void stop();
 
+  // Call when you want the server to stop and never start.
+  void decommission();
+
   std::function<TaskQueue *(void)> new_task_queue;
 
 protected:
@@ -900,6 +906,7 @@ class Server {
   virtual bool process_and_close_socket(socket_t sock);
 
   std::atomic<bool> is_running_{false};
+  std::atomic<bool> is_decommissioned_{false};
   std::atomic<bool> done_{false};
 
   struct MountPointEntry {
@@ -5736,6 +5743,8 @@ inline bool Server::listen(const std::string &host, int port,
 
 inline bool Server::is_running() const { return is_running_; }
 
+inline bool Server::is_decommissioned() const { return is_decommissioned_; }
+
 inline void Server::wait_until_ready() const {
   while (!is_running() && !done_) {
     std::this_thread::sleep_for(std::chrono::milliseconds{1});
@@ -5751,6 +5760,11 @@ inline void Server::stop() {
   }
 }
 
+inline void Server::decommission() {
+  is_decommissioned_ = true;
+  stop();
+}
+
 inline bool Server::parse_request_line(const char *s, Request &req) {
   auto len = strlen(s);
   if (len < 2 || s[len - 2] != '\r' || s[len - 1] != '\n') { return false; }
@@ -6143,6 +6157,11 @@ inline bool Server::listen_internal() {
   is_running_ = true;
   auto se = detail::scope_exit([&]() { is_running_ = false; });
 
+  // Do not start if we have been decommissioned.
+  // Note: it is vital we check this after we have set is_running to true,
+  // because that guarantees that a later call to stop will stop us.
+  if( is_decommissioned() ) { return false; }
+
   {
     std::unique_ptr<TaskQueue> task_queue(new_task_queue());
 

test/test.cc

@@ -4132,6 +4132,34 @@ TEST(ServerStopTest, ListenFailure) {
   t.join();
 }
 
+TEST(ServerStopTest, DecommissionBeforeStart) {
+  // This mutex is used to force the sequencing that may occur randomly
+  // in the real world: the server thread won't start until after the main thread
+  // wants it dead.
+  std::mutex threadStopper;
+  threadStopper.lock();
+
+  Server svr;
+  int port = 0;
+  auto thread = std::thread([&]() {
+    // Block until the main thread has requested a shutdown.
+    threadStopper.lock();
+    threadStopper.unlock();
+    port = svr.bind_to_any_port("localhost");
+    svr.listen_after_bind();
+  });
+
+  // Decommission the server before it has finished starting.
+  // Unlike stop, this isn't ignored.
+  svr.decommission();
+
+  // Allow the server thread to try starting.
+  threadStopper.unlock();
+
+  // This won't hang forever.
+  thread.join();
+}
+
 TEST(StreamingTest, NoContentLengthStreaming) {
   Server svr;