nghttpx: Support UNIX domain socket on frontend

This commit also fixes environment variables used to tell inherited
file descriptors to new binary are stacked up each time new binary is
executed.

src/shrpx.cc

@@ -48,6 +48,7 @@
 #include <iostream>
 #include <fstream>
 #include <vector>
+#include <initializer_list>
 
 #include <openssl/ssl.h>
 #include <openssl/err.h>
@@ -90,6 +91,13 @@ const int GRACEFUL_SHUTDOWN_SIGNAL = SIGQUIT;
 // binary is listening to.
 #define ENV_PORT "NGHTTPX_PORT"
 
+// Environment variable to tell new binary the listening socket's file
+// descriptor if frontend listens UNIX domain socket.
+#define ENV_UNIX_FD "NGHTTP2_UNIX_FD"
+// Environment variable to tell new binary the UNIX domain socket
+// path.
+#define ENV_UNIX_PATH "NGHTTP2_UNIX_PATH"
+
 namespace {
 int resolve_hostname(sockaddr_union *addr, size_t *addrlen,
                      const char *hostname, uint16_t port, int family) {
@@ -137,6 +145,85 @@ int resolve_hostname(sockaddr_union *addr, size_t *addrlen,
 }
 } // namespace
 
+namespace {
+void close_env_fd(std::initializer_list<const char *> envnames) {
+  for (auto envname : envnames) {
+    auto envfd = getenv(envname);
+    if (!envfd) {
+      continue;
+    }
+    auto fd = strtol(envfd, nullptr, 10);
+    close(fd);
+  }
+}
+} // namespace
+
+namespace {
+std::unique_ptr<AcceptHandler>
+create_unix_domain_acceptor(ConnectionHandler *handler) {
+  auto path = get_config()->host.get();
+  auto pathlen = strlen(path);
+  {
+    auto envfd = getenv(ENV_UNIX_FD);
+    auto envpath = getenv(ENV_UNIX_PATH);
+    if (envfd && envpath) {
+      auto fd = strtoul(envfd, nullptr, 10);
+
+      if (util::streq(envpath, path)) {
+        LOG(NOTICE) << "Listening on UNIX domain socket " << path;
+
+        return make_unique<AcceptHandler>(fd, handler);
+      }
+
+      LOG(WARN) << "UNIX domain socket path was changed between old binary ("
+                << envpath << ") and new binary (" << path << ")";
+      close(fd);
+    }
+  }
+
+#ifdef SOCK_NONBLOCK
+  auto fd = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0);
+  if (fd == -1) {
+    return nullptr;
+  }
+#else  // !SOCK_NONBLOCK
+  auto fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (fd == -1) {
+    return nullptr;
+  }
+  util::make_socket_nonblocking(fd);
+#endif // !SOCK_NONBLOCK
+  int val = 1;
+  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &val,
+                 static_cast<socklen_t>(sizeof(val))) == -1) {
+    close(fd);
+    return nullptr;
+  }
+
+  sockaddr_union addr;
+  addr.un.sun_family = AF_UNIX;
+  if (pathlen + 1 > sizeof(addr.un.sun_path)) {
+    LOG(FATAL) << "UNIX domain socket path " << path << " is too long > "
+               << sizeof(addr.un.sun_path);
+    return nullptr;
+  }
+  // copy path including terminal NULL
+  std::copy_n(path, pathlen + 1, addr.un.sun_path);
+
+  // unlink (remove) already existing UNIX domain socket path
+  unlink(path);
+
+  if (bind(fd, &addr.sa, sizeof(addr.un)) != 0 ||
+      listen(fd, get_config()->backlog) != 0) {
+    return nullptr;
+  }
+
+  LOG(NOTICE) << "Listening on UNIX domain socket " << path;
+
+  return make_unique<AcceptHandler>(fd, handler);
+}
+} // namespace
+
 namespace {
 std::unique_ptr<AcceptHandler> create_acceptor(ConnectionHandler *handler,
                                                int family) {
@@ -367,32 +454,45 @@ void exec_binary_signal_cb(struct ev_loop *loop, ev_signal *w, int revents) {
   size_t envlen = 0;
   for (char **p = environ; *p; ++p, ++envlen)
     ;
-  // 3 for missing fd4, fd6 and port.
+  // 3 for missing (fd4, fd6 and port) or (unix fd and unix path)
   auto envp = make_unique<char *[]>(envlen + 3 + 1);
   size_t envidx = 0;
 
-  auto acceptor4 = conn_handler->get_acceptor4();
-  if (acceptor4) {
-    std::string fd4 = ENV_LISTENER4_FD "=";
-    fd4 += util::utos(acceptor4->get_fd());
-    envp[envidx++] = strdup(fd4.c_str());
-  }
+  if (get_config()->host_unix) {
+    auto acceptor = conn_handler->get_acceptor4();
+    std::string fd = ENV_UNIX_FD "=";
+    fd += util::utos(acceptor->get_fd());
+    envp[envidx++] = strdup(fd.c_str());
 
-  auto acceptor6 = conn_handler->get_acceptor6();
-  if (acceptor6) {
-    std::string fd6 = ENV_LISTENER6_FD "=";
-    fd6 += util::utos(acceptor6->get_fd());
-    envp[envidx++] = strdup(fd6.c_str());
-  }
+    std::string path = ENV_UNIX_PATH "=";
+    path += get_config()->host.get();
+    envp[envidx++] = strdup(path.c_str());
+  } else {
+    auto acceptor4 = conn_handler->get_acceptor4();
+    if (acceptor4) {
+      std::string fd4 = ENV_LISTENER4_FD "=";
+      fd4 += util::utos(acceptor4->get_fd());
+      envp[envidx++] = strdup(fd4.c_str());
+    }
+
+    auto acceptor6 = conn_handler->get_acceptor6();
+    if (acceptor6) {
+      std::string fd6 = ENV_LISTENER6_FD "=";
+      fd6 += util::utos(acceptor6->get_fd());
+      envp[envidx++] = strdup(fd6.c_str());
+    }
 
-  std::string port = ENV_PORT "=";
-  port += util::utos(get_config()->port);
-  envp[envidx++] = strdup(port.c_str());
+    std::string port = ENV_PORT "=";
+    port += util::utos(get_config()->port);
+    envp[envidx++] = strdup(port.c_str());
+  }
 
   for (size_t i = 0; i < envlen; ++i) {
-    if (strcmp(ENV_LISTENER4_FD, environ[i]) == 0 ||
-        strcmp(ENV_LISTENER6_FD, environ[i]) == 0 ||
-        strcmp(ENV_PORT, environ[i]) == 0) {
+    if (util::startsWith(environ[i], ENV_LISTENER4_FD) ||
+        util::startsWith(environ[i], ENV_LISTENER6_FD) ||
+        util::startsWith(environ[i], ENV_PORT) ||
+        util::startsWith(environ[i], ENV_UNIX_FD) ||
+        util::startsWith(environ[i], ENV_UNIX_PATH)) {
       continue;
     }
 
@@ -528,16 +628,29 @@ int event_loop() {
     save_pid();
   }
 
-  auto acceptor6 = create_acceptor(conn_handler.get(), AF_INET6);
-  auto acceptor4 = create_acceptor(conn_handler.get(), AF_INET);
-  if (!acceptor6 && !acceptor4) {
-    LOG(FATAL) << "Failed to listen on address " << get_config()->host.get()
-               << ", port " << get_config()->port;
-    exit(EXIT_FAILURE);
-  }
+  if (get_config()->host_unix) {
+    close_env_fd({ENV_LISTENER4_FD, ENV_LISTENER6_FD});
+    auto acceptor = create_unix_domain_acceptor(conn_handler.get());
+    if (!acceptor) {
+      LOG(FATAL) << "Failed to listen on UNIX domain socket "
+                 << get_config()->host.get();
+      exit(EXIT_FAILURE);
+    }
 
-  conn_handler->set_acceptor4(std::move(acceptor4));
-  conn_handler->set_acceptor6(std::move(acceptor6));
+    conn_handler->set_acceptor4(std::move(acceptor));
+  } else {
+    close_env_fd({ENV_UNIX_FD});
+    auto acceptor6 = create_acceptor(conn_handler.get(), AF_INET6);
+    auto acceptor4 = create_acceptor(conn_handler.get(), AF_INET);
+    if (!acceptor6 && !acceptor4) {
+      LOG(FATAL) << "Failed to listen on address " << get_config()->host.get()
+                 << ", port " << get_config()->port;
+      exit(EXIT_FAILURE);
+    }
+
+    conn_handler->set_acceptor4(std::move(acceptor4));
+    conn_handler->set_acceptor6(std::move(acceptor6));
+  }
 
   ev_timer renew_ticket_key_timer;
   if (!get_config()->upstream_no_tls) {
@@ -787,6 +900,7 @@ void fill_default_config() {
   mod_config()->downstream_request_buffer_size = 16 * 1024;
   mod_config()->downstream_response_buffer_size = 16 * 1024;
   mod_config()->no_server_push = false;
+  mod_config()->host_unix = false;
 }
 } // namespace
 
@@ -829,7 +943,9 @@ Connections:
       << DEFAULT_DOWNSTREAM_PORT << R"(
   -f, --frontend=<HOST,PORT>
               Set  frontend  host and  port.   If  <HOST> is  '*',  it
-              assumes all addresses including both IPv4 and IPv6.
+              assumes  all addresses  including  both  IPv4 and  IPv6.
+              UNIX domain  socket can  be specified by  prefixing path
+              name with "unix:" (e.g., -funix:/var/run/nghttpx.sock)
               Default: )" << get_config()->host.get() << ","
       << get_config()->port << R"(
   --backlog=<N>
@@ -1885,7 +2001,7 @@ int main(int argc, char **argv) {
       auto pathlen = strlen(path);
 
       if (pathlen + 1 > sizeof(addr.addr.un.sun_path)) {
-        LOG(FATAL) << "path unix domain socket is bound to is too long > "
+        LOG(FATAL) << "UNIX domain socket path " << path << " is too long > "
                    << sizeof(addr.addr.un.sun_path);
         exit(EXIT_FAILURE);
       }

src/shrpx_config.cc

@@ -545,12 +545,22 @@ int parse_config(const char *opt, const char *optarg) {
   }
 
   if (util::strieq(opt, SHRPX_OPT_FRONTEND)) {
+    if (util::istartsWith(optarg, SHRPX_UNIX_PATH_PREFIX)) {
+      auto path = optarg + str_size(SHRPX_UNIX_PATH_PREFIX);
+      mod_config()->host = strcopy(path);
+      mod_config()->port = 0;
+      mod_config()->host_unix = true;
+
+      return 0;
+    }
+
     if (split_host_port(host, sizeof(host), &port, optarg) == -1) {
       return -1;
     }
 
     mod_config()->host = strcopy(host);
     mod_config()->port = port;
+    mod_config()->host_unix = false;
 
     return 0;
   }

src/shrpx_config.h

@@ -203,6 +203,8 @@ struct Config {
   ev_tstamp stream_write_timeout;
   ev_tstamp downstream_idle_read_timeout;
   ev_tstamp listener_disable_timeout;
+  // address of frontend connection.  This could be a path to UNIX
+  // domain socket.  In this case, |host_unix| must be true.
   std::unique_ptr<char[]> host;
   std::unique_ptr<char[]> private_key_file;
   std::unique_ptr<char[]> private_key_passwd;
@@ -279,6 +281,8 @@ struct Config {
   uid_t uid;
   gid_t gid;
   pid_t pid;
+  // frontend listening port.  0 if frontend listens on UNIX domain
+  // socket, in this case |host_unix| must be true.
   uint16_t port;
   // port in http proxy URI
   uint16_t downstream_http_proxy_port;
@@ -309,6 +313,8 @@ struct Config {
   bool no_host_rewrite;
   bool tls_ctx_per_worker;
   bool no_server_push;
+  // true if host contains UNIX domain socket path
+  bool host_unix;
 };
 
 const Config *get_config();

src/util.h

@@ -237,6 +237,10 @@ inline bool startsWith(const std::string &a, const std::string &b) {
   return startsWith(std::begin(a), std::end(a), std::begin(b), std::end(b));
 }
 
+inline bool startsWith(const char *a, const char *b) {
+  return startsWith(a, a + strlen(a), b, b + strlen(b));
+}
+
 struct CaseCmp {
   bool operator()(char lhs, char rhs) const {
     return lowcase(lhs) == lowcase(rhs);
@@ -342,6 +346,13 @@ bool streq(InputIt1 a, size_t alen, InputIt2 b, size_t blen) {
   return std::equal(a, a + alen, b);
 }
 
+inline bool streq(const char *a, const char *b) {
+  if (!a || !b) {
+    return false;
+  }
+  return streq(a, strlen(a), b, strlen(b));
+}
+
 template <typename InputIt, size_t N>
 bool streq_l(const char (&a)[N], InputIt b, size_t blen) {
   return streq(a, N - 1, b, blen);