Add feature: Inherit RPC socket from systemd.

Allow using systemd socket activation for aria2c RPC socket.
Require libsystemd to be available at build time.

configure.ac

@@ -67,6 +67,7 @@ ARIA2_ARG_WITHOUT([libz])
 ARIA2_ARG_WITH([tcmalloc])
 ARIA2_ARG_WITH([jemalloc])
 ARIA2_ARG_WITHOUT([libssh2])
+ARIA2_ARG_WITHOUT([systemd])
 
 ARIA2_ARG_DISABLE([ssl])
 ARIA2_ARG_DISABLE([bittorrent])
@@ -494,6 +495,19 @@ if test "x$with_libssh2" = "xyes"; then
   fi
 fi
 
+have_systemd=no
+if test "x$with_systemd" = "xyes"; then
+  PKG_CHECK_MODULES([SYSTEMD], [libsystemd], [have_systemd=yes], [have_systemd=no])
+  if test "x$have_systemd" = "xyes"; then
+    AC_DEFINE([HAVE_SYSTEMD], [1], [Define to 1 if you have systemd.])
+  else
+    AC_MSG_WARN([$SYSTEMD_PKG_ERRORS])
+    if test "x$with_systemd_requested" = "xyes"; then
+      ARIA2_DEP_NOT_MET([systemd])
+    fi
+  fi
+fi
+
 have_libcares=no
 if test "x$with_libcares" = "xyes"; then
   PKG_CHECK_MODULES([LIBCARES], [libcares >= 1.7.0], [have_libcares=yes],
@@ -645,6 +659,9 @@ AM_CONDITIONAL([HAVE_SQLITE3], [test "x$have_sqlite3" = "xyes"])
 # Set conditional for libssh2
 AM_CONDITIONAL([HAVE_LIBSSH2], [test "x$have_libssh2" = "xyes"])
 
+# Set conditional for systemd
+AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$have_systemd" = "xyes"])
+
 case "$host" in
   *solaris*)
     save_LIBS=$LIBS
@@ -1112,6 +1129,7 @@ LibExpat:       $have_libexpat (CFLAGS='$EXPAT_CFLAGS' LIBS='$EXPAT_LIBS')
 LibCares:       $have_libcares (CFLAGS='$LIBCARES_CFLAGS' LIBS='$LIBCARES_LIBS')
 Zlib:           $have_zlib (CFLAGS='$ZLIB_CFLAGS' LIBS='$ZLIB_LIBS')
 Libssh2:        $have_libssh2 (CFLAGS='$LIBSSH2_CFLAGS' LIBS='$LIBSSH2_LIBS')
+Systemd:        $have_systemd (CFLAGS='$SYSTEMD_CFLAGS' LIBS='$SYSTEMD_LIBS')
 Tcmalloc:       $have_tcmalloc (CFLAGS='$TCMALLOC_CFLAGS' LIBS='$TCMALLOC_LIBS')
 Jemalloc:       $have_jemalloc (CFLAGS='$JEMALLOC_CFLAGS' LIBS='$JEMALLOC_LIBS')
 Epoll:          $have_epoll

src/DownloadEngineFactory.cc

@@ -35,6 +35,9 @@
 #include "DownloadEngineFactory.h"
 
 #include <algorithm>
+#ifdef HAVE_SYSTEMD
+#include <systemd/sd-daemon.h>
+#endif // HAVE_SYSTEMD
 
 #include "Option.h"
 #include "RequestGroup.h"
@@ -205,16 +208,33 @@ std::unique_ptr<DownloadEngine> DownloadEngineFactory::newDownloadEngine(
     if (secure) {
       A2_LOG_NOTICE("RPC transport will be encrypted.");
     }
+#ifdef HAVE_SYSTEMD
+    int fds = sd_listen_fds(1);
+    if (0 < fds) {
+      for (int fd = SD_LISTEN_FDS_START; fd < SD_LISTEN_FDS_START + fds; fd++) {
+        auto httpListenCommand = make_unique<HttpListenCommand>(
+            e->newCUID(), e.get(), fd, secure);
+        if (httpListenCommand->listen()) {
+          e->addCommand(std::move(httpListenCommand));
+          ok = true;
+        }
+      }
+    } else
+#endif // HAVE_SYSTEMD
+    {
       static int families[] = {AF_INET, AF_INET6};
       size_t familiesLength = op->getAsBool(PREF_DISABLE_IPV6) ? 1 : 2;
       for (size_t i = 0; i < familiesLength; ++i) {
         auto httpListenCommand = make_unique<HttpListenCommand>(
-          e->newCUID(), e.get(), families[i], secure);
+            e->newCUID(), e.get(), families[i],
-      if (httpListenCommand->bindPort(op->getAsInt(PREF_RPC_LISTEN_PORT))) {
+            op->getAsInt(PREF_RPC_LISTEN_PORT),
+            secure);
+        if (httpListenCommand->listen()) {
           e->addCommand(std::move(httpListenCommand));
           ok = true;
         }
       }
+    }
     if (!ok) {
       throw DL_ABORT_EX("Failed to setup RPC server.");
     }

src/HttpListenCommand.cc

@@ -51,8 +51,14 @@
 namespace aria2 {
 
 HttpListenCommand::HttpListenCommand(cuid_t cuid, DownloadEngine* e, int family,
+                                     uint16_t port, bool secure)
+    : Command(cuid), e_(e), fd_(-1), family_(family), port_(port), secure_(secure)
+{
+}
+
+HttpListenCommand::HttpListenCommand(cuid_t cuid, DownloadEngine* e, int fd,
                                      bool secure)
-    : Command(cuid), e_(e), family_(family), secure_(secure)
+    : Command(cuid), e_(e), fd_(fd), family_(AF_INET), port_(0), secure_(secure)
 {
 }
 
@@ -89,27 +95,34 @@ bool HttpListenCommand::execute()
   return false;
 }
 
-bool HttpListenCommand::bindPort(uint16_t port)
+bool HttpListenCommand::listen()
 {
   if (serverSocket_) {
     e_->deleteSocketForReadCheck(serverSocket_, this);
   }
   serverSocket_ = std::make_shared<SocketCore>();
-  const int ipv = (family_ == AF_INET) ? 4 : 6;
+  std::string sListen;
   try {
+    if (fd_ < 0) {
       int flags = 0;
+      const int ipv = (family_ == AF_INET) ? 4 : 6;
+      sListen = fmt("TCP/IPv%d port %u", ipv, port_);
       if (e_->getOption()->getAsBool(PREF_RPC_LISTEN_ALL)) {
         flags = AI_PASSIVE;
       }
-    serverSocket_->bind(nullptr, port, family_, flags);
+      serverSocket_->bind(nullptr, port_, family_, flags);
+    } else {
+      sListen = fmt("file descriptor fd=%d", fd_);
+      serverSocket_->bindExistingFd(fd_);
+    }
     serverSocket_->beginListen();
-    A2_LOG_INFO(fmt(MSG_LISTENING_PORT, getCuid(), port));
+    A2_LOG_INFO(fmt(MSG_LISTENING_RPC, getCuid(), sListen.c_str()));
     e_->addSocketForReadCheck(serverSocket_, this);
-    A2_LOG_NOTICE(fmt(_("IPv%d RPC: listening on TCP port %u"), ipv, port));
+    A2_LOG_NOTICE(fmt(_("RPC: listening on %s"), sListen.c_str()));
     return true;
   }
   catch (RecoverableException& e) {
-    A2_LOG_ERROR_EX(fmt("IPv%d RPC: failed to bind TCP port %u", ipv, port), e);
+    A2_LOG_ERROR_EX(fmt("RPC: failed to listen on %s", sListen.c_str()), e);
     serverSocket_->closeConnection();
   }
   return false;

src/HttpListenCommand.h

@@ -47,18 +47,22 @@ class SocketCore;
 class HttpListenCommand : public Command {
 private:
   DownloadEngine* e_;
+  int fd_;
   int family_;
+  uint16_t port_;
   std::shared_ptr<SocketCore> serverSocket_;
   bool secure_;
 
 public:
-  HttpListenCommand(cuid_t cuid, DownloadEngine* e, int family, bool secure);
+  HttpListenCommand(cuid_t cuid, DownloadEngine* e, int family, uint16_t port, bool secure);
+
+  HttpListenCommand(cuid_t cuid, DownloadEngine* e, int fd, bool secure);
 
   virtual ~HttpListenCommand();
 
   virtual bool execute() CXX11_OVERRIDE;
 
-  bool bindPort(uint16_t port);
+  bool listen();
 };
 
 } // namespace aria2

src/Makefile.am

@@ -712,6 +712,7 @@ AM_CPPFLAGS = \
 	@LIBGMP_CFLAGS@ \
 	@LIBGCRYPT_CFLAGS@ \
 	@LIBSSH2_CFLAGS@ \
+	@SYSTEMD_CFLAGS@ \
 	@LIBCARES_CFLAGS@ \
 	@WSLAY_CFLAGS@ \
 	@TCMALLOC_CFLAGS@ \
@@ -735,6 +736,7 @@ EXTLDADD = @ALLOCA@ \
 	@LIBGMP_LIBS@ \
 	@LIBGCRYPT_LIBS@ \
 	@LIBSSH2_LIBS@ \
+	@SYSTEMD_LIBS@ \
 	@LIBCARES_LIBS@ \
 	@WSLAY_LIBS@ \
 	@TCMALLOC_LIBS@ \

src/SocketCore.cc

@@ -360,6 +360,18 @@ void SocketCore::bind(const struct sockaddr* addr, socklen_t addrlen)
   sockfd_ = fd;
 }
 
+void SocketCore::bindExistingFd(int fd)
+{
+  std::string error;
+  if (fd < 0) {
+    error = fmt("Invalid file descriptor fd=%d", fd);
+    throw DL_ABORT_EX(fmt(EX_SOCKET_BIND, error.c_str()));
+  }
+  util::make_fd_cloexec(fd);
+  applySocketBufferSize(fd);
+  sockfd_ = fd;
+}
+
 void SocketCore::beginListen()
 {
   if (listen(sockfd_, 1024) == -1) {

src/SocketCore.h

@@ -162,6 +162,11 @@ public:
   void bind(const char* addrp, uint16_t port, int family,
             int flags = AI_PASSIVE);
 
+  /**
+   * Bind to an existing file descriptor.
+   */
+  void bindExistingFd(int fd);
+
   /**
    * Listens form connection on it.
    * Call bind(uint16_t) before calling this function.

src/message.h

@@ -93,8 +93,8 @@
 #define MSG_CONTENT_DISPOSITION_DETECTED                        \
   "CUID#%" PRId64 " - Content-Disposition detected. Use %s as filename"
 #define MSG_PEER_BANNED "CUID#%" PRId64 " - Peer %s:%d banned."
-#define MSG_LISTENING_PORT                                      \
+#define MSG_LISTENING_RPC                                       \
-  "CUID#%" PRId64 " - Using port %d for accepting new connections"
+  "CUID#%" PRId64 " - Using %s for accepting new connections"
 #define MSG_BIND_FAILURE "CUID#%" PRId64 " - An error occurred while binding port=%d"
 #define MSG_INCOMING_PEER_CONNECTION                            \
   "CUID#%" PRId64 " - Incoming connection, adding new command CUID#%" PRId64 ""