libmicrohttpd2

mhd_send.c (58016B)

---

 /* SPDX-License-Identifier: LGPL-2.1-or-later OR (GPL-2.0-or-later WITH eCos-exception-2.0) */
 /*
   This file is part of GNU libmicrohttpd.
   Copyright (C) 2017-2025 Karlson2k (Evgeny Grin), Full re-write of buffering
                           and pushing, many bugs fixes, optimisations,
                           sendfile() porting
   Copyright (C) 2019 ng0 <ng0@n0.is>, Initial version of send() wrappers
 
   GNU libmicrohttpd is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.
 
   GNU libmicrohttpd is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.
 
   Alternatively, you can redistribute GNU libmicrohttpd and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of
   the License, or (at your option) any later version, together
   with the eCos exception, as follows:
 
     As a special exception, if other files instantiate templates or
     use macros or inline functions from this file, or you compile this
     file and link it with other works to produce a work based on this
     file, this file does not by itself cause the resulting work to be
     covered by the GNU General Public License. However the source code
     for this file must still be made available in accordance with
     section (3) of the GNU General Public License v2.
 
     This exception does not invalidate any other reasons why a work
     based on this file might be covered by the GNU General Public
     License.
 
   You should have received copies of the GNU Lesser General Public
   License and the GNU General Public License along with this library;
   if not, see <https://www.gnu.org/licenses/>.
 */
 
 /**
  * @file src/mhd2/mhd_send.c
  * @brief Implementation of send() wrappers and helper functions.
  * @author Karlson2k (Evgeny Grin)
  * @author ng0 (N. Gillmann)
  * @author Christian Grothoff
  */
 
 /* Worth considering for future improvements and additions:
  * NetBSD has no sendfile or sendfile64. The way to work
  * with this seems to be to mmap the file and write(2) as
  * large a chunk as possible to the socket. Alternatively,
  * use madvise(..., MADV_SEQUENTIAL). */
 
 #include "mhd_sys_options.h"
 
 #include <string.h>
 
 #include "sys_sockets_headers.h"
 #include "sys_ip_headers.h"
 #include "mhd_sockets_macros.h"
 #include "daemon_logger.h"
 #include "mhd_socket_error_funcs.h"
 
 #include "mhd_daemon.h"
 #include "mhd_connection.h"
 #include "mhd_response.h"
 
 #include "mhd_iovec.h"
 #ifdef HAVE_LINUX_SENDFILE
 #  include <sys/sendfile.h>
 #endif /* HAVE_LINUX_SENDFILE */
 
 #if defined(HAVE_FREEBSD_SENDFILE) || defined(HAVE_DARWIN_SENDFILE)
 #  include <sys/types.h>
 #  include <sys/socket.h>
 #  include <sys/uio.h>
 #endif /* HAVE_FREEBSD_SENDFILE || HAVE_DARWIN_SENDFILE */
 #ifdef HAVE_SYS_PARAM_H
 /* For FreeBSD version identification */
 #  include <sys/param.h>
 #endif /* HAVE_SYS_PARAM_H */
 #ifdef HAVE_SYSCONF
 #  include <unistd.h>
 #endif /* HAVE_SYSCONF */
 #include "mhd_assert.h"
 
 #include "mhd_limits.h"
 
 #ifdef MHD_SUPPORT_HTTPS
 #  include "mhd_tls_funcs.h"
 #endif
 
 #include "sckt_send.h"
 #include "mhd_send.h"
 
 #if defined(HAVE_SENDMSG) || defined(HAVE_WRITEV) || \
   defined(MHD_SOCKETS_KIND_WINSOCK)
 #  define mhd_USE_VECT_SEND 1
 #endif /* HAVE_SENDMSG || HAVE_WRITEV || MHD_SOCKETS_KIND_WINSOCK */
 
 
 #ifdef mhd_USE_VECT_SEND
 #  if (! defined(HAVE_SENDMSG) || ! defined(HAVE_DCLR_MSG_NOSIGNAL)) && \
   defined(mhd_SEND_SPIPE_SUPPRESS_POSSIBLE) && \
   defined(mhd_SEND_SPIPE_SUPPRESS_NEEDED)
 #    define mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED 1
 #  endif /* (!HAVE_SENDMSG || !HAVE_DCLR_MSG_NOSIGNAL) &&
             mhd_SEND_SPIPE_SUPPRESS_POSSIBLE && mhd_SEND_SPIPE_SUPPRESS_NEEDED */
 #endif /* mhd_USE_VECT_SEND */
 
 /**
  * sendfile() chuck size
  */
 #define mhd_SENFILE_CHUNK_SIZE         (0x20000)
 
 /**
  * sendfile() chuck size for thread-per-connection
  */
 #define mhd_SENFILE_CHUNK_SIZE_FOR_THR_P_C (0x200000)
 
 #if defined(HAVE_FREEBSD_SENDFILE) && defined(SF_FLAGS)
 /**
  * FreeBSD sendfile() flags
  */
 static int freebsd_sendfile_flags_;
 
 /**
  * FreeBSD sendfile() flags for thread-per-connection
  */
 static int freebsd_sendfile_flags_thd_p_c_;
 
 
 /**
  * Initialises variables for FreeBSD's sendfile()
  */
 static void
 freebsd_sendfile_init_ (void)
 {
   long sys_page_size = sysconf (_SC_PAGESIZE);
   if (0 >= sys_page_size)
   {   /* Failed to get page size. */
     freebsd_sendfile_flags_ = SF_NODISKIO;
     freebsd_sendfile_flags_thd_p_c_ = SF_NODISKIO;
   }
   else
   {
     freebsd_sendfile_flags_ =
       SF_FLAGS ((uint_least16_t) \
                 ((mhd_SENFILE_CHUNK_SIZE + sys_page_size - 1) / sys_page_size) \
                 & 0xFFFFU, SF_NODISKIO);
     freebsd_sendfile_flags_thd_p_c_ =
       SF_FLAGS ((uint_least16_t) \
                 ((mhd_SENFILE_CHUNK_SIZE_FOR_THR_P_C + sys_page_size - 1) \
                  / sys_page_size) & 0xFFFFU, SF_NODISKIO);
   }
 }
 
 
 #else  /* ! HAVE_FREEBSD_SENDFILE || ! SF_FLAGS */
 #  define freebsd_sendfile_init_() (void) 0
 #endif /* HAVE_FREEBSD_SENDFILE */
 
 
 #if defined(HAVE_SYSCONF) && defined(_SC_IOV_MAX)
 /**
  * Current IOV_MAX system value
  */
 static unsigned long mhd_iov_max_ = 0;
 
 static void
 iov_max_init_ (void)
 {
   long res = sysconf (_SC_IOV_MAX);
   if (res >= 0)
     mhd_iov_max_ = (unsigned long) res;
   else
   {
 #  if defined(IOV_MAX)
     mhd_iov_max_ = IOV_MAX;
 #  else  /* ! IOV_MAX */
     mhd_iov_max_ = 8; /* Should be the safe limit */
 #  endif /* ! IOV_MAX */
   }
 }
 
 
 /**
  * IOV_MAX (run-time) value
  */
 #  define mhd_IOV_MAX    mhd_iov_max_
 #else  /* ! HAVE_SYSCONF || ! _SC_IOV_MAX */
 #  define iov_max_init_() ((void) 0)
 #    if defined(IOV_MAX)
 
 /**
  * IOV_MAX (static) value
  */
 #      define mhd_IOV_MAX    IOV_MAX
 #  endif /* IOV_MAX */
 #endif /* ! HAVE_SYSCONF || ! _SC_IOV_MAX */
 
 
 void
 mhd_send_init_once (void)
 {
   /* FreeBSD 11 and later allow to specify read-ahead size
    * and handles SF_NODISKIO differently.
    * SF_FLAGS defined only on FreeBSD 11 and later. */
   freebsd_sendfile_init_ ();
 
   iov_max_init_ ();
 }
 
 
 /**
  * Set required TCP_NODELAY state for connection socket
  *
  * The function automatically updates sk.nodelay state.
  * @param sk the socket data
  * @param nodelay_state the requested new state of socket
  * @return true if succeed, false if failed or not supported
  *         by the current platform / kernel.
  */
 static MHD_FN_PAR_NONNULL_ALL_ bool
 mhd_connection_set_nodelay_state (struct mhd_ConnSocket *restrict sk,
                                   bool nodelay_state)
 {
 #ifdef HAVE_DCLR_TCP_NODELAY
   static const mhd_SCKT_OPT_BOOL off_val = 0;
   static const mhd_SCKT_OPT_BOOL on_val = 1;
   int err_code;
 
   if (mhd_T_IS_YES (sk->props.is_nonip))
     return false;
 
 #ifndef mhd_NODELAY_SET_PUSH_DATA_ALWAYS
   mhd_assert ((! nodelay_state) || (mhd_T_IS_NOT_YES (sk->state.nodelay)));
 #endif /* mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
   mhd_assert ((nodelay_state) || (mhd_T_IS_NOT_NO (sk->state.nodelay)));
 
   if (0 == mhd_setsockopt (sk->fd,
                            IPPROTO_TCP,
                            TCP_NODELAY,
                            (const void *) (nodelay_state ? &on_val : &off_val),
                            sizeof (off_val)))
   {
     sk->state.nodelay = nodelay_state ? mhd_T_YES : mhd_T_NO;
     return true;
   }
 
   err_code = mhd_SCKT_GET_LERR ();
   if ((mhd_T_IS_NOT_YES (sk->props.is_nonip)) &&
       (mhd_SCKT_ERR_IS_EINVAL (err_code) ||
        mhd_SCKT_ERR_IS_NOPROTOOPT (err_code) ||
        mhd_SCKT_ERR_IS_NOTSOCK (err_code)))
   {
     sk->props.is_nonip = mhd_T_YES;
   }
 #if 0 /* No messages, avoid potential message flood in the log */
   else
   {
     mhd_LOG_MSG (connection->daemon, MHD_SC_SOCKET_TCP_NODELAY_FAILED, \
                  "Failed to set required TCP_NODELAY option for the socket.");
   }
 #endif /* No messages */
 #else  /* ! TCP_NODELAY */
   (void) nodelay_state; /* Mute compiler warnings */
   sk->state.nodelay = mhd_T_NO;
 #endif /* ! TCP_NODELAY */
   return false;
 }
 
 
 /**
  * Set required cork state for connection socket
  *
  * The function automatically updates sk.corked state.
  *
  * @param sk the socket data
  * @param cork_state the requested new state of socket
  * @return true if succeed, false if failed or not supported
  *         by the current platform / kernel.
  */
 static MHD_FN_PAR_NONNULL_ALL_ bool
 mhd_connection_set_cork_state (struct mhd_ConnSocket *restrict sk,
                                bool cork_state)
 {
 #if defined(mhd_TCP_CORK_NOPUSH)
   static const mhd_SCKT_OPT_BOOL off_val = 0;
   static const mhd_SCKT_OPT_BOOL on_val = 1;
   int err_code;
 
   if (mhd_T_IS_YES (sk->props.is_nonip))
     return false;
 
   mhd_assert ((! cork_state) || (mhd_T_IS_NOT_YES (sk->state.corked)));
 #ifndef mhd_CORK_RESET_PUSH_DATA_ALWAYS
   mhd_assert ((cork_state) || (mhd_T_IS_NOT_NO (sk->state.corked)));
 #endif /* mhd_CORK_RESET_PUSH_DATA_ALWAYS */
 
   if (0 == mhd_setsockopt (sk->fd,
                            IPPROTO_TCP,
                            mhd_TCP_CORK_NOPUSH,
                            (const void *) (cork_state ? &on_val : &off_val),
                            sizeof (off_val)))
   {
     sk->state.corked = cork_state ? mhd_T_YES : mhd_T_NO;
     return true;
   }
 
   err_code = mhd_SCKT_GET_LERR ();
   if ((mhd_T_IS_NOT_YES (sk->props.is_nonip)) &&
       (mhd_SCKT_ERR_IS_EINVAL (err_code) ||
        mhd_SCKT_ERR_IS_NOPROTOOPT (err_code) ||
        mhd_SCKT_ERR_IS_NOTSOCK (err_code)))
   {
     sk->props.is_nonip = mhd_T_YES;
   }
 #if 0 /* No messages, avoid potential message flood in the log */
   else
   {
 #  ifdef TCP_CORK
     mhd_LOG_MSG (connection->daemon, MHD_SC_SOCKET_TCP_CORK_NOPUSH_FAILED, \
                  "Failed to set required TCP_CORK option for the socket.");
 #  else
     mhd_LOG_MSG (connection->daemon, MHD_SC_SOCKET_TCP_CORK_NOPUSH_FAILED, \
                  "Failed to set required TCP_NOPUSH option for the socket.");
 #  endif
   }
 #endif /* No messages */
 
 #else  /* ! mhd_TCP_CORK_NOPUSH */
   (void) cork_state; /* Mute compiler warnings. */
   sk->state.corked = mhd_T_NO;
 #endif /* ! mhd_TCP_CORK_NOPUSH */
   return false;
 }
 
 
 /**
  * Handle pre-send setsockopt calls.
  *
  * @param sk the socket data
  * @param plain_send set to true if plain send() or sendmsg() will be called,
  *                   set to false if TLS socket send(), sendfile() or
  *                   writev() will be called.
  * @param push_data whether to push data to the network from buffers after
  *                  the next call of send function.
  */
 static void
 pre_send_setopt (struct mhd_ConnSocket *restrict sk,
                  bool plain_send,
                  bool push_data)
 {
   /* Try to buffer data if not sending the final piece.
    * Final piece is indicated by push_data == true. */
   const bool buffer_data = (! push_data);
 
   if (mhd_T_IS_YES (sk->props.is_nonip))
     return;
 
   // TODO: support inheriting of TCP_NODELAY and TCP_NOPUSH from accept()
 
   /* The goal is to minimise the total number of additional sys-calls
    * before and after send().
    * The following tricky (over-)complicated algorithm typically use zero,
    * one or two additional sys-calls (depending on OS) for each response. */
 
   if (buffer_data)
   {
     /* Need to buffer data if possible. */
 #ifdef mhd_USE_MSG_MORE
     if (plain_send)
       return; /* Data is buffered by send() with MSG_MORE flag.
                * No need to check or change anything. */
 #else  /* ! mhd_USE_MSG_MORE */
     (void) plain_send; /* Mute compiler warning. */
 #endif /* ! mhd_USE_MSG_MORE */
 
 #ifdef mhd_TCP_CORK_NOPUSH
     if (mhd_T_IS_YES (sk->state.corked))
       return; /* The connection was already corked. */
 
     /* Prefer 'cork' over 'no delay' as the 'cork' buffers better, regardless
      * of the number of received ACKs. */
     if (mhd_connection_set_cork_state (sk, true))
       return; /* The connection has been corked. */
 
     /* Failed to cork the connection.
      * Really unlikely to happen on TCP connections. */
 #endif /* mhd_TCP_CORK_NOPUSH */
     if (mhd_T_IS_NO (sk->state.nodelay))
       return; /* TCP_NODELAY was not set for the socket.
                * Nagle's algorithm will buffer some data. */
 
     /* Try to reset TCP_NODELAY state for the socket.
      * Ignore possible error as no other options exist to
      * buffer data. */
     mhd_connection_set_nodelay_state (sk, false);
     /* TCP_NODELAY has been (hopefully) reset for the socket.
      * Nagle's algorithm will buffer some data. */
     return;
   }
 
   /* Need to push data after the next send() */
   /* If additional sys-call is required, prefer to make it only after the send()
    * (if possible) as this send() may consume only part of the prepared data and
    * more send() calls will be used. */
 #ifdef mhd_TCP_CORK_NOPUSH
 #  ifdef mhd_CORK_RESET_PUSH_DATA
 #    ifdef mhd_CORK_RESET_PUSH_DATA_ALWAYS
   /* Data can be pushed immediately by uncorking socket regardless of
    * cork state before. */
   /* This is typical for Linux, no other kernel with
    * such behaviour are known so far. */
 
   /* No need to check the current state of TCP_CORK / TCP_NOPUSH
    * as reset of cork will push the data anyway. */
   return; /* Data may be pushed by resetting of
            * TCP_CORK / TCP_NOPUSH after send() */
 #    else  /* ! mhd_CORK_RESET_PUSH_DATA_ALWAYS */
   /* Reset of TCP_CORK / TCP_NOPUSH will push the data
    * only if socket is corked. */
 
 #      ifdef mhd_NODELAY_SET_PUSH_DATA_ALWAYS
   /* Data can be pushed immediately by setting TCP_NODELAY regardless
    * of TCP_NODDELAY or corking state before. */
 
   /* Dead code currently, no known kernels with such behaviour and without
    * pushing by uncorking. */
   return; /* Data may be pushed by setting of TCP_NODELAY after send().
              No need to make extra sys-calls before send().*/
 #      else  /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
 
 /* These next comment blocks are just generic description for the possible
  * choices for the code below. */
 #        ifdef mhd_NODELAY_SET_PUSH_DATA
   /* Setting of TCP_NODELAY will push the data only if
    * both TCP_NODELAY and TCP_CORK / TCP_NOPUSH were not set. */
 
   /* Data can be pushed immediately by uncorking socket if
    * socket was corked before or by setting TCP_NODELAY if
    * socket was not corked and TCP_NODELAY was not set before. */
 
   /* This combination not possible currently as Linux is the only kernel that
    * pushes data by setting of TCP_NODELAY and Linux pushes data always
    * by TCP_NODELAY, regardless previous TCP_NODELAY state. */
 #        else  /* ! mhd_NODELAY_SET_PUSH_DATA */
   /* Data can be pushed immediately by uncorking socket or
    * can be pushed by send() on uncorked socket if
    * TCP_NODELAY was set *before*. */
 
   /* This is typical modern FreeBSD and OpenBSD behaviour. */
 #        endif /* ! mhd_NODELAY_SET_PUSH_DATA */
 
   if (mhd_T_IS_YES (sk->state.corked))
     return; /* Socket is corked. Data can be pushed by resetting of
              * TCP_CORK / TCP_NOPUSH after send() */
   else if (mhd_T_IS_NO (sk->state.corked))
   {
     /* The socket is not corked. */
     if (mhd_T_IS_YES (sk->state.nodelay))
       return; /* TCP_NODELAY was already set,
                * data will be pushed automatically by the next send() */
 #        ifdef mhd_NODELAY_SET_PUSH_DATA
     else if (mhd_T_IS_MAYBE (sk->state.nodelay))
     {
       /* Setting TCP_NODELAY may push data NOW.
        * Cork socket here and uncork after send(). */
       if (mhd_connection_set_cork_state (sk, true))
         return; /* The connection has been corked.
                  * Data can be pushed by resetting of
                  * TCP_CORK / TCP_NOPUSH after send() */
       else
       {
         /* The socket cannot be corked.
          * Really unlikely to happen on TCP connections */
         /* Have to set TCP_NODELAY.
          * If TCP_NODELAY real system state was OFF then
          * already buffered data may be pushed NOW, but it is unlikely
          * to happen as this is only a backup solution when corking has failed.
          * Ignore possible error here as no other options exist to
          * push data. */
         mhd_connection_set_nodelay_state (sk, true);
         /* TCP_NODELAY has been (hopefully) set for the socket.
          * The data will be pushed by the next send(). */
         return;
       }
     }
 #        endif /* mhd_NODELAY_SET_PUSH_DATA */
     else
     {
 #        ifdef mhd_NODELAY_SET_PUSH_DATA
       /* The socket is not corked and TCP_NODELAY is switched off. */
 #        else  /* ! mhd_NODELAY_SET_PUSH_DATA */
       /* The socket is not corked and TCP_NODELAY is not set or unknown. */
 #        endif /* ! mhd_NODELAY_SET_PUSH_DATA */
 
       /* At least one additional sys-call before send() is required. */
       /* Setting TCP_NODELAY is optimal here as data will be pushed
        * automatically by the next send() and no additional
        * sys-call are needed after the send(). */
       if (mhd_connection_set_nodelay_state (sk, true))
         return;
       else
       {
         /* Failed to set TCP_NODELAY for the socket.
          * Really unlikely to happen on TCP connections. */
         /* Cork the socket here and make additional sys-call
          * to uncork the socket after send(). This will push the data. */
         /* Ignore possible error here as no other options exist to
          * push data. */
         mhd_connection_set_cork_state (sk, true);
         /* The connection has been (hopefully) corked.
          * Data can be pushed by resetting of TCP_CORK / TCP_NOPUSH
          * after send() */
         return;
       }
     }
   }
   /* Corked state is unknown. Need to make a sys-call here otherwise
    * data may not be pushed. */
   if (mhd_connection_set_cork_state (sk, true))
     return; /* The connection has been corked.
              * Data can be pushed by resetting of
              * TCP_CORK / TCP_NOPUSH after send() */
   /* The socket cannot be corked.
    * Really unlikely to happen on TCP connections */
   if (mhd_T_IS_YES (sk->state.nodelay))
     return; /* TCP_NODELAY was already set,
              * data will be pushed by the next send() */
 
   /* Have to set TCP_NODELAY. */
 #        ifdef mhd_NODELAY_SET_PUSH_DATA
   /* If TCP_NODELAY state was unknown (external connection) then
    * already buffered data may be pushed here, but this is unlikely
    * to happen as it is only a backup solution when corking has failed. */
 #        endif /* mhd_NODELAY_SET_PUSH_DATA */
   /* Ignore possible error here as no other options exist to
    * push data. */
   mhd_connection_set_nodelay_state (sk, true);
   /* TCP_NODELAY has been (hopefully) set for the socket.
    * The data will be pushed by the next send(). */
   return;
 #      endif /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
 #    endif /* ! mhd_CORK_RESET_PUSH_DATA_ALWAYS */
 #  else  /* ! mhd_CORK_RESET_PUSH_DATA */
 
 #    ifndef mhd_NODELAY_SET_PUSH_DATA
   /* Neither uncorking the socket or setting TCP_NODELAY
    * push the data immediately. */
   /* The only way to push the data is to use send() on uncorked
    * socket with TCP_NODELAY switched on . */
 
   /* This is old FreeBSD and Darwin behaviour. */
 
   /* Uncork socket if socket wasn't uncorked. */
   if (mhd_T_IS_NOT_NO (sk->state.corked))
     mhd_connection_set_cork_state (sk, false);
 
   /* Set TCP_NODELAY if it wasn't set. */
   if (mhd_T_IS_NOT_YES (sk->state.nodelay))
     mhd_connection_set_nodelay_state (sk, true);
 
   return;
 #    else  /* mhd_NODELAY_SET_PUSH_DATA */
   /* Setting TCP_NODELAY push the data immediately. */
 
   /* Dead code currently as Linux kernel is only kernel which push by
    * setting TCP_NODELAY. The same kernel push data by resetting TCP_CORK. */
 #      ifdef mhd_NODELAY_SET_PUSH_DATA_ALWAYS
   return; /* Data may be pushed by setting of TCP_NODELAY after send().
              No need to make extra sys-calls before send().*/
 #      else  /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
   /* Cannot set TCP_NODELAY here as it would push data NOW.
    * Set TCP_NODELAY after the send(), together if uncorking if necessary. */
 #      endif /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
 #    endif /* mhd_NODELAY_SET_PUSH_DATA */
 #  endif /* ! mhd_CORK_RESET_PUSH_DATA */
 #else  /* ! mhd_TCP_CORK_NOPUSH */
   /* Buffering of data is controlled only by
    * Nagel's algorithm. */
   /* Set TCP_NODELAY if it wasn't set. */
   if (mhd_T_IS_NOT_YES (sk->state.nodelay))
     mhd_connection_set_nodelay_state (sk, true);
 #endif /* ! mhd_TCP_CORK_NOPUSH */
 }
 
 
 #ifndef mhd_CORK_RESET_PUSH_DATA_ALWAYS
 /**
  * Send zero-sized data
  *
  * This function use send of zero-sized data to kick data from the socket
  * buffers to the network. The socket must not be corked and must have
  * TCP_NODELAY switched on.
  * Used only as last resort option, when other options are failed due to
  * some errors.
  * Should not be called on typical data processing.
  * @return true if succeed, false if failed
  */
 static bool
 zero_send (struct mhd_ConnSocket *restrict sk)
 {
   static const int dummy = 0;
 
   if (mhd_T_IS_YES (sk->props.is_nonip))
     return false;
   mhd_assert (mhd_T_IS_NO (sk->state.corked));
   mhd_assert (mhd_T_IS_YES (sk->state.nodelay));
   if (0 == mhd_sys_send (sk->fd, &dummy, 0))
     return true;
 #if 0 /* No messages, avoid potential message flood in the log */
   mhd_LOG_MSG (connection->daemon, MHD_SC_SOCKET_ZERO_SEND_FAILED, \
                "Failed to push the data by zero-sized send.");
 #endif /* No messages */
   return false;
 }
 
 
 #endif /* ! mhd_CORK_RESET_PUSH_DATA_ALWAYS */
 
 /**
  * Handle post-send setsockopt calls.
  *
  * @param sk the socket data
  * @param plain_send_next set to true if plain send() or sendmsg() will be
  *                        called next,
  *                        set to false if TLS socket send(), sendfile() or
  *                        writev() will be called next.
  * @param push_data whether to push data to the network from buffers
  */
 static void
 post_send_setopt (struct mhd_ConnSocket *restrict sk,
                   bool plain_send_next,
                   bool push_data)
 {
   /* Try to buffer data if not sending the final piece.
    * Final piece is indicated by push_data == true. */
   const bool buffer_data = (! push_data);
 
   if (mhd_T_IS_YES (sk->props.is_nonip))
     return;
   if (buffer_data)
     return; /* Nothing to do after the send(). */
 
 #ifndef mhd_USE_MSG_MORE
   (void) plain_send_next; /* Mute compiler warning */
 #endif /* ! mhd_USE_MSG_MORE */
 
   /* Need to push data. */
 #ifdef mhd_TCP_CORK_NOPUSH
   if (mhd_T_IS_YES (sk->state.nodelay) && \
       mhd_T_IS_NO (sk->state.corked))
     return; /* Data has been already pushed by last send(). */
 
 #  ifdef mhd_CORK_RESET_PUSH_DATA_ALWAYS
 #    ifdef mhd_NODELAY_SET_PUSH_DATA_ALWAYS
 #      ifdef mhd_USE_MSG_MORE
   /* This is Linux kernel.
    * The socket is corked (or unknown) or 'no delay' is not set (or unknown).
    * There are options:
    * * Push the data by setting of TCP_NODELAY (without change
    *   of the cork on the socket),
    * * Push the data by resetting of TCP_CORK.
    * The optimal choice depends on the next final send functions
    * used on the same socket.
    *
    * In general on Linux kernel TCP_NODELAY always enabled is preferred,
    * as buffering is controlled by MSG_MORE or cork/uncork.
    *
    * If next send function will not support MSG_MORE (like sendfile()
    * or TLS-connection) than push data by setting TCP_NODELAY
    * so the socket may remain corked (no additional sys-call before
    * next send()).
    *
    * If send()/sendmsg() will be used next than push data by
    * resetting of TCP_CORK so next final send without MSG_MORE will push
    * data to the network (without additional sys-call to push data).  */
 
   if (mhd_T_IS_NOT_YES (sk->state.nodelay) ||
       (! plain_send_next))
   {
     if (mhd_connection_set_nodelay_state (sk, true))
       return; /* Data has been pushed by TCP_NODELAY. */
     /* Failed to set TCP_NODELAY for the socket.
      * Really unlikely to happen on TCP connections. */
     if (mhd_connection_set_cork_state (sk, false))
       return; /* Data has been pushed by uncorking the socket. */
     /* Failed to uncork the socket.
      * Really unlikely to happen on TCP connections. */
 
     /* The socket cannot be uncorked, no way to push data */
   }
   else
   {
     if (mhd_connection_set_cork_state (sk, false))
       return; /* Data has been pushed by uncorking the socket. */
     /* Failed to uncork the socket.
      * Really unlikely to happen on TCP connections. */
     if (mhd_connection_set_nodelay_state (sk, true))
       return; /* Data has been pushed by TCP_NODELAY. */
     /* Failed to set TCP_NODELAY for the socket.
      * Really unlikely to happen on TCP connections. */
 
     /* The socket cannot be uncorked, no way to push data */
   }
 #      else  /* ! mhd_USE_MSG_MORE */
   /* Push data by setting TCP_NODELAY here as uncorking here
    * would require corking the socket before sending the next response. */
   if (mhd_connection_set_nodelay_state (sk, true))
     return; /* Data was pushed by TCP_NODELAY. */
   /* Failed to set TCP_NODELAY for the socket.
    * Really unlikely to happen on TCP connections. */
   if (mhd_connection_set_cork_state (sk, false))
     return; /* Data was pushed by uncorking the socket. */
   /* Failed to uncork the socket.
    * Really unlikely to happen on TCP connections. */
 
   /* The socket remains corked, no way to push data */
 #      endif /* ! mhd_USE_MSG_MORE */
 #    else  /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
   if (mhd_connection_set_cork_state (sk, false))
     return; /* Data was pushed by uncorking the socket. */
   /* Failed to uncork the socket.
    * Really unlikely to happen on TCP connections. */
 
   /* Socket remains corked, no way to push data */
 #    endif /* ! mhd_NODELAY_SET_PUSH_DATA_ALWAYS */
 #  else  /* ! mhd_CORK_RESET_PUSH_DATA_ALWAYS */
   /* This is old FreeBSD or Darwin kernel. */
 
   if (mhd_T_IS_NO (sk->state.corked))
   {
     mhd_assert (mhd_T_IS_NOT_YES (sk->state.nodelay));
 
     /* Unlikely to reach this code.
      * TCP_NODELAY should be turned on before send(). */
     if (mhd_connection_set_nodelay_state (sk, true))
     {
       /* TCP_NODELAY has been set on uncorked socket.
        * Use zero-send to push the data. */
       if (zero_send (sk))
         return; /* The data has been pushed by zero-send. */
     }
 
     /* Failed to push the data by all means. */
     /* There is nothing left to try. */
   }
   else
   {
 #ifdef mhd_CORK_RESET_PUSH_DATA
     enum mhd_Tristate old_cork_state = sk->state.corked;
 #endif /* mhd_CORK_RESET_PUSH_DATA */
     /* The socket is corked or cork state is unknown. */
 
     if (mhd_connection_set_cork_state (sk, false))
     {
 #ifdef mhd_CORK_RESET_PUSH_DATA
       /* Modern FreeBSD or OpenBSD kernel */
       if (mhd_T_IS_YES (old_cork_state))
         return; /* Data has been pushed by uncorking the socket. */
 #endif /* mhd_CORK_RESET_PUSH_DATA */
 
       /* Unlikely to reach this code.
        * The data should be pushed by uncorking (FreeBSD) or
        * the socket should be uncorked before send(). */
       if (mhd_T_IS_YES (sk->state.nodelay) ||
           (mhd_connection_set_nodelay_state (sk, true)))
       {
         /* TCP_NODELAY is turned ON on uncorked socket.
          * Use zero-send to push the data. */
         if (zero_send (sk))
           return; /* The data has been pushed by zero-send. */
       }
     }
     /* Data cannot be pushed. */
   }
 #endif /* ! mhd_CORK_RESET_PUSH_DATA_ALWAYS */
 #else  /* ! mhd_TCP_CORK_NOPUSH */
   /* Corking is not supported. Buffering is controlled
    * by TCP_NODELAY only. */
   mhd_assert (mhd_T_IS_NOT_YES (sk->state.corked));
   if (mhd_T_IS_YES (sk->state.nodelay))
     return; /* Data was already pushed by send(). */
 
   /* Unlikely to reach this code.
    * TCP_NODELAY should be turned on before send(). */
   if (mhd_connection_set_nodelay_state (sk, true))
   {
     /* TCP_NODELAY has been set.
      * Use zero-send to try to push the data. */
     if (zero_send (sk))
       return; /* The data has been pushed by zero-send. */
   }
 
   /* Failed to push the data. */
 #endif /* ! mhd_TCP_CORK_NOPUSH */
 
 #if 0 /* No messages, avoid potential message flood in the log */
   mhd_LOG_MSG (connection->daemon, MHD_SC_SOCKET_FLUSH_LAST_PART_FAILED, \
                "Failed to force flush the last part of the response header " \
                "or the response content that might have been buffered by " \
                "the kernel. The client may experience some delay (usually " \
                "in range 200ms - 5 sec).");
 #endif /* No messages */
   return;
 }
 
 
 MHD_INTERNAL MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_IN_SIZE_ (3,2)
 MHD_FN_PAR_OUT_ (5) enum mhd_SocketError
 mhd_sckt_send (struct mhd_ConnSocket *restrict sk,
                size_t buf_size,
                const char buf[MHD_FN_PAR_DYN_ARR_SIZE_ (buf_size)],
                bool push_data,
                size_t *restrict sent)
 {
   /* plaintext transmission */
   ssize_t res;
   bool full_buf_sent;
 
   if (buf_size > MHD_SCKT_SEND_MAX_SIZE_)
   {
     buf_size = MHD_SCKT_SEND_MAX_SIZE_; /* send() return value limit */
     push_data = false; /* Incomplete send */
   }
 
   pre_send_setopt (sk, true, push_data);
 #ifdef mhd_USE_MSG_MORE
   res = mhd_sys_send4 (sk->fd,
                        buf,
                        buf_size,
                        push_data ? 0 : MSG_MORE);
 #else
   res = mhd_sys_send4 (sk->fd,
                        buf,
                        buf_size,
                        0);
 #endif
 
   if (0 >= res)
   {
     enum mhd_SocketError err;
 
     err = mhd_socket_error_get_from_sys_err (mhd_SCKT_GET_LERR ());
 
     if (mhd_SOCKET_ERR_AGAIN == err)
       mhd_SCKT_NET_ST_CLEAR_FLAG (&(sk->ready),
                                   mhd_SOCKET_NET_STATE_SEND_READY);
 
     return err;
   }
   *sent = (size_t) res;
 
   full_buf_sent = (buf_size == (size_t) res);
 
   if (! full_buf_sent || ! sk->props.is_nonblck)
     mhd_SCKT_NET_ST_CLEAR_FLAG (&(sk->ready),
                                 mhd_SOCKET_NET_STATE_SEND_READY);
 
   /* If there is a need to push the data from network buffers
    * call post_send_setopt(). */
   /* It's unknown whether sendfile() (or other send function without
    * MSG_MORE support) will be used for the next reply so assume
    * that next sending will be the same, like this call. */
   if (push_data && full_buf_sent)
     post_send_setopt (sk, true, push_data);
 
   return mhd_SOCKET_ERR_NO_ERROR;
 }
 
 
 #ifdef MHD_SUPPORT_HTTPS
 
 static MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_IN_SIZE_ (3,2)
 MHD_FN_PAR_OUT_ (5) enum mhd_SocketError
 mhd_send_tls (struct MHD_Connection *restrict c,
               size_t buf_size,
               const char buf[MHD_FN_PAR_DYN_ARR_SIZE_ (buf_size)],
               bool push_data,
               size_t *restrict sent)
 {
   /* TLS connection */
   const bool custm_trnsp = mhd_tls_conn_has_cstm_tr (c->tls);
   enum mhd_SocketError res;
 
   mhd_assert (mhd_C_HAS_TLS (c));
   mhd_assert (mhd_D_HAS_TLS (c->daemon));
   mhd_assert (0 != buf_size);
 
   if (! custm_trnsp)
     pre_send_setopt (&(c->sk), false, push_data);
 
   res = mhd_tls_conn_send (c->tls,
                            buf_size,
                            buf,
                            push_data,
                            sent);
 
   if (mhd_SOCKET_ERR_NO_ERROR != res)
   {
     if (mhd_SOCKET_ERR_AGAIN == res)
       c->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                     (((unsigned int) c->sk.ready)
                      & (~(enum mhd_SocketNetState)
                         mhd_SOCKET_NET_STATE_SEND_READY));
     return res;
   }
 
   if (! c->sk.props.is_nonblck)
     c->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                   (((unsigned int) c->sk.ready)
                    & (~(enum mhd_SocketNetState)
                       mhd_SOCKET_NET_STATE_SEND_READY));
 
   /* If there is a need to push the data from network buffers
    * call post_send_setopt(). */
   if ((! custm_trnsp) && push_data && (buf_size == *sent))
     post_send_setopt (&(c->sk), false, true);
 
   return mhd_SOCKET_ERR_NO_ERROR;
 }
 
 
 #endif /* MHD_SUPPORT_HTTPS */
 
 MHD_INTERNAL MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_IN_SIZE_ (3,2)
 MHD_FN_PAR_OUT_ (5) enum mhd_SocketError
 mhd_send_data (struct MHD_Connection *restrict connection,
                size_t buf_size,
                const char buf[MHD_FN_PAR_DYN_ARR_SIZE_ (buf_size)],
                bool push_data,
                size_t *restrict sent)
 {
   mhd_assert (MHD_INVALID_SOCKET != connection->sk.fd);
   mhd_assert (mhd_HTTP_STAGE_CLOSED != connection->stage);
 
 #ifdef MHD_SUPPORT_HTTPS
   if (mhd_C_HAS_TLS (connection))
     return mhd_send_tls (connection,
                          buf_size,
                          buf,
                          push_data,
                          sent);
 #endif /* MHD_SUPPORT_HTTPS */
 
   return mhd_sckt_send (&(connection->sk),
                         buf_size,
                         buf,
                         push_data,
                         sent);
 }
 
 
 MHD_INTERNAL
 MHD_FN_PAR_NONNULL_ (1) MHD_FN_PAR_NONNULL_ (3)
 MHD_FN_PAR_IN_SIZE_ (3,2) MHD_FN_PAR_IN_SIZE_ (6,5) enum mhd_SocketError
 mhd_send_hdr_and_body (struct MHD_Connection *restrict connection,
                        size_t header_size,
                        const char *restrict header,
                        bool never_push_hdr,
                        size_t body_size,
                        const char *restrict body,
                        bool complete_response,
                        size_t *restrict sent)
 {
   mhd_iov_ret_type res;
   bool send_error;
   bool push_hdr;
   bool push_body;
   MHD_Socket s = connection->sk.fd;
 #ifdef mhd_USE_VECT_SEND
 #if defined(HAVE_SENDMSG) || defined(HAVE_WRITEV)
   struct iovec vector[2];
 #ifdef HAVE_SENDMSG
   struct msghdr msg;
 #endif /* HAVE_SENDMSG */
 #endif /* HAVE_SENDMSG || HAVE_WRITEV */
 #ifdef _WIN32
   WSABUF vector[2];
   DWORD vec_sent;
 #endif /* _WIN32 */
   bool no_vec; /* Is vector-send() disallowed? */
 
   no_vec = false;
   no_vec = no_vec || (mhd_C_HAS_TLS (connection));
 #if (! defined(HAVE_SENDMSG) || ! defined(HAVE_DCLR_MSG_NOSIGNAL) ) && \
   defined(mhd_SEND_SPIPE_SUPPRESS_POSSIBLE) && \
   defined(mhd_SEND_SPIPE_SUPPRESS_NEEDED)
   no_vec = no_vec || (! connection->daemon->sigpipe_blocked &&
                       ! connection->sk.props.has_spipe_supp);
 #endif /* (!HAVE_SENDMSG || ! HAVE_DCLR_MSG_NOSIGNAL) &&
           mhd_SEND_SPIPE_SUPPRESS_POSSIBLE &&
           mhd_SEND_SPIPE_SUPPRESS_NEEDED */
 #endif /* mhd_USE_VECT_SEND */
 
   mhd_assert ( (NULL != body) || (0 == body_size) );
 
   mhd_assert (MHD_INVALID_SOCKET != s);
   mhd_assert (mhd_HTTP_STAGE_CLOSED != connection->stage);
 
   push_body = complete_response;
 
   if (! never_push_hdr)
   {
     if (! complete_response)
       push_hdr = true; /* Push the header as the client may react
                         * on header alone while the body data is
                         * being prepared. */
     else
     {
       if (1400 > (header_size + body_size))
         push_hdr = false; /* Do not push the header as complete
                            * reply is already ready and the whole
                            * reply most probably will fit into
                            * the single IP packet. */
       else
         push_hdr = true;   /* Push header alone so client may react
                            * on it while reply body is being delivered. */
     }
   }
   else
     push_hdr = false;
 
   if (complete_response && (0 == body_size))
     push_hdr = true; /* The header alone is equal to the whole response. */
 
 #ifndef mhd_USE_VECT_SEND
   no_vec = (no_vec || true);
 #else  /* mhd_USE_VECT_SEND */
   no_vec = (no_vec || (0 == body_size));
   no_vec = (no_vec || ((sizeof(mhd_iov_elmn_size) <= sizeof(size_t)) &&
                        (((size_t) mhd_IOV_ELMN_MAX_SIZE) < header_size)));
 #endif /* mhd_USE_VECT_SEND */
 
 
   if (no_vec)
   {
     enum mhd_SocketError ret;
     ret = mhd_send_data (connection,
                          header_size,
                          header,
                          push_hdr,
                          sent);
 
     if ((mhd_SOCKET_ERR_NO_ERROR == ret) &&
         (header_size == *sent) &&
         (0 != body_size) &&
         (header_size < header_size + body_size) &&
         (connection->sk.props.is_nonblck))
     {
       size_t sent_b;
       /* The header has been sent completely.
        * Try to send the reply body without waiting for
        * the next round. */
 
       ret = mhd_send_data (connection,
                            body_size,
                            body,
                            push_body,
                            &sent_b);
 
       if (mhd_SOCKET_ERR_NO_ERROR == ret)
         *sent += sent_b;
       else if (mhd_SOCKET_ERR_IS_HARD (ret))
         return ret; /* Unrecoverable error */
 
       return mhd_SOCKET_ERR_NO_ERROR; /* The header has been sent successfully */
     }
     return ret;
   }
 #ifdef mhd_USE_VECT_SEND
 
   mhd_assert (! mhd_C_HAS_TLS (connection));
 
   if (header_size > (header_size + body_size))
   {
     /* Return value limit */
     body_size = SIZE_MAX - header_size;
     complete_response = false;
     push_body = complete_response;
   }
   if (((mhd_iov_ret_type) (header_size + body_size)) < 0 ||
       ((size_t) (mhd_iov_ret_type) (header_size + body_size)) !=
       (header_size + body_size))
   {
     /* Send sys-call total amount limit */
     body_size = mhd_IOV_RET_MAX_SIZE - header_size;
     complete_response = false;
     push_body = complete_response;
   }
 
   pre_send_setopt (&(connection->sk),
 #ifdef HAVE_SENDMSG
                    true,
 #else  /* ! HAVE_SENDMSG */
                    false,
 #endif /* ! HAVE_SENDMSG */
                    push_hdr || push_body);
   send_error = false;
 #if defined(HAVE_SENDMSG) || defined(HAVE_WRITEV)
   vector[0].iov_base = mhd_DROP_CONST (header);
   vector[0].iov_len = header_size;
   vector[1].iov_base = mhd_DROP_CONST (body);
   vector[1].iov_len = body_size;
 
 #if defined(HAVE_SENDMSG)
   memset (&msg, 0, sizeof(msg));
   msg.msg_name = NULL;
   msg.msg_namelen = 0;
   msg.msg_iov = vector;
   msg.msg_iovlen = 2;
   msg.msg_control = NULL;
   msg.msg_controllen = 0;
   msg.msg_flags = 0;
 
   res = sendmsg (s, &msg, mhd_MSG_NOSIGNAL
 #  ifdef mhd_USE_MSG_MORE
                  | ((push_hdr || push_body) ? 0 : mhd_MSG_MORE)
 #  endif
                  );
 #elif defined(HAVE_WRITEV)
   res = writev (s, vector, 2);
 #endif /* HAVE_WRITEV */
   if (0 < res)
     *sent = (size_t) res;
   else
     send_error = true;
 #endif /* HAVE_SENDMSG || HAVE_WRITEV */
 #ifdef _WIN32
   if (((mhd_iov_elmn_size) body_size) != body_size)
   {
     /* Send item size limit */
     body_size = mhd_IOV_ELMN_MAX_SIZE;
     complete_response = false;
     push_body = complete_response;
   }
   vector[0].buf = (char *) mhd_DROP_CONST (header);
   vector[0].len = (unsigned long) header_size;
   vector[1].buf = (char *) mhd_DROP_CONST (body);
   vector[1].len = (unsigned long) body_size;
 
   res = WSASend (s, vector, 2, &vec_sent, 0, NULL, NULL);
   if (0 == res)
     *sent = (size_t) vec_sent;
   else
     send_error = true;
 #endif /* _WIN32 */
 
   if (send_error)
   {
     enum mhd_SocketError err;
 
     err = mhd_socket_error_get_from_sys_err (mhd_SCKT_GET_LERR ());
 
     if (mhd_SOCKET_ERR_AGAIN == err)
       connection->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                              (((unsigned int) connection->sk.ready)
                               & (~(enum mhd_SocketNetState)
                                  mhd_SOCKET_NET_STATE_SEND_READY));
 
     return err;
   }
   if (((header_size + body_size) > *sent)
       || ! connection->sk.props.is_nonblck)
     connection->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                            (((unsigned int) connection->sk.ready)
                             & (~(enum mhd_SocketNetState)
                                mhd_SOCKET_NET_STATE_SEND_READY));
 
   /* If there is a need to push the data from network buffers
    * call post_send_setopt(). */
   if ( (push_body) &&
        ((header_size + body_size) == *sent) )
   {
     /* Complete reply has been sent. */
     /* If TLS connection is used then next final send() will be
      * without MSG_MORE support. If non-TLS connection is used
      * it's unknown whether next 'send' will be plain send() / sendmsg() or
      * sendfile() will be used so assume that next final send() will be
      * the same, like for this response. */
     post_send_setopt (&(connection->sk),
 #ifdef HAVE_SENDMSG
                       true,  /* Assume the same type of the send function */
 #else  /* ! HAVE_SENDMSG */
                       false, /* Assume the same type of the send function */
 #endif /* ! HAVE_SENDMSG */
                       true);
   }
   else if ( (push_hdr) &&
             (header_size <= *sent))
   {
     /* The header has been sent completely and there is a
      * need to push the header data. */
     /* Luckily the type of send function will be used next is known. */
     post_send_setopt (&(connection->sk),
                       true,
                       true);
   }
 
   return mhd_SOCKET_ERR_NO_ERROR;
 #else  /* ! mhd_USE_VECT_SEND */
   mhd_assert (0 && "Should be unreachable");
   return mhd_SOCKET_ERR_INTERNAL; /* Unreachable. Mute warnings. */
 #endif /* ! mhd_USE_VECT_SEND */
 }
 
 
 #if defined(mhd_USE_SENDFILE)
 
 #if defined(HAVE_LINUX_SENDFILE) && defined(HAVE_SENDFILE64)
 #  define mhd_off_t off64_t
 #else
 #  define mhd_off_t off_t
 #endif
 
 MHD_INTERNAL MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_OUT_ (2) enum mhd_SocketError
 mhd_send_sendfile (struct MHD_Connection *restrict c,
                    size_t *restrict sent)
 {
   enum mhd_SocketError ret;
   const bool used_thr_p_c =
     mhd_D_HAS_THR_PER_CONN (c->daemon);
   const size_t chunk_size =
     used_thr_p_c ?
     mhd_SENFILE_CHUNK_SIZE_FOR_THR_P_C : mhd_SENFILE_CHUNK_SIZE;
   const int file_fd = c->rp.response->cntn.file.fd;
   mhd_off_t offset;
   size_t send_size = 0; /* Initialised to mute compiler warning */
   size_t sent_bytes;
   bool push_data;
   bool fallback_to_filereader;
   mhd_assert (mhd_REPLY_CNTN_LOC_FILE == c->rp.cntn_loc);
   mhd_assert (MHD_SIZE_UNKNOWN != c->rp.response->cntn_size);
   mhd_assert (chunk_size <= (size_t) SSIZE_MAX);
   mhd_assert (! mhd_C_HAS_TLS (c));
 
   mhd_assert (0 == send_size); /* Mute analyser warning */
   push_data = true;
   if (1)
   {
     bool too_large;
     uint_fast64_t left;
 
     offset = (mhd_off_t)
              (c->rp.rsp_cntn_read_pos + c->rp.response->cntn.file.offset);
     too_large = (((uint_fast64_t) offset) < c->rp.rsp_cntn_read_pos);
     too_large = too_large ||
                 (((uint_fast64_t) offset) !=
                  (c->rp.rsp_cntn_read_pos + c->rp.response->cntn.file.offset));
     too_large = too_large || (0 > offset);
     if (too_large)
     {   /* Retry to send with file reader and standard 'send()'. */
       c->rp.response->cntn.file.use_sf = false;
       return mhd_SOCKET_ERR_INTR;
     }
 
     left = c->rp.response->cntn_size - c->rp.rsp_cntn_read_pos;
 
     /* Do not allow system to stick sending on single fast connection:
      * use 128KiB chunks (2MiB for thread-per-connection). */
     if (chunk_size < left) /* This also limit to SSIZE_MAX automatically */
     {
       send_size = chunk_size;
       push_data = false; /* No need to push data, there is more to send. */
     }
     else
       send_size = (size_t) left;
   }
   mhd_assert (0 != send_size);
 
   pre_send_setopt (&(c->sk), false, push_data);
 
   sent_bytes = 0;
   ret = mhd_SOCKET_ERR_NO_ERROR;
   fallback_to_filereader = false;
 #if defined(HAVE_LINUX_SENDFILE)
   if (1)
   {
     ssize_t res;
 #ifndef HAVE_SENDFILE64
     ret = sendfile (c->sk.fd,
                     file_fd,
                     &offset,
                     send_size);
 #else  /* HAVE_SENDFILE64 */
     res = sendfile64 (c->sk.fd,
                       file_fd,
                       &offset,
                       send_size);
 #endif /* HAVE_SENDFILE64 */
     if (0 > res)
     {
       const int sk_err = mhd_SCKT_GET_LERR ();
 
       if ((EINVAL == sk_err) ||
           (EOVERFLOW == sk_err) ||
 #ifdef EIO
           (EIO == sk_err) ||
 #endif
 #ifdef EAFNOSUPPORT
           (EAFNOSUPPORT == sk_err) ||
 #endif
           (EOPNOTSUPP == sk_err))
         fallback_to_filereader = true;
       else
         ret = mhd_socket_error_get_from_sys_err (sk_err);
     }
     else
       sent_bytes = (size_t) res;
   }
 #elif defined(HAVE_FREEBSD_SENDFILE)
   if (1)
   {
     off_t sent_bytes_offt = 0;
     int flags = 0;
     bool sent_something = false;
 #ifdef SF_FLAGS
     flags = used_thr_p_c ?
             freebsd_sendfile_flags_thd_p_c_ : freebsd_sendfile_flags_;
 #endif /* SF_FLAGS */
     if (0 != sendfile (file_fd,
                        c->sk.fd,
                        offset,
                        send_size,
                        NULL,
                        &sent_bytes_offt,
                        flags))
     {
       const int sk_err = mhd_SCKT_GET_LERR ();
 
       sent_something =
         (((EAGAIN == sk_err) || (EBUSY == sk_err) || (EINTR == sk_err)) &&
          (0 != sent_bytes_offt));
 
       if (! sent_something)
       {
         enum mhd_SocketError err;
         if ((EINVAL == sk_err) ||
             (EIO == sk_err) ||
             (EOPNOTSUPP == sk_err))
           fallback_to_filereader = true;
         else
           ret = mhd_socket_error_get_from_sys_err (sk_err);
       }
     }
     else
       sent_something = true;
 
     if (sent_something)
     {
       mhd_assert (0 <= sent_bytes_offt);
       mhd_assert (SIZE_MAX >= sent_bytes_offt);
       sent_bytes = (size_t) sent_bytes_offt;
     }
   }
 #elif defined(HAVE_DARWIN_SENDFILE)
   if (1)
   {
     off_t len;
     bool sent_something;
 
     sent_something = false;
     len = (off_t) send_size; /* chunk always fit */
 
     if (0 != sendfile (file_fd,
                        c->sk.fd,
                        offset,
                        &len,
                        NULL,
                        0))
     {
       const int sk_err = mhd_SCKT_GET_LERR ();
 
       sent_something =
         ((EAGAIN == sk_err) || (EINTR == sk_err)) &&
         (0 != len);
 
       if (! sent_something)
       {
         if ((ENOTSUP == sk_err) ||
             (EOPNOTSUPP == sk_err))
           fallback_to_filereader = true;
         else
           ret = mhd_socket_error_get_from_sys_err (sk_err);
       }
     }
     else
       sent_something = true;
 
     if (sent_something)
     {
       mhd_assert (0 <= len);
       mhd_assert (SIZE_MAX >= len);
       sent_bytes = (size_t) len;
     }
   }
 #else
 #error No sendfile() function
 #endif
 
   mhd_assert (send_size >= sent_bytes);
 
   /* Some platforms indicate "beyond of the end of the file" by returning
    * success with zero bytes. Let filereader to re-detect this kind of error. */
   if ((fallback_to_filereader) ||
       ((mhd_SOCKET_ERR_NO_ERROR == ret) && (0 == sent_bytes)))
   {   /* Retry to send with file reader and standard 'send()'. */
     c->rp.response->cntn.file.use_sf = false;
     return mhd_SOCKET_ERR_INTR;
   }
 
   if ((mhd_SOCKET_ERR_AGAIN == ret) || ! c->sk.props.is_nonblck ||
       ((mhd_SOCKET_ERR_NO_ERROR == ret) && (send_size > sent_bytes)))
     c->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                   (((unsigned int) c->sk.ready)
                    & (~(enum mhd_SocketNetState)
                       mhd_SOCKET_NET_STATE_SEND_READY));
 
   if (mhd_SOCKET_ERR_NO_ERROR != ret)
     return ret;
 
   /* If there is a need to push the data from network buffers
    * call post_send_setopt(). */
   /* It's unknown whether sendfile() will be used in the next
    * response so assume that next response will be the same. */
   if ((push_data) &&
       (send_size == sent_bytes))
     post_send_setopt (&(c->sk), true, push_data);
 
   *sent = sent_bytes;
   return ret;
 }
 
 
 #endif /* mhd_USE_SENDFILE */
 
 #if defined(mhd_USE_VECT_SEND)
 
 
 /**
  * Function sends iov data by system sendmsg or writev function.
  *
  * Connection must be in non-TLS (non-HTTPS) mode.
  *
  * @param connection the MHD connection structure
  * @param r_iov the pointer to iov data structure with tracking
  * @param push_data set to true to force push the data to the network from
  *                  system buffers (usually set for the last piece of data),
  *                  set to false to prefer holding incomplete network packets
  *                  (more data will be send for the same reply).
  * @param[out] sent the pointer to get amount of actually sent bytes
  * @return mhd_SOCKET_ERR_NO_ERROR if send succeed (the @a sent gets
  *         the sent size) or socket error
  */
 static MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_OUT_ (4) enum mhd_SocketError
 send_iov_nontls (struct MHD_Connection *restrict connection,
                  struct mhd_iovec_track *const restrict r_iov,
                  bool push_data,
                  size_t *restrict sent)
 {
   bool send_error;
   size_t items_to_send;
 #ifndef MHD_SOCKETS_KIND_WINSOCK
   ssize_t res;
 #endif
 #ifdef HAVE_SENDMSG
   struct msghdr msg;
 #elif defined(MHD_SOCKETS_KIND_WINSOCK)
   DWORD bytes_sent;
   DWORD cnt_w;
 #endif /* MHD_SOCKETS_KIND_WINSOCK */
 
   mhd_assert (! mhd_C_HAS_TLS (connection));
   mhd_assert (! mhd_D_HAS_TLS (connection->daemon));
 
   mhd_assert (MHD_INVALID_SOCKET != connection->sk.fd);
   mhd_assert (mhd_HTTP_STAGE_CLOSED != connection->stage);
 
   send_error = false;
   items_to_send = r_iov->cnt - r_iov->sent;
 #ifdef mhd_IOV_MAX
   if (mhd_IOV_MAX < items_to_send)
   {
     mhd_assert (0 < mhd_IOV_MAX);
     if (0 == mhd_IOV_MAX)
       return mhd_SOCKET_ERR_INTERNAL; /* Should never happen */
     items_to_send = mhd_IOV_MAX;
     push_data = false; /* Incomplete response */
   }
 #endif /* mhd_IOV_MAX */
 #ifdef HAVE_SENDMSG
   memset (&msg, 0, sizeof(struct msghdr));
   msg.msg_name = NULL;
   msg.msg_namelen = 0;
   msg.msg_iov = r_iov->iov + r_iov->sent;
   msg.msg_iovlen = items_to_send;
   msg.msg_control = NULL;
   msg.msg_controllen = 0;
   msg.msg_flags = 0;
 
   pre_send_setopt (&(connection->sk), true, push_data);
   res = sendmsg (connection->sk.fd, &msg,
                  mhd_MSG_NOSIGNAL
 #  ifdef mhd_USE_MSG_MORE
                  | (push_data ? 0 : MSG_MORE)
 #  endif
                  );
   if (0 < res)
     *sent = (size_t) res;
   else
     send_error = true;
 #elif defined(HAVE_WRITEV)
   pre_send_setopt (&(connection->sk), false, push_data);
   res = writev (connection->sk.fd, r_iov->iov + r_iov->sent,
                 items_to_send);
   if (0 < res)
     *sent = (size_t) res;
   else
     send_error = true;
 #elif defined(MHD_SOCKETS_KIND_WINSOCK)
 #ifdef _WIN64
   if (items_to_send > ULONG_MAX)
   {
     cnt_w = ULONG_MAX;
     push_data = false; /* Incomplete response */
   }
   else
     cnt_w = (DWORD) items_to_send;
 #else  /* ! _WIN64 */
   cnt_w = (DWORD) items_to_send;
 #endif /* ! _WIN64 */
   pre_send_setopt (&(connection->sk), true, push_data);
   if (0 == WSASend (connection->sk.fd,
                     (LPWSABUF) (r_iov->iov + r_iov->sent),
                     cnt_w,
                     &bytes_sent, 0, NULL, NULL))
     *sent = (size_t) bytes_sent;
   else
     send_error = true;
 #else /* !HAVE_SENDMSG && !HAVE_WRITEV && !MHD_SOCKETS_KIND_WINSOCK */
 #error No vector-send function available
 #endif
 
   if (send_error)
   {
     enum mhd_SocketError err;
 
     err = mhd_socket_error_get_from_sys_err (mhd_SCKT_GET_LERR ());
 
     if (mhd_SOCKET_ERR_AGAIN == err)
       connection->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                              (((unsigned int) connection->sk.ready)
                               & (~(enum mhd_SocketNetState)
                                  mhd_SOCKET_NET_STATE_SEND_READY));
 
     return err;
   }
 
   /* Some data has been sent */
   if (1)
   {
     size_t track_sent = (size_t) *sent;
 
     if (! connection->sk.props.is_nonblck)
       connection->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                              (((unsigned int) connection->sk.ready)
                               & (~(enum mhd_SocketNetState)
                                  mhd_SOCKET_NET_STATE_SEND_READY));
 
     /* Adjust the internal tracking information for the iovec to
      * take this last send into account. */
     while ((0 != track_sent) && (r_iov->iov[r_iov->sent].iov_len <= track_sent))
     {
       track_sent -= r_iov->iov[r_iov->sent].iov_len;
       r_iov->sent++; /* The iov element has been completely sent */
       mhd_assert ((r_iov->cnt > r_iov->sent) || (0 == track_sent));
     }
 
     if (r_iov->cnt == r_iov->sent)
       post_send_setopt (&(connection->sk), true, push_data);
     else
     {
       connection->sk.ready = (enum mhd_SocketNetState) /* Clear 'send-ready' */
                              (((unsigned int) connection->sk.ready)
                               & (~(enum mhd_SocketNetState)
                                  mhd_SOCKET_NET_STATE_SEND_READY));
       if (0 != track_sent)
       {
         mhd_assert (r_iov->cnt > r_iov->sent);
         /* The last iov element has been partially sent */
         r_iov->iov[r_iov->sent].iov_base =
           (mhd_IOV_ELMN_PTR_TYPE)
           (((uint8_t *) r_iov->iov[r_iov->sent].iov_base)
            + track_sent);
         r_iov->iov[r_iov->sent].iov_len -= (mhd_iov_elmn_size) track_sent;
       }
     }
   }
 
   return mhd_SOCKET_ERR_NO_ERROR;
 }
 
 
 #endif /* mhd_USE_VECT_SEND */
 
 #if ! defined(mhd_USE_VECT_SEND) || defined(MHD_SUPPORT_HTTPS) || \
   defined(mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED)
 
 
 /**
  * Function sends iov data by sending buffers one-by-one by standard
  * data send function.
  *
  * Connection could be in HTTPS or non-HTTPS mode.
  *
  * @param connection the MHD connection structure
  * @param r_iov the pointer to iov data structure with tracking
  * @param push_data set to true to force push the data to the network from
  *                  system buffers (usually set for the last piece of data),
  *                  set to false to prefer holding incomplete network packets
  *                  (more data will be send for the same reply).
  * @param[out] sent the pointer to get amount of actually sent bytes
  * @return mhd_SOCKET_ERR_NO_ERROR if send succeed (the @a sent gets
  *         the sent size) or socket error
  */
 static MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_OUT_ (4) enum mhd_SocketError
 send_iov_emu (struct MHD_Connection *restrict connection,
               struct mhd_iovec_track *const restrict r_iov,
               bool push_data,
               size_t *restrict sent)
 {
   const bool non_blk = connection->sk.props.is_nonblck;
   size_t total_sent;
   size_t max_elelements_to_sent;
 
   mhd_assert (NULL != r_iov->iov);
   total_sent = 0;
   max_elelements_to_sent = 8; /* Do not make too many sys-calls for just one connection */
   do
   {
     enum mhd_SocketError res;
     size_t sent_el_size;
 
     if (total_sent > (size_t) (r_iov->iov[r_iov->sent].iov_len + total_sent))
       break; /* return value would overflow */
 
     res = mhd_send_data (connection,
                          r_iov->iov[r_iov->sent].iov_len,
                          (const char *) r_iov->iov[r_iov->sent].iov_base,
                          push_data && (r_iov->cnt == r_iov->sent + 1),
                          &sent_el_size);
     if (mhd_SOCKET_ERR_NO_ERROR == res)
     {
       /* Result is an error */
       if (0 == total_sent)
         return res; /* Nothing was sent, return error as is */
 
       if (mhd_SOCKET_ERR_IS_HARD (res))
         return res; /* Any kind of a hard error */
 
       break; /* Return the amount of the sent data */
     }
 
     total_sent += sent_el_size;
 
     if (r_iov->iov[r_iov->sent].iov_len != sent_el_size)
     {
       /* Incomplete buffer has been sent.
        * Adjust buffer of the last element. */
       r_iov->iov[r_iov->sent].iov_base =
         (mhd_IOV_ELMN_PTR_TYPE)
         (((uint8_t *) r_iov->iov[r_iov->sent].iov_base) + sent_el_size);
       r_iov->iov[r_iov->sent].iov_len -= (mhd_iov_elmn_size) sent_el_size;
 
       break; /* Return the amount of the sent data */
     }
     /* The iov element has been completely sent */
     r_iov->sent++;
   } while ((r_iov->cnt > r_iov->sent) && 0 != (--max_elelements_to_sent) &&
            (non_blk));
 
   mhd_assert (0 != total_sent);
   *sent = total_sent;
   return mhd_SOCKET_ERR_NO_ERROR;
 }
 
 
 #endif /* !mhd_USE_VECT_SEND || MHD_SUPPORT_HTTPS
           || mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED */
 
 MHD_INTERNAL MHD_FN_PAR_NONNULL_ALL_
 MHD_FN_PAR_OUT_ (4) enum mhd_SocketError
 mhd_send_iovec (struct MHD_Connection *restrict connection,
                 struct mhd_iovec_track *const restrict r_iov,
                 bool push_data,
                 size_t *restrict sent)
 {
 #ifdef mhd_USE_VECT_SEND
 #if defined(MHD_SUPPORT_HTTPS) || \
   defined(mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED)
   bool use_iov_send = true;
 #endif /* MHD_SUPPORT_HTTPS || mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED */
 #endif /* mhd_USE_VECT_SEND */
 
   mhd_assert (NULL != connection->rp.resp_iov.iov);
   mhd_assert (mhd_RESPONSE_CONTENT_DATA_IOVEC == \
               connection->rp.response->cntn_dtype);
   mhd_assert (connection->rp.resp_iov.cnt > connection->rp.resp_iov.sent);
 #ifdef mhd_USE_VECT_SEND
 #if defined(MHD_SUPPORT_HTTPS) || \
   defined(mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED)
   use_iov_send = use_iov_send &&
                  (! mhd_C_HAS_TLS (connection));
 #ifdef mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED
   use_iov_send = use_iov_send && (connection->daemon->sigpipe_blocked ||
                                   connection->sk.props.has_spipe_supp);
 #endif /* mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED */
   if (use_iov_send)
 #endif /* MHD_SUPPORT_HTTPS || mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED */
   return send_iov_nontls (connection, r_iov, push_data, sent);
 #endif /* mhd_USE_VECT_SEND */
 
 #if ! defined(mhd_USE_VECT_SEND) || defined(MHD_SUPPORT_HTTPS) || \
   defined(mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED)
   return send_iov_emu (connection, r_iov, push_data, sent);
 #endif /* !mhd_USE_VECT_SEND || MHD_SUPPORT_HTTPS
           || mhd_VECT_SEND_NEEDS_SPIPE_SUPPRESSED */
 }