build: assume POSIX select() is available

This change effectively changes an explicit compile-time #error with
a missing prototype error in environments not offering `select()`, and
save supported systems from performing an explicit feature check.

Refs:
https://pubs.opengroup.org/onlinepubs/009695399/
https://linux.die.net/man/2/select

CMake/unix-cache.cmake

@@ -226,7 +226,6 @@ set(HAVE_REALPATH 1)
 set(HAVE_RECV 1)
 set(HAVE_SA_FAMILY_T 1)
 set(HAVE_SCHED_YIELD 1)
-set(HAVE_SELECT 1)
 set(HAVE_SEND 1)
 if(APPLE OR
    CYGWIN OR

CMake/win32-cache.cmake

@@ -128,7 +128,6 @@ set(HAVE_POLL_H 0)
 set(HAVE_POSIX_STRERROR_R 0)
 set(HAVE_PWD_H 0)
 set(HAVE_RECV 1)
-set(HAVE_SELECT 1)
 set(HAVE_SEND 1)
 set(HAVE_SENDMMSG 0)
 set(HAVE_SENDMSG 0)

CMakeLists.txt

@@ -1640,7 +1640,6 @@ check_symbol_exists("recv"            "${CURL_INCLUDES}" HAVE_RECV)  # proto/bsd
 check_symbol_exists("send"            "${CURL_INCLUDES}" HAVE_SEND)  # proto/bsdsocket.h sys/types.h sys/socket.h
 check_function_exists("sendmsg"       HAVE_SENDMSG)
 check_function_exists("sendmmsg"      HAVE_SENDMMSG)
-check_symbol_exists("select"          "${CURL_INCLUDES}" HAVE_SELECT)  # proto/bsdsocket.h sys/select.h sys/socket.h
 check_symbol_exists("memrchr"         "string.h" HAVE_MEMRCHR)
 check_symbol_exists("alarm"           "unistd.h" HAVE_ALARM)
 check_symbol_exists("fcntl"           "fcntl.h" HAVE_FCNTL)

acinclude.m4

@@ -972,59 +972,6 @@ AC_DEFUN([CURL_CHECK_LIBS_CONNECT], [
 ])
 
 
-dnl CURL_CHECK_FUNC_SELECT
-dnl -------------------------------------------------
-dnl Test if the socket select() function is available.
-
-AC_DEFUN([CURL_CHECK_FUNC_SELECT], [
-  AC_REQUIRE([CURL_CHECK_STRUCT_TIMEVAL])
-  AC_REQUIRE([CURL_INCLUDES_BSDSOCKET])
-  AC_CHECK_HEADERS(sys/select.h)
-
-  AC_MSG_CHECKING([for select])
-  AC_LINK_IFELSE([
-    AC_LANG_PROGRAM([[
-      #undef inline
-      #ifdef _WIN32
-      #ifndef WIN32_LEAN_AND_MEAN
-      #define WIN32_LEAN_AND_MEAN
-      #endif
-      #include <winsock2.h>
-      #else
-      #include <sys/socket.h>
-      #include <sys/time.h>
-      #endif
-      #ifdef HAVE_SYS_TYPES_H
-      #include <sys/types.h>
-      #endif
-      #include <time.h>
-      #ifndef _WIN32
-      #ifdef HAVE_SYS_SELECT_H
-      #include <sys/select.h>
-      #elif defined(HAVE_UNISTD_H)
-      #include <unistd.h>
-      #endif
-      $curl_includes_bsdsocket
-      #endif
-    ]],[[
-      select(0, 0, 0, 0, 0);
-    ]])
-  ],[
-    AC_MSG_RESULT([yes])
-    curl_cv_select="yes"
-  ],[
-    AC_MSG_RESULT([no])
-    curl_cv_select="no"
-  ])
-
-  if test "$curl_cv_select" = "yes"; then
-    AC_DEFINE_UNQUOTED(HAVE_SELECT, 1,
-      [Define to 1 if you have the select function.])
-    curl_cv_func_select="yes"
-  fi
-])
-
-
 dnl CURL_VERIFY_RUNTIMELIBS
 dnl -------------------------------------------------
 dnl Verify that the shared libs found so far can be used when running

configure.ac

@@ -4178,8 +4178,6 @@ esac
 
 TYPE_SOCKADDR_STORAGE
 
-CURL_CHECK_FUNC_SELECT
-
 CURL_CHECK_FUNC_RECV
 CURL_CHECK_FUNC_SEND
 

lib/config-mac.h

@@ -52,7 +52,6 @@
 #define HAVE_SYS_IOCTL_H        1
 #define HAVE_ALARM              1
 #define HAVE_UTIME              1
-#define HAVE_SELECT             1
 #define HAVE_SOCKET             1
 #define HAVE_STRUCT_TIMEVAL     1
 

lib/config-os400.h

@@ -142,9 +142,6 @@
 /* Define to 1 if symbol `sa_family_t' exists */
 #define HAVE_SA_FAMILY_T        1
 
-/* Define to 1 if you have the select function. */
-#define HAVE_SELECT             1
-
 /* Define to 1 if you have the send function. */
 #define HAVE_SEND               1
 

lib/config-riscos.h

@@ -69,9 +69,6 @@
 /* Define if you have the <net/if.h> header file. */
 #define HAVE_NET_IF_H
 
-/* Define if you have the `select' function. */
-#define HAVE_SELECT
-
 /* Define if you have the `signal' function. */
 #define HAVE_SIGNAL
 

lib/config-win32.h

@@ -103,9 +103,6 @@
 /* Define if you have a working ioctlsocket FIONBIO function. */
 #define HAVE_IOCTLSOCKET_FIONBIO 1
 
-/* Define if you have the select function. */
-#define HAVE_SELECT 1
-
 /* Define if you have the setlocale function. */
 #define HAVE_SETLOCALE 1
 

lib/curl_config-cmake.h.in

@@ -460,9 +460,6 @@
 /* Define to 1 if you have the recv function. */
 #cmakedefine HAVE_RECV 1
 
-/* Define to 1 if you have the select function. */
-#cmakedefine HAVE_SELECT 1
-
 /* Define to 1 if you have the sched_yield function. */
 #cmakedefine HAVE_SCHED_YIELD 1
 

lib/curlx/wait.c

@@ -23,10 +23,6 @@
  ***************************************************************************/
 #include "curl_setup.h"
 
-#ifndef HAVE_SELECT
-#error "We cannot compile without select() support."
-#endif
-
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #elif defined(HAVE_UNISTD_H)

lib/select.c

@@ -23,10 +23,6 @@
  ***************************************************************************/
 #include "curl_setup.h"
 
-#if !defined(HAVE_SELECT) && !defined(HAVE_POLL)
-#error "We cannot compile without select() or poll() support."
-#endif
-
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #elif defined(HAVE_UNISTD_H)
@@ -40,7 +36,7 @@
 #include "curlx/timediff.h"
 #include "curlx/wait.h"
 
-#ifndef HAVE_POLL
+#ifndef HAVE_POLL  /* use select() */
 /*
  * This is a wrapper around select() to aid in Windows compatibility. A
  * negative timeout value makes this function wait indefinitely, unless no