Support nonblocking connection.

See jtv#487.  We used to have a `connection` class _hierarchy,_ and one of
those did something similar.  But this new class is much more limited in
scope and keeps things simple.

In the future hopefully this can form a basis for C++20 async support.
But for now, any application with a wait loop based on `poll()` or
`select()` should be able to use it.

Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.
@@ -346,7 +346,6 @@ am__set_TESTS_bases = \
   bases='$(TEST_LOGS)'; \
   bases=`for i in $$bases; do echo $$i; done | sed 's/\.log$$//'`; \
   bases=`echo $$bases`
-AM_TESTSUITE_SUMMARY_HEADER = ' for $(PACKAGE_STRING)'
 RECHECK_LOGS = $(TEST_LOGS)
 TEST_SUITE_LOG = test-suite.log
 TEST_EXTENSIONS = @EXEEXT@ .test
@@ -416,8 +415,6 @@ am__relativize = \
 DIST_ARCHIVES = $(distdir).tar.gz
 GZIP_ENV = --best
 DIST_TARGETS = dist-gzip
-# Exists only to be overridden by the user if desired.
-AM_DISTCHECK_DVI_TARGET = dvi
 distuninstallcheck_listfiles = find . -type f -print
 am__distuninstallcheck_listfiles = $(distuninstallcheck_listfiles) \
   | sed 's|^\./|$(prefix)/|' | grep -v '$(infodir)/dir$$'
@@ -848,7 +845,7 @@ $(TEST_SUITE_LOG): $(TEST_LOGS)
 	  test x"$$VERBOSE" = x || cat $(TEST_SUITE_LOG);		\
 	fi;								\
 	echo "$${col}$$br$${std}"; 					\
-	echo "$${col}Testsuite summary"$(AM_TESTSUITE_SUMMARY_HEADER)"$${std}";	\
+	echo "$${col}Testsuite summary for $(PACKAGE_STRING)$${std}";	\
 	echo "$${col}$$br$${std}"; 					\
 	create_testsuite_report --maybe-color;				\
 	echo "$$col$$br$$std";						\
@@ -1053,7 +1050,7 @@ distcheck: dist
 	    $(DISTCHECK_CONFIGURE_FLAGS) \
 	    --srcdir=../.. --prefix="$$dc_install_base" \
 	  && $(MAKE) $(AM_MAKEFLAGS) \
-	  && $(MAKE) $(AM_MAKEFLAGS) $(AM_DISTCHECK_DVI_TARGET) \
+	  && $(MAKE) $(AM_MAKEFLAGS) dvi \
 	  && $(MAKE) $(AM_MAKEFLAGS) check \
 	  && $(MAKE) $(AM_MAKEFLAGS) install \
 	  && $(MAKE) $(AM_MAKEFLAGS) installcheck \

NEWS

@@ -5,6 +5,7 @@
  - Fix warnings about `[[likely]]` in `if constexpr`.  (#475)
  - Clearer error for ambiguous string conversion of `char` type.  (#481)
  - Pseudo-statement in `prepare()` error was for the wrong statement.  (#488)
+ - New class, `connecting` for nonblocking connection to the database.  (#487)
 7.6.0
  - Removed bad string conversion to `std::basic_string_view<std::byte>`. (#463)
  - Add C++20 concepts: `binary`, `char_string`, `char_strings`.

aclocal.m4

@@ -1,4 +1,4 @@
-# generated automatically by aclocal 1.16.3 -*- Autoconf -*-
+# generated automatically by aclocal 1.16.2 -*- Autoconf -*-
 
 # Copyright (C) 1996-2020 Free Software Foundation, Inc.
 
@@ -1020,7 +1020,7 @@ AC_DEFUN([AM_AUTOMAKE_VERSION],
 [am__api_version='1.16'
 dnl Some users find AM_AUTOMAKE_VERSION and mistake it for a way to
 dnl require some minimum version.  Point them to the right macro.
-m4_if([$1], [1.16.3], [],
+m4_if([$1], [1.16.2], [],
       [AC_FATAL([Do not call $0, use AM_INIT_AUTOMAKE([$1]).])])dnl
 ])
 
@@ -1036,7 +1036,7 @@ m4_define([_AM_AUTOCONF_VERSION], [])
 # Call AM_AUTOMAKE_VERSION and AM_AUTOMAKE_VERSION so they can be traced.
 # This function is AC_REQUIREd by AM_INIT_AUTOMAKE.
 AC_DEFUN([AM_SET_CURRENT_AUTOMAKE_VERSION],
-[AM_AUTOMAKE_VERSION([1.16.3])dnl
+[AM_AUTOMAKE_VERSION([1.16.2])dnl
 m4_ifndef([AC_AUTOCONF_VERSION],
   [m4_copy([m4_PACKAGE_VERSION], [AC_AUTOCONF_VERSION])])dnl
 _AM_AUTOCONF_VERSION(m4_defn([AC_AUTOCONF_VERSION]))])
@@ -1724,7 +1724,12 @@ AC_DEFUN([AM_MISSING_HAS_RUN],
 [AC_REQUIRE([AM_AUX_DIR_EXPAND])dnl
 AC_REQUIRE_AUX_FILE([missing])dnl
 if test x"${MISSING+set}" != xset; then
-  MISSING="\${SHELL} '$am_aux_dir/missing'"
+  case $am_aux_dir in
+  *\ * | *\	*)
+    MISSING="\${SHELL} \"$am_aux_dir/missing\"" ;;
+  *)
+    MISSING="\${SHELL} $am_aux_dir/missing" ;;
+  esac
 fi
 # Use eval to expand $SHELL
 if eval "$MISSING --is-lightweight"; then

config-tests/concepts.cxx

@@ -4,8 +4,7 @@
 #include <vector>
 
 
-template<typename T>
-concept Foo = std::ranges::input_range<T>;
+template<typename T> concept Foo = std::ranges::input_range<T>;
 
 
 template<Foo F> auto foo(F const &r)

config/Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.

config/ltmain.sh

@@ -31,7 +31,7 @@
 
 PROGRAM=libtool
 PACKAGE=libtool
-VERSION="2.4.6 Debian-2.4.6-15"
+VERSION="2.4.6 Debian-2.4.6-14"
 package_revision=2.4.6
 
 
@@ -2141,7 +2141,7 @@ include the following information:
        compiler:       $LTCC
        compiler flags: $LTCFLAGS
        linker:         $LD (gnu? $with_gnu_ld)
-       version:        $progname $scriptversion Debian-2.4.6-15
+       version:        $progname $scriptversion Debian-2.4.6-14
        automake:       `($AUTOMAKE --version) 2>/dev/null |$SED 1q`
        autoconf:       `($AUTOCONF --version) 2>/dev/null |$SED 1q`
 

config/m4/libtool.m4

@@ -1071,11 +1071,11 @@ _LT_EOF
       # to the OS version, if on x86, and 10.4, the deployment
       # target defaults to 10.4. Don't you love it?
       case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[[912]]*)
+	10.0,*86*-darwin8*|10.0,*-darwin[[91]]*)
 	  _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
 	10.[[012]][[,.]]*)
 	  _lt_dar_allow_undefined='$wl-flat_namespace $wl-undefined ${wl}suppress' ;;
-	10.*|11.*)
+	10.*)
 	  _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
       esac
     ;;

configure

@@ -3978,7 +3978,12 @@ program_transform_name=`$as_echo "$program_transform_name" | sed "$ac_script"`
 am_aux_dir=`cd "$ac_aux_dir" && pwd`
 
 if test x"${MISSING+set}" != xset; then
-  MISSING="\${SHELL} '$am_aux_dir/missing'"
+  case $am_aux_dir in
+  *\ * | *\	*)
+    MISSING="\${SHELL} \"$am_aux_dir/missing\"" ;;
+  *)
+    MISSING="\${SHELL} $am_aux_dir/missing" ;;
+  esac
 fi
 # Use eval to expand $SHELL
 if eval "$MISSING --is-lightweight"; then
@@ -9026,11 +9031,11 @@ $as_echo "$lt_cv_ld_force_load" >&6; }
       # to the OS version, if on x86, and 10.4, the deployment
       # target defaults to 10.4. Don't you love it?
       case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[912]*)
+	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
 	  _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
 	10.[012][,.]*)
 	  _lt_dar_allow_undefined='$wl-flat_namespace $wl-undefined ${wl}suppress' ;;
-	10.*|11.*)
+	10.*)
 	  _lt_dar_allow_undefined='$wl-undefined ${wl}dynamic_lookup' ;;
       esac
     ;;

doc/Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.

include/Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.

include/pqxx/Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.

include/pqxx/connection.hxx

@@ -81,12 +81,14 @@ concept ZKey_ZValues = std::ranges::input_range<T> and requires(T t)
   {std::cbegin(t)};
   {
     std::get<0>(*std::cbegin(t))
-    } -> ZString;
+  }
+  ->ZString;
   {
     std::get<1>(*std::cbegin(t))
-    } -> ZString;
-} and std::tuple_size_v<typename std::ranges::iterator_t<T>::value_type>
-== 2;
+  }
+  ->ZString;
+}
+and std::tuple_size_v<typename std::ranges::iterator_t<T>::value_type> == 2;
 #endif // PQXX_HAVE_CONCEPTS
 } // namespace pqxx::internal
 
@@ -883,15 +885,27 @@ public:
   void close();
 
 private:
+  friend class connecting;
+  enum connect_mode
+  {
+    connect_nonblocking
+  };
+  connection(connect_mode, zview connection_string);
+
+  /// Poll for ongoing connection, try to progress towards completion.
+  /** Returns a pair of "now please wait to read data from socket" and "now
+   * please wait to write data to socket."  Both will be false when done.
+   *
+   * Throws an exception if polling indicates that the connection has failed.
+   */
+  std::pair<bool, bool> poll_connect();
+
   // Initialise based on connection string.
   void init(char const options[]);
   // Initialise based on parameter names and values.
   void init(char const *params[], char const *values[]);
   void complete_init();
 
-  void wait_read() const;
-  void wait_read(std::time_t seconds, long microseconds) const;
-
   result make_result(
     internal::pq::PGresult *pgr, std::shared_ptr<std::string> const &query,
     std::string_view desc = ""sv);
@@ -985,6 +999,71 @@ private:
 using connection_base = connection;
 
 
+/// An ongoing, non-blocking stepping stone to a connection.
+/** Use this when you want to create a connection to the database, but without
+ * blocking your whole thread.
+ *
+ * Connecting in this way is probably not "faster" (it's more complicated and
+ * has some extra overhead), but in some situations you can use it to make your
+ * application as a whole faster.  It all depends on having other useful work
+ * to do in the same thread, and being able to wait on a socket.  If you have
+ * other I/O going on at the same time, your event loop can wait for both the
+ * libpqxx socket and your own sockets, and wake up whenever any of them is
+ * ready to do work.
+ *
+ * Connecting in this way is not properly "asynchronous;" it's merely
+ * "nonblocking."  This means it's not a super-high-performance mechanism like
+ * you might get with e.g. @c io_uring.  In particular, if we need to look up
+ * the database hostname in DNS, that will happen synchronously.
+ *
+ * To use this, create the @c connecting object, passing a connection string.
+ * Then loop: If @c wait_to_read() returns true, wait for the socket to have
+ * incoming data on it.  If @c wait_to_write() returns true, wait wait for the
+ * socket to be ready for writing.  Repeat until @c done() returns true (or
+ * there is an exception).  Finally, call @c produce() to get the completed
+ * connection.  This will work only once on the @c connecting object.
+ */
+class PQXX_LIBEXPORT connecting
+{
+public:
+  /// Start connecting.
+  connecting(zview connection_string) :
+          m_conn{connection::connect_nonblocking, connection_string}
+  {}
+  connecting() : m_conn{connection::connect_nonblocking, ""_zv} {}
+
+  /// Get the socket.  This may change during the process.
+  int sock() const noexcept { return m_conn.sock(); }
+
+  /// Should we currently wait to @i read from the socket?
+  bool wait_to_read() const noexcept { return m_reading; }
+
+  /// Should we currently wait to @i write to the socket?
+  bool wait_to_write() const noexcept { return m_writing; }
+
+  /// Progress towards completion but don't block.
+  void process()
+  {
+    auto const [reading, writing]{m_conn.poll_connect()};
+    m_reading = reading;
+    m_writing = writing;
+  }
+
+  /// Is our connection finished?
+  bool done() const noexcept { return not m_reading and not m_writing; }
+
+  /// Produce the completed connection object.
+  /** Use this only once, after @c done() returned @c true.
+   */
+  connection produce();
+
+private:
+  connection m_conn;
+  bool m_reading{false};
+  bool m_writing{true};
+};
+
+
 template<typename T> inline std::string connection::quote(T const &t) const
 {
   if constexpr (nullness<T>::always_null)
@@ -1050,10 +1129,10 @@ inline connection::connection(MAPPING const &params)
 
 namespace pqxx::internal
 {
-PQXX_LIBEXPORT void wait_read(internal::pq::PGconn const *);
-PQXX_LIBEXPORT void wait_read(
-  internal::pq::PGconn const *, std::time_t seconds, long microseconds);
-PQXX_LIBEXPORT void wait_write(internal::pq::PGconn const *);
+/// Wait for a socket to be ready for reading/writing, or timeout.
+PQXX_LIBEXPORT void wait_fd(
+  int fd, bool for_read, bool for_write, unsigned seconds = 1,
+  unsigned microseconds = 0);
 } // namespace pqxx::internal
 
 #include "pqxx/internal/compiler-internal-post.hxx"

include/pqxx/strconv.hxx

@@ -424,8 +424,8 @@ template<typename TYPE> inline constexpr format param_format(TYPE const &)
  * we can reference them by a pointer.
  */
 template<class TYPE>
-concept binary = std::ranges::contiguous_range<TYPE> and
-  std::is_same_v<strip_t<value_type<TYPE>>, std::byte>;
+concept binary = std::ranges::contiguous_range<TYPE>
+  and std::is_same_v<strip_t<value_type<TYPE>>, std::byte>;
 #endif
 //@}
 } // namespace pqxx

include/pqxx/types.hxx

@@ -107,9 +107,8 @@ using value_type = decltype(*std::begin(std::declval<CONTAINER>()));
 #if defined(PQXX_HAVE_CONCEPTS)
 /// Concept: Any type that we can read as a string of @c char.
 template<typename STRING>
-concept char_string = std::ranges::contiguous_range<STRING> and
-                      std::same_as < strip_t<value_type<STRING>>,
-char > ;
+concept char_string = std::ranges::contiguous_range<STRING>
+  and std::same_as<strip_t<value_type<STRING>>, char>;
 
 /// Concept: Anything we can iterate to get things we can read as strings.
 template<typename RANGE>
@@ -119,7 +118,7 @@ concept char_strings =
 /// Concept: Anything we might want to treat as binary data.
 template<typename DATA>
 concept potential_binary = std::ranges::contiguous_range<DATA> and
-  (sizeof(value_type<DATA>) == 1);
+                           (sizeof(value_type<DATA>) == 1);
 #endif // PQXX_HAVE_CONCEPTS
 
 

include/pqxx/util.hxx

@@ -239,8 +239,7 @@ std::basic_string_view<std::byte> binary_cast(TYPE const &data)
 
 
 #if defined(PQXX_HAVE_CONCEPTS)
-template<typename CHAR>
-concept char_sized = (sizeof(CHAR) == 1);
+template<typename CHAR> concept char_sized = (sizeof(CHAR) == 1);
 #  define PQXX_CHAR_SIZED_ARG char_sized
 #else
 #  define PQXX_CHAR_SIZED_ARG typename

include/pqxx/zview.hxx

@@ -118,9 +118,9 @@ namespace pqxx::internal
  * support each of these individually.
  */
 template<typename T>
-concept ZString = std::is_convertible_v < strip_t<T>,
-char const * > or std::is_convertible_v<strip_t<T>, zview> or
-  std::is_convertible_v<T, std::string const &>;
+concept ZString = std::is_convertible_v<strip_t<T>, char const *> or
+                  std::is_convertible_v<strip_t<T>, zview> or
+                  std::is_convertible_v<T, std::string const &>;
 } // namespace pqxx::internal
 #endif // PQXX_HAVE_CONCEPTS
 

src/Makefile.in

@@ -1,4 +1,4 @@
-# Makefile.in generated by automake 1.16.3 from Makefile.am.
+# Makefile.in generated by automake 1.16.2 from Makefile.am.
 # @configure_input@
 
 # Copyright (C) 1994-2020 Free Software Foundation, Inc.