Add PQping and PQpingParams to libpq to allow detection of the server's

status, including a status where the server is running but refuses a
postgres connection.

Have pg_ctl use this new function.  This fixes the case where pg_ctl
reports that the server is not running (cannot connect) but in fact it
is running.

Author: bmomjian

doc/src/sgml/libpq.sgml

@@ -1511,6 +1511,74 @@ int PQbackendPID(const PGconn *conn);
      </listitem>
     </varlistentry>
 
+    <varlistentry id="libpq-pqpingparams">
+     <term><function>PQpingParams</function><indexterm><primary>PQpingParams</></></term>
+     <listitem>
+      <para>
+       <function>PQpingParams</function> indicates the status of the
+       server.  The currently recognized parameter key words are the
+       same as <function>PQconnectParams</>.
+
+<synopsis>
+PGPing PQpingParams(const char **keywords, const char **values, int expand_dbname);
+</synopsis>
+
+       It returns one of the following values:
+
+       <variablelist>
+        <varlistentry id="libpq-pqpingparams-pqaccess">
+         <term><literal>PQACCESS</literal></term>
+         <listitem>
+          <para>
+           The server is running and allows access.
+          </para>
+         </listitem>
+        </varlistentry>
+
+        <varlistentry id="libpq-pqpingparams-pqreject">
+         <term><literal>PQREJECT</literal></term>
+         <listitem>
+          <para>
+           The server is running but rejected a connection request.
+          </para>
+         </listitem>
+        </varlistentry>
+
+        <varlistentry id="libpq-pqpingparams-pqnoresponse">
+         <term><literal>PQNORESPONSE</literal></term>
+         <listitem>
+          <para>
+           The server did not respond.
+          </para>
+         </listitem>
+        </varlistentry>
+       </variablelist>
+
+      </para>
+
+     </listitem>
+    </varlistentry>
+
+    <varlistentry id="libpq-pqping">
+     <term><function>PQping</function><indexterm><primary>PQping</></></term>
+     <listitem>
+      <para>
+       Returns the status of the server.
+
+<synopsis>
+PGPing PQping(const char *conninfo);
+</synopsis>
+      </para>
+
+      <para>
+       This function uses the same <literal>conninfo</literal> parameter
+       key words as <function>PQconnectdb</>.  It returns the same
+       values as <function>PQpingParams</> above.
+      </para>
+
+     </listitem>
+    </varlistentry>
+
     <varlistentry id="libpq-pqconnectionneedspassword">
      <term><function>PQconnectionNeedsPassword</function><indexterm><primary>PQconnectionNeedsPassword</></></term>
      <listitem>

src/bin/pg_ctl/pg_ctl.c

@@ -136,7 +136,7 @@ static char **readfile(const char *path);
 static int	start_postmaster(void);
 static void read_post_opts(void);
 
-static bool test_postmaster_connection(bool);
+static PGPing test_postmaster_connection(bool);
 static bool postmaster_is_alive(pid_t pid);
 
 static char postopts_file[MAXPGPATH];
@@ -400,11 +400,10 @@ start_postmaster(void)
  * Note that the checkpoint parameter enables a Windows service control
  * manager checkpoint, it's got nothing to do with database checkpoints!!
  */
-static bool
+static PGPing
 test_postmaster_connection(bool do_checkpoint)
 {
-	PGconn	   *conn;
-	bool		success = false;
+	PGPing		ret = PQACCESS;	/* assume success for zero wait */
 	int			i;
 	char		portstr[32];
 	char	   *p;
@@ -508,18 +507,10 @@ test_postmaster_connection(bool do_checkpoint)
 
 	for (i = 0; i < wait_seconds; i++)
 	{
-		if ((conn = PQconnectdb(connstr)) != NULL &&
-			(PQstatus(conn) == CONNECTION_OK ||
-			 PQconnectionNeedsPassword(conn)))
-		{
-			PQfinish(conn);
-			success = true;
-			break;
-		}
+		if ((ret = PQping(connstr)) != PQNORESPONSE)
+			return ret;
 		else
 		{
-			PQfinish(conn);
-
 #if defined(WIN32)
 			if (do_checkpoint)
 			{
@@ -543,7 +534,8 @@ test_postmaster_connection(bool do_checkpoint)
 		}
 	}
 
-	return success;
+	/* value of last call to PQping */
+	return ret;
 }
 
 
@@ -746,9 +738,11 @@ do_start(void)
 
 	if (do_wait)
 	{
+		int status;
+		
 		print_msg(_("waiting for server to start..."));
 
-		if (test_postmaster_connection(false) == false)
+		if ((status = test_postmaster_connection(false)) == PQNORESPONSE)
 		{
 			write_stderr(_("%s: could not start server\n"
 						   "Examine the log output.\n"),
@@ -759,6 +753,9 @@ do_start(void)
 		{
 			print_msg(_(" done\n"));
 			print_msg(_("server started\n"));
+			if (status == PQREJECT)
+				write_stderr(_("warning:  could not connect, perhaps due to invalid authentication or\n"
+								"misconfiguration.\n"));
 		}
 	}
 	else

src/interfaces/libpq/exports.txt

@@ -157,3 +157,5 @@ PQescapeLiteral           154
 PQescapeIdentifier        155
 PQconnectdbParams         156
 PQconnectStartParams      157
+PQping                    158
+PQpingParams              159

src/interfaces/libpq/fe-connect.c

@@ -285,6 +285,7 @@ static bool connectOptions1(PGconn *conn, const char *conninfo);
 static bool connectOptions2(PGconn *conn);
 static int	connectDBStart(PGconn *conn);
 static int	connectDBComplete(PGconn *conn);
+static PGPing internal_ping(PGconn *conn);
 static PGconn *makeEmptyPGconn(void);
 static void fillPGconn(PGconn *conn, PQconninfoOption *connOptions);
 static void freePGconn(PGconn *conn);
@@ -375,6 +376,20 @@ PQconnectdbParams(const char **keywords,
 
 }
 
+PGPing
+PQpingParams(const char **keywords,
+				  const char **values,
+				  int expand_dbname)
+{
+	PGconn	   *conn = PQconnectStartParams(keywords, values, expand_dbname);
+	PGPing		ret;
+
+	ret = internal_ping(conn);
+	PQfinish(conn);
+
+	return ret;
+}
+
 /*
  *		PQconnectdb
  *
@@ -408,6 +423,18 @@ PQconnectdb(const char *conninfo)
 	return conn;
 }
 
+PGPing
+PQping(const char *conninfo)
+{
+	PGconn	   *conn = PQconnectStart(conninfo);
+	PGPing		ret;
+
+	ret = internal_ping(conn);
+	PQfinish(conn);
+
+	return ret;
+}
+
 /*
  *		PQconnectStartParams
  *
@@ -2513,6 +2540,32 @@ PQconnectPoll(PGconn *conn)
 }
 
 
+/*
+ * internal_ping
+ *	Determine if a server is running and if we can connect to it.
+ */
+PGPing
+internal_ping(PGconn *conn)
+{
+	if (conn && conn->status != CONNECTION_BAD)
+	{
+		(void) connectDBComplete(conn);
+
+		/*
+		 *	If the connection needs a password, we can consider the
+		 *	server as accepting connections.
+		 */
+	    if (conn && (conn->status != CONNECTION_BAD ||
+		    PQconnectionNeedsPassword(conn)))
+			return PQACCESS;
+		else
+			return PQREJECT;
+	}
+	else
+		return PQNORESPONSE;
+}
+
+
 /*
  * makeEmptyPGconn
  *	 - create a PGconn data structure with (as yet) no interesting data

src/interfaces/libpq/libpq-fe.h

@@ -107,6 +107,13 @@ typedef enum
 	PQERRORS_VERBOSE			/* all the facts, ma'am */
 } PGVerbosity;
 
+typedef enum
+{
+	PQACCESS,					/* connected to server */
+	PQREJECT,					/* server rejected access */
+	PQNORESPONSE				/* server did not respond */
+} PGPing;
+
 /* PGconn encapsulates a connection to the backend.
  * The contents of this struct are not supposed to be known to applications.
  */
@@ -403,6 +410,9 @@ extern int	PQendcopy(PGconn *conn);
 extern int	PQsetnonblocking(PGconn *conn, int arg);
 extern int	PQisnonblocking(const PGconn *conn);
 extern int	PQisthreadsafe(void);
+extern PGPing PQping(const char *conninfo);
+extern PGPing PQpingParams(const char **keywords,
+				  const char **values, int expand_dbname);
 
 /* Force the write buffer to be written (or at least try) */
 extern int	PQflush(PGconn *conn);