Modularize log_connections output

Convert the boolean log_connections GUC into a list GUC comprised of the
connection aspects to log.

This gives users more control over the volume and kind of connection
logging.

The current log_connections options are 'receipt', 'authentication', and
'authorization'. The empty string disables all connection logging. 'all'
enables all available connection logging.

For backwards compatibility, the most common values for the
log_connections boolean are still supported (on, off, 1, 0, true, false,
yes, no). Note that previously supported substrings of on, off, true,
false, yes, and no are no longer supported.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/flat/CAAKRu_b_smAHK0ZjrnL5GRxnAVWujEXQWpLXYzGbmpcZd3nLYw%40mail.gmail.com

src/backend/libpq/auth.c

@@ -38,6 +38,7 @@
 #include "postmaster/postmaster.h"
 #include "replication/walsender.h"
 #include "storage/ipc.h"
+#include "tcop/backend_startup.h"
 #include "utils/memutils.h"
 
 /*----------------------------------------------------------------
@@ -317,7 +318,8 @@ auth_failed(Port *port, int status, const char *logdetail)
 /*
  * Sets the authenticated identity for the current user.  The provided string
  * will be stored into MyClientConnectionInfo, alongside the current HBA
- * method in use.  The ID will be logged if log_connections is enabled.
+ * method in use.  The ID will be logged if log_connections has the
+ * 'authentication' option specified.
  *
  * Auth methods should call this routine exactly once, as soon as the user is
  * successfully authenticated, even if they have reasons to know that
@@ -349,7 +351,7 @@ set_authn_id(Port *port, const char *id)
 	MyClientConnectionInfo.authn_id = MemoryContextStrdup(TopMemoryContext, id);
 	MyClientConnectionInfo.auth_method = port->hba->auth_method;
 
-	if (Log_connections)
+	if (log_connections & LOG_CONNECTION_AUTHENTICATION)
 	{
 		ereport(LOG,
 				errmsg("connection authenticated: identity=\"%s\" method=%s "
@@ -633,7 +635,8 @@ ClientAuthentication(Port *port)
 #endif
 	}
 
-	if (Log_connections && status == STATUS_OK &&
+	if ((log_connections & LOG_CONNECTION_AUTHENTICATION) &&
+		status == STATUS_OK &&
 		!MyClientConnectionInfo.authn_id)
 	{
 		/*

src/backend/postmaster/postmaster.c

@@ -237,7 +237,6 @@ int			PreAuthDelay = 0;
 int			AuthenticationTimeout = 60;
 
 bool		log_hostname;		/* for ps display and logging */
-bool		Log_connections = false;
 
 bool		enable_bonjour = false;
 char	   *bonjour_name;

src/backend/tcop/backend_startup.c

@@ -34,13 +34,17 @@
 #include "tcop/backend_startup.h"
 #include "tcop/tcopprot.h"
 #include "utils/builtins.h"
+#include "utils/guc_hooks.h"
 #include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/timeout.h"
+#include "utils/varlena.h"
 
 /* GUCs */
 bool		Trace_connection_negotiation = false;
+uint32		log_connections = 0;
+char	   *log_connections_string = NULL;
 
 static void BackendInitialize(ClientSocket *client_sock, CAC_state cac);
 static int	ProcessSSLStartup(Port *port);
@@ -48,6 +52,7 @@ static int	ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done);
 static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
 static void process_startup_packet_die(SIGNAL_ARGS);
 static void StartupPacketTimeoutHandler(void);
+static bool validate_log_connections_options(List *elemlist, uint32 *flags);
 
 /*
  * Entry point for a new backend process.
@@ -201,8 +206,8 @@ BackendInitialize(ClientSocket *client_sock, CAC_state cac)
 	port->remote_host = MemoryContextStrdup(TopMemoryContext, remote_host);
 	port->remote_port = MemoryContextStrdup(TopMemoryContext, remote_port);
 
-	/* And now we can issue the Log_connections message, if wanted */
-	if (Log_connections)
+	/* And now we can log that the connection was received, if enabled */
+	if (log_connections & LOG_CONNECTION_RECEIPT)
 	{
 		if (remote_port[0])
 			ereport(LOG,
@@ -924,3 +929,155 @@ StartupPacketTimeoutHandler(void)
 {
 	_exit(1);
 }
+
+/*
+ * Helper for the log_connections GUC check hook.
+ *
+ * `elemlist` is a listified version of the string input passed to the
+ * log_connections GUC check hook, check_log_connections().
+ * check_log_connections() is responsible for cleaning up `elemlist`.
+ *
+ * validate_log_connections_options() returns false if an error was
+ * encountered and the GUC input could not be validated and true otherwise.
+ *
+ * `flags` returns the flags that should be stored in the log_connections GUC
+ * by its assign hook.
+ */
+static bool
+validate_log_connections_options(List *elemlist, uint32 *flags)
+{
+	ListCell   *l;
+	char	   *item;
+
+	/*
+	 * For backwards compatibility, we accept these tokens by themselves.
+	 *
+	 * Prior to PostgreSQL 18, log_connections was a boolean GUC that accepted
+	 * any unambiguous substring of 'true', 'false', 'yes', 'no', 'on', and
+	 * 'off'. Since log_connections became a list of strings in 18, we only
+	 * accept complete option strings.
+	 */
+	static const struct config_enum_entry compat_options[] = {
+		{"off", 0},
+		{"false", 0},
+		{"no", 0},
+		{"0", 0},
+		{"on", LOG_CONNECTION_ON},
+		{"true", LOG_CONNECTION_ON},
+		{"yes", LOG_CONNECTION_ON},
+		{"1", LOG_CONNECTION_ON},
+	};
+
+	*flags = 0;
+
+	/* If an empty string was passed, we're done */
+	if (list_length(elemlist) == 0)
+		return true;
+
+	/*
+	 * Now check for the backwards compatibility options. They must always be
+	 * specified on their own, so we error out if the first option is a
+	 * backwards compatibility option and other options are also specified.
+	 */
+	item = linitial(elemlist);
+
+	for (size_t i = 0; i < lengthof(compat_options); i++)
+	{
+		struct config_enum_entry option = compat_options[i];
+
+		if (pg_strcasecmp(item, option.name) != 0)
+			continue;
+
+		if (list_length(elemlist) > 1)
+		{
+			GUC_check_errdetail("Cannot specify log_connections option \"%s\" in a list with other options.",
+								item);
+			return false;
+		}
+
+		*flags = option.val;
+		return true;
+	}
+
+	/* Now check the aspect options. The empty string was already handled */
+	foreach(l, elemlist)
+	{
+		static const struct config_enum_entry options[] = {
+			{"receipt", LOG_CONNECTION_RECEIPT},
+			{"authentication", LOG_CONNECTION_AUTHENTICATION},
+			{"authorization", LOG_CONNECTION_AUTHORIZATION},
+			{"all", LOG_CONNECTION_ALL},
+		};
+
+		item = lfirst(l);
+		for (size_t i = 0; i < lengthof(options); i++)
+		{
+			struct config_enum_entry option = options[i];
+
+			if (pg_strcasecmp(item, option.name) == 0)
+			{
+				*flags |= option.val;
+				goto next;
+			}
+		}
+
+		GUC_check_errdetail("Invalid option \"%s\".", item);
+		return false;
+
+next:	;
+	}
+
+	return true;
+}
+
+
+/*
+ * GUC check hook for log_connections
+ */
+bool
+check_log_connections(char **newval, void **extra, GucSource source)
+{
+	uint32		flags;
+	char	   *rawstring;
+	List	   *elemlist;
+	bool		success;
+
+	/* Need a modifiable copy of string */
+	rawstring = pstrdup(*newval);
+
+	if (!SplitIdentifierString(rawstring, ',', &elemlist))
+	{
+		GUC_check_errdetail("Invalid list syntax in parameter \"log_connections\".");
+		pfree(rawstring);
+		list_free(elemlist);
+		return false;
+	}
+
+	/* Validation logic is all in the helper */
+	success = validate_log_connections_options(elemlist, &flags);
+
+	/* Time for cleanup */
+	pfree(rawstring);
+	list_free(elemlist);
+
+	if (!success)
+		return false;
+
+	/*
+	 * We succeeded, so allocate `extra` and save the flags there for use by
+	 * assign_log_connections().
+	 */
+	*extra = guc_malloc(ERROR, sizeof(int));
+	*((int *) *extra) = flags;
+
+	return true;
+}
+
+/*
+ * GUC assign hook for log_connections
+ */
+void
+assign_log_connections(const char *newval, void *extra)
+{
+	log_connections = *((int *) extra);
+}

src/backend/utils/init/postinit.c

@@ -54,6 +54,7 @@
 #include "storage/sinvaladt.h"
 #include "storage/smgr.h"
 #include "storage/sync.h"
+#include "tcop/backend_startup.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
@@ -252,7 +253,7 @@ PerformAuthentication(Port *port)
 	 */
 	disable_timeout(STATEMENT_TIMEOUT, false);
 
-	if (Log_connections)
+	if (log_connections & LOG_CONNECTION_AUTHORIZATION)
 	{
 		StringInfoData logmsg;
 

src/backend/utils/misc/guc_tables.c

@@ -1219,15 +1219,6 @@ struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
-	{
-		{"log_connections", PGC_SU_BACKEND, LOGGING_WHAT,
-			gettext_noop("Logs each successful connection."),
-			NULL
-		},
-		&Log_connections,
-		false,
-		NULL, NULL, NULL
-	},
 	{
 		{"trace_connection_negotiation", PGC_POSTMASTER, DEVELOPER_OPTIONS,
 			gettext_noop("Logs details of pre-authentication connection handshake."),
@@ -4886,6 +4877,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"log_connections", PGC_SU_BACKEND, LOGGING_WHAT,
+			gettext_noop("Logs specified aspects of connection establishment and setup."),
+			NULL,
+			GUC_LIST_INPUT
+		},
+		&log_connections_string,
+		"",
+		check_log_connections, assign_log_connections, NULL
+	},
+
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, NULL, NULL, NULL, NULL

src/backend/utils/misc/postgresql.conf.sample

@@ -21,7 +21,7 @@
 # require a server shutdown and restart to take effect.
 #
 # Any parameter can also be given as a command-line option to the server, e.g.,
-# "postgres -c log_connections=on".  Some parameters can be changed at run time
+# "postgres -c log_connections=all".  Some parameters can be changed at run time
 # with the "SET" SQL command.
 #
 # Memory units:  B  = bytes            Time units:  us  = microseconds
@@ -578,9 +578,11 @@
 					# actions running at least this number
 					# of milliseconds.
 #log_checkpoints = on
-#log_connections = off
+#log_connections = '' # log aspects of connection setup
+          # options include receipt, authentication, authorization,
+          # and all to log all of these aspects
 #log_disconnections = off
-#log_duration = off
+#log_duration = off # log statement duration
 #log_error_verbosity = default		# terse, default, or verbose messages
 #log_hostname = off
 #log_line_prefix = '%m [%p] '		# special values: