Add method for getting the full protocol version

ext/extconf.rb

@@ -316,6 +316,7 @@ module PG
   src + " int con(){ return PGRES_PIPELINE_SYNC; }"
 end
 have_func 'PQsetChunkedRowsMode', 'libpq-fe.h' # since PostgreSQL-17
+have_func 'PQfullProtocolVersion', 'libpq-fe.h' # since PostgreSQL-18
 have_func 'timegm'
 have_func 'rb_io_wait' # since ruby-3.0
 have_func 'rb_io_descriptor' # since ruby-3.1

ext/pg_connection.c

@@ -865,6 +865,31 @@ pgconn_protocol_version(VALUE self)
 	return INT2NUM(protocol_version);
 }
 
+#ifdef HAVE_PQFULLPROTOCOLVERSION
+/*
+ * call-seq:
+ *   conn.full_protocol_version -> Integer
+ *
+ * Interrogates the frontend/backend protocol being used, including minor version.
+ *
+ * Applications might wish to use this function to determine whether certain features are supported.
+ * The result is the major version multiplied by 10000 added to the minor version, e.g. 30002 for version 3.2.
+ * The protocol version will not change after connection startup is complete, but it could theoretically change during a connection reset.
+ * The 3.0 protocol is supported by PostgreSQL server versions 7.4 and above.
+ *
+ * PG::ConnectionBad is raised if the connection is bad.
+ */
+static VALUE
+pgconn_full_protocol_version(VALUE self)
+{
+	int protocol_version = PQfullProtocolVersion(pg_get_pgconn(self));
+	if (protocol_version == 0) {
+		pg_raise_conn_error( rb_eConnectionBad, self, "PQfullProtocolVersion() can't get protocol version");
+	}
+	return INT2NUM(protocol_version);
+}
+#endif
+
 /*
  * call-seq:
  *   conn.server_version -> Integer
@@ -4733,6 +4758,9 @@ init_pg_connection(void)
 	rb_define_method(rb_cPGconn, "transaction_status", pgconn_transaction_status, 0);
 	rb_define_method(rb_cPGconn, "parameter_status", pgconn_parameter_status, 1);
 	rb_define_method(rb_cPGconn, "protocol_version", pgconn_protocol_version, 0);
+#ifdef HAVE_PQFULLPROTOCOLVERSION
+	rb_define_method(rb_cPGconn, "full_protocol_version", pgconn_full_protocol_version, 0);
+#endif
 	rb_define_method(rb_cPGconn, "server_version", pgconn_server_version, 0);
 	rb_define_method(rb_cPGconn, "error_message", pgconn_error_message, 0);
 	rb_define_method(rb_cPGconn, "socket", pgconn_socket, 0);

spec/helpers.rb

@@ -682,6 +682,7 @@ def set_etc_hosts(hostaddr, hostname)
 	config.filter_run_excluding( :postgresql_12 ) if PG.library_version < 120000
 	config.filter_run_excluding( :postgresql_14 ) if PG.library_version < 140000
 	config.filter_run_excluding( :postgresql_17 ) if PG.library_version < 170000
+	config.filter_run_excluding( :postgresql_18 ) if PG.library_version < 180000
 	config.filter_run_excluding( :unix_socket ) if RUBY_PLATFORM=~/mingw|mswin/i
 	config.filter_run_excluding( :scheduler ) if RUBY_VERSION < "3.0" || (RUBY_PLATFORM =~ /mingw|mswin/ && RUBY_VERSION < "3.1") || !Fiber.respond_to?(:scheduler)
 	config.filter_run_excluding( :scheduler_address_resolve ) if RUBY_VERSION < "3.1"

spec/pg/connection_spec.rb

@@ -976,6 +976,18 @@
 		end
 	end
 
+	context :protocol_version, :postgresql_18 do
+		it "should retrieve the wrie protocol version" do
+			expect( @conn.full_protocol_version ).to eq 30000
+		end
+
+		it "should raise an error on a bad connection" do
+			conn = PG::Connection.connect_start( @conninfo )
+			conn.finish
+			expect{ conn.full_protocol_version }.to raise_error(PG::ConnectionBad)
+		end
+	end
+
 	it "allows a query to be cancelled" do
 		start = Time.now
 		@conn.set_notice_processor do |notice|