Add method for getting the full protocol version

PostgreSQL 18 added PQfullProtocolVersion() which return the full
protocol version used including the minor version, e.g. 3.0 or 3.2
rather than just 3. The new methods PG::Connection#full_protocol_version
retuns the version as major version * 10000 + minor version, e.g. 30002
for version 3.2.

Author: jeltz

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|