Client session tracking

README.md

@@ -197,6 +197,23 @@ statement = @client.prepare("SELECT * FROM users WHERE last_login >= ? AND locat
 result = statement.execute(1, "CA", :as => :array)
 ```
 
+Session Tracking information can be accessed with
+
+```ruby
+c = Mysql2::Client.new(
+  host: "127.0.0.1",
+  username: "root",
+  flags: "SESSION_TRACK",
+  init_command: "SET @@SESSION.session_track_schema=ON"
+)
+c.query("INSERT INTO test VALUES (1)")
+session_track_type = Mysql2::Client::SESSION_TRACK_SCHEMA
+session_track_data = c.session_track(session_track_type)
+```
+
+The types of session track types can be found at
+[https://dev.mysql.com/doc/refman/5.7/en/mysql-session-track-get-first.html](https://dev.mysql.com/doc/refman/5.7/en/mysql-session-track-get-first.html)
+
 ## Connection options
 
 You may set the following connection options in Mysql2::Client.new(...):

ext/mysql2/client.c

@@ -57,6 +57,17 @@ static ID intern_brackets, intern_merge, intern_merge_bang, intern_new_with_args
   #define MYSQL_LINK_VERSION MYSQL_SERVER_VERSION
 #endif
 
+/*
+ * mariadb-connector-c defines CLIENT_SESSION_TRACKING and SESSION_TRACK_TRANSACTION_TYPE
+ * while mysql-connector-c defines CLIENT_SESSION_TRACK and SESSION_TRACK_TRANSACTION_STATE
+ * This is a hack to take care of both clients.
+ */
+#if defined(CLIENT_SESSION_TRACK)
+#elif defined(CLIENT_SESSION_TRACKING)
+  #define CLIENT_SESSION_TRACK CLIENT_SESSION_TRACKING
+  #define SESSION_TRACK_TRANSACTION_STATE SESSION_TRACK_TRANSACTION_TYPE
+#endif
+
 /*
  * compatibility with mysql-connector-c 6.1.x, and with MySQL 5.7.3 - 5.7.10.
  */
@@ -1021,6 +1032,36 @@ static VALUE rb_mysql_client_last_id(VALUE self) {
   return ULL2NUM(mysql_insert_id(wrapper->client));
 }
 
+/* call-seq:
+ *    client.session_track
+ *
+ * Returns information about changes to the session state on the server.
+ */
+static VALUE rb_mysql_client_session_track(VALUE self, VALUE type) {
+#ifdef CLIENT_SESSION_TRACK
+  const char *data;
+  size_t length;
+  my_ulonglong retVal;
+  GET_CLIENT(self);
+
+  REQUIRE_CONNECTED(wrapper);
+  retVal = mysql_session_track_get_first(wrapper->client, NUM2INT(type), &data, &length);
+  if (retVal != 0) {
+    return Qnil;
+  }
+  VALUE rbAry = rb_ary_new();
+  VALUE rbFirst = rb_str_new(data, length);
+  rb_ary_push(rbAry, rbFirst);
+  while(mysql_session_track_get_next(wrapper->client, NUM2INT(type), &data, &length) == 0) {
+    VALUE rbNext = rb_str_new(data, length);
+    rb_ary_push(rbAry, rbNext);
+  }
+  return rbAry;
+#else
+  return Qnil;
+#endif
+}
+
 /* call-seq:
  *    client.affected_rows
  *
@@ -1441,6 +1482,7 @@ void init_mysql2_client() {
   rb_define_method(cMysql2Client, "query_info_string", rb_mysql_info, 0);
   rb_define_method(cMysql2Client, "ssl_cipher", rb_mysql_get_ssl_cipher, 0);
   rb_define_method(cMysql2Client, "encoding", rb_mysql_client_encoding, 0);
+  rb_define_method(cMysql2Client, "session_track", rb_mysql_client_session_track, 1);
 
   rb_define_private_method(cMysql2Client, "connect_timeout=", set_connect_timeout, 1);
   rb_define_private_method(cMysql2Client, "read_timeout=", set_read_timeout, 1);
@@ -1613,6 +1655,17 @@ void init_mysql2_client() {
       INT2NUM(0));
 #endif
 
+#ifdef CLIENT_SESSION_TRACK
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK"), INT2NUM(CLIENT_SESSION_TRACK));
+  /* From mysql_com.h -- but stable from at least 5.7.4 through 8.0.20 */
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_SYSTEM_VARIABLES"), INT2NUM(SESSION_TRACK_SYSTEM_VARIABLES));
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_SCHEMA"), INT2NUM(SESSION_TRACK_SCHEMA));
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_STATE_CHANGE"), INT2NUM(SESSION_TRACK_STATE_CHANGE));
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_GTIDS"), INT2NUM(SESSION_TRACK_GTIDS));
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_TRANSACTION_CHARACTERISTICS"), INT2NUM(SESSION_TRACK_TRANSACTION_CHARACTERISTICS));
+  rb_const_set(cMysql2Client, rb_intern("SESSION_TRACK_TRANSACTION_STATE"), INT2NUM(SESSION_TRACK_TRANSACTION_STATE));
+#endif
+
 #if defined(FULL_SSL_MODE_SUPPORT) // MySQL 5.7.11 and above
   rb_const_set(cMysql2Client, rb_intern("SSL_MODE_DISABLED"), INT2NUM(SSL_MODE_DISABLED));
   rb_const_set(cMysql2Client, rb_intern("SSL_MODE_PREFERRED"), INT2NUM(SSL_MODE_PREFERRED));

spec/mysql2/client_spec.rb

@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-RSpec.describe Mysql2::Client do
+RSpec.describe Mysql2::Client do # rubocop:disable Metrics/BlockLength
   context "using defaults file" do
     let(:cnf_file) { File.expand_path('../../my.cnf', __FILE__) }
 
@@ -1026,6 +1026,49 @@ def run_gc
     expect(@client).to respond_to(:ping)
   end
 
+  context "session_track" do
+    before(:each) do
+      unless Mysql2::Client.const_defined?(:SESSION_TRACK)
+        skip('Server versions must be MySQL 5.7 later.')
+      end
+      @client.query("SET @@SESSION.session_track_system_variables='*';")
+    end
+
+    it "returns changes system variables for SESSION_TRACK_SYSTEM_VARIABLES" do
+      @client.query("SET @@SESSION.session_track_state_change=ON;")
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_SYSTEM_VARIABLES)
+      expect(res).to eq(%w[session_track_state_change ON])
+    end
+
+    it "returns database name for SESSION_TRACK_SCHEMA" do
+      @client.query("USE information_schema")
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_SCHEMA)
+      expect(res).to eq(["information_schema"])
+    end
+
+    it "returns multiple session track type values when available" do
+      @client.query("SET @@SESSION.session_track_transaction_info='CHARACTERISTICS'")
+
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_TRANSACTION_STATE)
+      expect(res).to eq(["________"])
+
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_TRANSACTION_CHARACTERISTICS)
+      expect(res).to eq([""])
+
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_STATE_CHANGE)
+      expect(res).to be_nil
+
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_SYSTEM_VARIABLES)
+      expect(res).to eq(%w[session_track_transaction_info CHARACTERISTICS])
+    end
+
+    it "returns empty array if session track type not found" do
+      @client.query("SET @@SESSION.session_track_state_change=ON;")
+      res = @client.session_track(Mysql2::Client::SESSION_TRACK_TRANSACTION_CHARACTERISTICS)
+      expect(res).to be_nil
+    end
+  end
+
   context "select_db" do
     before(:each) do
       2.times do |i|