Add initial logical replication handling

Author: jgaskins

spec/pg/replication_spec.cr

@@ -0,0 +1,110 @@
+require "../spec_helper"
+
+struct TestMessageHandler
+  include PG::Replication::Handler
+
+  def received(msg : PG::Replication::Begin)
+    pp begin: msg
+  end
+
+  def received(msg : PG::Replication::Message)
+    pp message: msg
+  end
+
+  def received(msg : PG::Replication::Commit)
+    pp commit: msg
+  end
+
+  def received(msg : PG::Replication::Origin)
+  end
+
+  def received(msg : PG::Replication::Relation)
+    pp relation: msg
+  end
+
+  def received(msg : PG::Replication::Type)
+  end
+
+  def received(msg : PG::Replication::Insert)
+    pp insert: msg
+  end
+
+  def received(msg : PG::Replication::Update)
+    pp update: msg
+  end
+
+  def received(msg : PG::Replication::Delete)
+    pp delete: msg
+  end
+
+  def received(msg : PG::Replication::Truncate)
+  end
+
+  def received(msg : PG::Replication::StreamStart)
+  end
+
+  def received(msg : PG::Replication::StreamStop)
+  end
+
+  def received(msg : PG::Replication::StreamCommit)
+  end
+
+  def received(msg : PG::Replication::StreamAbort)
+  end
+
+  def received(msg : PG::Replication::BeginPrepare)
+  end
+
+  def received(msg : PG::Replication::Prepare)
+  end
+
+  def received(msg : PG::Replication::CommitPrepared)
+  end
+
+  def received(msg : PG::Replication::RollbackPrepared)
+  end
+
+  def received(msg : PG::Replication::StreamPrepare)
+  end
+
+  def received(msg : PG::Replication::TupleData)
+  end
+end
+
+describe PG::Replication do
+  it "consumes the WAL" do
+    publication_name = "test_publication_#{Random::Secure.hex}"
+    slot_name = "test_slot_#{Random::Secure.hex}"
+    table_name = "test_table_#{Random::Secure.hex}"
+    handler = TestMessageHandler.new
+    PG_DB.exec "CREATE PUBLICATION #{publication_name} FOR ALL TABLES"
+    PG_DB.exec "SELECT pg_create_logical_replication_slot($1, 'pgoutput')", slot_name
+    subscriber = PG.connect_replication(DB_URL, handler: handler, publication_name: publication_name, slot_name: slot_name)
+    sleep 100.milliseconds
+    PG_DB.exec "DROP TABLE IF EXISTS #{table_name}"
+    PG_DB.exec <<-SQL
+      CREATE TABLE #{table_name}(
+        id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+        string TEXT,
+        number INT8
+      )
+      SQL
+    id = PG_DB.query_one <<-SQL, as: UUID
+      INSERT INTO #{table_name} (string, number)
+      VALUES ('foo', 1)
+      RETURNING id
+      SQL
+
+    PG_DB.exec "UPDATE #{table_name} SET string = 'bar' WHERE id = $1", id
+    PG_DB.exec "UPDATE #{table_name} SET number = 2 WHERE id = $1", id
+
+    sleep 100.milliseconds
+
+    pp handler
+  ensure
+    subscriber.try &.close
+    PG_DB.exec "SELECT pg_drop_replication_slot($1)", slot_name
+    PG_DB.exec "DROP PUBLICATION IF EXISTS #{publication_name}"
+    PG_DB.exec "DROP TABLE IF EXISTS #{table_name}"
+  end
+end

src/pg.cr

@@ -31,6 +31,10 @@ module PG
     ListenConnection.new(url, channels, blocking, &blk)
   end
 
+  def self.connect_replication(url, *, handler, publication_name, slot_name)
+    Replication::Connection.new(url, handler, publication_name: publication_name, slot_name: slot_name)
+  end
+
   class ListenConnection
     @conn : PG::Connection
 

src/pg/connection.cr

@@ -17,7 +17,7 @@ module PG
       super(options)
 
       begin
-        @connection.connect
+        @connection.connect(replication: @connection.conninfo.replication)
       rescue ex
         raise DB::ConnectionRefused.new(cause: ex)
       end
@@ -95,6 +95,14 @@ module PG
       end
     end
 
+    protected def listen_replication(publication_name : String, slot_name : String, blocking : Bool = false, &block : Replication::Frame ->)
+      if blocking
+        @connection.start_replication_frame_loop(publication_name, slot_name, &block)
+      else
+        spawn { @connection.start_replication_frame_loop(publication_name, slot_name, &block) }
+      end
+    end
+
     def version
       vers = connection.server_parameters["server_version"].partition(' ').first.split('.').map(&.to_i)
       {major: vers[0], minor: vers[1], patch: vers[2]? || 0}