Class: EventMachine::Protocols::Postgres3
- Inherits:
-
Connection
- Object
- Connection
- EventMachine::Protocols::Postgres3
- Includes:
- PostgresPR
- Defined in:
- lib/em/protocols/postgres3.rb
Overview
PROVISIONAL IMPLEMENTATION of an evented Postgres client. This implements version 3 of the Postgres wire protocol, which will work with any Postgres version from roughly 7.4 onward.
Objective: we want to access Postgres databases without requiring threads. Until now this has been a problem because the Postgres client implementations have all made use of blocking I/O calls, which is incompatible with a thread-free evented model.
But rather than re-implement the Postgres Wire3 protocol, we’re taking advantage of the existing postgres-pr library, which was originally written by Michael Neumann but (at this writing) appears to be no longer maintained. Still, it’s in basically a production-ready state, and the wire protocol isn’t that complicated anyway.
We need to monkeypatch StringIO because it lacks the #readbytes method needed by postgres-pr.
We’re tucking in a bunch of require statements that may not be present in garden-variety EM installations. Until we find a good way to only require these if a program requires postgres, this file will need to be required explicitly.
The StringIO monkeypatch is lifted verbatim from the standard library readbytes.rb, which adds method #readbytes directly to class IO. But StringIO is not a subclass of IO.
We cloned the handling of postgres messages from lib/postgres-pr/connection.rb in the postgres-pr library, and modified it for event-handling.
TODO: The password handling in dispatch_conn_message is totally incomplete.
We return Deferrables from the user-level operations surfaced by this interface. Experimentally, we’re using the pattern of always returning a boolean value as the first argument of a deferrable callback to indicate success or failure. This is instead of the traditional pattern of calling Deferrable#succeed or #fail, and requiring the user to define both a callback and an errback function.
Usage
EM.run {
db = EM.connect_unix_domain( "/tmp/.s.PGSQL.5432", EM::P::Postgres3 )
db.connect( dbname, username, psw ).callback do |status|
if status
db.query( "select * from some_table" ).callback do |status, result, errors|
if status
result.rows.each do |row|
p row
end
end
end
end
end
}
Instance Attribute Summary
Attributes inherited from Connection
Instance Method Summary collapse
- #connect(db, user, psw = nil) ⇒ Object
-
#dispatch_conn_message(msg) ⇒ Object
Cloned and modified from the postgres-pr.
-
#dispatch_query_message(msg) ⇒ Object
Cloned and modified from the postgres-pr.
-
#initialize ⇒ Postgres3
constructor
A new instance of Postgres3.
- #query(sql) ⇒ Object
- #receive_data(data) ⇒ Object
- #unbind ⇒ Object
Methods inherited from Connection
#associate_callback_target, #close_connection, #close_connection_after_writing, #comm_inactivity_timeout, #comm_inactivity_timeout=, #connection_completed, #detach, #error?, #get_outbound_data_size, #get_peer_cert, #get_peername, #get_pid, #get_sock_opt, #get_sockname, #get_status, new, #notify_readable=, #notify_readable?, #notify_writable=, #notify_writable?, #pause, #paused?, #pending_connect_timeout, #pending_connect_timeout=, #post_init, #proxy_incoming_to, #proxy_target_unbound, #reconnect, #resume, #send_data, #send_datagram, #send_file_data, #set_comm_inactivity_timeout, #set_pending_connect_timeout, #ssl_handshake_completed, #ssl_verify_peer, #start_tls, #stop_proxying, #stream_file_data
Constructor Details
#initialize ⇒ Postgres3
Returns a new instance of Postgres3.
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# File 'lib/em/protocols/postgres3.rb', line 110 def initialize @data = "" @params = {} end |
Instance Method Details
#connect(db, user, psw = nil) ⇒ Object
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# File 'lib/em/protocols/postgres3.rb', line 115 def connect db, user, psw=nil d = EM::DefaultDeferrable.new d.timeout 15 if @pending_query || @pending_conn d.succeed false, "Operation already in progress" else @pending_conn = d prms = {"user"=>user, "database"=>db} @user = user if psw @password = psw #prms["password"] = psw end send_data PostgresPR::StartupMessage.new( 3 << 16, prms ).dump end d end |
#dispatch_conn_message(msg) ⇒ Object
Cloned and modified from the postgres-pr.
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# File 'lib/em/protocols/postgres3.rb', line 180 def msg case msg when AuthentificationClearTextPassword raise ArgumentError, "no password specified" if @password.nil? send_data PasswordMessage.new(@password).dump when AuthentificationCryptPassword raise ArgumentError, "no password specified" if @password.nil? send_data PasswordMessage.new(@password.crypt(msg.salt)).dump when AuthentificationMD5Password raise ArgumentError, "no password specified" if @password.nil? require 'digest/md5' m = Digest::MD5.hexdigest(@password + @user) m = Digest::MD5.hexdigest(m + msg.salt) m = 'md5' + m send_data PasswordMessage.new(m).dump when AuthentificationKerberosV4, AuthentificationKerberosV5, AuthentificationSCMCredential raise "unsupported authentification" when AuthentificationOk when ErrorResponse raise msg.field_values.join("\t") when NoticeResponse @notice_processor.call(msg) if @notice_processor when ParameterStatus @params[msg.key] = msg.value when BackendKeyData # TODO #p msg when ReadyForQuery # TODO: use transaction status pc,@pending_conn = @pending_conn,nil pc.succeed true else raise "unhandled message type" end end |
#dispatch_query_message(msg) ⇒ Object
Cloned and modified from the postgres-pr.
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# File 'lib/em/protocols/postgres3.rb', line 222 def msg case msg when DataRow @r.rows << msg.columns when CommandComplete @r.cmd_tag = msg.cmd_tag when ReadyForQuery pq,@pending_query = @pending_query,nil pq.succeed true, @r, @e when RowDescription @r.fields = msg.fields when CopyInResponse when CopyOutResponse when EmptyQueryResponse when ErrorResponse # TODO @e << msg when NoticeResponse @notice_processor.call(msg) if @notice_processor else # TODO end end |
#query(sql) ⇒ Object
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# File 'lib/em/protocols/postgres3.rb', line 135 def query sql d = EM::DefaultDeferrable.new d.timeout 15 if @pending_query || @pending_conn d.succeed false, "Operation already in progress" else @r = PostgresPR::Connection::Result.new @e = [] @pending_query = d send_data PostgresPR::Query.dump(sql) end d end |
#receive_data(data) ⇒ Object
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# File 'lib/em/protocols/postgres3.rb', line 152 def receive_data data @data << data while @data.length >= 5 pktlen = @data[1...5].unpack("N").first if @data.length >= (1 + pktlen) pkt = @data.slice!(0...(1+pktlen)) m = StringIO.open( pkt, "r" ) {|io| PostgresPR::Message.read( io ) } if @pending_conn m elsif @pending_query m else raise "Unexpected message from database" end else break # very important, break out of the while end end end |
#unbind ⇒ Object
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# File 'lib/em/protocols/postgres3.rb', line 173 def unbind if o = (@pending_query || @pending_conn) o.succeed false, "lost connection" end end |