Included Modules

EventMachine::Protocols::Postgres3

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the existing postgres-pr library, which was originally written by Michael Neumann but (at this writing) appears to be no longer maintained.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
}

Public Class Methods

new() click to toggle source
# File lib/em/protocols/postgres3.rb, line 110
def initialize
  @data = ""
  @params = {}
end

Public Instance Methods

connect(db, user, psw=nil) click to toggle source
# 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) click to toggle source

Cloned and modified from the postgres-pr.

# File lib/em/protocols/postgres3.rb, line 180
def dispatch_conn_message 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) click to toggle source

Cloned and modified from the postgres-pr.

# File lib/em/protocols/postgres3.rb, line 222
def dispatch_query_message 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) click to toggle source
# 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) click to toggle source
# 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
        dispatch_conn_message m
      elsif @pending_query
        dispatch_query_message m
      else
        raise "Unexpected message from database"
      end
    else
      break # very important, break out of the while
    end
  end
end
unbind() click to toggle source
# File lib/em/protocols/postgres3.rb, line 173
def unbind
  if o = (@pending_query || @pending_conn)
    o.succeed false, "lost connection"
  end
end

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