require 'eventmachine'
require 'oj'
require 'faye/websocket'
+require 'record_filters'
+require 'load_param'
+# Patch in user, last_log_id and filters fields into the Faye::Websocket class.
+module Faye
+ class WebSocket
+ attr_accessor :user
+ attr_accessor :last_log_id
+ attr_accessor :filters
+ end
+end
+
+# Store the filters supplied by the user that will be applied to the logs table
+# to determine which events to return to the listener.
+class Filter
+ include LoadParam
+
+ attr_accessor :filters
+
+ def initialize p
+ @params = p
+ load_filters_param
+ end
+
+ def params
+ @params
+ end
+end
+
+# Manages websocket connections, accepts subscription messages and publishes
+# log table events.
class EventBus
+ include CurrentApiClient
+ include RecordFilters
+
+ # used in RecordFilters
+ def model_class
+ Log
+ end
+
+ # Initialize EventBus. Takes no parameters.
def initialize
@channel = EventMachine::Channel.new
- @bgthread = nil
+ @mtx = Mutex.new
+ @bgthread = false
end
- def on_connect ws
- sub = @channel.subscribe do |msg|
- puts "sending #{msg}"
- ws.send({:message => "log"}.to_json)
- end
+ # Push out any pending events to the connection +ws+
+ # +id+ the id of the most recent row in the log table, may be nil
+ def push_events ws, id = nil
+ begin
+ # Must have at least one filter set up to receive events
+ if ws.filters.length > 0
+ # Start with log rows readable by user, sorted in ascending order
+ logs = Log.readable_by(ws.user).order("id asc")
+
+ if ws.last_log_id
+ # Client is only interested in log rows that are newer than the
+ # last log row seen by the client.
+ logs = logs.where("logs.id > ?", ws.last_log_id)
+ elsif id
+ # No last log id, so only look at the most recently changed row
+ logs = logs.where("logs.id = ?", id.to_i)
+ else
+ return
+ end
- ws.on :message do |event|
- puts "got #{event.data}"
- ws.send(event.data)
+ # Now process filters provided by client
+ cond_out = []
+ param_out = []
+ ws.filters.each do |filter|
+ ft = record_filters filter.filters, Log
+ cond_out += ft[:cond_out]
+ param_out += ft[:param_out]
+ end
+
+ # Add filters to query
+ if cond_out.any?
+ logs = logs.where(cond_out.join(' OR '), *param_out)
+ end
+
+ # Finally execute query and actually send the matching log rows
+ logs.each do |l|
+ ws.send(l.as_api_response.to_json)
+ ws.last_log_id = l.id
+ end
+ elsif id
+ # No filters set up, so just record the sequence number
+ ws.last_log_id = id.to_i
+ end
+ rescue Exception => e
+ puts "Error publishing event: #{$!}"
+ puts "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
+ ws.send ({status: 500, message: 'error'}.to_json)
+ ws.close
end
+ end
+
+ # Handle inbound subscribe or unsubscribe message.
+ def handle_message ws, event
+ begin
+ # Parse event data as JSON
+ p = (Oj.load event.data).symbolize_keys
+
+ if p[:method] == 'subscribe'
+ # Handle subscribe event
+
+ if p[:last_log_id]
+ # Set or reset the last_log_id. The event bus only reports events
+ # for rows that come after last_log_id.
+ ws.last_log_id = p[:last_log_id].to_i
+ end
- ws.on :close do |event|
- p [:close, event.code, event.reason]
- @channel.unsubscribe sub
- ws = nil
+ if ws.filters.length < MAX_FILTERS
+ # Add a filter. This gets the :filters field which is the same
+ # format as used for regular index queries.
+ ws.filters << Filter.new(p)
+ ws.send ({status: 200, message: 'subscribe ok'}.to_json)
+
+ # Send any pending events
+ push_events ws
+ else
+ ws.send ({status: 403, message: "maximum of #{MAX_FILTERS} filters allowed per connection"}.to_json)
+ end
+
+ elsif p[:method] == 'unsubscribe'
+ # Handle unsubscribe event
+
+ len = ws.filters.length
+ ws.filters.select! { |f| not ((f.filters == p[:filters]) or (f.filters.empty? and p[:filters].nil?)) }
+ if ws.filters.length < len
+ ws.send ({status: 200, message: 'unsubscribe ok'}.to_json)
+ else
+ ws.send ({status: 404, message: 'filter not found'}.to_json)
+ end
+
+ else
+ ws.send ({status: 400, message: "missing or unrecognized method"}.to_json)
end
+ rescue Oj::Error => e
+ ws.send ({status: 400, message: "malformed request"}.to_json)
+ rescue Exception => e
+ puts "Error handling message: #{$!}"
+ puts "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
+ ws.send ({status: 500, message: 'error'}.to_json)
+ ws.close
+ end
+ end
+
+ # Constant maximum number of filters, to avoid silly huge database queries.
+ MAX_FILTERS = 16
+
+ # Called by RackSocket when a new websocket connection has been established.
+ def on_connect ws
+
+ # Disconnect if no valid API token.
+ # current_user is included from CurrentApiClient
+ if not current_user
+ ws.send ({status: 401, message: "Valid API token required"}.to_json)
+ ws.close
+ return
+ end
+
+ # Initialize our custom fields on the websocket connection object.
+ ws.user = current_user
+ ws.filters = []
+ ws.last_log_id = nil
+
+ # Subscribe to internal postgres notifications through @channel. This will
+ # call push_events when a notification comes through.
+ sub = @channel.subscribe do |msg|
+ push_events ws, msg
+ end
+
+ # Set up callback for inbound message dispatch.
+ ws.on :message do |event|
+ handle_message ws, event
+ end
+
+ # Set up socket close callback
+ ws.on :close do |event|
+ @channel.unsubscribe sub
+ ws = nil
+ end
+ # Start up thread to monitor the Postgres database, if none exists already.
+ @mtx.synchronize do
unless @bgthread
@bgthread = true
Thread.new do
begin
conn.async_exec "LISTEN logs"
while true
+ # wait_for_notify will block until there is a change
+ # notification from Postgres about the logs table, then push
+ # the notification into the EventMachine channel. Each
+ # websocket connection subscribes to the other end of the
+ # channel and calls #push_events to actually dispatch the
+ # events to the client.
conn.wait_for_notify do |channel, pid, payload|
- puts "Received a NOTIFY on channel #{channel}"
- puts "from PG backend #{pid}"
- puts "saying #{payload}"
- @channel.push true
+ @channel.push payload
end
end
ensure
conn.async_exec "UNLISTEN *"
end
end
+ @bgthread = false
end
end
+ end
+ # Since EventMachine is an asynchronous event based dispatcher, #on_connect
+ # does not block but instead returns immediately after having set up the
+ # websocket and notification channel callbacks.
end
end
projects / arvados.git / blobdiff