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
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, fid
+ def initialize p
@params = p
- @filter_id = fid
load_filters_param
end
def params
@params
end
-
- def filter_id
- @filter_id
- end
end
+# Manages websocket connections, accepts subscription messages and publishes
+# log table events.
class EventBus
include CurrentApiClient
include RecordFilters
Log
end
- # used in RecordFilters
- def table_name
- model_class.table_name
- end
-
+ # Initialize EventBus. Takes no parameters.
def initialize
@channel = EventMachine::Channel.new
@mtx = Mutex.new
@bgthread = false
- @filter_id_counter = 0
- end
-
- def alloc_filter_id
- (@filter_id_counter += 1)
end
- def push_events ws, msg = nil
+ # 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")
+ cond_id = nil
+ cond_out = []
+ param_out = []
+
if ws.last_log_id
- # Only interested in log rows that are new
- logs = logs.where("logs.id > ?", ws.last_log_id)
- elsif msg
+ # Client is only interested in log rows that are newer than the
+ # last log row seen by the client.
+ cond_id = "logs.id > ?"
+ param_out << ws.last_log_id
+ elsif id
# No last log id, so only look at the most recently changed row
- logs = logs.where("logs.id = ?", msg.to_i)
+ cond_id = "logs.id = ?"
+ param_out << id.to_i
else
return
end
# Now process filters provided by client
- cond_out = []
- param_out = []
ws.filters.each do |filter|
- ft = record_filters filter.filters
- cond_out += ft[:cond_out]
- param_out += ft[:param_out]
+ ft = record_filters filter.filters, Log
+ if ft[:cond_out].any?
+ # Join the clauses within a single subscription filter with AND
+ # so it is consistent with regular queries
+ cond_out << "(#{ft[:cond_out].join ') AND ('})"
+ param_out += ft[:param_out]
+ end
end
# Add filters to query
if cond_out.any?
- logs = logs.where(cond_out.join(' OR '), *param_out)
+ # Join subscriptions with OR
+ logs = logs.where(cond_id + " AND ((#{cond_out.join ') OR ('}))", *param_out)
+ else
+ logs = logs.where(cond_id, *param_out)
end
- # Finally execute query and send matching rows
+ # 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 msg
+ elsif id
# No filters set up, so just record the sequence number
- ws.last_log_id = msg.to_i
+ ws.last_log_id = id.to_i
end
rescue Exception => e
- puts "Error publishing event: #{$!}"
- puts "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
+ Rails.logger.warn "Error publishing event: #{$!}"
+ Rails.logger.warn "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
+
+ 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
+ Rails.logger.warn "Error handling message: #{$!}"
+ Rails.logger.warn "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|
- begin
- p = (Oj.load event.data).symbolize_keys
- if p[:method] == 'subscribe'
- if p[:last_log_id]
- ws.last_log_id = p[:last_log_id].to_i
- end
-
- if ws.filters.length < MAX_FILTERS
- filter_id = alloc_filter_id
- ws.filters.push Filter.new(p, filter_id)
- ws.send ({status: 200, message: 'subscribe ok', filter_id: filter_id}.to_json)
- push_events ws
- else
- ws.send ({status: 403, message: "maximum of #{MAX_FILTERS} filters allowed per connection"}.to_json)
- end
- elsif p[:method] == 'unsubscribe'
- if filter_id = p[:filter_id]
- filter_id = filter_id.to_i
- len = ws.filters.length
- ws.filters = ws.filters.select { |f| f.filter_id != filter_id }
- if ws.filters.length < len
- ws.send ({status: 200, message: 'unsubscribe ok', filter_id: filter_id}.to_json)
- else
- ws.send ({status: 404, message: 'filter_id not found', filter_id: filter_id}.to_json)
- end
- else
- ws.send ({status: 400, message: 'must provide filter_id'}.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
+ 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
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|
@channel.push payload
end
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