X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/4eb42fd91dc5e50840e0d3db5d5201561602a508..88c382d13b3d6e6f3b03ba0d5139ad9552c3c359:/services/api/lib/eventbus.rb

diff --git a/services/api/lib/eventbus.rb b/services/api/lib/eventbus.rb
index ac023e5c03..ac53876122 100644
--- a/services/api/lib/eventbus.rb
+++ b/services/api/lib/eventbus.rb
@@ -1,9 +1,14 @@
+# If any threads raise an unhandled exception, make them all die.
+# We trust a supervisor like runit to restart the server in this case.
+Thread.abort_on_exception = true
+
 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
@@ -12,26 +17,25 @@ module Faye
   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
@@ -41,134 +45,210 @@ class EventBus
     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
+  # Push out any pending events to the connection +ws+
+  # +notify_id+  the id of the most recent row in the log table, may be nil
+  #
+  # This accepts a websocket and a notify_id (this is the row id from Postgres
+  # LISTEN/NOTIFY, it may be nil if called from somewhere else)
+  #
+  # It queries the database for log rows that are either
+  #  a) greater than ws.last_log_id, which is the last log id which was a candidate to be sent out
+  #  b) if ws.last_log_id is nil, then it queries rows starting with notify_id
+  #
+  # Regular Arvados permissions are applied using readable_by() and filters using record_filters()
+  # To avoid clogging up the database, queries are limited to batches of 100.  It will schedule a new
+  # push_events call if there are more log rows to send.
+  def push_events ws, notify_id
+    begin
+      if !notify_id.nil? and !ws.last_log_id.nil? and notify_id <= ws.last_log_id
+        # This notify is for a row we've handled already.
+        return
+      end
 
-  def push_events ws, msg = 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
-            # Only interested in log rows that are new
-            logs = logs.where("logs.id > ?", ws.last_log_id)
-          elsif msg
-            # No last log id, so only look at the most recently changed row
-            logs = logs.where("logs.id = ?", msg.to_i)
-          else
-            return
-          end
+      # 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")
 
-          # 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]
+        cond_id = nil
+        cond_out = []
+        param_out = []
+
+        if !ws.last_log_id.nil?
+          # 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 !notify_id.nil?
+          # No last log id, so look at rows starting with notify id
+          cond_id = "logs.id >= ?"
+          param_out << notify_id
+        else
+          # No log id to start from, nothing to do, return
+          return
+        end
+
+        # Now build filters provided by client
+        ws.filters.each do |filter|
+          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)
-          end
+        # Add filters to query
+        if cond_out.any?
+          # 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
+
+        # Execute query and actually send the matching log rows
+        count = 0
+        limit = 10
 
-          # Finally execute query and send matching rows
-          logs.each do |l|
-            ws.send(l.as_api_response.to_json)
-            ws.last_log_id = l.id
+        logs.limit(limit).each do |l|
+          ws.send(l.as_api_response.to_json)
+          ws.last_log_id = l.id
+          count += 1
+        end
+
+        if count == limit
+          # Number of rows returned was capped by limit(), we need to schedule
+          # another query to get more logs (will start from last_log_id
+          # reported by current query)
+          EventMachine::next_tick do
+            push_events ws, nil
           end
-        elsif msg
-          # No filters set up, so just record the sequence number
-          ws.last_log_id = msg.to_i
+        elsif !notify_id.nil? and (ws.last_log_id.nil? or notify_id > ws.last_log_id)
+          # Number of rows returned was less than cap, but the notify id is
+          # higher than the last id visible to the client, so update last_log_id
+          ws.last_log_id = notify_id
+        end
+      elsif !notify_id.nil?
+        # No filters set up, so just record the sequence number
+        ws.last_log_id = notify_id
+      end
+    rescue ArgumentError => e
+      # There was some kind of user error.
+      Rails.logger.warn "Error publishing event: #{$!}"
+      ws.send ({status: 500, message: $!}.to_json)
+      ws.close
+    rescue => e
+      Rails.logger.warn "Error publishing event: #{$!}"
+      Rails.logger.warn "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
+      ws.send ({status: 500, message: $!}.to_json)
+      ws.close
+      # These exceptions typically indicate serious server trouble:
+      # out of memory issues, database connection problems, etc.  Go ahead and
+      # crash; we expect that a supervisor service like runit will restart us.
+      raise
+    end
+  end
+
+  # Handle inbound subscribe or unsubscribe message.
+  def handle_message ws, event
+    begin
+      begin
+        # Parse event data as JSON
+        p = (Oj.load event.data).symbolize_keys
+        filter = Filter.new(p)
+      rescue Oj::Error => e
+        ws.send ({status: 400, message: "malformed request"}.to_json)
+        return
+      end
+
+      if p[:method] == 'subscribe'
+        # Handle subscribe event
+
+        if p[:last_log_id]
+          # Set or reset the last_log_id.  The event bus only reports events
+          # for rows that come after last_log_id.
+          ws.last_log_id = p[:last_log_id].to_i
         end
-      rescue Exception => e
-        puts "Error publishing event: #{$!}"
-        puts "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
-        ws.send ({status: 500, message: 'error'}.to_json)
-        ws.close
+
+        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
+          ws.send ({status: 200, message: 'subscribe ok', filter: p}.to_json)
+
+          # Send any pending events
+          push_events ws, nil
+        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 => 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
@@ -179,8 +259,14 @@ class EventBus
             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
+                  @channel.push payload.to_i
                 end
               end
             ensure
@@ -190,8 +276,13 @@ class EventBus
               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