in log_tail_follow, emit recent messages at top of live stream. fixes #1590

diff --git a/services/api/app/controllers/arvados/v1/jobs_controller.rb b/services/api/app/controllers/arvados/v1/jobs_controller.rb
index b51115e103444185fa947301b35521e4679b076f..41cbfd4b0eedce85f749d9a349a5e854907f341f 100644 (file)
--- a/services/api/app/controllers/arvados/v1/jobs_controller.rb
+++ b/services/api/app/controllers/arvados/v1/jobs_controller.rb
@@ -42,8 +42,9 @@ class Arvados::V1::JobsController < ApplicationController
 
   class LogStreamer
     Q_UPDATE_INTERVAL = 12
-    def initialize(job)
+    def initialize(job, opts={})
       @job = job
+      @opts = opts
     end
     def each
       if @job.finished_at
@@ -81,6 +82,19 @@ class Arvados::V1::JobsController < ApplicationController
       end
       @redis = Redis.new(:timeout => 0)
       @redis.subscribe(@job.uuid) do |event|
+        if @redis.exists @job.uuid
+          # A log buffer exists. Start by showing the last few KB.
+          @redis.
+            getrange(@job.uuid, 0 - [@opts[:buffer_size], 1].max, -1).
+            sub(/^[^\n]*\n?/, '').
+            split("\n").
+            each do |line|
+            yield "#{line}\n"
+          end
+        end
+        # TODO: avoid duplicating the last few lines of the log
+        # file. Use the fact that timestamps are lexicographically
+        # ordered.
         event.message do |channel, msg|
           if msg == "end"
             @redis.unsubscribe @job.uuid
@@ -92,12 +106,19 @@ class Arvados::V1::JobsController < ApplicationController
     end
   end
 
+  def self._log_tail_follow_requires_parameters
+    {
+      buffer_size: {type: 'integer', required: false}
+    }
+  end
   def log_tail_follow
     if !@object.andand.uuid
       return render_not_found
     end
     self.response.headers['Last-Modified'] = Time.now.ctime.to_s
-    self.response_body = LogStreamer.new @object
+    self.response_body = LogStreamer.new @object, {
+      buffer_size: (params[:buffer_size] || 2**13)
+    }
   end
 
   def queue