cmd/jujud: upgrader skips unnecessary downloads

cmd/jujud/upgrade.go

 package main
 
 import (
         "fmt"
         "launchpad.net/juju-core/downloader"
         "launchpad.net/juju-core/environs"
         "launchpad.net/juju-core/environs/agent"
         "launchpad.net/juju-core/log"
         "launchpad.net/juju-core/state"
         "launchpad.net/juju-core/state/watcher"
@@ skipping 157 matching lines @@
                                 download, downloadTools, downloadDone = nil, nil, nil
                         }
                         // Ignore the proposed tools if we're already running the
                         // proposed version.
                         if vers == version.Current.Number {
                                 noDelay()
                                 break
                         }
                         binary := version.Current
                         binary.Number = vers
-
                         if tools, err := agent.ReadTools(u.dataDir, binary); err == nil {
-                                // The tools have already been downloaded, so use them.
+                                // The exact tools have already been downloaded, so use them.
                                 return u.upgradeReady(currentTools, tools)
                         }
+
+                        // Try to find the proposed tools in the environment, and fall back
+                        // to the most recent version no later than the proposed.
                         flags := environs.CompatVersion
                         if cfg.Development() {
                                 flags |= environs.DevVersion
                         }
                         tools, err := environs.FindTools(environ, binary, flags)
                         if err != nil {
                                 log.Errorf("cmd/jujud: upgrader error finding tools for %v: %v", binary, err)
                                 noDelay()
                                 // TODO(rog): poll until tools become available.
                                 break
                         }
                         if tools.Binary != binary {
                                 if tools.Number == version.Current.Number {
                                         // TODO(rog): poll until tools become available.
                                         log.Warningf("cmd/jujud: upgrader: version %v requested but found only current version: %v", binary, tools.Number)
                                         noDelay()
                                         break
                                 }
                                 log.Warningf("cmd/jujud: upgrader cannot find exact tools match for %s; using %s instead", binary, tools.Binary)
                         }
+                        if tools, err := agent.ReadTools(u.dataDir, tools.Binary); err == nil {
+                                // The best available tools have already been downloaded, so use them.
+                                return u.upgradeReady(currentTools, tools)
+                        }
+
                         log.Infof("cmd/jujud: upgrader downloading %q", tools.URL)
                         download = downloader.New(tools.URL, "")
                         downloadTools = tools
                         downloadDone = download.Done()
                 case status := <-downloadDone:
                         tools := downloadTools
                         download, downloadTools, downloadDone = nil, nil, nil
                         if status.Err != nil {
                                 log.Errorf("cmd/jujud: upgrader download of %v failed: %v", tools.Binary, status.Err)
                                 noDelay()
@@ skipping 37 matching lines @@
                 select {
                 case <-t.Dying():
                         time.Sleep(d)
                         delayed.Kill(nil)
                 case <-delayed.Dying():
                         return
                 }
         }()
         return &delayed
 }