errors: Improve tests, unify interfaces, wrapping

worker/uniter/charm/bundles.go

 // Copyright 2012-2014 Canonical Ltd.
 // Licensed under the AGPLv3, see LICENCE file for details.
 
 package charm
 
 import (
         "fmt"
         "os"
         "path"
 
@@ skipping 30 matching lines @@
 }
 
 // download fetches the supplied charm and checks that it has the correct sha256
 // hash, then copies it into the directory. If a value is received on abort, the
 // download will be stopped.
 func (d *BundlesDir) download(info BundleInfo, abort <-chan struct{}) (err error) {
         archiveURL, disableSSLHostnameVerification, err := info.ArchiveURL()
         if err != nil {
                 return err
         }
-        defer errors.Contextf(&err, "failed to download charm %q from %q", info.URL(), archiveURL)
+        defer errors.Maskf(&err, "failed to download charm %q from %q", info.URL(), archiveURL)
         dir := d.downloadsPath()
         if err := os.MkdirAll(dir, 0755); err != nil {
                 return err
         }
         aurl := archiveURL.String()
         logger.Infof("downloading %s from %s", info.URL(), aurl)
         if disableSSLHostnameVerification {
                 logger.Infof("SSL hostname verification disabled")
         }
         dl := downloader.New(aurl, dir, disableSSLHostnameVerification)
@@ skipping 41 matching lines @@
 // bundle identified by url will be, or has been, saved.
 func (d *BundlesDir) bundleURLPath(url *charm.URL) string {
         return path.Join(d.path, charm.Quote(url.String()))
 }
 
 // downloadsPath returns the path to the directory into which charms are
 // downloaded.
 func (d *BundlesDir) downloadsPath() string {
         return path.Join(d.path, "downloads")
 }