Raise exception if show-build-log doesn't find the build log

Previously it would print nothing and then exit with success. Better
to tell the user that an error occurred.

Example of the new error:

    ERROR: No build log for artifact
    6fb39673b8f9a1c9848063f5132aa958ffa75f2be61a8dde68ebb11f5a3c4a5f found
    on cache server http://cache.baserock.org:8080/

Change-Id: Icf8ceef60eb497ff90e00391d442a394e3d76f10

1 files changed, 14 insertions, 5 deletions

diff --git a/morphlib/plugins/show_build_log_plugin.py b/morphlib/plugins/show_build_log_plugin.py
index 6f22036a..38b62540 100644
--- a/morphlib/plugins/show_build_log_plugin.py
+++ b/morphlib/plugins/show_build_log_plugin.py
@@ -86,11 +86,20 @@ class ShowBuildLog(cliapp.Plugin):
         if cache_key:
             url = urlparse.urljoin(artifact_cache_server,
                 '/1.0/artifacts?filename=%s.build-log' % source.cache_key)
-            build_log = urllib.urlopen(url)
-            build_output = []
-            for line in build_log:
-                build_output.append(str(line))
-            self.app.output.write(''.join(build_output))
+            response = urllib.urlopen(url)
+            if response.getcode() == 200:
+                build_output = []
+                for line in response:
+                    build_output.append(str(line))
+                self.app.output.write(''.join(build_output))
+            elif response.getcode() == 404:
+                raise cliapp.AppException(
+                    'No build log for artifact %s found on cache server %s' %
+                    (source.cache_key, artifact_cache_server))
+            else:
+                raise cliapp.AppException(
+                    'Error connecting to cache server %s: %s' %
+                    (artifact_cache_server, response.getcode()))
         else:
             raise cliapp.AppException('Component not found in the given '
                                       'system.')