swift result download: Correctly handle "204 No content" status

autopkgtest.py

@@ -269,6 +269,8 @@ class AutoPackageTest(object):
             f = urlopen(url)
             if f.getcode() == 200:
                 result_paths = f.read().strip().splitlines()
+            elif f.getcode() == 204:  # No content
+                result_paths = []
             else:
                 self.log_error('Failure to fetch swift results from %s: %u' %
                                (url, f.getcode()))

tests/mock_swift.py

@@ -85,7 +85,7 @@ class SwiftHTTPRequestHandler(BaseHTTPRequestHandler):
             find_adapter = lambda i: (i >= 0) and (i + 1) or None
             objs = set([o[:find_adapter(o.find(d))] for o in objs])
 
-        self.send_response(200)
+        self.send_response(objs and 200 or 204)  # 204: "No Content"
         self.send_header('Content-type', 'text/plain')
         self.end_headers()
         self.wfile.write(('\n'.join(sorted(objs)) + '\n').encode('UTF-8'))

tests/test_autopkgtest.py

@@ -247,7 +247,7 @@ lightgreen 1 i386 green 2
             'series/amd64/g/green/20150101_100201@': (4, 'green 2'),
         }})
 
-        self.do_test(
+        out = self.do_test(
             [],
             # FIXME: while we only submit requests through AMQP, but don't consider
             # their results, we don't expect this to hold back stuff.
@@ -257,6 +257,9 @@ lightgreen 1 i386 green 2
              r'autopkgtest for lightgreen 1: .*amd64.*Regression.*i386.*in progress',
              r'autopkgtest for darkgreen 1: .*amd64.*in progress.*i386.*Pass'])
 
+        # not expecting any failures to retrieve from swift
+        self.assertNotIn('Failure', out, out)
+
         # there should be some pending ones
         self.assertIn('darkgreen 1 amd64 green 2', self.pending_requests)
         self.assertIn('lightgreen 1 i386 green 2', self.pending_requests)