Rewrite constraints docs to be more helpful

juju/charm/tests/test_bundle.py

 import os
 import hashlib
 import inspect
 import shutil
+import stat
 import yaml
 import zipfile
 
 from juju.lib.testing import TestCase
 from juju.lib.filehash import compute_file_hash
 from juju.charm.metadata import MetaData
 from juju.charm.bundle import CharmBundle
 from juju.errors import CharmError
 from juju.charm.directory import CharmDirectory
 from juju.charm.provider import get_charm_from_path
@@ skipping 173 matching lines @@
 
         # Verify we can extract it over again
         os.remove(sym_path)
         os.symlink('./config.yaml', sym_path)
         charm_dir = CharmDirectory(charm_path)
         bundle = charm_dir.as_bundle()
         bundle.extract_to(extract_dir)
         self.assertEqual(os.readlink(os.path.join(extract_dir, 'foobar')),
                         './config.yaml')
 
+    def test_extract_symlink_mode(self):
+        # lp:973260 - charms packed by different tools that record symlink
+        # mode permissions differently (ie the charm store) don't extract
+        # correctly.
+        charm_path = self.copy_charm()
+        sym_path = os.path.join(charm_path, 'foobar')
+        os.symlink('metadata.yaml', sym_path)
+        charm_dir = CharmDirectory(charm_path)
+        normal_path = charm_dir.as_bundle().path
+        zf_src = zipfile.ZipFile(normal_path, "r")
+        foreign_path = os.path.join(self.makeDir(), "store.charm")
+        zf_dst = zipfile.ZipFile(foreign_path, "w")
+        for info in zf_src.infolist():
+            if info.filename == "foobar":
+                # This is what the charm store does:
+                info.external_attr = (stat.S_IFLNK | 0777) << 16
+            zf_dst.writestr(info, zf_src.read(info.filename))
+        zf_src.close()
+        zf_dst.close()
+
+        bundle = CharmBundle(foreign_path)
+        extract_dir = self.makeDir()
+        bundle.extract_to(extract_dir)
+        self.assertIn("foobar", os.listdir(extract_dir))
+        self.assertTrue(os.path.islink(os.path.join(extract_dir, "foobar")))
+        self.assertEqual(os.readlink(os.path.join(extract_dir, 'foobar')),
+                        'metadata.yaml')
+
     def test_as_directory(self):
         filename = self.makeFile()
         charm = get_charm_from_path(self.filename)
         f2 = charm.as_directory()
 
         # f2 should be a charm directory
         self.assertInstance(f2, CharmDirectory)
         self.assertInstance(f2.get_sha256(), basestring)
         # verify that it was extracted to a new temp dirname
         self.assertNotEqual(f2.path, filename)
 
         fn = os.path.split(f2.path)[1]
         # verify that it used the expected prefix
         self.assertStartsWith(fn, "tmp")