fix: populate etag / generation / metageneration properties during do…

…wnload (googleapis#488)

Populate properties during download functions via Blob._extract_headers_from_download.

Additionally, update documentation for running system tests to use Python 3.8 instead of Python 3.7 to align with nox.

Closes googleapis#490.

CONTRIBUTING.rst

@@ -133,13 +133,13 @@ Running System Tests
 
 - To run system tests, you can execute::
 
-   $ nox -s system-3.7
+   $ nox -s system-3.8
    $ nox -s system-2.7
 
   .. note::
 
       System tests are only configured to run under Python 2.7 and
-      Python 3.7. For expediency, we do not run them in older versions
+      Python 3.8. For expediency, we do not run them in older versions
       of Python 3.
 
   This alone will not run the tests. You'll need to change some local

google/cloud/storage/blob.py

@@ -858,6 +858,11 @@ def _extract_headers_from_download(self, response):
         self.cache_control = response.headers.get("Cache-Control", None)
         self.storage_class = response.headers.get("X-Goog-Storage-Class", None)
         self.content_language = response.headers.get("Content-Language", None)
+        self._properties["etag"] = response.headers.get("ETag", None)
+        self._properties["generation"] = response.headers.get("X-goog-generation", None)
+        self._properties["metageneration"] = response.headers.get(
+            "X-goog-metageneration", None
+        )
         #  'X-Goog-Hash': 'crc32c=4gcgLQ==,md5=CS9tHYTtyFntzj7B9nkkJQ==',
         x_goog_hash = response.headers.get("X-Goog-Hash", "")
 

tests/system/test_blob.py

@@ -173,26 +173,38 @@ def test_blob_crud_w_user_project(
     # Exercise 'objects.insert' w/ userProject.
     blob.upload_from_filename(info["path"])
     gen0 = blob.generation
+    etag0 = blob.etag
 
     # Upload a second generation of the blob
     blob.upload_from_string(gen1_payload)
     gen1 = blob.generation
+    etag1 = blob.etag
 
     blob0 = with_user_project.blob("SmallFile", generation=gen0)
     blob1 = with_user_project.blob("SmallFile", generation=gen1)
 
     # Exercise 'objects.get' w/ generation
-    assert with_user_project.get_blob(blob.name).generation == gen1
-    assert with_user_project.get_blob(blob.name, generation=gen0).generation == gen0
+    blob1 = with_user_project.get_blob(blob.name)
+    assert blob1.generation == gen1
+    assert blob1.etag == etag1
+    blob0 = with_user_project.get_blob(blob.name, generation=gen0)
+    assert blob0.generation == gen0
+    assert blob0.etag == etag0
 
     try:
         # Exercise 'objects.get' (metadata) w/ userProject.
         assert blob.exists()
         blob.reload()
 
         # Exercise 'objects.get' (media) w/ userProject.
+        blob0 = with_user_project.blob("SmallFile", generation=gen0)
+        blob1 = with_user_project.blob("SmallFile", generation=gen1)
+        assert blob0.etag is None
+        assert blob1.etag is None
         assert blob0.download_as_bytes() == gen0_payload
         assert blob1.download_as_bytes() == gen1_payload
+        assert blob0.etag == etag0
+        assert blob1.etag == etag1
 
         # Exercise 'objects.patch' w/ userProject.
         blob0.content_language = "en"
@@ -468,10 +480,14 @@ def test_blob_download_as_text(
     blob = shared_bucket.blob("MyBuffer")
     payload = "Hello World"
     blob.upload_from_string(payload)
+    etag = blob.etag
     blobs_to_delete.append(blob)
 
+    blob = shared_bucket.blob("MyBuffer")
+    assert blob.etag is None
     stored_contents = blob.download_as_text()
     assert stored_contents == payload
+    assert blob.etag == etag
 
 
 def test_blob_upload_w_gzip_encoded_download_raw(

tests/unit/test_blob.py

@@ -1035,8 +1035,11 @@ def test__extract_headers_from_download_gzipped(self):
                 "Content-Language": "ko-kr",
                 "Cache-Control": "max-age=1337;public",
                 "Content-Encoding": "gzip",
+                "Etag": "kittens",
                 "X-Goog-Storage-Class": "STANDARD",
                 "X-Goog-Hash": "crc32c=4gcgLQ==,md5=CS9tHYTtyFntzj7B9nkkJQ==",
+                "X-goog-generation": 42,
+                "X-goog-metageneration": 4,
             },
             # { "x": 5 } gzipped
             content=b"\x1f\x8b\x08\x00\xcfo\x17_\x02\xff\xabVP\xaaP\xb2R0U\xa8\x05\x00\xa1\xcaQ\x93\n\x00\x00\x00",
@@ -1050,6 +1053,9 @@ def test__extract_headers_from_download_gzipped(self):
         self.assertEqual(blob.storage_class, "STANDARD")
         self.assertEqual(blob.md5_hash, "CS9tHYTtyFntzj7B9nkkJQ==")
         self.assertEqual(blob.crc32c, "4gcgLQ==")
+        self.assertEqual(blob.etag, "kittens")
+        self.assertEqual(blob.generation, 42)
+        self.assertEqual(blob.metageneration, 4)
 
     def test__extract_headers_from_download_empty(self):
         blob_name = "blob-name"
@@ -1064,8 +1070,11 @@ def test__extract_headers_from_download_empty(self):
                 "Content-Language": "en-US",
                 "Cache-Control": "max-age=1337;public",
                 "Content-Encoding": "gzip",
+                "Etag": "kittens",
                 "X-Goog-Storage-Class": "STANDARD",
                 "X-Goog-Hash": "crc32c=4/c+LQ==,md5=CS9tHYTt/+ntzj7B9nkkJQ==",
+                "X-goog-generation": 42,
+                "X-goog-metageneration": 4,
             },
             content=b"",
         )
@@ -1074,6 +1083,9 @@ def test__extract_headers_from_download_empty(self):
         self.assertEqual(blob.content_language, "en-US")
         self.assertEqual(blob.md5_hash, "CS9tHYTt/+ntzj7B9nkkJQ==")
         self.assertEqual(blob.crc32c, "4/c+LQ==")
+        self.assertEqual(blob.etag, "kittens")
+        self.assertEqual(blob.generation, 42)
+        self.assertEqual(blob.metageneration, 4)
 
     def test__extract_headers_from_download_w_hash_response_header_none(self):
         blob_name = "blob-name"