feat(storage): new option to disable decompressive transcoding (#8834)

For objects stored in gzip format (and with contentEncoding == "gzip")
GCS over HTTP automatically decompresses the object during download.
Some applications may want to read the object in compressed format.
Support this use-case with a new option (`AcceptEncoding`) for
`Client::ReadObject()`, and a new helper function (`AcceptEncodingGzip()
`) that returns this option with the correct value.

google/cloud/storage/client.h

@@ -1064,20 +1064,23 @@ class Client {
    *     Valid types for this operation include `DisableCrc32cChecksum`,
    *     `DisableMD5Hash`, `IfGenerationMatch`, `EncryptionKey`, `Generation`,
    *     `IfGenerationMatch`, `IfGenerationNotMatch`, `IfMetagenerationMatch`,
-   *     `IfMetagenerationNotMatch`, `ReadFromOffset`, `ReadRange`, `ReadLast`
-   *     and `UserProject`.
+   *     `IfMetagenerationNotMatch`, `ReadFromOffset`, `ReadRange`, `ReadLast`,
+   *     `UserProject`, and `AcceptEncoding`.
    *
    * @par Idempotency
    * This is a read-only operation and is always idempotent.
    *
    * @par Example
    * @snippet storage_object_samples.cc read object
    *
-   * @par Example
+   * @par Example: read only a sub-range in the object.
    * @snippet storage_object_samples.cc read object range
    *
    * @par Example: read a object encrypted with a CSEK.
    * @snippet storage_object_csek_samples.cc read encrypted object
+   *
+   * @par Example: disable decompressive transcoding.
+   * @snippet storage_object_samples.cc read object gzip
    */
   template <typename... Options>
   ObjectReadStream ReadObject(std::string const& bucket_name,

google/cloud/storage/examples/storage_object_samples.cc

@@ -326,6 +326,22 @@ void ReadObjectIntoMemory(google::cloud::storage::Client client,
   (std::move(client), argv.at(0), argv.at(1));
 }
 
+void ReadObjectGzip(google::cloud::storage::Client client,
+                    std::vector<std::string> const& argv) {
+  //! [read object gzip]
+  namespace gcs = ::google::cloud::storage;
+  [](gcs::Client client, std::string const& bucket_name,
+     std::string const& object_name) {
+    auto is =
+        client.ReadObject(bucket_name, object_name, gcs::AcceptEncodingGzip());
+    auto const contents = std::string{std::istream_iterator<char>(is), {}};
+    if (!is.status().ok()) throw std::runtime_error(is.status().message());
+    std::cout << "The object has " << contents.size() << " characters\n";
+  }
+  //! [read object gzip]
+  (std::move(client), argv.at(0), argv.at(1));
+}
+
 void DeleteObject(google::cloud::storage::Client client,
                   std::vector<std::string> const& argv) {
   //! [delete object] [START storage_delete_file]
@@ -691,6 +707,9 @@ void RunAll(std::vector<std::string> const& argv) {
   std::cout << "\nRunning ReadObjectRange() example" << std::endl;
   ReadObjectRange(client, {bucket_name, object_name, "1000", "2000"});
 
+  std::cout << "\nRunning ReadObjectGzip() example" << std::endl;
+  ReadObjectGzip(client, {bucket_name, object_name});
+
   std::cout << "\nRunning UpdateObjectMetadata() example" << std::endl;
   UpdateObjectMetadata(client,
                        {bucket_name, object_name, "test-label", "test-value"});
@@ -793,6 +812,7 @@ int main(int argc, char* argv[]) {
       make_entry("read-object", {"<object-name>"}, ReadObject),
       make_entry("read-object-range", {"<object-name>", "<start>", "<end>"},
                  ReadObjectRange),
+      make_entry("read-object-gzip", {"<object-name>"}, ReadObjectGzip),
       make_entry("read-object-into-memory", {"<object-name>"},
                  ReadObjectIntoMemory),
       make_entry("delete-object", {"<object-name>"}, DeleteObject),

google/cloud/storage/internal/curl_client.cc

@@ -1199,6 +1199,7 @@ StatusOr<std::unique_ptr<ObjectReadSource>> CurlClient::ReadObjectXml(
   // None of the IfGeneration*Match nor IfMetageneration*Match can be set. This
   // is checked by the caller (in this class).
   builder.AddOption(request.GetOption<UserProject>());
+  builder.AddOption(request.GetOption<AcceptEncoding>());
 
   //
   // Apply the options from GenericRequestBase<> that are set, translating

google/cloud/storage/internal/object_requests.h

@@ -169,7 +169,7 @@ class ReadObjectRangeRequest
           ReadObjectRangeRequest, DisableCrc32cChecksum, DisableMD5Hash,
           EncryptionKey, Generation, IfGenerationMatch, IfGenerationNotMatch,
           IfMetagenerationMatch, IfMetagenerationNotMatch, ReadFromOffset,
-          ReadRange, ReadLast, UserProject> {
+          ReadRange, ReadLast, UserProject, AcceptEncoding> {
  public:
   using GenericObjectRequest::GenericObjectRequest;
 

google/cloud/storage/tests/decompressive_transcoding_integration_test.cc

@@ -127,6 +127,81 @@ TEST_F(DecompressiveTranscodingIntegrationTest, WriteAndReadXml) {
   ASSERT_NE(decompressed.substr(0, 32), contents.substr(0, 32));
 }
 
+TEST_F(DecompressiveTranscodingIntegrationTest, WriteAndReadCompressedJson) {
+  // TODO(storage-testbench#321) - fix transcoding support in the emulator
+  if (UsingEmulator()) GTEST_SKIP();
+
+  auto const gzip_filename = google::cloud::internal::GetEnv(
+                                 "GOOGLE_CLOUD_CPP_STORAGE_TEST_GZIP_FILENAME")
+                                 .value_or("");
+  ASSERT_FALSE(gzip_filename.empty());
+  std::ifstream gz(gzip_filename, std::ios::binary);
+  auto const contents = std::string{std::istreambuf_iterator<char>(gz), {}};
+  ASSERT_TRUE(gz.good());
+
+  auto client = Client(
+      Options{}
+          .set<TransferStallTimeoutOption>(std::chrono::seconds(3))
+          .set<RetryPolicyOption>(LimitedErrorCountRetryPolicy(5).clone()));
+
+  auto object_name = MakeRandomObjectName();
+  auto insert = client.InsertObject(
+      bucket_name(), object_name, contents, IfGenerationMatch(0),
+      WithObjectMetadata(
+          ObjectMetadata().set_content_encoding("gzip").set_content_type(
+              "text/plain")));
+  ASSERT_STATUS_OK(insert);
+  ScheduleForDelete(*insert);
+  EXPECT_EQ(insert->content_encoding(), "gzip");
+  EXPECT_EQ(insert->content_type(), "text/plain");
+
+  auto reader =
+      client.ReadObject(bucket_name(), object_name, AcceptEncodingGzip(),
+                        IfGenerationNotMatch(0));
+  ASSERT_STATUS_OK(reader.status());
+  auto compressed = std::string{std::istreambuf_iterator<char>(reader), {}};
+  ASSERT_STATUS_OK(reader.status());
+
+  ASSERT_EQ(compressed.substr(0, 32), contents.substr(0, 32));
+}
+
+TEST_F(DecompressiveTranscodingIntegrationTest, WriteAndReadCompressedXml) {
+  // TODO(storage-testbench#321) - fix transcoding support in the emulator
+  if (UsingEmulator()) GTEST_SKIP();
+
+  auto const gzip_filename = google::cloud::internal::GetEnv(
+                                 "GOOGLE_CLOUD_CPP_STORAGE_TEST_GZIP_FILENAME")
+                                 .value_or("");
+  ASSERT_FALSE(gzip_filename.empty());
+  std::ifstream gz(gzip_filename, std::ios::binary);
+  auto const contents = std::string{std::istreambuf_iterator<char>(gz), {}};
+  ASSERT_TRUE(gz.good());
+
+  auto client = Client(
+      Options{}
+          .set<TransferStallTimeoutOption>(std::chrono::seconds(3))
+          .set<RetryPolicyOption>(LimitedErrorCountRetryPolicy(5).clone()));
+
+  auto object_name = MakeRandomObjectName();
+  auto insert = client.InsertObject(
+      bucket_name(), object_name, contents, IfGenerationMatch(0),
+      WithObjectMetadata(
+          ObjectMetadata().set_content_encoding("gzip").set_content_type(
+              "text/plain")));
+  ASSERT_STATUS_OK(insert);
+  ScheduleForDelete(*insert);
+  EXPECT_EQ(insert->content_encoding(), "gzip");
+  EXPECT_EQ(insert->content_type(), "text/plain");
+
+  auto reader =
+      client.ReadObject(bucket_name(), object_name, AcceptEncodingGzip());
+  ASSERT_STATUS_OK(reader.status());
+  auto compressed = std::string{std::istreambuf_iterator<char>(reader), {}};
+  ASSERT_STATUS_OK(reader.status());
+
+  ASSERT_EQ(compressed.substr(0, 32), contents.substr(0, 32));
+}
+
 }  // anonymous namespace
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace storage

google/cloud/storage/well_known_headers.h

@@ -277,6 +277,39 @@ EncryptionKeyData CreateKeyFromGenerator(Generator& gen) {
   return EncryptionDataFromBinaryKey(key);
 }
 
+/**
+ * Modify the accepted encodings.
+ *
+ * When using HTTP, GCS decompresses gzip-encoded objects by default:
+ *
+ *     https://cloud.google.com/storage/docs/transcoding
+ *
+ * Setting this option to `gzip` disables automatic decompression. This can be
+ * useful for applications wanting to operate with the compressed data. Setting
+ * this option to `identity`, or not setting this option, returns decompressed
+ * data.
+ *
+ * @note Note that decompressive transcoding only apply to objects that are
+ *     compressed with `gzip` and have their `content_encoding()` attribute set
+ *     accordingly. At the time of this writing GCS does not decompress objects
+ *     stored with other compression algorithms, nor does it detect the object
+ *     compression based on the object name or its contents.
+ *
+ * @see `AcceptEncodingGzip()` is a helper function to disable decompressive
+ *     encoding.
+ */
+struct AcceptEncoding
+    : public internal::WellKnownHeader<AcceptEncoding, std::string> {
+  using WellKnownHeader<AcceptEncoding, std::string>::WellKnownHeader;
+  static char const* header_name() { return "Accept-Encoding"; }
+};
+
+inline AcceptEncoding AcceptEncodingGzip() { return AcceptEncoding("gzip"); }
+
+inline AcceptEncoding AcceptEncodingIdentity() {
+  return AcceptEncoding("identity");
+}
+
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace storage
 }  // namespace cloud