feat(storage): support AuthorityOption

[coryan]

If present, use the AuthorityOption to configure the Host: header
or the .set_authority() attribute in grpc::ClientContext. By
default, configure AuthorityOption to be storage.googleapis.com,
applications can override this when initializing the storage::Client.

There is already an issue open to add per-call Options that would
provide more fine-grained control of this field.

Fixes #3317. I am adding a node to #8164 because we will need to undo some of this work to support per-call options.

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This change is 

[google-cloud-cpp-bot]

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[codecov]

Codecov Report

Merging #8462 (82ae158) into main (44e7fea) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #8462   +/-   ##
=======================================
  Coverage   93.88%   93.88%           
=======================================
  Files        1451     1451           
  Lines      125175   125231   +56     
=======================================
+ Hits       117515   117569   +54     
- Misses       7660     7662    +2     

Impacted Files	Coverage Δ
google/cloud/storage/internal/curl_client.cc	98.22% <100.00%> (+<0.01%)	⬆️
google/cloud/storage/internal/curl_client_test.cc	99.44% <100.00%> (+<0.01%)	⬆️
google/cloud/storage/internal/grpc_client.cc	88.33% <100.00%> (+0.83%)	⬆️
google/cloud/storage/internal/grpc_client_test.cc	99.81% <100.00%> (+<0.01%)	⬆️
google/cloud/internal/async_rpc_details.h	94.44% <0.00%> (-5.56%)	⬇️
google/cloud/pubsub/subscriber_connection_test.cc	97.22% <0.00%> (-0.70%)	⬇️

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[dbolduc]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @coryan)

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google/cloud/storage/internal/curl_client.cc, line 117 at r1 (raw file):

  // or their own proxy, and need to provide the target's service host.
  if (!options.get<AuthorityOption>().empty()) {
    return absl::StrCat("Host: ", options.get<AuthorityOption>());

Consider:

if (options.has<AuthorityOption>()) {
  auto const auth = options.get<AuthorityOption>();
  if (!auth.empty()) return absl::StrCat("Host: ", auth);
}

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google/cloud/storage/internal/curl_client.cc, line 119 at r1 (raw file):

    return absl::StrCat("Host: ", options.get<AuthorityOption>());
  }
  auto const& endpoint = options.get<RestEndpointOption>();

Hmm... do you think we should add a note here saying that AuthorityOption takes precedence over storage::RestEndpointOption ?

google-cloud-cpp/google/cloud/storage/options.h

Line 69 in 12e6cd8

/// Configure the REST endpoint for the GCS client library.

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google/cloud/storage/internal/grpc_client_test.cc, line 354 at r1 (raw file):

  EXPECT_CALL(*mock, WriteObject)
      .WillOnce([this](std::unique_ptr<grpc::ClientContext> context) {
        auto metadata = GetMetadata(*context);

Check AuthorityOption here?

EXPECT_EQ(CurrentOptions().get<AuthorityOption>(), kAuthority);

[coryan]

Reviewable status: 2 of 5 files reviewed, all discussions resolved (waiting on @dbolduc)

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google/cloud/storage/internal/curl_client.cc, line 117 at r1 (raw file):

Previously, dbolduc (Darren Bolduc) wrote…

Consider:

if (options.has<AuthorityOption>) {
  auto const auth = options.get<AuthorityOption>();
  if (!auth.empty()) return absl::StrCat("Host: ", auth);
}

Done. Though a slightly different implementation, note that not options.has<AuthorityOption>() implies options.get<AuthorityOption>().empty().

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google/cloud/storage/internal/curl_client.cc, line 119 at r1 (raw file):

Previously, dbolduc (Darren Bolduc) wrote…

Hmm... do you think we should add a note here saying that AuthorityOption takes precedence over storage::RestEndpointOption ?

google-cloud-cpp/google/cloud/storage/options.h

Line 69 in 12e6cd8

/// Configure the REST endpoint for the GCS client library.

Done.

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google/cloud/storage/internal/grpc_client_test.cc, line 354 at r1 (raw file):

Previously, dbolduc (Darren Bolduc) wrote…

Check AuthorityOption here?

EXPECT_EQ(CurrentOptions().get<AuthorityOption>(), kAuthority);

Done.

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[dbolduc]

Done. Though a slightly different implementation, note that not options.has<AuthorityOption>() implies options.get<AuthorityOption>().empty().

Part of the motivation for checking .has<>() was to avoid constructing the empty string once when the option is not present. But maybe that is not worth the trouble.

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