v1.20.0 Release

Bigtable

No user-facing changes.

Pub/Sub

BREAKING CHANGES:

While the Pub/Sub library is not GA, and breaking changes are to be expected, we
are close enough to a GA release that we think highlighting them is important.

• Simplify the concurrency control configuration in pubsub::SubscriberOptions.
  Applications only need to set the maximum number of messages that will be
  scheduled in parallel.

• Remove pubsub::AckHandler::ack_id() accessor. We believe application
  developers should have no need for this field.

• Rename pubsub::SubscriptionOptions to pubsub::SubscriberOptions as these
  are bound to a specific subscriber object.

• Change the pubsub::Subscriber API. A Subscriber is now bound to a specific
  Cloud Pub/Sub subscription, with a fixed set of SuscriptionOptions, just
  like a pubsub::Publisher is bound to a specific topic and a set of
  PublisherOptions. In addition to making publishers and subscribers more
  symmetrical, this makes the library more consistent with the Cloud Pub/Sub
  library for other languages. Finally, note that we are planning to rename
  SubscriptionOptions to SubscriberOptions in a future PR too.

• Remove option to disable retries in Publisher::Publish. This is redundant as
  the application can set a "no retries" retry policy. This is more consistent
  with other Cloud Pub/Sub libraries. We include an example showing how to
  configure a "no retries" retry policy.

• Fix inconsistent naming for PublisherOptions attributes controlling the
  maximum number of messages per batch and the maximum number of bytes per
  batch.

• Rename the {Topic,Snapshot,Subscription}MutationBuilder classes, removing
  Mutation from their names. This makes the C++ library more familiar for
  Cloud Pub/Sub developers coming from other languages.

• Simplify the message flow control configuration. Now that the library uses
  streaming pulls, the low water marks are not used. The application developer
  simply sets limits for the number of messages (and/or bytes) outstanding.
  These limits are propagated to the service, and the service will stop
  streaming if too many messages (or bytes) are outstanding.

Spanner

No user-facing changes.

Storage

BREAKING CHANGES:

• Our public headers no longer include nlohmann/json.hpp. Please update your
  code to directly include this header if you need it. We believe it is not a
  good practice to depend on indirectly included headers, but do feel we should
  warn our customers of this change.

OTHER CHANGES:

• Unexpected curl errors will now be retried (#5312)
• docs: add error handling example from client->ReadObject() (#5274)
• feat(storage): Create an example for Client::DeleteResumableUpload()
• doc: prefer UBLA references over bucket-policy-only

Common Libraries

• Fixed occasional crash on background thread shutdown (#5324)
• GCP_LOG now serializes its output to std::clog (#5179)