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The google-cloud-cpp public API

This document describes what constitutes google-cloud-cpp's public API.

As this project follows Google's OSS Library Breaking Change Policy, any breaking changes in the public API require increasing the major version number in the library.

While we take commercially reasonable efforts to prevent breaks in the public API, it is possible that backwards incompatible changes go undetected and, therefore, undocumented. We apologize if this is the case and welcome feedback or bug reports to rectify the problem.

We make no guarantees and make no effort to maintain compatibility for any functions, classes, libraries, files, targets or any other artifact that is not explicitly included in the public API.

Note that this document has no bearing on the Google Cloud Platform deprecation policy described at https://cloud.google.com/terms.

Previous versions of the library will remain available on the GitHub Releases page. In many cases, you will be able to use an older version even if a newer version has changes that you are unable (or do not have time) to adopt.

We think this document covers all interface points. If we missed something please file a GitHub issue.

Public API Overview

The public API includes:

  • Any C++ names, including macros, classes, structs, typedefs, functions, enums, etc. in public namespaces.
  • Public namespaces are of the form:
    • google::cloud
    • google::cloud::mocks
    • google::cloud::${library} and google::cloud::${library}_mocks where ${library} matches the regular expression ^[a-z][a-z_]*$ and ${library} is not internal.
    • google::cloud::${library}_v${number} and google::cloud::${library}_v${number}_mocks where ${library} matches ^[a-z][a-z]*$ and ${number} matches ^[0-9][0-9]*$. In the common case ${number} is a single digit..
  • C++ header file names in google/cloud/*.h or google/cloud/${library}/*.h, and google/cloud/${library}/v${number}, where ${library} matches the regular expression ^[a-z][a-z_]*$ (but it is not internal), and ${number} matches ^[0-9][0-9]*.
  • CMake targets with the google-cloud-cpp:: prefix.
  • Bazel targets in the top-level directory (e.g. //:storage).
  • pkg-config modules starting with google_cloud_cpp_.
  • Environment variables defined in the documentation.

The public API excludes:

  • Any C++ symbol or file that includes internal, impl, test, detail, benchmark, sample, or example in its fully qualified name or path.
  • Any CMake target that includes internal or experimental in its name.
  • Any Bazel target that includes internal or experimental in its name.
  • Environment variables with EXPERIMENTAL in their name.
  • We are not talking about the gRPC or REST APIs exposed by Google Cloud servers. This is beyond the scope of what the client library can control.

We are also talking only about API stability -- the ABI is subject to change without notice. You should not assume that binary artifacts (e.g. static libraries, shared objects, dynamically loaded libraries, object files) created with one version of the library are usable with newer/older versions of the library. The ABI may, and does, change on "minor revisions".

Guidelines

We request that our customers adhere to the following guidelines to avoid accidentally depending on parts of the library we do not consider to be part of the public API and therefore may change (including removal) without notice:

  • You should only include headers matching the google/cloud/${library}/*.h, google/cloud/${library}/mock/*.h or google/cloud/*.h patterns.
  • You should NOT directly include headers in any subdirectories, such as google/cloud/${library}/internal.
  • The files included from our public headers are not part of our public API. Depending on indirect includes may break your build in the future, as we may change a header "foo.h" to stop including "bar.h" if "foo.h" no longer needs the symbols in "bar.h". To avoid having your code broken, you should directly include the public headers that define all the symbols you use (this is sometimes known as include what you use).
  • Any file or symbol that lives within a directory or namespace containing internal, impl, test, detail, benchmark, sample, or example, is explicitly not part of our public API.
  • Any file or symbol with Impl or impl in its name is not part of our public API.
  • Any symbol with experimental in its name is not part of the public API.
  • You should avoid naming our inline namespaces (even avoid spelling the preprocessor names like GOOGLE_CLOUD_CPP_NS) and instead rely on them being a transparent versioning mechanism that you almost certainly don't care about. If you do spell out specific inline namespace names, your code will be tightly coupled with that specific version and will likely break when upgrading to a new version of our library.

Beyond the C++ API

Applications developers interact with a C++ library through more than just the C++ symbols and headers. They also need to reference the name of the library in their build scripts. Depending on the build system they use this may be a CMake target, a Bazel rule, a pkg-config module, or just the name of some object in the file system.

As with the C++ API, we try to avoid breaking changes to these interface points. We treat breaking changes to these interface points like any other breaking change.

Experimental Libraries

From time to time we add libraries to google-cloud-cpp to validate new designs, expose experimental (or otherwise not generally available) GCP features, or simply because a library is not yet complete. Such libraries will have experimental in their CMake target and Bazel rule names. The README file for these libraries will also document that they are experimental. Such libraries are subject to change, including removal, without notice. This includes, but it is not limited to, all their symbols, pre-processor macros, files, targets, rules, and installed artifacts.

Bazel rules

Only the rules exported at the top-level directory are intended for customer use, e.g.,//:spanner. Experimental rules have experimental in their name, e.g. //:experimental-logging. As previously stated, experimental rules are subject to change or removal without notice.

CMake targets and packages

Only CMake packages starting with the google_cloud_cpp_ prefix are intended for customer use. Only targets starting with google-cloud-cpp::, are intended for customer use. Experimental targets have experimental in their name (e.g. google-cloud-cpp::experimental-logging). As previously stated, experimental targets are subject to change or removal without notice.

pkg-config modules

Only modules starting with google_cloud_cpp_ are intended for customer use.

Unsupported use cases

We try to provide stable names for the previously described mechanisms:

  • Bazel rules,
  • CMake targets loaded via find_package(),
  • pkg-config modules

It is certainly possible to use the library using other approaches. While these may work, we may accidentally break these from time to time. Examples of such, and the recommended alternatives, include:

  • CMake's FetchContent and/or git submodules: in these approaches the google-cloud-cpp library becomes a subdirectory of a larger CMake build We do not test google-cloud-cpp in these configurations, and we find them brittle as all CMake targets become visible to the larger project. This is both prone to conflicts, and makes it impossible to enforce that some targets are only for testing or are implementation details. Applications may want to consider source package managers, such as vcpkg, or CMake super builds via ExternalProject_Add() as alternatives.

  • Using library names directly: applications should not use the library names, e.g., by using -lgoogle_cloud_cpp_bigtable in build scripts. We may need to split or merge libraries over time, making such names unstable. Applications should use CMake targets, e.g., google-cloud-cpp::bigtable, or pkg-config modules, e.g., $(pkg-config google_cloud_cpp_bigtable --libs) instead.

Environment Variables

Environment variables referenced in our documentation come with the same guarantees as our public APIs. That is, we are committed to supporting their behavior unless the behavior affects experimental components, or the environment variable itself is experimental.

Telemetry Data

The library can be configured to produce telemetry data, such as logs or traces. We make no guarantees around the contents of such data. For example, we may change the format of our logs, or the names of our spans without notice.

The APIs to programmatically enable logging and tracing have the same guarantees as any other public APIs in our libraries.

Documentation and Comments

The documentation (and its links) is intended for human consumption and not third party websites, or automation (such as scripts scraping the contents). The contents and links of our documentation may change without notice.