Understanding the Code Base

Google APIs Client Library for C++

A C++ library for client applications to access Google APIs.

This document provides an overview of the primary components and classes defined and used within the client library runtime. This may help understanding how the the library is organized and where to find the implementation of different concepts and activities. This Developer's Guide introduces and uses many of these components to illustrate how to perform key activities. Complete technical reference documentation for all the APIs is available in the Doxygen-generated API documentation.

See Understanding the Scope for an abstract overview of the scope and types of activities typically covered by the libraries.

Client Service Layer	Role Using Cloud Services. C++ Location `googleapis/client/service` C++ Module Client Service Layer Components and Libraries `googleapis_http` The current runtime packaging is coarser than the implementation architecture. These components are grouped together with the Transport Layer. The components in the Client Service Layer generally fall into two sub-categories: Core Components `ClientService` `ClientServiceRequest` Interaction Components `MediaUploader` `ServiceRequestPager`
HTTP Transport Layer	Role Sending HTTP Requests. C++ Location `googleapis/client/transport` Production runtime components. `googleapis/client/transport/test` Testing and diagnostic components. C++ SubModules Core Components Concrete Transports Testing Support Components and Libraries `googleapis_http` The core Http Transport Layer runtime components are lumped in here. `googleapis_http_curl_http` Contains `CurlHttpTransportFactory`. `googleapis_http_scribes` Contains various concrete `HttpScribe` implementations. `googleapis_http_jsonplayback` Contains `JsonPlaybackHttpTransport` for testing and debugging. `googleapis_http_transport_test` Contains the `HttpTransportTestFixture`. The C++ module breakdown of this layer is for dependency management. For an introductory overview, components in this layer usually fall into one of these functional groups: (Abstract) Core Components `HttpAuthorization` `HttpRequest` `HttpResponse` `HttpTransport` `HttpTransportFactory` `HttpScribe` Supporting Components `HttpRequestState` `HttpTransportErrorHandler` `HttpTransportOptions` `HttpTransportLayerConfig` Concrete Extensions `CurlHttpTransportFactory` `MockHttpTransportFactory` `HtmlScribe`
Authorization Module	Role Using Credentials. C++ Location `googleapis/client/auth` C++ SubModules Generic Components OAuth 2.0 Module Components and Libraries `googleapis_http` The Generic Components added by the Authorization Module are lumped together in the same library as the HTTP Transport Layer. `googleapis_oauth2` Contains the components supporting OAuth 2.0. The Authorization Module components fall into two groups: OAuth 2.0 Support `OAuth2AuthorizationFlow` `OAuth2Credential` `OAuth2ClientSpec` Generic Credential Management `CredentialStore` `FileCredentialStore`
Data Layer	Role Working with Data. C++ Location `googleapis/client/data` C++ SubModules Raw Data Management Manages reading and writing binary data streams. Data Encoder/Decoders Transforms the data within binary data streams (e.g. encryption). Data Encoder/Decoders (Abstract) JSON Support JSON Support using JsonCpp Components and Libraries `googleapis_utils` Raw data management and simple codecs are lumped in here. `googleapis_openssl_codec` An encryption/decryption codec implemented using OpenSSL ciphers. `googleapis_json` Abstract JSON support `googleapis_jsoncpp` Concrete JSON support using JsonCpp The C++ module breakdown of this layer is for dependency management. For an introductory overview, components of this layer fall into one of these functional groups: Data Access and Management `DataReader` `DataWriter` Various specializations of reader/writer. In-memory File Composite IStream `Codec` JSON Support `SerializableJson` `JsonCppData`
Platform Layer	Role Working with C++. C++ Location `googleapis/client/util` Components specific to the Google APIs Client Library for C++ `googleapis/base` `googleapis/util` This is not currently well defined. They are typically components that are in other Google open source projects but do not have an authoritative project of their own. Note that `googleapis/util` is not the same as `googleapis/client/utils` which is a well-defined module introduced by Google APIs Client for C++. C++ SubModules File Support URI Support Embedded Web Server General Programming Support Components and Libraries `googleapis_utils` Provides most of the Platform Layer in addition to the basic data and codec implementations for the Data Layer. `googleapis_mongoose` Contains the implementation of MongooseWebServer. `googleapis_gtest_main` Implements main() for gtest but adds a temporary directory which is cleared out after running the tests. `googleapis_internal` Contains implementation details not yet officially exported. This includes a few classes that are part of the public API that do not yet been moved elsewhere. The Platform Layer contains a lot of miscellaneous components. They can be roughly categorized as follows: Foundation Types See Foundation Types. `DateTime` `Closure` `Executor` `Mutex` `Status` `Strings` Other Modules `File` `StrCat()` and other string operations