C++ client library

[alyssasuiyiguo]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @alyssasuiyiguo, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This PR introduces a new C++ client library designed to interact with the Data Commons API. It provides structured methods for fetching data, specifically implementing functionalities to retrieve property values and observations from the API. The library leverages modern C++ features and integrates popular third-party libraries for HTTP requests and JSON parsing, making it a robust foundation for C++ applications needing Data Commons integration.

Highlights

• New C++ Client Library: A foundational C++ client library for the Data Commons API has been added, enabling C++ applications to programmatically access Data Commons data.
• API Interaction: Implemented GetPropertyValues and GetObservations methods to query the Data Commons API for specific data points, handling request construction and response parsing.
• Dependency Management: Utilizes CMake's FetchContent to manage external dependencies like cpr for HTTP requests and nlohmann/json for efficient JSON serialization and deserialization.
• Build System Setup: A comprehensive CMakeLists.txt is included to facilitate easy building of the library and an example executable, ensuring cross-platform compatibility.
• Example Usage: An examples/main.cpp file demonstrates how to initialize the client and make calls to the GetObservations (and GetPropertyValues as a commented-out example) endpoint, providing a quick start for users.

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[gemini-code-assist]

Code Review

This pull request introduces a new C++ client library for the Data Commons API. The implementation uses cpr for HTTP requests and nlohmann/json for JSON handling, which are fetched via CMake's FetchContent. The overall structure is good, but there are a few important issues to address. Most critically, a hardcoded API key is present in the example code, which is a major security risk. There is also a bug in GetPropertyValues where a property name is hardcoded. Additionally, I've provided some suggestions to improve code clarity and error handling.

[gemini-code-assist]

A hardcoded API key is present in the example. This is a major security vulnerability. API keys and other secrets should never be committed to source code. It's recommended to load the key from an environment variable or a configuration file at runtime.

To use std::getenv, you'll also need to add #include <cstdlib> at the top of the file.

Suggested change

	// NOTE: Please provide a valid API key.
	datacommons::DataCommons dc("AIzaSyCTI4Xz-UW_G2Q2RfknhcfdAnTHq5X5XuI");
	// NOTE: Please provide a valid API key via the DATACOMMONS_API_KEY environment variable.
	const char* api_key = std::getenv("DATACOMMONS_API_KEY");
	if (!api_key) {
	std::cerr << "Error: DATACOMMONS_API_KEY environment variable not set." << std::endl;
	return 1;
	}
	datacommons::DataCommons dc(api_key);

[gemini-code-assist]

The property to look for in the response JSON is hardcoded to "name". This is incorrect and should use the prop argument passed to the function. This bug prevents retrieving values for any property other than name.

                if (data["arcs"].contains(prop)) {
                    for (const auto& node : data["arcs"][prop]["nodes"]) {

[gemini-code-assist]

The field dcid in the PropertyValue struct is misleading. The implementation populates this field with the provenanceId from the API response, not a dcid. Renaming it to provenance_id would make the code clearer and less prone to misuse.

Suggested change

	std::string dcid;
	std::string provenance_id;

[gemini-code-assist]

Writing errors directly to std::cerr is not ideal for a library, as it removes control from the client application on how to handle or log errors. A better approach would be to propagate errors to the caller, for example by throwing an exception or returning an object that encapsulates the result or error. This would allow the user of your library to implement their own error handling logic (e.g., logging to a file, showing a UI message).