CPP SDK

[bhardwajparth51]

What does this PR do?

Adds a C++ SDK generator targeting C++20. The generated SDK is monolithic and header-only—users can drop include/appwrite into their project and link against cpr and nlohmann/json without any precompilation or complex build step.

Key Features of the C++ SDK:

• Monolithic Header-only: Simple integration with a single include/appwrite/services.hpp entry point. No separate compilation units or static/dynamic linking required for the SDK itself.
• Concurrent Dispatch via ThreadPool: API calls are dispatched onto a dedicated ThreadPool. The queue is bounded at 1,024 tasks as intentional backpressure — typical SDK workloads never approach this limit.
• Modern C++20 Async: The Task<T> type provides a coroutine-compatible interface (co_await), allowing async API calls to feel natural while maintaining readability.
• Robust Transport Layer: Full support for chunked multi-part uploads, binary responses (callBytes), and automatic x-appwrite-id propagation for resumable-style large file handling.
• Topological Model Sorting: Automatically resolves circular dependencies in model definitions at generation time, ensuring the monolithic header compiles without forward declaration conflicts.
• Thread-Safety: The Client uses a copy-on-write config pattern via shared_ptr<const Config> with mutex protection, making it safe for concurrent use across multiple threads.

Test Plan

Verified with 443 passing assertions against the Appwrite Mock API via Cpp20Test.php. The suite covers:

• Complete REST lifecycle (GET/POST/PUT/PATCH/DELETE).
• Large file chunked uploads with x-appwrite-id propagation.
• Binary response handling and error model parsing.
• Correctness of all Query, Permission, and ID helper builders.

Related PRs and Issues

Contributing Guidelines

Yes

[greptile-apps]

Greptile Summary

This PR adds a complete C++20 SDK generator targeting Appwrite, producing a monolithic header-only library with coroutine-based async dispatch, chunked file uploads, and Realtime WebSocket support. All P0/P1 issues from prior review rounds (dangling getHeaders() reference, subIdCounter data race, Subscription use-after-free, subscribe() deadlock, spurious 10 ms sleep, missing RetryPolicy retry coverage) have been addressed in this revision.

Confidence Score: 4/5

Safe to merge; remaining findings are P2 suggestions that do not block production use.

All previously flagged P0/P1 issues are resolved. Two new P2 findings remain: cancellation not honored during retry sleeps in upload_chunks, and Subscription::callback being a detached copy that silently ignores post-call mutations. Neither causes a crash or data loss.

templates/cpp/include/client.hpp.twig (retry cancellation gap), templates/cpp/include/services.hpp.twig (Subscription callback copy semantics)

Important Files Changed

Filename	Overview
templates/cpp/include/client.hpp.twig	Core Client class with ThreadPool, retry logic, chunked upload, and async dispatch — previously flagged issues resolved; two P2 concerns remain (cancellation not checked during retry sleeps, multipart rebuilt on every retry)
templates/cpp/include/services.hpp.twig	Generated service classes and Realtime WebSocket support — previously flagged deadlock, subIdCounter race, and use-after-free resolved; Subscription::callback is copied into both returned struct and dispatch map, meaning post-call mutations silently have no effect
templates/cpp/include/base.hpp.twig	Exception hierarchy, Result/Result, Task coroutine type, BinaryResponse, and SocketBackend interface — well-implemented with correct move-only semantics
templates/cpp/include/core.hpp.twig	Helper classes (Query, Permission, Role, Id, InputFile, Operator) — well-structured; InputFile::fromPath throws AppwriteException, consistent with the SDK error model
src/SDK/Language/Cpp.php	PHP generator — return types, dispatch blocks, input types, and default generation all consistent; TYPE_FILE non-required guard present; DFS topological sort correctly handles model ordering
tests/Cpp20Test.php	Integration test suite with 443 assertions covering REST lifecycle, chunked uploads, binary responses, and helper builders

_{Reviews (9): Last reviewed commit: "fix(cpp): return getHeaders by value to ..." | Re-trigger Greptile}

[bhardwajparth51]

@ChiragAgg5k could you run jobs/workflows