Platform Layer

Platform support, POSIX-only subsystems, platform guards, and portability rules.

Platform Support Overview

Platform	Status	Notes
Linux	Full	Primary development platform. All tests pass.
macOS	Full	POSIX-compatible. Same as Linux.
Windows	Partial	CMake links `ws2_32`. POSIX-only subsystems need Win32 platform guards (known gaps).
Android	Partial	StoragePaths uses SDL3 when available. SDL3 must be provided by the parent project (CNA).
Emscripten	Partial	Compiles cleanly. Some features throw `PlatformNotSupportedException` at runtime.

POSIX-Only Subsystems

These subsystems currently use POSIX-specific APIs and are documented as known bugs, not completed features:

Subsystem	POSIX API Used	Status
`System::Net::Sockets`	`<sys/socket.h>`, `<unistd.h>`	POSIX-only
`System::IO::RandomAccess`	`pread`, `pwrite`, `fsync`	Done (has Win32 fallback)
`System::AppDomain / AppContext`	`/proc/self/exe`	Linux-only
`System::TimeZoneInfo`	`localtime_r`, `/usr/share/zoneinfo`	POSIX-only

Platform Guard Rules

These rules are enforced project-wide (see CLAUDE.md):

POSIX includes (<unistd.h>, <sys/socket.h>, etc.) must not appear in public .hpp headers.
Platform-specific code lives only in .cpp files.
Use #ifdef _WIN32 / #elif defined(__EMSCRIPTEN__) / #else (POSIX) guards.
On unsupported platforms, throw System::PlatformNotSupportedException with a clear message.
Emscripten builds must compile without errors even when features are runtime-unavailable.

Example Guard Pattern

// In a .cpp file — platform-specific implementation
#ifdef _WIN32
    #include <windows.h>
    // Win32 implementation
#elif defined(__EMSCRIPTEN__)
    throw System::PlatformNotSupportedException("Not available on Emscripten.");
#else
    #include <unistd.h>
    // POSIX implementation
#endif

Windows-Specific

CMake automatically links ws2_32 on Windows for socket support:

if(WIN32)
    target_link_libraries(SHARP_RUNTIME PRIVATE ws2_32)
endif()

Android-Specific

On Android, SharpRuntime::Storage::StoragePaths uses SDL3 APIs to determine storage paths:

SDL_GetPrefPath() for the isolated storage root
SDL_GetAndroidInternalStoragePath() as fallback

SDL3 headers and library must be available via the parent project before add_subdirectory(sharp-runtime) is called.

Emscripten-Specific

Emscripten (WebAssembly) support requires:

All platform-guarded code must be guarded by #elif defined(__EMSCRIPTEN__)
Features that cannot work in a browser should throw PlatformNotSupportedException
The build must produce zero errors

StoragePaths

include/SharpRuntime/Storage/StoragePaths.hpp | src/SharpRuntime/Storage/StoragePaths.cpp

Provides platform-aware isolated storage paths:

std::filesystem::path root = SharpRuntime::Storage::StoragePaths::GetIsolatedStorageRoot();

Implementation varies by platform: uses SDL_GetPrefPath on Android, appropriate paths on other platforms.

Network Sockets

include/System/Net/Sockets/

Status: POSIX-only

Class	Header
`TcpClient`	`System/Net/Sockets/TcpClient.hpp`
`UdpClient`	`System/Net/Sockets/UdpClient.hpp`
`NetworkStream`	`System/Net/Sockets/NetworkStream.hpp`

These use <sys/socket.h> and related POSIX headers. Windows and Emscripten support is incomplete.

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