refactor(build): keep the native library file names in one module

scripts/build_local_artifacts.py

@@ -29,6 +29,7 @@
 
 import os
 import sys
+import runpy
 import shutil
 import argparse
 import platform
@@ -43,12 +44,11 @@
 # Where the package loads the library from at runtime for an editable install.
 PACKAGE_LIBS_DIR = Path("src/c2pa/libs")
 
-# Library file name per OS (matches what setup.py/lib.py load at runtime).
-LIB_NAMES = {
-    "darwin": "libc2pa_c.dylib",
-    "linux": "libc2pa_c.so",
-    "windows": "c2pa_c.dll",
-}
+# Library file name per sys.platform, loaded by path: importing the c2pa
+# package would load the native library.
+LIB_NAMES = runpy.run_path(
+    str(Path(__file__).resolve().parents[1] / "src/c2pa/_library_names.py")
+)["LIBRARY_NAMES"]
 
 
 def get_platform_identifier():
@@ -180,7 +180,7 @@ def build_native(c2pa_rs_path, debug=False):
     """Build the FFI crate for the host arch. Returns the built library path."""
     profile = "debug" if debug else "release"
     run_cargo(c2pa_rs_path, debug=debug)
-    lib_name = LIB_NAMES[platform.system().lower()]
+    lib_name = LIB_NAMES[sys.platform]
     lib = c2pa_rs_path / "target" / profile / lib_name
     if not lib.is_file():
         print(f"Error: expected built library not found: {lib}")

setup.py

@@ -14,6 +14,7 @@
 from setuptools import setup, find_namespace_packages
 import sys
 import platform
+import runpy
 import shutil
 from pathlib import Path
 import toml
@@ -26,16 +27,19 @@ def get_version():
 VERSION = get_version()
 PACKAGE_NAME = "c2pa-python"  # Define package name as a constant
 
+# Loaded by path: importing the c2pa package would load the native library
+LIBRARY_NAMES = runpy.run_path("src/c2pa/_library_names.py")["LIBRARY_NAMES"]
+
 # Based on what c2pa-rs repo publishes: each platform folder and the
 # native library in it that src/c2pa/lib.py loads
 PLATFORM_FOLDERS = {
-    'universal-apple-darwin': 'libc2pa_c.dylib',
-    'aarch64-apple-darwin': 'libc2pa_c.dylib',
-    'x86_64-apple-darwin': 'libc2pa_c.dylib',
-    'x86_64-pc-windows-msvc': 'c2pa_c.dll',
-    'aarch64-pc-windows-msvc': 'c2pa_c.dll',
-    'x86_64-unknown-linux-gnu': 'libc2pa_c.so',
-    'aarch64-unknown-linux-gnu': 'libc2pa_c.so',
+    'universal-apple-darwin': LIBRARY_NAMES['darwin'],
+    'aarch64-apple-darwin': LIBRARY_NAMES['darwin'],
+    'x86_64-apple-darwin': LIBRARY_NAMES['darwin'],
+    'x86_64-pc-windows-msvc': LIBRARY_NAMES['win32'],
+    'aarch64-pc-windows-msvc': LIBRARY_NAMES['win32'],
+    'x86_64-unknown-linux-gnu': LIBRARY_NAMES['linux'],
+    'aarch64-unknown-linux-gnu': LIBRARY_NAMES['linux'],
 }
 
 # Directory structure

src/c2pa/_library_names.py

@@ -0,0 +1,21 @@
+"""File names of the native c2pa library, keyed by sys.platform.
+
+Standard library only: setup.py and scripts/build_local_artifacts.py load
+this file by path, because importing the c2pa package loads the library.
+"""
+
+import sys
+
+LIBRARY_NAMES = {
+    "darwin": "libc2pa_c.dylib",
+    "linux": "libc2pa_c.so",
+    "win32": "c2pa_c.dll",
+}
+
+
+def get_library_name() -> str:
+    """Return the native library file name for the running platform."""
+    library_name = LIBRARY_NAMES.get(sys.platform)
+    if library_name is None:
+        raise RuntimeError(f"Unsupported platform: {sys.platform}")
+    return library_name

src/c2pa/c2pa.py

@@ -29,6 +29,7 @@
 from typing import Optional, Union, Callable, Any, overload
 import io
 from .lib import dynamically_load_library, record_owner_pid, is_foreign_process
+from ._library_names import get_library_name
 import mimetypes
 from itertools import count
 
@@ -144,12 +145,7 @@ def _validate_library_exports(lib):
 
 
 # Determine the library name based on the platform
-if sys.platform == "win32":  # pragma: no cover
-    _lib_name_default = "c2pa_c.dll"
-elif sys.platform == "darwin":  # pragma: no cover
-    _lib_name_default = "libc2pa_c.dylib"
-else:  # pragma: no cover
-    _lib_name_default = "libc2pa_c.so"
+_lib_name_default = get_library_name()
 
 # Check for C2PA_LIBRARY_NAME environment variable
 env_lib_name = os.environ.get("C2PA_LIBRARY_NAME")

src/c2pa/lib.py

@@ -13,6 +13,8 @@
 from typing import Optional
 from enum import Enum
 
+from ._library_names import get_library_name
+
 # Debug flag for library loading
 DEBUG_LIBRARY_LOADING = False
 
@@ -219,14 +221,7 @@ def dynamically_load_library(
     Returns:
         The loaded library or None if loading failed
     """
-    if sys.platform == "darwin":
-        c2pa_lib_name = "libc2pa_c.dylib"
-    elif sys.platform == "linux":
-        c2pa_lib_name = "libc2pa_c.so"
-    elif sys.platform == "win32":
-        c2pa_lib_name = "c2pa_c.dll"
-    else:
-        raise RuntimeError(f"Unsupported platform: {sys.platform}")
+    c2pa_lib_name = get_library_name()
 
     if DEBUG_LIBRARY_LOADING:  # pragma: no cover
         logger.info(f"Current working directory: {Path.cwd()}")