bindings: python: optionally include module in sdist

Optionally vendor libgpiod source into sdist so that the Python module can
be built from source, even with a missing or mismatched system libgpiod.

Add two new environment variables "LINK_SYSTEM_LIBGPIOD" and
"LIBGPIOD_VERSION" to control what kind of package setup.py will build.

In order to build an sdist or wheel package with a vendored libgpiod a
version must be specified via the "LIBGPIOD_VERSION" environment variable.

This will instruct setup.py to verify the given version against the list
in sha256sums.asc and ensure it meets or exceeds a LIBGPIOD_MINIMUM_VERSION
required for compatibility with the bindings.

It will then fetch the tarball matching the requested version from
mirrors.edge.kernel.org, verify the sha256 signature, unpack it, and copy
the lib and include directories into the package root so they can be
included in sdist or used to build a binary wheel.

eg: LIBGPIOD_VERSION=2.1.0 python3 setup.py sdist

Will build a source distribution with gpiod version 2.1.0 source included.

It will also save the gpiod version into "libgpiod-version.txt" so that it
can be passed to the build when the sdist is built by pip.

Requiring an explicit version ensures that the Python bindings - which
can be changed and versions independent of libgpiod - are built against a
stable libgpiod release.

In order to force a package with vendored gpiod source to link the system
libgpiod, the "LINK_SYSTEM_LIBGPIOD" environment variable can be used:

eg: LINK_SYSTEM_LIBGPIOD=1 pip install libgpiod

Signed-off-by: Phil Howard <phil@gadgetoid.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

3 files changed, 207 insertions, 12 deletions

diff --git a/bindings/python/MANIFEST.in b/bindings/python/MANIFEST.in
index 459b3170..efdfd185 100644
--- a/bindings/python/MANIFEST.in
+++ b/bindings/python/MANIFEST.in
@@ -3,6 +3,7 @@
 
 include setup.py
 include README.md
+include libgpiod-version.txt
 
 recursive-include gpiod *.py
 recursive-include tests *.py
@@ -12,3 +13,7 @@ recursive-include gpiod/ext *.h
 
 recursive-include tests/gpiosim *.c
 recursive-include tests/procname *.c
+
+recursive-include lib *.c
+recursive-include lib *.h
+recursive-include include *.h
diff --git a/bindings/python/pyproject.toml b/bindings/python/pyproject.toml
index fcf6bbe4..f6bf43c0 100644
--- a/bindings/python/pyproject.toml
+++ b/bindings/python/pyproject.toml
@@ -2,4 +2,4 @@
 # SPDX-FileCopyrightText: 2023 Phil Howard <phil@gadgetoid.com>
 
 [build-system]
-requires = ["setuptools", "wheel"]
+requires = ["setuptools", "wheel", "packaging"]
diff --git a/bindings/python/setup.py b/bindings/python/setup.py
index c8db0a0e..904b5f3f 100644
--- a/bindings/python/setup.py
+++ b/bindings/python/setup.py
@@ -1,24 +1,216 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 # SPDX-FileCopyrightText: 2022 Bartosz Golaszewski <brgl@bgdev.pl>
 
-from os import environ, path
-from setuptools import setup, Extension, find_packages
+from os import getenv, path, unlink
+from shutil import copytree, rmtree
+
+from setuptools import Extension, find_packages, setup
 from setuptools.command.build_ext import build_ext as orig_build_ext
-from shutil import rmtree
+from setuptools.command.sdist import log
+from setuptools.command.sdist import sdist as orig_sdist
+from setuptools.errors import BaseError
+
+LINK_SYSTEM_LIBGPIOD = getenv("LINK_SYSTEM_LIBGPIOD") == "1"
+LIBGPIOD_MINIMUM_VERSION = "2.1.0"
+LIBGPIOD_VERSION = getenv("LIBGPIOD_VERSION")
+GPIOD_WITH_TESTS = getenv("GPIOD_WITH_TESTS") == "1"
+SRC_BASE_URL = "https://mirrors.edge.kernel.org/pub/software/libs/libgpiod/"
+TAR_FILENAME = "libgpiod-{version}.tar.gz"
+ASC_FILENAME = "sha256sums.asc"
+SHA256_CHUNK_SIZE = 2048
+
+# __version__
+with open("gpiod/version.py", "r") as fd:
+    exec(fd.read())
+
+
+def sha256(filename):
+    """
+    Return a sha256sum for a specific filename, loading the file in chunks
+    to avoid potentially excessive memory use.
+    """
+    from hashlib import sha256
+
+    sha256sum = sha256()
+    with open(filename, "rb") as f:
+        for chunk in iter(lambda: f.read(SHA256_CHUNK_SIZE), b""):
+            sha256sum.update(chunk)
+
+    return sha256sum.hexdigest()
+
+
+def find_sha256sum(asc_file, tar_filename):
+    """
+    Search through a local copy of sha256sums.asc for a specific filename
+    and return the associated sha256 sum.
+    """
+    with open(asc_file, "r") as f:
+        for line in f:
+            line = line.strip().split("  ")
+            if len(line) == 2 and line[1] == tar_filename:
+                return line[0]
+
+    raise BaseError(f"no signature found for {tar_filename}")
+
+
+def fetch_tarball(command):
+    """
+    Verify the requested LIBGPIOD_VERSION tarball exists in sha256sums.asc,
+    fetch it from https://mirrors.edge.kernel.org/pub/software/libs/libgpiod/
+    and verify its sha256sum.
+
+    If the check passes, extract the tarball and copy the lib and include
+    dirs into our source tree.
+    """
+
+    # If no LIBGPIOD_VERSION is specified in env, just run the command
+    if LIBGPIOD_VERSION is None:
+        return command
+
+    # If LIBGPIOD_VERSION is specified, apply the tarball wrapper
+    def wrapper(self):
+        # Just-in-time import of tarfile and urllib.request so these are
+        # not required for Yocto to build a vendored or linked package
+        import tarfile
+        from tempfile import TemporaryDirectory
+        from urllib.request import urlretrieve
+
+        from packaging.version import Version
+
+        # The "build" frontend will run setup.py twice within the same
+        # temporary output directory. First for "sdist" and then for "wheel"
+        # This would cause the build to fail with dirty "lib" and "include"
+        # directories.
+        # If the version in "libgpiod-version.txt" already matches our
+        # requested tarball, then skip the fetch altogether.
+        try:
+            if open("libgpiod-version.txt", "r").read() == LIBGPIOD_VERSION:
+                log.info(f"skipping tarball fetch")
+                command(self)
+                return
+        except OSError:
+            pass
+
+        # Early exit for build tree with dirty lib/include dirs
+        for check_dir in "lib", "include":
+            if path.isdir(f"./{check_dir}"):
+                raise BaseError(f"refusing to overwrite ./{check_dir}")
+
+        with TemporaryDirectory(prefix="libgpiod-") as temp_dir:
+            tarball_filename = TAR_FILENAME.format(version=LIBGPIOD_VERSION)
+            tarball_url = f"{SRC_BASE_URL}{tarball_filename}"
+            asc_url = f"{SRC_BASE_URL}{ASC_FILENAME}"
+
+            log.info(f"fetching: {asc_url}")
+
+            asc_filename, _ = urlretrieve(asc_url, path.join(temp_dir, ASC_FILENAME))
+
+            tarball_sha256 = find_sha256sum(asc_filename, tarball_filename)
+
+            if Version(LIBGPIOD_VERSION) < Version(LIBGPIOD_MINIMUM_VERSION):
+                raise BaseError(f"requires libgpiod>={LIBGPIOD_MINIMUM_VERSION}")
+
+            log.info(f"fetching: {tarball_url}")
+
+            downloaded_tarball, _ = urlretrieve(
+                tarball_url, path.join(temp_dir, tarball_filename)
+            )
+
+            log.info(f"verifying: {tarball_filename}")
+            if sha256(downloaded_tarball) != tarball_sha256:
+                raise BaseError(f"signature mismatch for {tarball_filename}")
+
+            # Unpack the downloaded tarball
+            log.info(f"unpacking: {tarball_filename}")
+            with tarfile.open(downloaded_tarball) as f:
+                f.extractall(temp_dir)
+
+            # Copy the include and lib directories we need to build libgpiod
+            base_dir = path.join(temp_dir, f"libgpiod-{LIBGPIOD_VERSION}")
+            copytree(path.join(base_dir, "include"), "./include")
+            copytree(path.join(base_dir, "lib"), "./lib")
+
+        # Save the libgpiod version for sdist
+        open("libgpiod-version.txt", "w").write(LIBGPIOD_VERSION)
+
+        # Run the command
+        command(self)
+
+        # Clean up the build directory
+        rmtree("./lib", ignore_errors=True)
+        rmtree("./include", ignore_errors=True)
+        unlink("libgpiod-version.txt")
+
+    return wrapper
 
 
 class build_ext(orig_build_ext):
     """
-    setuptools install all C extentions even if they're excluded in setup().
-    As a workaround - remove the tests directory right after all extensions
-    were built (and possibly copied to the source directory if inplace is set).
+    Wrap build_ext to amend the module sources and settings to build
+    the bindings and gpiod into a combined module when a version is
+    specified and LINK_SYSTEM_LIBGPIOD=1 is not present in env.
+
+    run is wrapped with @fetch_tarball in order to fetch the sources
+    needed to build binary wheels when LIBGPIOD_VERSION is specified, eg:
+
+    LIBGPIOD_VERSION="2.0.2" python3 -m build .
     """
 
+    @fetch_tarball
     def run(self):
+        # Try to get the gpiod version from the .txt file included in sdist
+        try:
+            libgpiod_version = open("libgpiod-version.txt", "r").read()
+        except OSError:
+            libgpiod_version = LIBGPIOD_VERSION
+
+        if libgpiod_version and not LINK_SYSTEM_LIBGPIOD:
+            # When building the extension from an sdist with a vendored
+            # amend gpiod._ext sources and settings accordingly.
+            gpiod_ext = self.ext_map["gpiod._ext"]
+            gpiod_ext.sources += [
+                "lib/chip.c",
+                "lib/chip-info.c",
+                "lib/edge-event.c",
+                "lib/info-event.c",
+                "lib/internal.c",
+                "lib/line-config.c",
+                "lib/line-info.c",
+                "lib/line-request.c",
+                "lib/line-settings.c",
+                "lib/misc.c",
+                "lib/request-config.c",
+            ]
+            gpiod_ext.libraries = []
+            gpiod_ext.include_dirs = ["include", "lib", "gpiod/ext"]
+            gpiod_ext.extra_compile_args.append(
+                f'-DGPIOD_VERSION_STR="{libgpiod_version}"',
+            )
+
         super().run()
+
+        # We don't ever want the module tests directory in our package
+        # since this might include gpiosim._ext or procname._ext from a
+        # previous dirty build tree.
         rmtree(path.join(self.build_lib, "tests"), ignore_errors=True)
 
 
+class sdist(orig_sdist):
+    """
+    Wrap sdist in order to fetch the libgpiod source files for vendoring
+    into a source distribution.
+
+    run is wrapped with @fetch_tarball in order to fetch the sources
+    needed to build binary wheels when LIBGPIOD_VERSION is specified, eg:
+
+    LIBGPIOD_VERSION="2.0.2" python3 -m build . --sdist
+    """
+
+    @fetch_tarball
+    def run(self):
+        super().run()
+
+
 gpiod_ext = Extension(
     "gpiod._ext",
     sources=[
@@ -50,19 +242,17 @@ procname_ext = Extension(
 )
 
 extensions = [gpiod_ext]
-if environ.get("GPIOD_WITH_TESTS") == "1":
+if GPIOD_WITH_TESTS:
     extensions.append(gpiosim_ext)
     extensions.append(procname_ext)
 
-with open("gpiod/version.py", "r") as fd:
-    exec(fd.read())
-
 setup(
     name="gpiod",
+    url="https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git",
     packages=find_packages(exclude=["tests", "tests.*"]),
     python_requires=">=3.9.0",
     ext_modules=extensions,
-    cmdclass={"build_ext": build_ext},
+    cmdclass={"build_ext": build_ext, "sdist": sdist},
     version=__version__,
     author="Bartosz Golaszewski",
     author_email="brgl@bgdev.pl",