cephadm: add a pythonic build.py for constructing the cephadm binary

As discussed in a ceph orch meeting, the build.sh script was deemed
"unpythonic". This script is a first attempt to do it more pythonic
with fewer explicit version checks.

This change minimizes the existing build.sh to simply call build.py.
We can completely eliminate build.sh at a later time if desired.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

2 files changed, 159 insertions, 43 deletions

diff --git a/src/cephadm/build.py b/src/cephadm/build.py
new file mode 100755
index 00000000000..4e97f5d3757
--- /dev/null
+++ b/src/cephadm/build.py
@@ -0,0 +1,158 @@
+#!/usr/bin/python3
+"""Build cephadm from one or more files into a standalone executable.
+"""
+# TODO: If cephadm is being built and packaged within a format such as RPM
+# do we have to do anything special wrt passing in the version
+# of python to build with? Even with the intermediate cmake layer?
+
+import argparse
+import logging
+import os
+import pathlib
+import shutil
+import subprocess
+import tempfile
+import sys
+
+HAS_ZIPAPP = False
+try:
+    import zipapp
+
+    HAS_ZIPAPP = True
+except ImportError:
+    pass
+
+
+log = logging.getLogger(__name__)
+
+
+def _reexec(python):
+    """Switch to the selected version of python by exec'ing into the desired
+    python path.
+    Sets the _BUILD_PYTHON_SET env variable as a sentinel to indicate exec has
+    been performed.
+    """
+    env = os.environ.copy()
+    env["_BUILD_PYTHON_SET"] = python
+    os.execvpe(python, [python, __file__] + sys.argv[1:], env)
+
+
+def _did_rexec():
+    """Returns true if the process has already exec'ed into the desired python
+    version.
+    """
+    return bool(os.environ.get("_BUILD_PYTHON_SET", ""))
+
+
+def _build(dest, src):
+    """Build the binary."""
+    os.chdir(src)
+    tempdir = pathlib.Path(tempfile.mkdtemp(suffix=".cephadm.build"))
+    log.debug("working in %s", tempdir)
+    try:
+        if os.path.isfile("requirements.txt"):
+            _install_deps(tempdir)
+        log.info("Copying contents")
+        # TODO: currently the only file relevant to a compiled cephadm is the
+        # cephadm.py file. Once cephadm is broken up into multiple py files
+        # (and possibly other libs from python-common, etc) we'll want some
+        # sort organized structure to track what gets copied into the
+        # dir to be zipped. For now we just have a simple call to copy
+        # (and rename) the one file we care about.
+        shutil.copy("cephadm.py", tempdir / "__main__.py")
+        _compile(dest, tempdir)
+    finally:
+        shutil.rmtree(tempdir)
+
+
+def _compile(dest, tempdir):
+    """Compile the zipapp."""
+    # TODO we could explicitly pass a python version here
+    log.info("Constructing the zipapp file")
+    try:
+        zipapp.create_archive(
+            source=tempdir,
+            target=dest,
+            interpreter=sys.executable,
+            compressed=True,
+        )
+        log.info("Zipapp created with compression")
+    except TypeError:
+        # automatically fall back to uncompressed
+        zipapp.create_archive(
+            source=tempdir,
+            target=dest,
+            interpreter=sys.executable,
+        )
+        log.info("Zipapp created without compression")
+
+
+def _install_deps(tempdir):
+    """Install dependencies with pip."""
+    # TODO we could explicitly pass a python version here
+    log.info("Installing dependencies")
+    # apparently pip doesn't have an API, just a cli.
+    subprocess.check_call(
+        [
+            sys.executable,
+            "-m",
+            "pip",
+            "install",
+            "--requirement",
+            "requirements.txt",
+            "--target",
+            tempdir,
+        ]
+    )
+
+
+def main():
+    handler = logging.StreamHandler(sys.stdout)
+    handler.setFormatter(logging.Formatter("cephadm/build.py: %(message)s"))
+    log.addHandler(handler)
+    log.setLevel(logging.INFO)
+
+    log.debug("argv: %r", sys.argv)
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "dest", help="Destination path name for new cephadm binary"
+    )
+    parser.add_argument(
+        "--source", help="Directory containing cephadm sources"
+    )
+    parser.add_argument(
+        "--python", help="The path to the desired version of python"
+    )
+    args = parser.parse_args()
+
+    if not _did_rexec() and args.python:
+        _reexec(args.python)
+
+    log.info(
+        "Python Version: {v.major}.{v.minor}.{v.micro}".format(
+            v=sys.version_info
+        )
+    )
+    log.info("Args: %s", vars(args))
+    if not HAS_ZIPAPP:
+        # Unconditionally display an error that the version of python
+        # lacks zipapp (probably too old).
+        print("error: zipapp module not found", file=sys.stderr)
+        print(
+            "(zipapp is available in Python 3.5 or later."
+            " are you using a new enough version?)",
+            file=sys.stderr,
+        )
+        sys.exit(2)
+    if args.source:
+        source = pathlib.Path(args.source).absolute()
+    else:
+        source = pathlib.Path(__file__).absolute().parent
+    dest = pathlib.Path(args.dest).absolute()
+    log.info("Source Dir: %s", source)
+    log.info("Destination Path: %s", dest)
+    _build(dest, source)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/cephadm/build.sh b/src/cephadm/build.sh
index 00bd4c74925..84b58f14f57 100755
--- a/src/cephadm/build.sh
+++ b/src/cephadm/build.sh
@@ -1,47 +1,5 @@
 #!/bin/bash -ex
 
-SCRIPT_NAME=$(basename ${BASH_SOURCE[0]})
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
-clean_up() {
-    if [ -e ${buildir} ]; then
-        rm -rf ${builddir}
-    fi
-}
-trap clean_up EXIT
-
-PYTHON=$(which python3)
-
-# Create build directory and install required dependencies
-target_fpath=${SCRIPT_DIR}/cephadm
-if [ -n "$1" ]; then
-    target_fpath="$1"
-fi
-builddir=$(mktemp -d)
-if [ -e "requirements.txt" ]; then
-    $PYTHON -m pip install -r requirements.txt --target ${builddir}
-fi
-
-# Make sure all newly created source files are copied here as well!
-cp ${SCRIPT_DIR}/cephadm.py ${builddir}/__main__.py
-
-version=$($PYTHON --version)
-if [[ "$version" =~ ^Python[[:space:]]([[:digit:]]+)\.([[:digit:]]+)\.([[:digit:]]+)$ ]]; then
-    major=${BASH_REMATCH[1]}
-    minor=${BASH_REMATCH[2]}
-
-    compress=""
-    if [[ "$major" -ge 3 && "$minor" -ge 7 ]]; then
-        echo "Python version compatible with --compress, compressing cephadm binary"
-        compress="--compress"
-    elif [[ "$major" -lt 3 || "$major" -eq 3 && "$minor" -lt 5 ]]; then
-	echo "zipapp module requires Python35 or greater"
-	exit 1
-    fi
-
-    $PYTHON -mzipapp -p $PYTHON ${builddir} ${compress} --output $target_fpath
-    echo written to ${target_fpath}
-else
-    echo "Couldn't parse Python version"
-    exit 1
-fi
+exec python3 $SCRIPT_DIR/build.py "$@"