Add packaging-21.0

lib/packaging/_musllinux.py

@@ -0,0 +1,136 @@
+"""PEP 656 support.
+
+This module implements logic to detect if the currently running Python is
+linked against musl, and what musl version is used.
+"""
+
+import contextlib
+import functools
+import operator
+import os
+import re
+import struct
+import subprocess
+import sys
+from typing import IO, Iterator, NamedTuple, Optional, Tuple
+
+
+def _read_unpacked(f: IO[bytes], fmt: str) -> Tuple[int, ...]:
+    return struct.unpack(fmt, f.read(struct.calcsize(fmt)))
+
+
+def _parse_ld_musl_from_elf(f: IO[bytes]) -> Optional[str]:
+    """Detect musl libc location by parsing the Python executable.
+
+    Based on: https://gist.github.com/lyssdod/f51579ae8d93c8657a5564aefc2ffbca
+    ELF header: https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html
+    """
+    f.seek(0)
+    try:
+        ident = _read_unpacked(f, "16B")
+    except struct.error:
+        return None
+    if ident[:4] != tuple(b"\x7fELF"):  # Invalid magic, not ELF.
+        return None
+    f.seek(struct.calcsize("HHI"), 1)  # Skip file type, machine, and version.
+
+    try:
+        # e_fmt: Format for program header.
+        # p_fmt: Format for section header.
+        # p_idx: Indexes to find p_type, p_offset, and p_filesz.
+        e_fmt, p_fmt, p_idx = {
+            1: ("IIIIHHH", "IIIIIIII", (0, 1, 4)),  # 32-bit.
+            2: ("QQQIHHH", "IIQQQQQQ", (0, 2, 5)),  # 64-bit.
+        }[ident[4]]
+    except KeyError:
+        return None
+    else:
+        p_get = operator.itemgetter(*p_idx)
+
+    # Find the interpreter section and return its content.
+    try:
+        _, e_phoff, _, _, _, e_phentsize, e_phnum = _read_unpacked(f, e_fmt)
+    except struct.error:
+        return None
+    for i in range(e_phnum + 1):
+        f.seek(e_phoff + e_phentsize * i)
+        try:
+            p_type, p_offset, p_filesz = p_get(_read_unpacked(f, p_fmt))
+        except struct.error:
+            return None
+        if p_type != 3:  # Not PT_INTERP.
+            continue
+        f.seek(p_offset)
+        interpreter = os.fsdecode(f.read(p_filesz)).strip("\0")
+        if "musl" not in interpreter:
+            return None
+        return interpreter
+    return None
+
+
+class _MuslVersion(NamedTuple):
+    major: int
+    minor: int
+
+
+def _parse_musl_version(output: str) -> Optional[_MuslVersion]:
+    lines = [n for n in (n.strip() for n in output.splitlines()) if n]
+    if len(lines) < 2 or lines[0][:4] != "musl":
+        return None
+    m = re.match(r"Version (\d+)\.(\d+)", lines[1])
+    if not m:
+        return None
+    return _MuslVersion(major=int(m.group(1)), minor=int(m.group(2)))
+
+
+@functools.lru_cache()
+def _get_musl_version(executable: str) -> Optional[_MuslVersion]:
+    """Detect currently-running musl runtime version.
+
+    This is done by checking the specified executable's dynamic linking
+    information, and invoking the loader to parse its output for a version
+    string. If the loader is musl, the output would be something like::
+
+        musl libc (x86_64)
+        Version 1.2.2
+        Dynamic Program Loader
+    """
+    with contextlib.ExitStack() as stack:
+        try:
+            f = stack.enter_context(open(executable, "rb"))
+        except IOError:
+            return None
+        ld = _parse_ld_musl_from_elf(f)
+    if not ld:
+        return None
+    proc = subprocess.run([ld], stderr=subprocess.PIPE, universal_newlines=True)
+    return _parse_musl_version(proc.stderr)
+
+
+def platform_tags(arch: str) -> Iterator[str]:
+    """Generate musllinux tags compatible to the current platform.
+
+    :param arch: Should be the part of platform tag after the ``linux_``
+        prefix, e.g. ``x86_64``. The ``linux_`` prefix is assumed as a
+        prerequisite for the current platform to be musllinux-compatible.
+
+    :returns: An iterator of compatible musllinux tags.
+    """
+    sys_musl = _get_musl_version(sys.executable)
+    if sys_musl is None:  # Python not dynamically linked against musl.
+        return
+    for minor in range(sys_musl.minor, -1, -1):
+        yield f"musllinux_{sys_musl.major}_{minor}_{arch}"
+
+
+if __name__ == "__main__":  # pragma: no cover
+    import sysconfig
+
+    plat = sysconfig.get_platform()
+    assert plat.startswith("linux-"), "not linux"
+
+    print("plat:", plat)
+    print("musl:", _get_musl_version(sys.executable))
+    print("tags:", end=" ")
+    for t in platform_tags(re.sub(r"[.-]", "_", plat.split("-", 1)[-1])):
+        print(t, end="\n      ")