Initial commit

.gitignore

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+# Created by https://www.toptal.com/developers/gitignore/api/python
+# Edit at https://www.toptal.com/developers/gitignore?templates=python
+
+### Python ###
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# poetry
+#   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
+#poetry.lock
+
+# pdm
+#   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
+#pdm.lock
+#   pdm stores project-wide configurations in .pdm.toml, but it is recommended to not include it
+#   in version control.
+#   https://pdm.fming.dev/#use-with-ide
+.pdm.toml
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# PyCharm
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#.idea/
+
+### Python Patch ###
+# Poetry local configuration file - https://python-poetry.org/docs/configuration/#local-configuration
+poetry.toml
+
+# ruff
+.ruff_cache/
+
+# LSP config files
+pyrightconfig.json
+
+# End of https://www.toptal.com/developers/gitignore/api/python

LICENSE

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+MIT License
+
+Copyright (c) 2023 Samuel FORESTIER
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# hosts_resolver
+
+> Zero-dependency Python module to resolve names using /etc/hosts alone
+
+## Rationale
+
+Sometimes we only want to resolve names using /etc/hosts entries without performing DNS requests (thus `socket.getaddrinfo` is out of the equation).
+
+So there are three options :
+
+* manually parse /etc/hosts
+* call `getent` program and parse its output
+* use this module (which binds libc `gethostent` function) !
+
+## Limitations
+
+- `gethostent` is not reentrant (see GETHOSTBYNAME(3))
+- `gethostent` is not thread-safe (see GETHOSTBYNAME(3))
+- glibc implementations does not support IPv6 addresses (see GETHOSTBYNAME(3))
+- behavior is **undefined** when using multiple context managers simultaneously
+
+## Installation
+
+```bash
+pip3 install hosts_resolver-*-py3-none-any.whl
+```
+
+## Usage
+
+### From API
+
+```python
+from hosts_resolver import get_hosts_resolver
+
+with get_hosts_resolver() as hosts_resolver:
+    print(hosts_resolver.resolve("localhost"))
+
+# -> IPv4Address('127.0.0.1')
+```
+
+### From CLI
+
+> Why bother ?? You should be looking at `getent` !
+
+```bash
+python3 hosts_resolver.py -j localhost
+# -> {"localhost": "127.0.0.1"}
+```
+
+## Development
+
+```bash
+pip3 install -r requirements-dev.txt
+
+pylint src/
+mypy src/
+isort --check src/
+black --check src/
+
+python3 -m build
+```

pyproject.toml

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+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "hosts_resolver"
+version = "1.0.0"
+authors = [
+    {name = "Samuel FORESTIER", email = "dev+hostsresolver@samuel.domains"},
+]
+description = "Zero-dependency Python module to resolve names using /etc/hosts alone"
+readme = "README.md"
+requires-python = ">=3.6"
+keywords = ["DNS", "gethostent", "hosts"]
+license = {text = "MIT"}
+classifiers=[
+    "Development Status :: 5 - Production/Stable",
+    "Environment :: Console",
+    "Intended Audience :: Developers",
+    "Intended Audience :: System Administrators",
+    "License :: OSI Approved :: MIT License",
+    "Natural Language :: English",
+    "Operating System :: POSIX :: BSD",
+    "Operating System :: POSIX :: Linux",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.6",
+    "Programming Language :: Python :: 3.7",
+    "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
+    "Topic :: Internet :: Name Service (DNS)",
+]
+
+[project.scripts]
+hosts_resolver = "hosts_resolver.hosts_resolver:main"
+
+[project.urls]
+Repository = "https://git.forestier.app/HorlogeSkynet/hosts_resolver"
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.setuptools.package-data]
+hosts_resolver = ["py.typed"]
+
+[tool.pylint.MASTER]
+load-plugins = ["pylint_secure_coding_standard"]
+
+[tool.black]
+line-length = 100
+target-version = ["py36"]
+
+[tool.isort]
+profile = "black"
+line_length = 100
+py_version = 36

requirements-dev.txt

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+black~=23.3.0
+build~=0.10.0
+isort~=5.12.0
+mypy~=1.3.0
+pylint~=2.17.4
+pylint-secure-coding-standard~=1.4.1

setup.py

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+from setuptools import setup
+
+setup()

src/hosts_resolver/hosts_resolver.py

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+"""hosts_resolver module"""
+
+import argparse
+import contextlib
+import ctypes
+import ipaddress
+import json
+import logging
+import os
+import socket
+import sys
+import typing
+from pathlib import Path
+
+
+class _Hostent(ctypes.Structure):  # pylint: disable=too-few-public-methods
+    """hostent netdb.h structure ctypes mapping"""
+
+    _fields_ = [
+        ("h_name", ctypes.c_char_p),
+        ("h_aliases", ctypes.POINTER(ctypes.c_char_p)),
+        ("h_addrtype", ctypes.c_int),
+        ("h_length", ctypes.c_int),
+        ("h_addr_list", ctypes.POINTER(ctypes.POINTER(ctypes.c_ubyte))),
+    ]
+
+
+_IPAddress = typing.Union[ipaddress.IPv4Address, ipaddress.IPv6Address]
+
+_libc = ctypes.CDLL("libc.so.6")
+
+# From <netdb.h> :
+## struct hostent *gethostent(void);
+_gethostent = _libc.gethostent
+_gethostent.restype = ctypes.POINTER(_Hostent)
+_gethostent.argtypes = ()
+
+# void endhostent(void);
+_endhostent = _libc.endhostent
+_endhostent.restype = None
+_endhostent.argtypes = ()
+
+_logger = logging.getLogger(Path(__file__).stem)
+
+
+class _HostsResolver:
+    """
+    _HostsResolver context manager definition.
+
+    Use this CM to resolve name using /etc/hosts entries without any DNS request or subprocess call.
+
+    Known limitations:
+      - `gethostent` is not reentrant (see GETHOSTBYNAME(3))
+      - `gethostent` is not thread-safe (see GETHOSTBYNAME(3))
+      - glibc implementations does not support IPv6 addresses (see GETHOSTBYNAME(3))
+      - behavior is **undefined** when using multiple context managers simultaneously
+    """
+
+    def __init__(self) -> None:
+        self._cached_aliases: typing.Dict[str, _IPAddress] = {}
+
+    def __enter__(self) -> "_HostsResolver":
+        return self
+
+    def __exit__(self, _, __, ___):
+        _endhostent()
+
+    def resolve(self, name: typing.Union[str, _IPAddress]) -> _IPAddress:
+        """Try to lazily resolve `name` using /etc/hosts entries. Results are cached"""
+        # don't try to resolve IP addresses for idempotency !
+        with contextlib.suppress(ValueError):
+            return ipaddress.ip_address(name)
+
+        while True:
+            # fetch result from cache (if present)
+            with contextlib.suppress(KeyError):
+                return self._cached_aliases[name]  # type: ignore[index]
+
+            # fetch "next" hosts entry
+            entry_ptr = ctypes.cast(_gethostent(), ctypes.POINTER(_Hostent))
+            if not entry_ptr:
+                _logger.debug("no more hosts entry")
+                break
+
+            # dereference structure pointer
+            entry = entry_ptr.contents
+
+            # decode entry "name"
+            aliases = [entry.h_name.decode("ascii")]
+
+            _logger.debug("got new hosts entry: %s", aliases[0])
+
+            # decode entry "aliases"
+            i = 0
+            h_aliases = ctypes.cast(entry.h_aliases, ctypes.POINTER(ctypes.c_char_p))
+            while h_aliases[i]:
+                aliases.append(h_aliases[i].decode("ascii"))
+                _logger.debug("found new alias for %s: %s", aliases[0], aliases[-1])
+                i += 1
+
+            # decode "network addresses" from raw bytes array
+            addresses = ctypes.cast(
+                entry.h_addr_list,
+                ctypes.POINTER(ctypes.POINTER(ctypes.c_ubyte * entry.h_length)),
+            )
+            address = ipaddress.ip_address(bytes(addresses[0].contents))
+
+            # populate cache with all entry aliases
+            for alias in aliases:
+                _logger.debug("caching %s as %s...", address, alias)
+                self._cached_aliases[alias] = address
+
+        raise socket.gaierror(f"could not resolve: {name}")
+
+
+@contextlib.contextmanager
+def get_hosts_resolver() -> typing.Generator[_HostsResolver, None, None]:
+    """Return an `_HostsResolver` instance to use as a context manager"""
+    with _HostsResolver() as hosts_resolver:
+        yield hosts_resolver
+
+
+def main() -> typing.NoReturn:
+    """Main entry point"""
+    parser = argparse.ArgumentParser(
+        description="Zero-dependency Python module to resolve names using /etc/hosts alone"
+    )
+
+    parser.add_argument(
+        "-v",
+        "--version",
+        action="version",
+        version="%(prog)s 1.0.0",
+    )
+    parser.add_argument(
+        "-d",
+        "--debug",
+        action="store_true",
+        help="enable debug mode",
+    )
+    parser.add_argument(
+        "-j",
+        "--json",
+        action="store_true",
+        help="output results as JSON",
+    )
+    parser.add_argument(
+        "names",
+        nargs="+",
+        help="names to resolve using /etc/hosts",
+    )
+
+    args = parser.parse_args()
+
+    logging.basicConfig(level=logging.DEBUG if args.debug else logging.INFO)
+
+    results: typing.Dict[str, typing.Optional[str]] = {}
+    with get_hosts_resolver() as hosts_resolver:
+        for name in args.names:
+            try:
+                results[name] = str(hosts_resolver.resolve(name))
+            except socket.gaierror:
+                # if JSON output is disabled, exit fast to prevent inconsistent output
+                if not args.json:
+                    raise
+
+                _logger.exception("resolution failed for %s", name)
+                results[name] = None
+
+    if args.json:
+        print(json.dumps(results, indent=4 if args.debug else None))
+    else:
+        print(os.linesep.join(results.values()))  # type: ignore[arg-type]
+
+    # exit with error if (at least) a resolution failed
+    sys.exit(not all(results.values()))
+
+
+if __name__ == "__main__":
+    main()