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def init(
    self,
    *,
    directory: typing.Optional[PathLike] = None,
    packages: typing.Optional[
        typing.List[typing.Union[str, typing.Tuple[str, str]]]
    ] = None,
    html: bool = False,
    check_dir: bool = True,
    follow_symlink: bool = False,
) -> None:
    self.directory = directory
    self.packages = packages
    self.all_directories = self.get_directories(directory, packages)
    self.html = html
    self.config_checked = False
    self.follow_symlink = follow_symlink
    if check_dir and directory is not None and not os.path.isdir(directory):
        raise RuntimeError(f“Directory ‘{directory}‘ does not exist”)

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def get_directories(
    self,
    directory: typing.Optional[PathLike] = None,
    packages: typing.Optional[
        typing.List[typing.Union[str, typing.Tuple[str, str]]]
    ] = None,
) -> typing.List[PathLike]:
    “””
    Given directory and packages arguments, return a list of all the
    directories that should be used for serving static files from.
    “””
    directories = []
    if directory is not None:
        directories.append(directory)
    for package in packages or []:
        if isinstance(package, tuple):
            package, statics_dir = package
        else:
            statics_dir = “statics”
        spec = importlib.util.find_spec(package)
        assert spec is not None, f“Package {package!r} could not be found.”
        assert spec.origin is not None, f“Package {package!r} could not be found.”
        package_directory = os.path.normpath(
            os.path.join(spec.origin, “..”, statics_dir)
        )
        assert os.path.isdir(
            package_directory
        ), f“Directory ‘{statics_dir!r}‘ in package {package!r} could not be found.”
        directories.append(package_directory)
    return directories

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def get_path(self, scope: Scope) -> str:
    “””
    Given the ASGI scope, return the path string to serve up,
    with OS specific path separators, and any ‘..’, ‘.’ components removed.
    “””
    return os.path.normpath(os.path.join(*scope[“path”].split(“/“)))

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async def get_response(self, path: str, scope: Scope) -> Response:
    “””
    Returns an HTTP response, given the incoming path, method and request headers.
    “””
    if scope[“method”] not in (“GET”, “HEAD”):
        raise HTTPException(status_code=405)
    try:
        full_path, stat_result = await anyio.to_thread.run_sync(
            self.lookup_path, path
        )
    except PermissionError:
        raise HTTPException(status_code=401)
    except OSError:
        raise
    if stat_result and stat.S_ISREG(stat_result.st_mode):
        # We have a static file to serve.
        return self.file_response(full_path, stat_result, scope)
    elif stat_result and stat.S_ISDIR(stat_result.st_mode) and self.html:
        # We’re in HTML mode, and have got a directory URL.
        # Check if we have ‘index.html’ file to serve.
        index_path = os.path.join(path, “index.html”)
        full_path, stat_result = await anyio.to_thread.run_sync(
            self.lookup_path, index_path
        )
        if stat_result is not None and stat.S_ISREG(stat_result.st_mode):
            if not scope[“path”].endswith(“/“):
                # Directory URLs should redirect to always end in “/“.
                url = URL(scope=scope)
                url = url.replace(path=url.path + “/“)
                return RedirectResponse(url=url)
            return self.file_response(full_path, stat_result, scope)
    if self.html:
        # Check for ‘404.html’ if we’re in HTML mode.
        full_path, stat_result = await anyio.to_thread.run_sync(
            self.lookup_path, “404.html”
        )
        if stat_result and stat.S_ISREG(stat_result.st_mode):
            return FileResponse(
                full_path,
                stat_result=stat_result,
                method=scope[“method”],
                status_code=404,
            )
    raise HTTPException(status_code=404)

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def lookup_path(
    self, path: str
) -> typing.Tuple[str, typing.Optional[os.stat_result]]:
    for directory in self.all_directories:
        joined_path = os.path.join(directory, path)
        if self.follow_symlink:
            full_path = os.path.abspath(joined_path)
        else:
            full_path = os.path.realpath(joined_path)
        directory = os.path.realpath(directory)
        if os.path.commonpath([full_path, directory]) != directory:
            # Don’t allow misbehaving clients to break out of the static files
            # directory.
            continue
        try:
            return full_path, os.stat(full_path)
        except (FileNotFoundError, NotADirectoryError):
            continue
    return “”, None

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def file_response(
    self,
    full_path: PathLike,
    stat_result: os.stat_result,
    scope: Scope,
    status_code: int = 200,
) -> Response:
    method = scope[“method”]
    request_headers = Headers(scope=scope)
    response = FileResponse(
        full_path, status_code=status_code, stat_result=stat_result, method=method
    )
    if self.is_not_modified(response.headers, request_headers):
        return NotModifiedResponse(response.headers)
    return response

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async def check_config(self) -> None:
    “””
    Perform a one-off configuration check that StaticFiles is actually
    pointed at a directory, so that we can raise loud errors rather than
    just returning 404 responses.
    “””
    if self.directory is None:
        return
    try:
        stat_result = await anyio.to_thread.run_sync(os.stat, self.directory)
    except FileNotFoundError:
        raise RuntimeError(
            f“StaticFiles directory ‘{self.directory}‘ does not exist.”
        )
    if not (stat.S_ISDIR(stat_result.st_mode) or stat.S_ISLNK(stat_result.st_mode)):
        raise RuntimeError(
            f“StaticFiles path ‘{self.directory}‘ is not a directory.”
        )

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def is_not_modified(
    self, response_headers: Headers, request_headers: Headers
) -> bool:
    “””
    Given the request and response headers, return True if an HTTP
    “Not Modified” response could be returned instead.
    “””
    try:
        if_none_match = request_headers[“if-none-match”]
        etag = response_headers[“etag”]
        if if_none_match == etag:
            return True
    except KeyError:
        pass
    try:
        if_modified_since = parsedate(request_headers[“if-modified-since”])
        last_modified = parsedate(response_headers[“last-modified”])
        if (
            if_modified_since is not None
            and last_modified is not None
            and if_modified_since >= last_modified
        ):
            return True
    except KeyError:
        pass
    return False