django.core-files
Storage类可以比喻成File的容器。它可以是本地文件系统，也可以是远端的FTP服务器。它定义了标准接口，用于访问或者修改文件。
class Storage(object):
"""
A base storage class, providing some default behaviors that all other
storage systems can inherit or override, as necessary.
"""
# The following methods represent a public interface to private methods.
# These shouldn't be overridden by subclasses unless absolutely necessary.
def open(self, name, mode='rb'):
"""
Retrieves the specified file from storage.
"""
return self._open(name, mode)
def save(self, name, content):
"""
Saves new content to the file specified by name. The content should be
a proper File object or any python file-like object, ready to be read
from the beginning.
"""
# Get the proper name for the file, as it will actually be saved.
if name is None:
name = content.name
if not hasattr(content, 'chunks'):
content = File(content)
name = self.get_available_name(name)
name = self._save(name, content)
# Store filenames with forward slashes, even on Windows
return force_text(name.replace('\\', '/'))
# These methods are part of the public API, with default implementations.
def get_valid_name(self, name):
"""
Returns a filename, based on the provided filename, that's suitable for
use in the target storage system.
"""
return get_valid_filename(name)
def get_available_name(self, name):
"""
Returns a filename that's free on the target storage system, and
available for new content to be written to.
"""
dir_name, file_name = os.path.split(name)
file_root, file_ext = os.path.splitext(file_name)
# If the filename already exists, add an underscore and a random 7
# character alphanumeric string (before the file extension, if one
# exists) to the filename until the generated filename doesn't exist.
while self.exists(name):
# file_ext includes the dot.
name = os.path.join(dir_name, "%s_%s%s" % (file_root, get_random_string(7), file_ext))
return name
主要看open和save方法。通过name标识符，打开或者保存相应的文件。他们其实都调用了_open和_save方法，子类只要复写这两个方法即可。
get_valid_name和get_available_name方法，是用来生成随机文件名，防止多线程冲突。
继续看Storage的定义：
def path(self, name):
"""
Returns a local filesystem path where the file can be retrieved using
Python's built-in open() function. Storage systems that can't be
accessed using open() should *not* implement this method.
"""
raise NotImplementedError("This backend doesn't support absolute paths.")
# The following methods form the public API for storage systems, but with
# no default implementations. Subclasses must implement *all* of these.
def delete(self, name):
"""
Deletes the specified file from the storage system.
"""
raise NotImplementedError('subclasses of Storage must provide a delete() method')
def exists(self, name):
"""
Returns True if a file referenced by the given name already exists in the
storage system, or False if the name is available for a new file.
"""
raise NotImplementedError('subclasses of Storage must provide an exists() method')
def listdir(self, path):
"""
Lists the contents of the specified path, returning a 2-tuple of lists;
the first item being directories, the second item being files.
"""
raise NotImplementedError('subclasses of Storage must provide a listdir() method')
def size(self, name):
"""
Returns the total size, in bytes, of the file specified by name.
"""
raise NotImplementedError('subclasses of Storage must provide a size() method')
子类需要实现这几个方法，来支持增加，删除，访问文件大小，列表的一系列的容器功能。
其中Sotage的一个子类FileSystemStorage，经常被用到。
class FileSystemStorage(Storage):
"""
Standard filesystem storage
"""
def __init__(self, location=None, base_url=None, file_permissions_mode=None,
directory_permissions_mode=None):
if location is None:
location = settings.MEDIA_ROOT
self.base_location = location
self.location = abspathu(self.base_location)
if base_url is None:
base_url = settings.MEDIA_URL
elif not base_url.endswith('/'):
base_url += '/'
self.base_url = base_url
self.file_permissions_mode = (
file_permissions_mode if file_permissions_mode is not None
else settings.FILE_UPLOAD_PERMISSIONS
)
self.directory_permissions_mode = (
directory_permissions_mode if directory_permissions_mode is not None
else settings.FILE_UPLOAD_DIRECTORY_PERMISSIONS
)
因为FileSystemStorage是本地文件系统，必需指定location(目录)，file_permissions_mode(文件权限)，directory_permissions_mode(目录权限)，还有base_url(用来web通过url访问)。
def _open(self, name, mode='rb'):
return File(open(self.path(name), mode))
def delete(self, name):
assert name, "The name argument is not allowed to be empty."
name = self.path(name)
# If the file exists, delete it from the filesystem.
# Note that there is a race between os.path.exists and os.remove:
# if os.remove fails with ENOENT, the file was removed
# concurrently, and we can continue normally.
if os.path.exists(name):
try:
os.remove(name)
except OSError as e:
if e.errno != errno.ENOENT:
raise
def exists(self, name):
return os.path.exists(self.path(name))
def listdir(self, path):
path = self.path(path)
directories, files = [], []
for entry in os.listdir(path):
if os.path.isdir(os.path.join(path, entry)):
directories.append(entry)
else:
files.append(entry)
return directories, files
def path(self, name):
return safe_join(self.location, name)
def size(self, name):
return os.path.getsize(self.path(name))
def url(self, name):
if self.base_url is None:
raise ValueError("This file is not accessible via a URL.")
return urljoin(self.base_url, filepath_to_uri(name))
def accessed_time(self, name):
return datetime.fromtimestamp(os.path.getatime(self.path(name)))
def created_time(self, name):
return datetime.fromtimestamp(os.path.getctime(self.path(name)))
def modified_time(self, name):
return datetime.fromtimestamp(os.path.getmtime(self.path(name)))
以上是FileSystemStorage的实现，它复写了父类的方法，都是以os.path模块实现的。
_save的实现比较复杂，这是因为多线程的同步。
def _save(self, name, content):
full_path = self.path(name)
# Create any intermediate directories that do not exist.
# Note that there is a race between os.path.exists and os.makedirs:
# if os.makedirs fails with EEXIST, the directory was created
# concurrently, and we can continue normally. Refs #16082.
directory = os.path.dirname(full_path)
if not os.path.exists(directory):
try:
if self.directory_permissions_mode is not None:
# os.makedirs applies the global umask, so we reset it,
# for consistency with file_permissions_mode behavior.
old_umask = os.umask(0)
try:
os.makedirs(directory, self.directory_permissions_mode)
finally:
os.umask(old_umask)
else:
os.makedirs(directory)
except OSError as e:
if e.errno != errno.EEXIST:
raise
if not os.path.isdir(directory):
raise IOError("%s exists and is not a directory." % directory)
# There's a potential race condition between get_available_name and
# saving the file; it's possible that two threads might return the
# same name, at which point all sorts of fun happens. So we need to
# try to create the file, but if it already exists we have to go back
# to get_available_name() and try again.
while True:
try:
# This file has a file path that we can move.
if hasattr(content, 'temporary_file_path'):
file_move_safe(content.temporary_file_path(), full_path)
# This is a normal uploadedfile that we can stream.
else:
# This fun binary flag incantation makes os.open throw an
# OSError if the file already exists before we open it.
flags = (os.O_WRONLY | os.O_CREAT | os.O_EXCL |
getattr(os, 'O_BINARY', 0))
# The current umask value is masked out by os.open!
fd = os.open(full_path, flags, 0o666)
_file = None
try:
locks.lock(fd, locks.LOCK_EX)
for chunk in content.chunks():
if _file is None:
mode = 'wb' if isinstance(chunk, bytes) else 'wt'
_file = os.fdopen(fd, mode)
_file.write(chunk)
finally:
locks.unlock(fd)
if _file is not None:
_file.close()
else:
os.close(fd)
except OSError as e:
if e.errno == errno.EEXIST:
# Ooops, the file exists. We need a new file name.
name = self.get_available_name(name)
full_path = self.path(name)
else:
raise
else:
# OK, the file save worked. Break out of the loop.
break
_save方法，首先新建目录，然后获取文件名，锁定，再将数据写入到文件中。