path: root/fs/remote.py

"""

fs.remote
=========

Utilities for interfacing with remote filesystems


This module provides reusable utility functions that can be used to construct
FS subclasses interfacing with a remote filesystem.  These include:

  * RemoteFileBuffer:  a file-like object that locally buffers the contents of
                       a remote file, writing them back on flush() or close().

  * ConnectionManagerFS:  a WrapFS subclass that tracks the connection state
                          of a remote FS, and allows client code to wait for
                          a connection to be re-established.

   * CacheFS:  a WrapFS subclass that caches file and directory meta-data in
               memory, to speed access to a remote FS.

"""

from __future__ import with_statement

import sys
import os
import time
import copy
from errno import EINVAL

from fs.base import FS, threading
from fs.wrapfs import WrapFS, wrap_fs_methods
from fs.wrapfs.lazyfs import LazyFS
from fs.path import *
from fs.errors import *
from fs.local_functools import wraps
from fs.filelike import StringIO, SpooledTemporaryFile, FileWrapper
from fs import SEEK_SET, SEEK_CUR, SEEK_END


class RemoteFileBuffer(FileWrapper):
    """File-like object providing buffer for local file operations.

    Instances of this class manage a local tempfile buffer corresponding
    to the contents of a remote file.  All reads and writes happen locally,
    with the content being copied to the remote file only on flush() or
    close().  Writes to the remote file are performed using the setcontents()
    method on the owning FS object.

    The intended use-case is for a remote filesystem (e.g. S3FS) to return
    instances of this class from its open() method, and to provide the
    file-uploading logic in its setcontents() method, as in the following
    pseudo-code::

        def open(self,path,mode="r"):
            rf = self._get_remote_file(path)
            return RemoteFileBuffer(self,path,mode,rf)

        def setcontents(self,path,file):
            self._put_remote_file(path,file)

    The contents of the remote file are read into the buffer on-demand.
    """

    max_size_in_memory = 1024 * 8

    def __init__(self, fs, path, mode, rfile=None, write_on_flush=True):
        """RemoteFileBuffer constructor.

        The owning filesystem, path and mode must be provided.  If the
        optional argument 'rfile' is provided, it must be a read()-able
        object or a string containing the initial file contents.
        """
        wrapped_file = SpooledTemporaryFile(max_size=self.max_size_in_memory)
        self.fs = fs
        self.path = path
        self.write_on_flush = write_on_flush
        self._changed = False
        self._readlen = 0 # How many bytes already loaded from rfile
        self._rfile = None # Reference to remote file object 
        self._eof = False # Reached end of rfile?
        if getattr(fs,"_lock",None) is not None:
            self._lock = fs._lock.__class__()
        else:
            self._lock = threading.RLock()
        
        if "r" in mode or "+" in mode or "a" in mode:
            if rfile is None:
                # File was just created, force to write anything
                self._changed = True
                self._eof = True
                
            if not hasattr(rfile, "read"):
                rfile = StringIO(unicode(rfile))
                
            self._rfile = rfile
        else:
            # Do not use remote file object
            self._eof = True
            self._rfile = None
            if rfile is not None and hasattr(rfile,"close"):
                rfile.close()
        super(RemoteFileBuffer,self).__init__(wrapped_file,mode)
        # FIXME: What if mode with position on eof?
        if "a" in mode:
            # Not good enough...
            self.seek(0, SEEK_END)

    def __del__(self):
        #  Don't try to close a partially-constructed file
        if "_lock" in self.__dict__:
            if not self.closed:
                self.close()

    def _write(self,data,flushing=False):
        with self._lock:
            #  Do we need to discard info from the buffer?
            toread = len(data) - (self._readlen - self.wrapped_file.tell())
            if toread > 0:
                if not self._eof:
                    self._fillbuffer(toread)
                else:
                    self._readlen += toread
            self._changed = True
            self.wrapped_file.write(data)

    def _read_remote(self, length=None):
        """Read data from the remote file into the local buffer."""
        chunklen = 1024 * 256
        bytes_read = 0
        while True:
            toread = chunklen
            if length is not None and length - bytes_read < chunklen:
                toread = length - bytes_read
            if not toread:
                break
             
            data = self._rfile.read(toread)
            datalen = len(data)
            if not datalen:
                self._eof = True
                break
            
            bytes_read += datalen 
            self.wrapped_file.write(data)
            
            if datalen < toread:
                # We reached EOF,
                # no more reads needed
                self._eof = True
                break
        
        if self._eof and self._rfile is not None:
            self._rfile.close()
        self._readlen += bytes_read
    
    def _fillbuffer(self, length=None):  
        """Fill the local buffer, leaving file position unchanged.

        This method is used for on-demand loading of data from the remote file
        into the buffer.  It reads 'length' bytes from rfile and writes them
        into the buffer, seeking back to the original file position.
        """
        curpos = self.wrapped_file.tell()
        if length == None:
            if not self._eof:
                # Read all data and we didn't reached EOF
                # Merge endpos - tell + bytes from rfile
                self.wrapped_file.seek(0, SEEK_END)
                self._read_remote()
                self._eof = True
                self.wrapped_file.seek(curpos)
               
        elif not self._eof:
            if curpos + length > self._readlen:
                # Read all data and we didn't reached EOF
                # Load endpos - tell() + len bytes from rfile
                toload = length - (self._readlen - curpos)
                self.wrapped_file.seek(0, SEEK_END)
                self._read_remote(toload)
                self.wrapped_file.seek(curpos)
        
    def _read(self, length=None):
        if length < 0:
            length = None
        with self._lock:
            self._fillbuffer(length)
            data = self.wrapped_file.read(length if length != None else -1)
            if not data:
                data = None
            return data

    def _seek(self,offset,whence=SEEK_SET):
        with self._lock:
            if not self._eof:
                # Count absolute position of seeking
                if whence == SEEK_SET:
                    abspos = offset
                elif whence == SEEK_CUR:
                    abspos =  offset + self.wrapped_file.tell()
                elif whence == SEEK_END:
                    abspos = None
                else:
                    raise IOError(EINVAL, 'Invalid whence')
            
                if abspos != None:
                    toread = abspos - self._readlen
                    if toread > 0:
                        self.wrapped_file.seek(self._readlen)
                        self._fillbuffer(toread)
                else:
                    self.wrapped_file.seek(self._readlen)
                    self._fillbuffer()
                
            self.wrapped_file.seek(offset, whence)

    def _truncate(self,size):
        with self._lock:
            if not self._eof and self._readlen < size:
                # Read the rest of file
                self._fillbuffer(size - self._readlen)
                # Lock rfile
                self._eof = True  
            elif self._readlen >= size:
                # Crop rfile metadata
                self._readlen = size if size != None else 0
                # Lock rfile
                self._eof = True

            self.wrapped_file.truncate(size)
            self._changed = True
                
            self.flush()
            if self._rfile is not None:
                self._rfile.close()

    def flush(self):
        with self._lock:
            self.wrapped_file.flush()
            if self.write_on_flush:
                self._setcontents()

    def _setcontents(self):
        if not self._changed:
            # Nothing changed, no need to write data back
            return
        
        # If not all data loaded, load until eof
        if not self._eof:
            self._fillbuffer()
            
        if "w" in self.mode or "a" in self.mode or "+" in self.mode:
            pos = self.wrapped_file.tell()
            self.wrapped_file.seek(0)
            self.fs.setcontents(self.path, self.wrapped_file)
            self.wrapped_file.seek(pos)
    
    def close(self):
        with self._lock:
            if not self.closed:
                self._setcontents()
                if self._rfile is not None:
                    self._rfile.close()
                super(RemoteFileBuffer,self).close()


class ConnectionManagerFS(LazyFS):
    """FS wrapper providing simple connection management of a remote FS.

    The ConnectionManagerFS class is designed to wrap a remote FS object
    and provide some convenience methods for dealing with its remote
    connection state.

    The boolean attribute 'connected' indicates whether the remote fileystem
    has an active connection, and is initially True.  If any of the remote
    filesystem methods raises a RemoteConnectionError, 'connected' will
    switch to False and remain so until a successful remote method call.

    Application code can use the method 'wait_for_connection' to block
    until the connection is re-established.  Currently this reconnection
    is checked by a simple polling loop; eventually more sophisticated
    operating-system integration may be added.

    Since some remote FS classes can raise RemoteConnectionError during
    initialisation, this class makes use of lazy initialization. The
    remote FS can be specified as an FS instance, an FS subclass, or a
    (class,args) or (class,args,kwds) tuple. For example::

        >>> fs = ConnectionManagerFS(MyRemoteFS("http://www.example.com/"))
        Traceback (most recent call last):
            ...
        RemoteConnectionError: couldn't connect to "http://www.example.com/"
        >>> fs = ConnectionManagerFS((MyRemoteFS,["http://www.example.com/"]))
        >>> fs.connected
        False
        >>>

    """

    poll_interval = 1

    def __init__(self,wrapped_fs,poll_interval=None,connected=True):
        super(ConnectionManagerFS,self).__init__(wrapped_fs)
        if poll_interval is not None:
            self.poll_interval = poll_interval
        self._connection_cond = threading.Condition()
        self._poll_thread = None
        self._poll_sleeper = threading.Event()
        self.connected = connected

    def setcontents(self, path, data, chunk_size=64*1024):
        return self.wrapped_fs.setcontents(path, data, chunk_size=chunk_size)

    def __getstate__(self):
        state = super(ConnectionManagerFS,self).__getstate__()
        del state["_connection_cond"]
        del state["_poll_sleeper"]
        state["_poll_thread"] = None
        return state

    def __setstate__(self,state):
        super(ConnectionManagerFS,self).__setstate__(state)
        self._connection_cond = threading.Condition()
        self._poll_sleeper = threading.Event()
        
    def wait_for_connection(self,timeout=None):
        self._connection_cond.acquire()
        try:
            if not self.connected:
                if not self._poll_thread:
                    target = self._poll_connection
                    self._poll_thread = threading.Thread(target=target)
                    self._poll_thread.daemon = True
                    self._poll_thread.start()
                self._connection_cond.wait(timeout)
        finally:
            self._connection_cond.release()

    def _poll_connection(self):
        while not self.connected and not self.closed:
            try:
                self.wrapped_fs.isdir("")
            except RemoteConnectionError:
                self._poll_sleeper.wait(self.poll_interval)
                self._poll_sleeper.clear()
            except FSError:
                break
            else:
                break
        self._connection_cond.acquire()
        try:
            if not self.closed:
                self.connected = True
            self._poll_thread = None
            self._connection_cond.notifyAll()
        finally:
            self._connection_cond.release()

    def close(self):
        if not self.closed:
            try:
                super(ConnectionManagerFS,self).close()
            except (RemoteConnectionError,):
                pass
            if self._poll_thread:
                self.connected = True
                self._poll_sleeper.set()
                self._poll_thread.join()
                self._poll_thread = None

def _ConnectionManagerFS_method_wrapper(func):
    """Method wrapper for ConnectionManagerFS.

    This method wrapper keeps an eye out for RemoteConnectionErrors and
    adjusts self.connected accordingly.
    """
    @wraps(func)
    def wrapper(self,*args,**kwds):
        try:
            result = func(self,*args,**kwds)
        except RemoteConnectionError:
            self.connected = False
            raise
        except FSError:
            self.connected = True
            raise
        else:
            self.connected = True
            return result
    return wrapper
 
wrap_fs_methods(_ConnectionManagerFS_method_wrapper,ConnectionManagerFS)


def _cached_method(func):
    """Method decorator that caches results for CacheFS."""
    @wraps(func)
    def wrapper(self,path="",*args,**kwds):
        try:
            (success,result) = self._cache_get(path,func.__name__,args,kwds)
        except KeyError:
            try:
                res = func(self,path,*args,**kwds)
            except Exception, e:
                self._cache_set(path,func.__name__,args,kwds,(False,e))
                raise
            else:
                self._cache_set(path,func.__name__,args,kwds,(True,res))
                return copy.copy(res)
        else:
            if not success:
                raise result
            else:
                return copy.copy(result)
    return wrapper


class CacheFS(WrapFS):
    """Simple wrapper to cache meta-data of a remote filesystems.

    This FS wrapper implements a simplistic cache that can help speed up
    access to a remote filesystem.  File and directory meta-data is cached
    but the actual file contents are not.
    """

    def __init__(self,fs,timeout=1):
        """CacheFS constructor.

        The optional argument 'timeout' specifies the cache timeout in
        seconds.  The default timeout is 1 second.  To prevent cache
        entries from ever timing out, set it to None.
        """
        self.timeout = timeout
        self._cache = {"":{}}
        super(CacheFS,self).__init__(fs)

    def _path_cache(self,path):
        cache = self._cache
        for name in iteratepath(path):
            cache = cache.setdefault(name,{"":{}})
        return cache

    def _cache_get(self,path,func,args,kwds):
        now = time.time()
        cache = self._path_cache(path)
        key = (tuple(args),tuple(sorted(kwds.iteritems())))
        (t,v) = cache[""][func][key]
        if self.timeout is not None:
            if t < now - self.timeout:
                raise KeyError
        return v

    def _cache_set(self,path,func,args,kwds,v):
        t = time.time()
        cache = self._path_cache(path)
        key = (tuple(args),tuple(sorted(kwds.iteritems())))
        cache[""].setdefault(func,{})[key] = (t,v)

    def _uncache(self,path,added=False,removed=False,unmoved=False):
        cache = self._cache
        names = list(iteratepath(path))
        # If it's not the root dir, also clear some items for ancestors
        if names:
            # Clear cached 'getinfo' and 'getsize' for all ancestors 
            for name in names[:-1]:
                cache[""].pop("getinfo",None)
                cache[""].pop("getsize",None)
                cache = cache.get(name,None)
                if cache is None:
                    return 
            # Adjust cached 'listdir' for parent directory.
            # TODO: account for whether it was added, removed, or unmoved
            cache[""].pop("getinfo",None)
            cache[""].pop("getsize",None)
            cache[""].pop("listdir",None)
            cache[""].pop("listdirinfo",None)
        # Clear all cached info for the path itself.
        if names:
            cache[names[-1]] = {"":{}}
        else:
            cache[""] = {}

    @_cached_method
    def exists(self,path):
        return super(CacheFS,self).exists(path)

    @_cached_method
    def isdir(self,path):
        return super(CacheFS,self).isdir(path)

    @_cached_method
    def isfile(self,path):
        return super(CacheFS,self).isfile(path)

    @_cached_method
    def listdir(self,path="",**kwds):
        return super(CacheFS,self).listdir(path,**kwds)

    @_cached_method
    def listdirinfo(self,path="",**kwds):
        return super(CacheFS,self).listdirinfo(path,**kwds)

    @_cached_method
    def getinfo(self,path):
        return super(CacheFS,self).getinfo(path)

    @_cached_method
    def getsize(self,path):
        return super(CacheFS,self).getsize(path)

    @_cached_method
    def getxattr(self,path,name,default=None):
        return super(CacheFS,self).getxattr(path,name,default)

    @_cached_method
    def listxattrs(self,path):
        return super(CacheFS,self).listxattrs(path)

    def open(self,path,mode="r"):
        f = super(CacheFS,self).open(path,mode)
        self._uncache(path,unmoved=True)
        return f

    def setcontents(self, path, contents='', chunk_size=64*1024):
        res = super(CacheFS,self).setcontents(path, contents, chunk_size=chunk_size)
        self._uncache(path,unmoved=True)
        return res

    def getcontents(self,path):
        res = super(CacheFS,self).getcontents(path)
        self._uncache(path,unmoved=True)
        return res

    def makedir(self,path,**kwds):
        super(CacheFS,self).makedir(path,**kwds)
        self._uncache(path,added=True)

    def remove(self,path):
        super(CacheFS,self).remove(path)
        self._uncache(path,removed=True)

    def removedir(self,path,**kwds):
        super(CacheFS,self).removedir(path,**kwds)
        self._uncache(path,removed=True)

    def rename(self,src,dst):
        super(CacheFS,self).rename(src,dst)
        self._uncache(src,removed=True)
        self._uncache(dst,added=True)

    def copy(self,src,dst,**kwds):
        super(CacheFS,self).copy(src,dst,**kwds)
        self._uncache(dst,added=True)

    def copydir(self,src,dst,**kwds):
        super(CacheFS,self).copydir(src,dst,**kwds)
        self._uncache(dst,added=True)

    def move(self,src,dst,**kwds):
        super(CacheFS,self).move(src,dst,**kwds)
        self._uncache(src,removed=True)
        self._uncache(dst,added=True)

    def movedir(self,src,dst,**kwds):
        super(CacheFS,self).movedir(src,dst,**kwds)
        self._uncache(src,removed=True)
        self._uncache(dst,added=True)

    def setxattr(self,path,name,value):
        self._uncache(path,unmoved=True)
        return super(CacheFS,self).setxattr(path,name,value)

    def delxattr(self,path,name):
        self._uncache(path,unmoved=True)
        return super(CacheFS,self).delxattr(path,name)