1 files changed, 99 insertions, 1 deletions
diff --git a/lib/git/index.py b/lib/git/index.py
index 1c531712..1e67d6d1 100644
--- a/lib/git/index.py
+++ b/lib/git/index.py
@@ -7,11 +7,109 @@
 Module containing Index implementation, allowing to perform all kinds of index
 manipulations such as querying and merging.
 """
+import struct
+import binascii
+import mmap
+
+class IndexEntry(tuple):
+	"""
+	Allows convenient access to IndexEntry data without completely unpacking it.
+	
+	Attributes usully accessed often are cached in the tuple whereas others are 
+	unpacked on demand.
+	"""
 
 class Index(object):
 	"""
 	Implements an Index that can be manipulated using a native implementation in 
-	order to safe git command function calls wherever possible.
+	order to save git command function calls wherever possible.
 	
 	It provides custom merging facilities and to create custom commits.
 	"""
+	__slots__ = ( "version", "entries" )
+	
+	def __init__(self, stream = None):
+		"""
+		Initialize this Index instance, optionally from the given ``stream``
+		
+		Note
+			Reading is based on the dulwich project.
+		"""
+		self.entries = dict()
+		self.version = -1
+		if stream is not None:
+			self._read_from_stream(stream)
+	
+	def _read_entry(self, stream):
+		"""Return: One entry of the given stream"""
+		beginoffset = stream.tell()
+		ctime = struct.unpack(">8s", stream.read(8))[0]
+		mtime = struct.unpack(">8s", stream.read(8))[0]
+		(dev, ino, mode, uid, gid, size, sha, flags) = \
+			struct.unpack(">LLLLLL20sH", stream.read(20 + 4 * 6 + 2))
+		path_size = flags & 0x0fff
+		path = stream.read(path_size)
+		
+		real_size = ((stream.tell() - beginoffset + 8) & ~7)
+		data = stream.read((beginoffset + real_size) - stream.tell())
+		return IndexEntry((path, ctime, mtime, dev, ino, mode, uid, gid, size, 
+				binascii.hexlify(sha), path_size))
+		
+	
+	def _read_header(self, stream):
+		"""Return tuple(version_long, num_entries) from the given stream"""
+		type_id = stream.read(4)
+		if type_id != "DIRC":
+			raise AssertionError("Invalid index file header: %r" % type_id)
+		version, num_entries = struct.unpack(">LL", stream.read(4 * 2))
+		assert version in (1, 2)
+		return version, num_entries
+		
+	def _read_from_stream(self, stream):
+		"""
+		Initialize this instance with index values read from the given stream
+		"""
+		self.version, num_entries = self._read_header(stream)
+		self.entries = dict()
+		count = 0
+		while count < num_entries:
+			entry = self._read_entry(stream)
+			self.entries[entry[0]] = entry[1:]
+			count += 1
+		# END for each entry
+	
+	@classmethod
+	def from_file(cls, file_path):
+		"""
+		Returns
+			Index instance as recreated from the given stream.
+			
+		``file_pa ``
+			File path pointing to git index file
+		"""
+		fp = open(file_path, "r")
+		
+		# try memory map for speed
+		stream = fp
+		try:
+			stream = mmap.mmap(fp.fileno(), 0, access=mmap.ACCESS_READ)
+		except Exception:
+			pass
+		# END memory mapping
+		
+		try:
+			return cls(stream)
+		finally:
+			fp.close()
+		
+	def write(self, stream):
+		"""
+		Write the current state to the given stream
+		
+		``stream``
+			File-like object
+		
+		Returns
+			self
+		"""
+		raise NotImplementedError( "TODO" )