1 files changed, 138 insertions, 0 deletions
diff --git a/lib/git/index/fun.py b/lib/git/index/fun.py
new file mode 100644
index 00000000..2e653ea6
--- /dev/null
+++ b/lib/git/index/fun.py
@@ -0,0 +1,138 @@
+"""
+Contains standalone functions to accompany the index implementation and make it
+more versatile
+"""
+from git.utils import (
+							IndexFileSHA1Writer, 
+						)
+
+from typ import (
+					IndexEntry,
+					CE_NAMEMASK
+				)
+
+from util import 	(
+					pack, 
+					unpack
+					)
+
+from binascii import (
+						hexlify, 
+						unhexlify
+					)
+
+__all__ = ('write_cache', 'read_cache' )
+
+def write_cache_entry(entry, stream):
+	"""Write the given entry to the stream"""
+	beginoffset = stream.tell()
+	write = stream.write
+	write(entry[4])			# ctime
+	write(entry[5])			# mtime
+	path = entry[3]
+	plen = len(path) & CE_NAMEMASK		# path length
+	assert plen == len(path), "Path %s too long to fit into index" % entry[3]
+	flags = plen | entry[2]
+	write(pack(">LLLLLL20sH", entry[6], entry[7], entry[0],
+								entry[8], entry[9], entry[10], unhexlify(entry[1]), flags))
+	write(path)
+	real_size = ((stream.tell() - beginoffset + 8) & ~7)
+	write("\0" * ((beginoffset + real_size) - stream.tell()))
+
+def write_cache(entries, stream, extension_data=None, ShaStreamCls=IndexFileSHA1Writer):
+	"""Write the cache represented by entries to a stream
+	:param entries: **sorted** list of entries
+	:param stream: stream to wrap into the AdapterStreamCls - it is used for
+		final output.
+	:param ShaStreamCls: Type to use when writing to the stream. It produces a sha
+		while writing to it, before the data is passed on to the wrapped stream
+	:param extension_data: any kind of data to write as a trailer, it must begin
+		a 4 byte identifier, followed by its size ( 4 bytes )"""
+	# wrap the stream into a compatible writer
+	stream = ShaStreamCls(stream)
+
+	# header
+	version = 2
+	stream.write("DIRC")
+	stream.write(pack(">LL", version, len(entries)))
+
+	# body
+	for entry in entries:
+		write_cache_entry(entry, stream)
+	# END for each entry
+
+	# write previously cached extensions data
+	if extension_data is not None:
+		stream.write(extension_data)
+
+	# write the sha over the content
+	stream.write_sha()
+	
+def read_entry(stream):
+	"""Return: One entry of the given stream"""
+	beginoffset = stream.tell()
+	ctime = unpack(">8s", stream.read(8))[0]
+	mtime = unpack(">8s", stream.read(8))[0]
+	(dev, ino, mode, uid, gid, size, sha, flags) = \
+		unpack(">LLLLLL20sH", stream.read(20 + 4 * 6 + 2))
+	path_size = flags & CE_NAMEMASK
+	path = stream.read(path_size)
+
+	real_size = ((stream.tell() - beginoffset + 8) & ~7)
+	data = stream.read((beginoffset + real_size) - stream.tell())
+	return IndexEntry((mode, hexlify(sha), flags, path, ctime, mtime, dev, ino, uid, gid, size))
+
+def read_header(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 = unpack(">LL", stream.read(4 * 2))
+		
+		# TODO: handle version 3: extended data, see read-cache.c
+		assert version in (1, 2)
+		return version, num_entries
+
+def entry_key(*entry):
+	""":return: Key suitable to be used for the index.entries dictionary
+	:param *entry: One instance of type BaseIndexEntry or the path and the stage"""
+	if len(entry) == 1:
+		return (entry[0].path, entry[0].stage)
+	else:
+		return tuple(entry)
+	# END handle entry
+
+def read_cache(stream):
+	"""Read a cache file from the given stream
+	:return: tuple(version, entries_dict, extension_data, content_sha)
+		* version is the integer version number
+		* entries dict is a dictionary which maps IndexEntry instances to a path
+			at a stage
+		* extension_data is '' or 4 bytes of type + 4 bytes of size + size bytes
+		* content_sha is a 20 byte sha on all cache file contents"""
+	version, num_entries = read_header(stream)
+	count = 0
+	entries = dict()
+	while count < num_entries:
+		entry = read_entry(stream)
+		# entry_key would be the method to use, but we safe the effort
+		entries[(entry.path, entry.stage)] = entry
+		count += 1
+	# END for each entry
+
+	# the footer contains extension data and a sha on the content so far
+	# Keep the extension footer,and verify we have a sha in the end
+	# Extension data format is:
+	# 4 bytes ID
+	# 4 bytes length of chunk
+	# repeated 0 - N times
+	extension_data = stream.read(~0)
+	assert len(extension_data) > 19, "Index Footer was not at least a sha on content as it was only %i bytes in size" % len(extension_data)
+
+	content_sha = extension_data[-20:]
+
+	# truncate the sha in the end as we will dynamically create it anyway
+	extension_data = extension_data[:-20]
+	
+	return (version, entries, extension_data, content_sha)
+