From 8d2b04c56f7620be21434dfffaa0b02371c6f973 Mon Sep 17 00:00:00 2001
From: JustAnotherArchivist <JustAnotherArchivist@users.noreply.github.com>
Date: Thu, 2 Feb 2023 09:04:08 +0000
Subject: [PATCH] Add torrent-tiny

---
 torrent-tiny | 150 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100755 torrent-tiny

diff --git a/torrent-tiny b/torrent-tiny
new file mode 100755
index 0000000..0d88bca
--- /dev/null
+++ b/torrent-tiny
@@ -0,0 +1,150 @@
+#!/usr/bin/env python3
+import enum
+import hashlib
+import sys
+
+
+class ParserState(enum.Enum):
+	NONE = 0
+	DICTIONARY = 1
+	LIST = 2
+
+
+class Placeholder:
+	def __init__(self, s):
+		self._s = s
+
+	def __repr__(self):
+		return self._s
+
+
+dictEntry = Placeholder('dict')
+listEntry = Placeholder('list')
+
+
+class CopyingFileReader:
+	'''All reads to the underlying file-like object are copied to write, which must be a callable accepting the data.'''
+
+	def __init__(self, fp, write):
+		self.fp = fp
+		self.write = write
+
+	def read(self, *args, **kwargs):
+		data = self.fp.read(*args, **kwargs)
+		self.write(data)
+		return data
+
+
+def read_str(fp, c):
+	'''Reads a string from the current position with c being the first character of the length (having been read already)'''
+	length = read_int(fp, c, end = b':')
+	s = fp.read(length)
+	if len(s) != length:
+		raise ValueError
+	try:
+		s = s.decode('utf-8')
+	except UnicodeDecodeError:
+		pass
+	return s
+
+
+def read_int(fp, c = b'', end = b'e'):
+	'''Reads an int from the current position with c optionally being the first digit'''
+	i = c
+	while True:
+		c = fp.read(1)
+		if c == end:
+			break
+		elif c in b'0123456789':
+			i += c
+		else:
+			raise ValueError
+	i = int(i.decode('ascii'))
+	return i
+
+
+def read_or_stack_value(fp, stateStack, c = b''):
+	if not c:
+		c = fp.read(1)
+	if c == b'l':
+		stateStack.append(ParserState.LIST)
+		return listEntry
+	elif c == b'd':
+		stateStack.append(ParserState.DICTIONARY)
+		return dictEntry
+	elif c == b'i':
+		return read_int(fp)
+	elif c in b'0123456789': # String value
+		return read_str(fp, c)
+	else:
+		raise ValueError
+
+
+def bdecode(fp, display = False, infoWrite = None):
+	c = fp.read(1)
+	if c != b'd':
+		raise ValueError
+	stateStack = [ParserState.NONE, ParserState.DICTIONARY]
+	inInfo = False
+	print_ = print if display else (lambda *args, **kwargs: None)
+	print_(f'(global): {dictEntry}')
+	while stateStack:
+		state = stateStack[-1]
+		indent = '  ' * (len(stateStack) - 1)
+		if state == ParserState.DICTIONARY:
+			c = fp.read(1)
+			if c == b'e': # End of dict
+				stateStack.pop(-1)
+				if len(stateStack) == 2 and inInfo and infoWrite:
+					inInfo = False
+					fp = fp.fp
+				continue
+			elif c in b'0123456789': # Key
+				key = read_str(fp, c)
+				if len(stateStack) == 2 and key == b'info' and infoWrite: # If in global dict and this is the 'info' value and a copy is desired...
+					inInfo = True
+					fp = CopyingFileReader(fp, infoWrite)
+				v = read_or_stack_value(fp, stateStack)
+				print_(f'{indent}{key!r}: {v!r}')
+			else:
+				raise ValueError
+		elif state == ParserState.LIST:
+			c = fp.read(1)
+			if c == b'e':
+				stateStack.pop(-1)
+				continue
+			else:
+				v = read_or_stack_value(fp, stateStack, c)
+				print_(f'{indent}- {v!r}')
+		elif state == ParserState.NONE:
+			assert len(stateStack) == 1
+			return
+
+
+def print_torrent(fp):
+	bdecode(fp, display = True)
+
+
+def get_info_hash(fp):
+	hasher = hashlib.sha1()
+	bdecode(fp, infoWrite = hasher.update)
+	return hasher.hexdigest()
+
+
+def main():
+	if len(sys.argv) < 3 or sys.argv[1] not in ('print', 'infohash'):
+		print('Usage: torrent-tiny MODE FILE [FILE...]', file = sys.stderr)
+		print('MODEs: print, infohash', file = sys.stderr)
+		sys.exit(1)
+
+	mode = sys.argv[1]
+	for fn in sys.argv[2:]:
+		with open(fn, 'rb') as fp:
+			if mode == 'print':
+				print_torrent(fp)
+			elif mode == 'infohash':
+				print(get_info_hash(fp))
+
+
+if __name__ == '__main__':
+	main()