Move to a text format

src/entry.py

@@ -2,7 +2,7 @@ from collections import namedtuple
 
 import hashing
 
-# Entry(bytes[32], bytes[32], bytes[32], bytes[0…2¹⁶-1])
+# Entry(bytes[32], bytes[32], bytes[32], str)
 Entry = namedtuple('Entry', ['salt', 'hashed_host', 'fingerprint', 'comment'])
 
 class UnacceptableComment(Exception): pass
@@ -47,10 +47,4 @@ def create_entry(domain, port, fingerprint, comment):
 	if '\n' in comment:
 		raise UnacceptableComment('Comment contains newlines')
 
-	comment_encoded = comment.encode('utf-8')
-
-	# Comment may be at max 2¹⁶-1 bytes long
-	if len(comment_encoded) >= 1<<16:
-		raise UnacceptableComment('Comment length of %i bytes is too long' % len(comment_encoded))
-
-	return Entry(salt, hashed_host, fingerprint, comment_encoded)
+	return Entry(salt, hashed_host, fingerprint, comment)

src/read_file.py

@@ -1,67 +1,113 @@
+import base64
+
 import entry
 
 class FileFormatError(Exception): pass
 
 class VersionMismatch(Exception): pass
 
-def check_header(f):
-	"""check_header(file(rb))
-	Throw an error if the header isn't good"""
-	# Magic is b'WOT'
-	magic = f.read(3)
-	if magic != b'WOT':
+def parse_header(header):
+	"""parse_header(bytes) → str
+	Throw an error if the header isn't good and return the file comment
+	(if any) if it is"""
+	assert type(header) == bytes
+
+	magic = header[0:6]
+	if magic != b'SSHWOT':
 		raise FileFormatError('Invalid magic')
 
 	# Version 0 is the current one
-	version = f.read(1)
+	version = header[6:7]
 	if version == b'':
-		raise FileFormatError('Unexpected end of file')
-	if version != b'\0':
+		raise FileFormatError('No newline after header')
+	if version != b'0':
 		raise VersionMismatch('Version %i not supported' % version[0])
 
-def read_entry(f):
-	"""read_entry(file(rb)) → Entry / None
-	Returns None if the end of file has been reached"""
-	# u8[32]: salt
-	salt = f.read(32)
-	if len(salt) == 0:
-		# End of file has been reached, return None to mark that
-		return None
-	elif len(salt) != 32:
-		raise FileFormatError('Unexpected end of file')
+	# See if we have a comment
+	if header[7:8] == b' ':
+		# It says we have
+		if header[8:9] == b'\n':
+			# No, we don't, but we do have a space telling we
+			# have. The header is malformed
+			raise FileFormatError('Missing comment or spurious space in the header')
+		else:
+			# Yes, we do
+			# Check it ends with a newline
+			if header[-1] != 0x0a:
+				raise FileFormatError('Missing newline at the end of the header')
 
-	# u8[32]: hashed_host
-	hashed_host = f.read(32)
-	if len(hashed_host) != 32:
-		raise FileFormatError('Unexpected end of file')
+			try:
+				file_comment = header[8:-1].decode('utf-8')
+			except UnicodeDecodeError:
+				raise FileFormatError('Comment is not valid utf-8')
 
-	# u8[32]: fingerprint
-	fingerprint = f.read(32)
-	if len(fingerprint) != 32:
-		raise FileFormatError('Unexpected end of file')
+			return file_comment
 
-	# u16le: comment_length
-	length_bytes = f.read(2)
-	if len(length_bytes) != 2:
-		raise FileFormatError('Unexpected end of file')
-	comment_length = length_bytes[0] | length_bytes[1] << 8
+	elif header[7:8] == b'\n':
+		# No, we have newline
+		return ''
 
-	# u8[comment_length]: comment
-	comment = f.read(comment_length)
-	if len(comment) != comment_length:
-		raise FileFormatError('Unexpected end of file')
+	else:
+		# No, we have something else
+		raise FileFormatError("Expected a space or a newline but got '%s' instead" % header[7:].decode('utf-8'))
+
+def parse_entry(line):
+	"""parse_entry(bytes) → Entry"""
+	assert type(line) == bytes
+
+	def extract_b64_field(rest):
+		"""extract_b64_field(bytes) → (bytes: decoded_field, bytes:rest)"""
+		field_b64 = rest[0:44]
+		if len(field_b64) != 44:
+			raise FileFormatError('Unexpected end of line')
+		try:
+			field = base64.b64decode(field_b64, validate = True)
+		except (ValueError, base64.binascii.Error) as err:
+			raise FileFormatError('Malformed base64 string: %s' % field_b64.decode('utf-8')) from err
+
+		return field, rest[44:]
+
+	salt, rest = extract_b64_field(line)
+	hashed_host, rest = extract_b64_field(rest)
+	fingerprint, rest = extract_b64_field(rest)
+
+	# What do we have after that?
+	if rest[0:1] == b' ':
+		# A comment?
+		if rest[1:2] == b'\n':
+			# No, but it says we have. It's malformed
+			raise FileFormatError('Missing comment or spurious space in the entry')
+		else:
+			# Yes. Make sure it ends in a newline
+			if rest[-1] != 0x0a:
+				raise FileFormatError('No newline after entry')
+
+			try:
+				comment = rest[1:-1].decode('utf-8')
+			except UnicodeDecodeError:
+				raise FileFormatError('Comment is not valid utf-8')
+
+	elif rest[0:1] == b'\n':
+		# A newline
+		comment = ''
+
+	else:
+		# Something else
+		raise FileFormatError('Expected a space or a newline but got "%s" instead' % rest.decode('utf-8'))
 
 	return entry.Entry(salt, hashed_host, fingerprint, comment)
 
 def read(f):
-	"""read_file(file(rb)) → [Entry]"""
-	check_header(f)
+	"""read(file(rb)) → ([Entry]: entries, str: file_comment)"""
+	lines = [line for line in f]
+
+	if len(lines) == 0:
+		raise FileFormatError('Missing header')
+
+	file_comment = parse_header(lines[0])
 
 	entries = []
-	while True:
-		# Read until we reach the end of file
-		entry = read_entry(f)
-		if entry is None: break
-		entries.append(entry)
+	for line in lines[1:]:
+		entries.append(parse_entry(line))
 
-	return entries
+	return entries, file_comment

src/write_file.py

@@ -1,39 +1,53 @@
-def write_header(f):
-	"""write_header(file(wb))
+import base64
+
+def write_header(f, file_comment):
+	"""write_header(file(wb), str)
 	Writes the header to the given file."""
-	# b'WOT' magic
-	f.write(b'WOT')
+	assert type(file_comment) == str
+	# b'SSHWOT' magic
+	f.write(b'SSHWOT')
 	# Version number
-	f.write(bytes([0]))
+	f.write(b'0')
+	# b' ' + file_comment, if there is one
+	if len(file_comment) > 0:
+		f.write(b' ')
+		assert b'\n' not in file_comment
+		f.write(file_comment)
+	# End of header marked with b'\n'
+	f.write(b'\n')
 
 def write_entry(f, salt, hashed_host, fingerprint, comment):
-	"""write_entry(file(wb), bytes[32], bytes[32], bytes[32], bytes[0…2¹⁶-1])
+	"""write_entry(file(wb), bytes[32], bytes[32], bytes[32], str)
 	Writes an entry to the given file."""
 	assert type(salt) == bytes and len(salt) == 32
 	assert type(hashed_host) == bytes and len(hashed_host) == 32
 	assert type(fingerprint) == bytes and len(fingerprint) == 32
-	assert type(comment) == bytes and 0 <= len(comment) <= (1<<16) - 1
+	assert type(comment) == str
 
-	# u8[32]: salt
-	f.write(salt)
+	# base64 encoded (44 bytes): salt
+	f.write(base64.b64encode(salt))
 
-	# u8[32]: hashed_host
-	f.write(hashed_host)
+	# base64 encoded (44 bytes): hashed_host
+	f.write(base64.b64encode(hashed_host))
 
-	# u8[32]: fingerprint
-	f.write(fingerprint)
+	# base64 encoded (44 bytes): fingerprint
+	f.write(base64.b64encode(fingerprint))
 
-	# u16le: len(comment)
-	comment_len = len(comment)
-	f.write(bytes([comment_len & 0xff, comment_len >> 8]))
+	# b' ' + comment, if there is one
+	if len(comment) > 0:
+		f.write(b' ')
+		assert '\n' not in comment
+		f.write(comment.encode('utf-8'))
 
-	# u8[]: comment
-	f.write(comment)
+	# End of entry marked with b'\n'
+	f.write(b'\n')
 
-def write(f, entries):
-	"""write(file(wb), [Entry])
+def write(f, entries, file_comment = ''):
+	"""write(file(wb), [Entry], str)
 	Creates a file containing all of the entries"""
-	write_header(f)
+	assert type(file_comment) == str
+
+	write_header(f, file_comment)
 	
 	for entry in entries:
 		write_entry(f, entry.salt, entry.hashed_host, entry.fingerprint, entry.comment)