115 lines
3.1 KiB
Python
115 lines
3.1 KiB
Python
import base64
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import entry
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# TODO: Include file number in the error info
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class FileFormatError(Exception): pass
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class VersionMismatch(Exception): pass
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def parse_header(header):
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"""parse_header(bytes) → str
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Throw an error if the header isn't good and return the file comment
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(if any) if it is"""
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assert type(header) == bytes
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magic = header[0:6]
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if magic != b'SSHWOT':
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raise FileFormatError('Invalid magic')
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# Version 0 is the current one
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version = header[6:7]
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if version == b'':
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raise FileFormatError('No newline after header')
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if version != b'0':
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raise VersionMismatch('Version %i not supported' % version[0])
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# See if we have a comment
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if header[7:8] == b' ':
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# It says we have
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if header[8:9] == b'\n':
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# No, we don't, but we do have a space telling we
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# have. The header is malformed
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raise FileFormatError('Missing comment or spurious space in the header')
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else:
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# Yes, we do
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# Check it ends with a newline
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if header[-1] != 0x0a:
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raise FileFormatError('Missing newline at the end of the header')
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try:
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file_comment = header[8:-1].decode('utf-8')
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except UnicodeDecodeError:
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raise FileFormatError('Comment is not valid utf-8')
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return file_comment
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elif header[7:8] == b'\n':
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# No, we have newline
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return ''
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else:
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# No, we have something else
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raise FileFormatError("Expected a space or a newline but got '%s' instead" % header[7:].decode('utf-8'))
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def parse_entry(line):
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"""parse_entry(bytes) → Entry"""
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assert type(line) == bytes
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def extract_b64_field(rest):
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"""extract_b64_field(bytes) → (bytes: decoded_field, bytes:rest)"""
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field_b64 = rest[0:44]
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if len(field_b64) != 44:
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raise FileFormatError('Unexpected end of line')
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try:
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field = base64.b64decode(field_b64, validate = True)
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except (ValueError, base64.binascii.Error) as err:
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raise FileFormatError('Malformed base64 string: %s' % field_b64.decode('utf-8')) from err
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return field, rest[44:]
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salt, rest = extract_b64_field(line)
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hashed_host, rest = extract_b64_field(rest)
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fingerprint, rest = extract_b64_field(rest)
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# What do we have after that?
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if rest[0:1] == b' ':
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# A comment?
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if rest[1:2] == b'\n':
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# No, but it says we have. It's malformed
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raise FileFormatError('Missing comment or spurious space in the entry')
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else:
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# Yes. Make sure it ends in a newline
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if rest[-1] != 0x0a:
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raise FileFormatError('No newline after entry')
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try:
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comment = rest[1:-1].decode('utf-8')
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except UnicodeDecodeError:
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raise FileFormatError('Comment is not valid utf-8')
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elif rest[0:1] == b'\n':
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# A newline
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comment = ''
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else:
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# Something else
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raise FileFormatError('Expected a space or a newline but got "%s" instead' % rest.decode('utf-8'))
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return entry.Entry(salt, hashed_host, fingerprint, comment)
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def read(f):
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"""read(file(rb)) → ([Entry]: entries, str: file_comment)"""
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lines = [line for line in f]
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if len(lines) == 0:
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raise FileFormatError('Missing header')
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file_comment = parse_header(lines[0])
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entries = []
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for line in lines[1:]:
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entries.append(parse_entry(line))
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return entries, file_comment
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