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# Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Functions that load and write PEM-encoded files."""
import base64
import typing
# Should either be ASCII strings or bytes.
FlexiText = typing.Union[str, bytes]
def _markers(pem_marker: FlexiText) -> typing.Tuple[bytes, bytes]:
"""
Returns the start and end PEM markers, as bytes.
"""
if not isinstance(pem_marker, bytes):
pem_marker = pem_marker.encode("ascii")
return (
b"-----BEGIN " + pem_marker + b"-----",
b"-----END " + pem_marker + b"-----",
)
def _pem_lines(contents: bytes, pem_start: bytes, pem_end: bytes) -> typing.Iterator[bytes]:
"""Generator over PEM lines between pem_start and pem_end."""
in_pem_part = False
seen_pem_start = False
for line in contents.splitlines():
line = line.strip()
# Skip empty lines
if not line:
continue
# Handle start marker
if line == pem_start:
if in_pem_part:
raise ValueError('Seen start marker "%r" twice' % pem_start)
in_pem_part = True
seen_pem_start = True
continue
# Skip stuff before first marker
if not in_pem_part:
continue
# Handle end marker
if in_pem_part and line == pem_end:
in_pem_part = False
break
# Load fields
if b":" in line:
continue
yield line
# Do some sanity checks
if not seen_pem_start:
raise ValueError('No PEM start marker "%r" found' % pem_start)
if in_pem_part:
raise ValueError('No PEM end marker "%r" found' % pem_end)
def load_pem(contents: FlexiText, pem_marker: FlexiText) -> bytes:
"""Loads a PEM file.
:param contents: the contents of the file to interpret
:param pem_marker: the marker of the PEM content, such as 'RSA PRIVATE KEY'
when your file has '-----BEGIN RSA PRIVATE KEY-----' and
'-----END RSA PRIVATE KEY-----' markers.
:return: the base64-decoded content between the start and end markers.
@raise ValueError: when the content is invalid, for example when the start
marker cannot be found.
"""
# We want bytes, not text. If it's text, it can be converted to ASCII bytes.
if not isinstance(contents, bytes):
contents = contents.encode("ascii")
(pem_start, pem_end) = _markers(pem_marker)
pem_lines = [line for line in _pem_lines(contents, pem_start, pem_end)]
# Base64-decode the contents
pem = b"".join(pem_lines)
return base64.standard_b64decode(pem)
def save_pem(contents: bytes, pem_marker: FlexiText) -> bytes:
"""Saves a PEM file.
:param contents: the contents to encode in PEM format
:param pem_marker: the marker of the PEM content, such as 'RSA PRIVATE KEY'
when your file has '-----BEGIN RSA PRIVATE KEY-----' and
'-----END RSA PRIVATE KEY-----' markers.
:return: the base64-encoded content between the start and end markers, as bytes.
"""
(pem_start, pem_end) = _markers(pem_marker)
b64 = base64.standard_b64encode(contents).replace(b"\n", b"")
pem_lines = [pem_start]
for block_start in range(0, len(b64), 64):
block = b64[block_start : block_start + 64]
pem_lines.append(block)
pem_lines.append(pem_end)
pem_lines.append(b"")
return b"\n".join(pem_lines)
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