Add imap-dl, a simple imap downloader

getmail upstream appears to have no plans to convert to python3 in the
near future.

Some of us use only a minimal subset of features of getmail, and it
would be nice to have something simpler, with the main complexity
offloaded to the modern python3 stdlib.

This patch represents a squashed series of changes from both Jameson
Graef Rollins and Daniel Kahn Gillmor (dkg), though dkg is primarily
responsible for any remaining bugs.

Thanks to Sean Whitton for useful and significant feedback.

Signed-off-by: Jameson Graef Rollins <jrollins@finestructure.net>
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

1 files changed, 278 insertions, 0 deletions

diff --git a/imap-dl b/imap-dl
new file mode 100755
index 0000000..318c0bc
--- /dev/null
+++ b/imap-dl
@@ -0,0 +1,278 @@
+#!/usr/bin/python3
+# PYTHON_ARGCOMPLETE_OK
+# -*- coding: utf-8 -*-
+
+# Copyright (C) 2019 Daniel Kahn Gillmor
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or (at
+# your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+DESCRIPTION = '''A simple replacement for a minimalist use of getmail.
+
+In particular, if you use getmail to reach an IMAP server as though it
+were POP (retrieving from the server and optionally deleting), you can
+point this script to the getmail config and it should do the same
+thing.
+
+It tries to ensure that the configuration file is of the expected
+type, and will terminate raising an exception, and it should not lose
+messages.
+
+If there's any interest in supporting other similarly simple use cases
+for getmail, patches are welcome.
+
+If you've never used getmail, you can make the simplest possible
+config file like so:
+
+----------
+[retriever]
+server = mail.example.net
+username = foo
+password = sekr1t!
+
+[destination]
+path = /home/foo/Maildir
+
+[options]
+delete = True
+----------
+'''
+
+import re
+import sys
+import ssl
+import enum
+import time
+import imaplib
+import logging
+import mailbox
+import os.path
+import argparse
+import statistics
+import configparser
+
+from typing import Dict, List, Union, Tuple
+
+try:
+    import argcomplete #type: ignore
+except ImportError:
+    argcomplete = None
+
+class Splitter(object):
+    def __init__(self, name:str, match:bytes):
+        self._splitter = re.compile(match)
+        self._name = name
+    def breakup(self, line:bytes) -> Dict[str,int]:
+        match = self._splitter.match(line)
+        if not match:
+            raise Exception(f'malformed {self._name} line {line!r}')
+        ret:Dict[str,int] = {}
+        i:str
+        for i in ['id', 'uid', 'size']:
+            ret[i] = int(match[i])
+        return ret
+
+OnSizeMismatch = enum.Enum('OnSizeMismatch', 'warn error none')
+
+# b'1 (UID 160 RFC822.SIZE 1867)' -> {id: 1, uid: 160, size: 1867}
+_summary_re = rb'^(?P<id>[0-9]+) \(UID (?P<uid>[0-9]+) RFC822.SIZE (?P<size>[0-9]+)\)$'
+summary_splitter = Splitter('summary', _summary_re)
+# b'1 (UID 160 BODY[] {1867}' -> {id: 1, uid: 160, size: 1867}
+_fetch_re = rb'^(?P<id>[0-9]+) \(UID (?P<uid>[0-9]+) (FLAGS \([\\A-Za-z ]*\) )?BODY\[\] \{(?P<size>[0-9]+)\}$'
+fetch_splitter = Splitter('fetch', _fetch_re)
+
+def scan_msgs(configfile:str, verbose:bool) -> None:
+    conf = configparser.ConfigParser()
+    conf.read_file(open(configfile, 'r'))
+    oldloglevel = logging.getLogger().getEffectiveLevel()
+    conf_verbose = conf.getint('options', 'verbose', fallback=1)
+    if conf_verbose > 1:
+        verbose = True
+    if verbose:
+        logging.getLogger().setLevel(logging.INFO)
+    logging.info('pulling from config file %s', configfile)
+    delete = conf.getboolean('options', 'delete', fallback=False)
+    read_all = conf.getboolean('options', 'read_all', fallback=True)
+    if not read_all:
+        raise NotImplementedError('imap-dl only supports options.read_all=True, got False')
+    rtype = conf.get('retriever', 'type', fallback='SimpleIMAPSSLRetriever')
+    if rtype.lower() != 'simpleimapsslretriever':
+        raise NotImplementedError(f'imap-dl only supports retriever.type=SimpleIMAPSSLRetriever, got {rtype}')
+    # FIXME: handle `retriever.record_mailbox`
+    dtype = conf.get('destination', 'type', fallback='Maildir')
+    if dtype.lower() != 'maildir':
+        raise NotImplementedError(f'imap-dl only supports destination.type=Maildir, got {dtype}')
+    dst = conf.get('destination', 'path')
+    dst = os.path.expanduser(dst)
+    if os.path.exists(dst) and not os.path.isdir(dst):
+        raise Exception('expected destination directory, but %s is not a directory'%(dst,))
+    mdst:mailbox.Maildir = mailbox.Maildir(dst, create=True)
+    ca_certs = conf.get('retriever', 'ca_certs', fallback=None)
+    on_size_mismatch_str:str = conf.get('options', 'on_size_mismatch', fallback='error').lower()
+    try:
+        on_size_mismatch:OnSizeMismatch = OnSizeMismatch.__members__[on_size_mismatch_str]
+    except KeyError:
+        raise Exception(f'options.on_size_mismatch value should be one of:\n'
+                        '{list(OnSizeMismatch.__members__.keys())}\n'
+                        '(found "{on_size_mismatch_str}")')
+
+    ctx = ssl.create_default_context(cafile=ca_certs)
+    server:str = conf.get('retriever', 'server')
+    with imaplib.IMAP4_SSL(host=server, #type: ignore
+                           port=int(conf.get('retriever', 'port', fallback=993)),
+                           ssl_context=ctx) as imap:
+        username:str = conf.get('retriever', 'username')
+        logging.info('Logging in as %s', username)
+        resp:Tuple[str, List[Union[bytes,Tuple[bytes,bytes]]]]
+        resp = imap.login(username, conf.get('retriever', 'password'))
+        if resp[0] != 'OK':
+            raise Exception(f'login failed with {resp} as user {username} on {server}')
+        if verbose: # only enable debugging after login to avoid leaking credentials in the log
+            imap.debug = 4
+        logging.info("capabilities reported: %s", ', '.join(imap.capabilities))
+        resp = imap.select(readonly=not delete)
+        if resp[0] != 'OK':
+            raise Exception(f'selection failed: {resp}')
+        if len(resp[1]) != 1:
+            raise Exception(f'expected exactly one EXISTS response from select, got {resp[1]}')
+        data:Union[bytes,Tuple[bytes,bytes]] = resp[1][0]
+        if not isinstance(data, bytes):
+            raise Exception(f'expected bytes in response to SELECT, got {data}')
+        n:int = int(data)
+        if n == 0:
+            logging.info('No messages to retrieve')
+        else:
+            pull_msgs(imap, n, mdst, on_size_mismatch, delete)
+    logging.getLogger().setLevel(oldloglevel)
+
+def pull_msgs(imap:imaplib.IMAP4_SSL, n:int, mdst:mailbox.Maildir,
+              on_size_mismatch:OnSizeMismatch, delete:bool) -> None:
+    sizes_mismatched:List[int] = []
+    resp:Tuple[str, List[Union[bytes,Tuple[bytes,bytes]]]]
+    resp = imap.fetch('1:%d'%(n), '(UID RFC822.SIZE)')
+    if resp[0] != 'OK':
+        raise Exception(f'initial FETCH 1:{n} not OK ({resp})')
+
+    pending:List[Dict[str,int]] = []
+    for data in resp[1]:
+        if not isinstance(data, bytes):
+            raise TypeError(f'Expected bytes, got {type(data)}')
+        pending.append(summary_splitter.breakup(data))
+
+    sizes:Dict[int,int] = {}
+    for m in pending:
+        sizes[m['uid']] = m['size']
+    fetched:Dict[int,int] = {}
+    uids = ','.join(map(str, sorted([x['uid'] for x in pending])))
+    totalbytes = sum([x['size'] for x in pending])
+    logging.info('Fetching %d messages, expecting %d bytes of message content',
+                 len(pending), totalbytes)
+    # FIXME: sort by size?
+    # FIXME: fetch in batches or singly instead of all-at-once?
+    # FIXME: rolling deletion?
+    # FIXME: asynchronous work?
+    before = time.perf_counter()
+    resp = imap.uid('FETCH', uids, '(UID BODY.PEEK[])')
+    after = time.perf_counter()
+    if resp[0] != 'OK':
+        raise Exception('UID fetch failed {resp[0]}')
+    expected_objects:int = len(pending) * 2
+    if len(resp[1]) != expected_objects:
+        raise Exception(f'expected {expected_objects} responses for fetch, got {len(resp[1])}')
+    for n in range(0, expected_objects, 2):
+        # expected response is one "fetch" line, followed by a close-paren item
+        data = resp[1][n]
+        if not isinstance(data, tuple) or len(data) != 2:
+            raise Exception(f'expected 2-part tuple, got {type(data)}')
+
+        closeparen = resp[1][n+1]
+        if not isinstance(closeparen, bytes) or closeparen != b')':
+            raise Exception('Expected close parenthesis after message fetch')
+
+        m = fetch_splitter.breakup(data[0])
+        if m['size'] != len(data[1]):
+            raise Exception(f'expected {m["size"]} octets, got {len(data[1])}')
+        if m['size'] != sizes[m['uid']]:
+            if on_size_mismatch == OnSizeMismatch.warn:
+                if len(sizes_mismatched) == 0:
+                    logging.warning('size mismatch: summary said %d octets, fetch sent %d',
+                                    sizes[m['uid']], m['size'])
+                elif len(sizes_mismatched) == 1:
+                    logging.warning('size mismatch: (mismatches after the first suppressed until summary)')
+                sizes_mismatched.append(sizes[m['uid']] - m['size'])
+            elif on_size_mismatch == OnSizeMismatch.error:
+                raise Exception(f"size mismatch: summary said {sizes[m['uid']]} octets, "
+                                "fetch sent {m['size']}\n"
+                                "(set options.on_size_mismatch to none or warn to avoid hard failure)")
+        # convert any CRLF line-endings to UNIX standard line-
+        # endings:
+        fname = mdst.add(data[1].replace(b'\r\n', b'\n'))
+        logging.info('stored message %d/%d (uid %d, %d bytes) in %s',
+                     len(fetched) + 1, len(pending), m['uid'], m['size'], fname)
+        del sizes[m['uid']]
+        fetched[m['uid']] = m['size']
+    if sizes:
+        logging.warning('unhandled UIDs: %s', sizes)
+    logging.info('%d bytes of %d messages fetched in %g seconds (~%g KB/s)',
+                 sum(fetched.values()), len(fetched), after - before,
+                 sum(fetched.values())/((after - before)*1024))
+    if on_size_mismatch == OnSizeMismatch.warn and len(sizes_mismatched) > 1:
+        logging.warning('%d size mismatches out of %d messages (mismatches in bytes: mean %f, stddev %f)',
+                        len(sizes_mismatched), len(fetched),
+                        statistics.mean(sizes_mismatched),
+                        statistics.stdev(sizes_mismatched))
+    if delete:
+        logging.info('trying to delete %d messages from IMAP store', len(fetched))
+        resp = imap.uid('STORE', ','.join(map(str, fetched.keys())), '+FLAGS', r'(\Deleted)')
+        if resp[0] != 'OK':
+            raise Exception(f'failed to set \\Deleted flag: {resp}')
+        resp = imap.expunge()
+        if resp[0] != 'OK':
+            raise Exception(f'failed to expunge! {resp}')
+    else:
+        logging.info('not deleting any messages, since options.delete is not set')
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(
+        description=DESCRIPTION,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+    )
+    parser.add_argument(
+        'config', nargs='+', metavar='CONFIG',
+        help="configuration file")
+    parser.add_argument(
+        '-v', '--verbose', action='store_true',
+        help="verbose log output")
+
+    if argcomplete:
+        argcomplete.autocomplete(parser)
+    elif '_ARGCOMPLETE' in os.environ:
+        logging.error('Argument completion requested but the "argcomplete" '
+                      'module is not installed. '
+                      'Maybe you want to "apt install python3-argcomplete"')
+        sys.exit(1)
+
+    args = parser.parse_args()
+
+    if args.verbose:
+        logging.getLogger().setLevel(logging.INFO)
+
+    errs = {}
+    for confname in args.config:
+        try:
+            scan_msgs(confname, args.verbose)
+        except imaplib.IMAP4.error as e:
+            logging.error('IMAP failure for config file %s: %s', confname, e)
+            errs[confname] = e
+    if errs:
+        exit(1)