Source code for mail_deduplicate.mail

# Copyright Kevin Deldycke <kevin@deldycke.com> and contributors.
#
# 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 2
# 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, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
from __future__ import annotations

import contextlib
import email
import hashlib
import inspect
import logging
import mailbox
import os
import re
from functools import cached_property

import arrow
from tabulate import tabulate

from mail_deduplicate import CTIME, MINIMAL_HEADERS_COUNT, TooFewHeaders


class DedupMail:
    """Message with deduplication-specific properties and utilities.

    Extends `standard library's mailbox.Message
    <https://github.com/python/cpython/blob/45ffab40e86777ecd49786a2c18c0c044ef0cb5b/Lib/mailbox.py#L1489-L1523>`_,
    and shouldn't be used directly, but composed with ``mailbox.Message`` sub-classes.
    """

    def __init__(self, message=None) -> None:
        """Initialize a pre-parsed ``Message`` instance the same way the default factory
        in Python's ``mailbox`` module does."""
        # Hunt down in our parent classes (but ourself) the first one inheriting the
        # mailbox.Message class. That way we can get to the original factory.
        orig_message_klass = None
        mro = inspect.getmro(self.__class__)
        for i, klass in enumerate(mro[1:], 1):
            if issubclass(klass, mailbox.Message):
                orig_message_klass = mro[i - 1]
                break
        assert orig_message_klass

        # Call original object initialization from the right message class we
        # inherits from mailbox.Message.
        super(orig_message_klass, self).__init__(message)  # type: ignore[arg-type]

        # Normalized path to the mailbox this message originates from.
        self.source_path = None

        # Mail ID used to uniquely refers to it in the context of its source.
        self.mail_id = None

        # Real filesystem location of the mail. Returns the individual mail's file
        # for folder-based box types (maildir & co.), but returns the whole box path
        # for file-based boxes (mbox & co.). Only used by regexp-based selection
        # strategies.
        self.path = None

        # Global config.
        self.conf = None

    def add_box_metadata(self, box, mail_id):
        """Post-instantiation utility to attach to mail some metadata derived from its
        parent box.

        Called right after the ``__init__()`` constructor.

        This allows the mail to carry its own information on its origin box and index.
        """
        self.source_path = box._path
        self.mail_id = mail_id

        # Extract file name and close it right away to reclaim memory.
        mail_file = box.get_file(mail_id)
        self.path = mail_file._file.name
        mail_file.close()

    def __repr__(self) -> str:
        return f"<{self.__class__.__name__} {self.source_path}:{self.mail_id}>"

    @cached_property
    def uid(self):
        """Unique ID of the mail."""
        return self.source_path, self.mail_id

    @cached_property
    def timestamp(self):
        """Compute the normalized canonical timestamp of the mail.

        Sourced from the message's ``Date`` header by default. In the case of
        ``maildir``, can be sourced from the email's file from the filesystem.

        .. warning::
            ``ctime`` does not refer to creation time on POSIX systems, but
            rather `the last time the inode data changed
            <https://userprimary.net/posts/2007/11/18/ctime-in-unix-means-last-change-time-not-create-time/>`_.

        .. todo::
            Investigate what `mailbox.MaildirMessage.get_date()
            <https://docs.python.org/3.11/library/mailbox.html#mailbox.MaildirMessage.get_date>`_
            does and if we can use it.
        """
        if self.conf.time_source == CTIME:
            return os.path.getctime(self.path)

        # Fetch from the date header.
        value = self.get("Date")
        with contextlib.suppress(ValueError):
            return email.utils.mktime_tz(email.utils.parsedate_tz(value))

    @cached_property
    def size(self):
        """Returns canonical mail size.

        Size is computed as the length of the message body, i.e. the payload of the mail
        stripped of all its headers, not from the mail file persisting on the file-
        system.

        .. todo::
            Allow customization of the way the size is computed, by getting the file
            size instead for example:
            ```python
            size = os.path.getsize(mail_file)
            ```
        """
        return len("".join(self.body_lines))

    @cached_property
    def body_lines(self):
        """Return a normalized list of lines from message's body."""
        body = []
        if self.preamble is not None:
            body.extend(self.preamble.splitlines(keepends=True))

        for part in self.walk():
            if part.is_multipart():
                continue

            ctype = part.get_content_type()
            cte = part.get_params(header="Content-Transfer-Encoding")
            if (ctype is not None and not ctype.startswith("text")) or (
                cte is not None and cte[0][0].lower() == "8bit"
            ):
                part_body = part.get_payload(decode=False)
            else:
                charset = part.get_content_charset()
                if charset is None or len(charset) == 0:
                    charsets = ["ascii", "utf-8"]
                else:
                    charsets = [charset]

                part_body = part.get_payload(decode=True)
                for enc in charsets:
                    try:
                        part_body = part_body.decode(enc)
                        break
                    except UnicodeDecodeError:
                        continue
                    except LookupError:
                        continue
                else:
                    part_body = part.get_payload(decode=False)

            body.extend(part_body.splitlines(keepends=True))

        if self.epilogue is not None:
            body.extend(self.epilogue.splitlines(keepends=True))
        return body

    @cached_property
    def subject(self):
        """Normalized subject.

        Only used for debugging and human-friendly logging.
        """
        subject = self.get("Subject", "")
        subject, _ = re.subn(r"\s+", " ", subject)
        return subject

    def hash_key(self):
        """Returns the canonical hash of a mail.

        .. caution::
            This method hasn't been made explicitly into a cached property in order to
            reduce the overall memory footprint.
        """
        logging.debug(f"Serialized headers: {self.serialized_headers()!r}")
        hash_value = hashlib.sha224(self.serialized_headers()).hexdigest()
        logging.debug(f"Hash: {hash_value}")
        return hash_value

    @cached_property
    def hash_raw_body(self):
        """Returns the canonical body hash of a mail."""
        serialized_raw_body = "\n".join(self.body_lines).encode("utf-8")
        hash_value = hashlib.sha224(serialized_raw_body).hexdigest()
        logging.debug(f"Body raw hash: {hash_value}")
        return hash_value

    @cached_property
    def hash_normalized_body(self):
        """Returns the normalized body hash of a mail."""
        serialized_normalized_body = "".join(
            [re.sub(r"\s", "", line) for line in self.body_lines],
        ).encode("utf-8")
        hash_value = hashlib.sha224(serialized_normalized_body).hexdigest()
        logging.debug(f"Body normalized hash: {hash_value}")
        return hash_value

    @cached_property
    def canonical_headers(self):
        """Returns the full list of all canonical headers names and values in
        preparation for hashing."""
        canonical_headers = []

        for header_id in self.conf.hash_headers:
            # Skip absent header.
            if header_id not in self:
                continue

            # Fetch all occurrences of the header.
            canonical_values = []
            for header_value in self.get_all(header_id):
                normalized_value = self.normalize_header_value(header_id, header_value)
                if re.search(r"\S", normalized_value):
                    canonical_values.append(normalized_value)
            canonical_value = "\n".join(canonical_values)

            canonical_headers.append((header_id, canonical_value))

        # Cast to a tuple to prevent any modification.
        return tuple(canonical_headers)

    def pretty_canonical_headers(self):
        """Renders a table of headers names and values used to produce the mail's hash.

        .. caution::
            This method hasn't been made explicitly into a cached property in order to
            reduce the overall memory footprint.

        Returns a string ready to be printed.
        """
        table = [["Header ID", "Header value"], *list(self.canonical_headers)]
        return "\n" + tabulate(table, tablefmt="fancy_grid", headers="firstrow")

    def serialized_headers(self):
        """Serialize the canonical headers into a single string ready to be hashed.

        At this point we should have at an absolute minimum of headers.

        .. caution::
            This method hasn't been made explicitly into a cached property in order to
            reduce the overall memory footprint.
        """
        headers_count = len(self.canonical_headers)
        if headers_count < MINIMAL_HEADERS_COUNT:
            logging.warning(self.pretty_canonical_headers())
            msg = f"{headers_count} headers found out of {MINIMAL_HEADERS_COUNT}."
            raise TooFewHeaders(
                msg,
            )
        else:
            logging.debug(self.pretty_canonical_headers())

        return "\n".join(
            [f"{h_id}: {h_value}" for h_id, h_value in self.canonical_headers],
        ).encode("utf-8")

    @staticmethod
    def normalize_header_value(header_id, value):
        """Normalize and clean-up header value into its canonical form.

        Always returns a unicode string.
        """
        # Problematic when reading utf8 emails
        # this will ensure value is always string
        if isinstance(value, bytes):
            value = value.decode("utf-8", "replace")
        elif isinstance(value, email.header.Header):
            value = str(value)

        # Normalize white spaces.
        value = re.sub(r"\s+", " ", value).strip()

        # Trim Subject prefixes automatically added by mailing list software,
        # since the mail could have been cc'd to multiple lists, in which case
        # it will receive a different prefix for each, but this shouldn't be
        # treated as a real difference between duplicate mails.
        if header_id == "subject":
            subject = value
            while True:
                matching = re.match(
                    r"([Rr]e: )*(\[\w[\w_-]+\w\] )+(.+)",
                    subject,
                    re.DOTALL,
                )
                if not matching:
                    break
                subject = matching.group(3)
                # show_progress("Trimmed Subject to %s" % subject)
            return subject

        if header_id == "content-type":
            # Apparently list servers actually munge Content-Type
            # e.g. by stripping the quotes from charset="us-ascii".
            # Section 5.1 of RFC2045 says that either form is valid
            # (and they are equivalent).
            #
            # Additionally, with multipart/mixed, boundary delimiters can
            # vary by recipient.  We need to allow for duplicates coming
            # from multiple recipients, since for example you could be
            # signed up to the same list twice with different addresses.
            # Or maybe someone bounces you a load of mail some of which is
            # from a mailing list you're both subscribed to - then it's
            # still useful to be able to eliminate duplicates.
            return re.sub(";.*", "", value)

        if header_id == "date":
            # Date timestamps can differ by seconds or hours for various
            # reasons, so let's only honour the date for now and normalize them
            # to UTC timezone.
            try:
                parsed = email.utils.parsedate_tz(value)
                if not parsed:
                    raise TypeError
                utc_timestamp = email.utils.mktime_tz(parsed)
                return arrow.get(utc_timestamp).format("YYYY-MM-DD")
            except (TypeError, ValueError):
                return value

        elif header_id in ["to", "message-id"]:
            # Sometimes email.parser strips the <> brackets from a To:
            # header which has a single address.  I have seen this happen
            # for only one mail in a duplicate pair.  I'm not sure why
            # (presumably the parser uses email.utils.unquote somewhere in
            # its code path which was only triggered by that mail and not
            # its sister mail), but to be safe, we should always strip the
            # <> brackets to avoid this difference preventing duplicate
            # detection.
            if re.match("^<[^<>,]+>$", value):
                return email.utils.unquote(value)

        return value