path: root/synapse/media/media_repository.py

#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2018-2021 The Matrix.org Foundation C.I.C.
# Copyright 2014-2016 OpenMarket Ltd
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
import errno
import logging
import os
import shutil
from io import BytesIO
from typing import IO, TYPE_CHECKING, Dict, List, Optional, Set, Tuple

import attr
from matrix_common.types.mxc_uri import MXCUri

import twisted.internet.error
import twisted.web.http
from twisted.internet.defer import Deferred

from synapse.api.errors import (
    Codes,
    FederationDeniedError,
    HttpResponseException,
    NotFoundError,
    RequestSendFailed,
    SynapseError,
    cs_error,
)
from synapse.api.ratelimiting import Ratelimiter
from synapse.config.repository import ThumbnailRequirement
from synapse.http.server import respond_with_json
from synapse.http.site import SynapseRequest
from synapse.logging.context import defer_to_thread
from synapse.logging.opentracing import trace
from synapse.media._base import (
    FileInfo,
    Responder,
    ThumbnailInfo,
    get_filename_from_headers,
    respond_404,
    respond_with_multipart_responder,
    respond_with_responder,
)
from synapse.media.filepath import MediaFilePaths
from synapse.media.media_storage import MediaStorage
from synapse.media.storage_provider import StorageProviderWrapper
from synapse.media.thumbnailer import Thumbnailer, ThumbnailError
from synapse.media.url_previewer import UrlPreviewer
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.databases.main.media_repository import LocalMedia, RemoteMedia
from synapse.types import UserID
from synapse.util.async_helpers import Linearizer
from synapse.util.retryutils import NotRetryingDestination
from synapse.util.stringutils import random_string

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)

# How often to run the background job to update the "recently accessed"
# attribute of local and remote media.
UPDATE_RECENTLY_ACCESSED_TS = 60 * 1000  # 1 minute
# How often to run the background job to check for local and remote media
# that should be purged according to the configured media retention settings.
MEDIA_RETENTION_CHECK_PERIOD_MS = 60 * 60 * 1000  # 1 hour


class MediaRepository:
    def __init__(self, hs: "HomeServer"):
        self.hs = hs
        self.auth = hs.get_auth()
        self.client = hs.get_federation_client()
        self.clock = hs.get_clock()
        self.server_name = hs.hostname
        self.store = hs.get_datastores().main
        self.max_upload_size = hs.config.media.max_upload_size
        self.max_image_pixels = hs.config.media.max_image_pixels
        self.unused_expiration_time = hs.config.media.unused_expiration_time
        self.max_pending_media_uploads = hs.config.media.max_pending_media_uploads

        Thumbnailer.set_limits(self.max_image_pixels)

        self.primary_base_path: str = hs.config.media.media_store_path
        self.filepaths: MediaFilePaths = MediaFilePaths(self.primary_base_path)

        self.dynamic_thumbnails = hs.config.media.dynamic_thumbnails
        self.thumbnail_requirements = hs.config.media.thumbnail_requirements

        self.remote_media_linearizer = Linearizer(name="media_remote")

        self.recently_accessed_remotes: Set[Tuple[str, str]] = set()
        self.recently_accessed_locals: Set[str] = set()

        self.federation_domain_whitelist = (
            hs.config.federation.federation_domain_whitelist
        )
        self.prevent_media_downloads_from = hs.config.media.prevent_media_downloads_from

        self.download_ratelimiter = Ratelimiter(
            store=hs.get_storage_controllers().main,
            clock=hs.get_clock(),
            cfg=hs.config.ratelimiting.remote_media_downloads,
        )

        # List of StorageProviders where we should search for media and
        # potentially upload to.
        storage_providers = []

        for (
            clz,
            provider_config,
            wrapper_config,
        ) in hs.config.media.media_storage_providers:
            backend = clz(hs, provider_config)
            provider = StorageProviderWrapper(
                backend,
                store_local=wrapper_config.store_local,
                store_remote=wrapper_config.store_remote,
                store_synchronous=wrapper_config.store_synchronous,
            )
            storage_providers.append(provider)

        self.media_storage: MediaStorage = MediaStorage(
            self.hs, self.primary_base_path, self.filepaths, storage_providers
        )

        self.clock.looping_call(
            self._start_update_recently_accessed, UPDATE_RECENTLY_ACCESSED_TS
        )

        # Media retention configuration options
        self._media_retention_local_media_lifetime_ms = (
            hs.config.media.media_retention_local_media_lifetime_ms
        )
        self._media_retention_remote_media_lifetime_ms = (
            hs.config.media.media_retention_remote_media_lifetime_ms
        )

        # Check whether local or remote media retention is configured
        if (
            hs.config.media.media_retention_local_media_lifetime_ms is not None
            or hs.config.media.media_retention_remote_media_lifetime_ms is not None
        ):
            # Run the background job to apply media retention rules routinely,
            # with the duration between runs dictated by the homeserver config.
            self.clock.looping_call(
                self._start_apply_media_retention_rules,
                MEDIA_RETENTION_CHECK_PERIOD_MS,
            )

        if hs.config.media.url_preview_enabled:
            self.url_previewer: Optional[UrlPreviewer] = UrlPreviewer(
                hs, self, self.media_storage
            )
        else:
            self.url_previewer = None

    def _start_update_recently_accessed(self) -> Deferred:
        return run_as_background_process(
            "update_recently_accessed_media", self._update_recently_accessed
        )

    def _start_apply_media_retention_rules(self) -> Deferred:
        return run_as_background_process(
            "apply_media_retention_rules", self._apply_media_retention_rules
        )

    async def _update_recently_accessed(self) -> None:
        remote_media = self.recently_accessed_remotes
        self.recently_accessed_remotes = set()

        local_media = self.recently_accessed_locals
        self.recently_accessed_locals = set()

        await self.store.update_cached_last_access_time(
            local_media, remote_media, self.clock.time_msec()
        )

    def mark_recently_accessed(self, server_name: Optional[str], media_id: str) -> None:
        """Mark the given media as recently accessed.

        Args:
            server_name: Origin server of media, or None if local
            media_id: The media ID of the content
        """
        if server_name:
            self.recently_accessed_remotes.add((server_name, media_id))
        else:
            self.recently_accessed_locals.add(media_id)

    @trace
    async def create_media_id(self, auth_user: UserID) -> Tuple[str, int]:
        """Create and store a media ID for a local user and return the MXC URI and its
        expiration.

        Args:
            auth_user: The user_id of the uploader

        Returns:
            A tuple containing the MXC URI of the stored content and the timestamp at
            which the MXC URI expires.
        """
        media_id = random_string(24)
        now = self.clock.time_msec()
        await self.store.store_local_media_id(
            media_id=media_id,
            time_now_ms=now,
            user_id=auth_user,
        )
        return f"mxc://{self.server_name}/{media_id}", now + self.unused_expiration_time

    @trace
    async def reached_pending_media_limit(self, auth_user: UserID) -> Tuple[bool, int]:
        """Check if the user is over the limit for pending media uploads.

        Args:
            auth_user: The user_id of the uploader

        Returns:
            A tuple with a boolean and an integer indicating whether the user has too
            many pending media uploads and the timestamp at which the first pending
            media will expire, respectively.
        """
        pending, first_expiration_ts = await self.store.count_pending_media(
            user_id=auth_user
        )
        return pending >= self.max_pending_media_uploads, first_expiration_ts

    @trace
    async def verify_can_upload(self, media_id: str, auth_user: UserID) -> None:
        """Verify that the media ID can be uploaded to by the given user. This
        function checks that:

        * the media ID exists
        * the media ID does not already have content
        * the user uploading is the same as the one who created the media ID
        * the media ID has not expired

        Args:
            media_id: The media ID to verify
            auth_user: The user_id of the uploader
        """
        media = await self.store.get_local_media(media_id)
        if media is None:
            raise SynapseError(404, "Unknow media ID", errcode=Codes.NOT_FOUND)

        if media.user_id != auth_user.to_string():
            raise SynapseError(
                403,
                "Only the creator of the media ID can upload to it",
                errcode=Codes.FORBIDDEN,
            )

        if media.media_length is not None:
            raise SynapseError(
                409,
                "Media ID already has content",
                errcode=Codes.CANNOT_OVERWRITE_MEDIA,
            )

        expired_time_ms = self.clock.time_msec() - self.unused_expiration_time
        if media.created_ts < expired_time_ms:
            raise NotFoundError("Media ID has expired")

    @trace
    async def update_content(
        self,
        media_id: str,
        media_type: str,
        upload_name: Optional[str],
        content: IO,
        content_length: int,
        auth_user: UserID,
    ) -> None:
        """Update the content of the given media ID.

        Args:
            media_id: The media ID to replace.
            media_type: The content type of the file.
            upload_name: The name of the file, if provided.
            content: A file like object that is the content to store
            content_length: The length of the content
            auth_user: The user_id of the uploader
        """
        file_info = FileInfo(server_name=None, file_id=media_id)
        fname = await self.media_storage.store_file(content, file_info)
        logger.info("Stored local media in file %r", fname)

        await self.store.update_local_media(
            media_id=media_id,
            media_type=media_type,
            upload_name=upload_name,
            media_length=content_length,
            user_id=auth_user,
        )

        try:
            await self._generate_thumbnails(None, media_id, media_id, media_type)
        except Exception as e:
            logger.info("Failed to generate thumbnails: %s", e)

    @trace
    async def create_content(
        self,
        media_type: str,
        upload_name: Optional[str],
        content: IO,
        content_length: int,
        auth_user: UserID,
    ) -> MXCUri:
        """Store uploaded content for a local user and return the mxc URL

        Args:
            media_type: The content type of the file.
            upload_name: The name of the file, if provided.
            content: A file like object that is the content to store
            content_length: The length of the content
            auth_user: The user_id of the uploader

        Returns:
            The mxc url of the stored content
        """

        media_id = random_string(24)

        file_info = FileInfo(server_name=None, file_id=media_id)

        fname = await self.media_storage.store_file(content, file_info)

        logger.info("Stored local media in file %r", fname)

        await self.store.store_local_media(
            media_id=media_id,
            media_type=media_type,
            time_now_ms=self.clock.time_msec(),
            upload_name=upload_name,
            media_length=content_length,
            user_id=auth_user,
        )

        try:
            await self._generate_thumbnails(None, media_id, media_id, media_type)
        except Exception as e:
            logger.info("Failed to generate thumbnails: %s", e)

        return MXCUri(self.server_name, media_id)

    def respond_not_yet_uploaded(self, request: SynapseRequest) -> None:
        respond_with_json(
            request,
            504,
            cs_error("Media has not been uploaded yet", code=Codes.NOT_YET_UPLOADED),
            send_cors=True,
        )

    async def get_local_media_info(
        self, request: SynapseRequest, media_id: str, max_timeout_ms: int
    ) -> Optional[LocalMedia]:
        """Gets the info dictionary for given local media ID. If the media has
        not been uploaded yet, this function will wait up to ``max_timeout_ms``
        milliseconds for the media to be uploaded.

        Args:
            request: The incoming request.
            media_id: The media ID of the content. (This is the same as
                the file_id for local content.)
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.

        Returns:
            Either the info dictionary for the given local media ID or
            ``None``. If ``None``, then no further processing is necessary as
            this function will send the necessary JSON response.
        """
        wait_until = self.clock.time_msec() + max_timeout_ms
        while True:
            # Get the info for the media
            media_info = await self.store.get_local_media(media_id)
            if not media_info:
                logger.info("Media %s is unknown", media_id)
                respond_404(request)
                return None

            if media_info.quarantined_by:
                logger.info("Media %s is quarantined", media_id)
                respond_404(request)
                return None

            # The file has been uploaded, so stop looping
            if media_info.media_length is not None:
                return media_info

            # Check if the media ID has expired and still hasn't been uploaded to.
            now = self.clock.time_msec()
            expired_time_ms = now - self.unused_expiration_time
            if media_info.created_ts < expired_time_ms:
                logger.info("Media %s has expired without being uploaded", media_id)
                respond_404(request)
                return None

            if now >= wait_until:
                break

            await self.clock.sleep(0.5)

        logger.info("Media %s has not yet been uploaded", media_id)
        self.respond_not_yet_uploaded(request)
        return None

    async def get_local_media(
        self,
        request: SynapseRequest,
        media_id: str,
        name: Optional[str],
        max_timeout_ms: int,
        federation: bool = False,
    ) -> None:
        """Responds to requests for local media, if exists, or returns 404.

        Args:
            request: The incoming request.
            media_id: The media ID of the content. (This is the same as
                the file_id for local content.)
            name: Optional name that, if specified, will be used as
                the filename in the Content-Disposition header of the response.
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            federation: whether the local media being fetched is for a federation request

        Returns:
            Resolves once a response has successfully been written to request
        """
        media_info = await self.get_local_media_info(request, media_id, max_timeout_ms)
        if not media_info:
            return

        self.mark_recently_accessed(None, media_id)

        media_type = media_info.media_type
        if not media_type:
            media_type = "application/octet-stream"
        media_length = media_info.media_length
        upload_name = name if name else media_info.upload_name
        url_cache = media_info.url_cache

        file_info = FileInfo(None, media_id, url_cache=bool(url_cache))

        responder = await self.media_storage.fetch_media(file_info)
        if federation:
            await respond_with_multipart_responder(
                self.clock, request, responder, media_info
            )
        else:
            await respond_with_responder(
                request, responder, media_type, media_length, upload_name
            )

    async def get_remote_media(
        self,
        request: SynapseRequest,
        server_name: str,
        media_id: str,
        name: Optional[str],
        max_timeout_ms: int,
        ip_address: str,
        use_federation_endpoint: bool,
    ) -> None:
        """Respond to requests for remote media.

        Args:
            request: The incoming request.
            server_name: Remote server_name where the media originated.
            media_id: The media ID of the content (as defined by the remote server).
            name: Optional name that, if specified, will be used as
                the filename in the Content-Disposition header of the response.
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            ip_address: the IP address of the requester
            use_federation_endpoint: whether to request the remote media over the new
                federation `/download` endpoint

        Returns:
            Resolves once a response has successfully been written to request
        """
        if (
            self.federation_domain_whitelist is not None
            and server_name not in self.federation_domain_whitelist
        ):
            raise FederationDeniedError(server_name)

        # Don't let users download media from domains listed in the config, even
        # if we might have the media to serve. This is Trust & Safety tooling to
        # block some servers' media from being accessible to local users.
        # See `prevent_media_downloads_from` config docs for more info.
        if server_name in self.prevent_media_downloads_from:
            respond_404(request)
            return

        self.mark_recently_accessed(server_name, media_id)

        # We linearize here to ensure that we don't try and download remote
        # media multiple times concurrently
        key = (server_name, media_id)
        async with self.remote_media_linearizer.queue(key):
            responder, media_info = await self._get_remote_media_impl(
                server_name,
                media_id,
                max_timeout_ms,
                self.download_ratelimiter,
                ip_address,
                use_federation_endpoint,
            )

        # We deliberately stream the file outside the lock
        if responder and media_info:
            upload_name = name if name else media_info.upload_name
            await respond_with_responder(
                request,
                responder,
                media_info.media_type,
                media_info.media_length,
                upload_name,
            )
        else:
            respond_404(request)

    async def get_remote_media_info(
        self,
        server_name: str,
        media_id: str,
        max_timeout_ms: int,
        ip_address: str,
        use_federation: bool,
    ) -> RemoteMedia:
        """Gets the media info associated with the remote file, downloading
        if necessary.

        Args:
            server_name: Remote server_name where the media originated.
            media_id: The media ID of the content (as defined by the remote server).
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            ip_address: IP address of the requester
            use_federation: if a download is necessary, whether to request the remote file
                over the federation `/download` endpoint

        Returns:
            The media info of the file
        """
        if (
            self.federation_domain_whitelist is not None
            and server_name not in self.federation_domain_whitelist
        ):
            raise FederationDeniedError(server_name)

        # We linearize here to ensure that we don't try and download remote
        # media multiple times concurrently
        key = (server_name, media_id)
        async with self.remote_media_linearizer.queue(key):
            responder, media_info = await self._get_remote_media_impl(
                server_name,
                media_id,
                max_timeout_ms,
                self.download_ratelimiter,
                ip_address,
                use_federation,
            )

        # Ensure we actually use the responder so that it releases resources
        if responder:
            with responder:
                pass

        return media_info

    async def _get_remote_media_impl(
        self,
        server_name: str,
        media_id: str,
        max_timeout_ms: int,
        download_ratelimiter: Ratelimiter,
        ip_address: str,
        use_federation_endpoint: bool,
    ) -> Tuple[Optional[Responder], RemoteMedia]:
        """Looks for media in local cache, if not there then attempt to
        download from remote server.

        Args:
            server_name: Remote server_name where the media originated.
            media_id: The media ID of the content (as defined by the
                remote server).
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            download_ratelimiter: a ratelimiter limiting remote media downloads, keyed to
                requester IP.
            ip_address: the IP address of the requester
            use_federation_endpoint: whether to request the remote media over the new federation
            /download endpoint

        Returns:
            A tuple of responder and the media info of the file.
        """
        media_info = await self.store.get_cached_remote_media(server_name, media_id)

        # file_id is the ID we use to track the file locally. If we've already
        # seen the file then reuse the existing ID, otherwise generate a new
        # one.

        # If we have an entry in the DB, try and look for it
        if media_info:
            file_id = media_info.filesystem_id
            file_info = FileInfo(server_name, file_id)

            if media_info.quarantined_by:
                logger.info("Media is quarantined")
                raise NotFoundError()

            if not media_info.media_type:
                media_info = attr.evolve(
                    media_info, media_type="application/octet-stream"
                )

            responder = await self.media_storage.fetch_media(file_info)
            if responder:
                return responder, media_info

        # Failed to find the file anywhere, lets download it.

        try:
            if not use_federation_endpoint:
                media_info = await self._download_remote_file(
                    server_name,
                    media_id,
                    max_timeout_ms,
                    download_ratelimiter,
                    ip_address,
                )
            else:
                media_info = await self._federation_download_remote_file(
                    server_name,
                    media_id,
                    max_timeout_ms,
                    download_ratelimiter,
                    ip_address,
                )

        except SynapseError:
            raise
        except Exception as e:
            # An exception may be because we downloaded media in another
            # process, so let's check if we magically have the media.
            media_info = await self.store.get_cached_remote_media(server_name, media_id)
            if not media_info:
                raise e

        file_id = media_info.filesystem_id
        if not media_info.media_type:
            media_info = attr.evolve(media_info, media_type="application/octet-stream")
        file_info = FileInfo(server_name, file_id)

        # We generate thumbnails even if another process downloaded the media
        # as a) it's conceivable that the other download request dies before it
        # generates thumbnails, but mainly b) we want to be sure the thumbnails
        # have finished being generated before responding to the client,
        # otherwise they'll request thumbnails and get a 404 if they're not
        # ready yet.
        await self._generate_thumbnails(
            server_name, media_id, file_id, media_info.media_type
        )

        responder = await self.media_storage.fetch_media(file_info)
        return responder, media_info

    async def _download_remote_file(
        self,
        server_name: str,
        media_id: str,
        max_timeout_ms: int,
        download_ratelimiter: Ratelimiter,
        ip_address: str,
    ) -> RemoteMedia:
        """Attempt to download the remote file from the given server name,
        using the given file_id as the local id.

        Args:
            server_name: Originating server
            media_id: The media ID of the content (as defined by the
                remote server). This is different than the file_id, which is
                locally generated.
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            download_ratelimiter: a ratelimiter limiting remote media downloads, keyed to
                requester IP
            ip_address: the IP address of the requester

        Returns:
            The media info of the file.
        """

        file_id = random_string(24)

        file_info = FileInfo(server_name=server_name, file_id=file_id)

        async with self.media_storage.store_into_file(file_info) as (f, fname):
            try:
                length, headers = await self.client.download_media(
                    server_name,
                    media_id,
                    output_stream=f,
                    max_size=self.max_upload_size,
                    max_timeout_ms=max_timeout_ms,
                    download_ratelimiter=download_ratelimiter,
                    ip_address=ip_address,
                )
            except RequestSendFailed as e:
                logger.warning(
                    "Request failed fetching remote media %s/%s: %r",
                    server_name,
                    media_id,
                    e,
                )
                raise SynapseError(502, "Failed to fetch remote media")

            except HttpResponseException as e:
                logger.warning(
                    "HTTP error fetching remote media %s/%s: %s",
                    server_name,
                    media_id,
                    e.response,
                )
                if e.code == twisted.web.http.NOT_FOUND:
                    raise e.to_synapse_error()
                raise SynapseError(502, "Failed to fetch remote media")

            except SynapseError:
                logger.warning(
                    "Failed to fetch remote media %s/%s", server_name, media_id
                )
                raise
            except NotRetryingDestination:
                logger.warning("Not retrying destination %r", server_name)
                raise SynapseError(502, "Failed to fetch remote media")
            except Exception:
                logger.exception(
                    "Failed to fetch remote media %s/%s", server_name, media_id
                )
                raise SynapseError(502, "Failed to fetch remote media")

            if b"Content-Type" in headers:
                media_type = headers[b"Content-Type"][0].decode("ascii")
            else:
                media_type = "application/octet-stream"
            upload_name = get_filename_from_headers(headers)
            time_now_ms = self.clock.time_msec()

            # Multiple remote media download requests can race (when using
            # multiple media repos), so this may throw a violation constraint
            # exception. If it does we'll delete the newly downloaded file from
            # disk (as we're in the ctx manager).
            #
            # However: we've already called `finish()` so we may have also
            # written to the storage providers. This is preferable to the
            # alternative where we call `finish()` *after* this, where we could
            # end up having an entry in the DB but fail to write the files to
            # the storage providers.
            await self.store.store_cached_remote_media(
                origin=server_name,
                media_id=media_id,
                media_type=media_type,
                time_now_ms=time_now_ms,
                upload_name=upload_name,
                media_length=length,
                filesystem_id=file_id,
            )

        logger.info("Stored remote media in file %r", fname)

        return RemoteMedia(
            media_origin=server_name,
            media_id=media_id,
            media_type=media_type,
            media_length=length,
            upload_name=upload_name,
            created_ts=time_now_ms,
            filesystem_id=file_id,
            last_access_ts=time_now_ms,
            quarantined_by=None,
        )

    async def _federation_download_remote_file(
        self,
        server_name: str,
        media_id: str,
        max_timeout_ms: int,
        download_ratelimiter: Ratelimiter,
        ip_address: str,
    ) -> RemoteMedia:
        """Attempt to download the remote file from the given server name.
        Uses the given file_id as the local id and downloads the file over the federation
        v1 download endpoint

        Args:
            server_name: Originating server
            media_id: The media ID of the content (as defined by the
                remote server). This is different than the file_id, which is
                locally generated.
            max_timeout_ms: the maximum number of milliseconds to wait for the
                media to be uploaded.
            download_ratelimiter: a ratelimiter limiting remote media downloads, keyed to
                requester IP
            ip_address: the IP address of the requester

        Returns:
            The media info of the file.
        """

        file_id = random_string(24)

        file_info = FileInfo(server_name=server_name, file_id=file_id)

        async with self.media_storage.store_into_file(file_info) as (f, fname):
            try:
                res = await self.client.federation_download_media(
                    server_name,
                    media_id,
                    output_stream=f,
                    max_size=self.max_upload_size,
                    max_timeout_ms=max_timeout_ms,
                    download_ratelimiter=download_ratelimiter,
                    ip_address=ip_address,
                )
                # if we had to fall back to the _matrix/media endpoint it will only return
                # the headers and length, check the length of the tuple before unpacking
                if len(res) == 3:
                    length, headers, json = res
                else:
                    length, headers = res
            except RequestSendFailed as e:
                logger.warning(
                    "Request failed fetching remote media %s/%s: %r",
                    server_name,
                    media_id,
                    e,
                )
                raise SynapseError(502, "Failed to fetch remote media")

            except HttpResponseException as e:
                logger.warning(
                    "HTTP error fetching remote media %s/%s: %s",
                    server_name,
                    media_id,
                    e.response,
                )
                if e.code == twisted.web.http.NOT_FOUND:
                    raise e.to_synapse_error()
                raise SynapseError(502, "Failed to fetch remote media")

            except SynapseError:
                logger.warning(
                    "Failed to fetch remote media %s/%s", server_name, media_id
                )
                raise
            except NotRetryingDestination:
                logger.warning("Not retrying destination %r", server_name)
                raise SynapseError(502, "Failed to fetch remote media")
            except Exception:
                logger.exception(
                    "Failed to fetch remote media %s/%s", server_name, media_id
                )
                raise SynapseError(502, "Failed to fetch remote media")

            if b"Content-Type" in headers:
                media_type = headers[b"Content-Type"][0].decode("ascii")
            else:
                media_type = "application/octet-stream"
            upload_name = get_filename_from_headers(headers)
            time_now_ms = self.clock.time_msec()

            # Multiple remote media download requests can race (when using
            # multiple media repos), so this may throw a violation constraint
            # exception. If it does we'll delete the newly downloaded file from
            # disk (as we're in the ctx manager).
            #
            # However: we've already called `finish()` so we may have also
            # written to the storage providers. This is preferable to the
            # alternative where we call `finish()` *after* this, where we could
            # end up having an entry in the DB but fail to write the files to
            # the storage providers.
            await self.store.store_cached_remote_media(
                origin=server_name,
                media_id=media_id,
                media_type=media_type,
                time_now_ms=time_now_ms,
                upload_name=upload_name,
                media_length=length,
                filesystem_id=file_id,
            )

        logger.debug("Stored remote media in file %r", fname)

        return RemoteMedia(
            media_origin=server_name,
            media_id=media_id,
            media_type=media_type,
            media_length=length,
            upload_name=upload_name,
            created_ts=time_now_ms,
            filesystem_id=file_id,
            last_access_ts=time_now_ms,
            quarantined_by=None,
        )

    def _get_thumbnail_requirements(
        self, media_type: str
    ) -> Tuple[ThumbnailRequirement, ...]:
        scpos = media_type.find(";")
        if scpos > 0:
            media_type = media_type[:scpos]
        return self.thumbnail_requirements.get(media_type, ())

    def _generate_thumbnail(
        self,
        thumbnailer: Thumbnailer,
        t_width: int,
        t_height: int,
        t_method: str,
        t_type: str,
    ) -> Optional[BytesIO]:
        m_width = thumbnailer.width
        m_height = thumbnailer.height

        if m_width * m_height >= self.max_image_pixels:
            logger.info(
                "Image too large to thumbnail %r x %r > %r",
                m_width,
                m_height,
                self.max_image_pixels,
            )
            return None

        if thumbnailer.transpose_method is not None:
            m_width, m_height = thumbnailer.transpose()

        if t_method == "crop":
            return thumbnailer.crop(t_width, t_height, t_type)
        elif t_method == "scale":
            t_width, t_height = thumbnailer.aspect(t_width, t_height)
            t_width = min(m_width, t_width)
            t_height = min(m_height, t_height)
            return thumbnailer.scale(t_width, t_height, t_type)

        return None

    async def generate_local_exact_thumbnail(
        self,
        media_id: str,
        t_width: int,
        t_height: int,
        t_method: str,
        t_type: str,
        url_cache: bool,
    ) -> Optional[str]:
        input_path = await self.media_storage.ensure_media_is_in_local_cache(
            FileInfo(None, media_id, url_cache=url_cache)
        )

        try:
            thumbnailer = Thumbnailer(input_path)
        except ThumbnailError as e:
            logger.warning(
                "Unable to generate a thumbnail for local media %s using a method of %s and type of %s: %s",
                media_id,
                t_method,
                t_type,
                e,
            )
            return None

        with thumbnailer:
            t_byte_source = await defer_to_thread(
                self.hs.get_reactor(),
                self._generate_thumbnail,
                thumbnailer,
                t_width,
                t_height,
                t_method,
                t_type,
            )

        if t_byte_source:
            try:
                file_info = FileInfo(
                    server_name=None,
                    file_id=media_id,
                    url_cache=url_cache,
                    thumbnail=ThumbnailInfo(
                        width=t_width,
                        height=t_height,
                        method=t_method,
                        type=t_type,
                        length=t_byte_source.tell(),
                    ),
                )

                output_path = await self.media_storage.store_file(
                    t_byte_source, file_info
                )
            finally:
                t_byte_source.close()

            logger.info("Stored thumbnail in file %r", output_path)

            t_len = os.path.getsize(output_path)

            await self.store.store_local_thumbnail(
                media_id, t_width, t_height, t_type, t_method, t_len
            )

            return output_path

        # Could not generate thumbnail.
        return None

    async def generate_remote_exact_thumbnail(
        self,
        server_name: str,
        file_id: str,
        media_id: str,
        t_width: int,
        t_height: int,
        t_method: str,
        t_type: str,
    ) -> Optional[str]:
        input_path = await self.media_storage.ensure_media_is_in_local_cache(
            FileInfo(server_name, file_id)
        )

        try:
            thumbnailer = Thumbnailer(input_path)
        except ThumbnailError as e:
            logger.warning(
                "Unable to generate a thumbnail for remote media %s from %s using a method of %s and type of %s: %s",
                media_id,
                server_name,
                t_method,
                t_type,
                e,
            )
            return None

        with thumbnailer:
            t_byte_source = await defer_to_thread(
                self.hs.get_reactor(),
                self._generate_thumbnail,
                thumbnailer,
                t_width,
                t_height,
                t_method,
                t_type,
            )

        if t_byte_source:
            try:
                file_info = FileInfo(
                    server_name=server_name,
                    file_id=file_id,
                    thumbnail=ThumbnailInfo(
                        width=t_width,
                        height=t_height,
                        method=t_method,
                        type=t_type,
                        length=t_byte_source.tell(),
                    ),
                )

                output_path = await self.media_storage.store_file(
                    t_byte_source, file_info
                )
            finally:
                t_byte_source.close()

            logger.info("Stored thumbnail in file %r", output_path)

            t_len = os.path.getsize(output_path)

            await self.store.store_remote_media_thumbnail(
                server_name,
                media_id,
                file_id,
                t_width,
                t_height,
                t_type,
                t_method,
                t_len,
            )

            return output_path

        # Could not generate thumbnail.
        return None

    @trace
    async def _generate_thumbnails(
        self,
        server_name: Optional[str],
        media_id: str,
        file_id: str,
        media_type: str,
        url_cache: bool = False,
    ) -> Optional[dict]:
        """Generate and store thumbnails for an image.

        Args:
            server_name: The server name if remote media, else None if local
            media_id: The media ID of the content. (This is the same as
                the file_id for local content)
            file_id: Local file ID
            media_type: The content type of the file
            url_cache: If we are thumbnailing images downloaded for the URL cache,
                used exclusively by the url previewer

        Returns:
            Dict with "width" and "height" keys of original image or None if the
            media cannot be thumbnailed.
        """
        requirements = self._get_thumbnail_requirements(media_type)
        if not requirements:
            return None

        input_path = await self.media_storage.ensure_media_is_in_local_cache(
            FileInfo(server_name, file_id, url_cache=url_cache)
        )

        try:
            thumbnailer = Thumbnailer(input_path)
        except ThumbnailError as e:
            logger.warning(
                "Unable to generate thumbnails for remote media %s from %s of type %s: %s",
                media_id,
                server_name,
                media_type,
                e,
            )
            return None

        with thumbnailer:
            m_width = thumbnailer.width
            m_height = thumbnailer.height

            if m_width * m_height >= self.max_image_pixels:
                logger.info(
                    "Image too large to thumbnail %r x %r > %r",
                    m_width,
                    m_height,
                    self.max_image_pixels,
                )
                return None

            if thumbnailer.transpose_method is not None:
                m_width, m_height = await defer_to_thread(
                    self.hs.get_reactor(), thumbnailer.transpose
                )

            # We deduplicate the thumbnail sizes by ignoring the cropped versions if
            # they have the same dimensions of a scaled one.
            thumbnails: Dict[Tuple[int, int, str], str] = {}
            for requirement in requirements:
                if requirement.method == "crop":
                    thumbnails.setdefault(
                        (requirement.width, requirement.height, requirement.media_type),
                        requirement.method,
                    )
                elif requirement.method == "scale":
                    t_width, t_height = thumbnailer.aspect(
                        requirement.width, requirement.height
                    )
                    t_width = min(m_width, t_width)
                    t_height = min(m_height, t_height)
                    thumbnails[(t_width, t_height, requirement.media_type)] = (
                        requirement.method
                    )

            # Now we generate the thumbnails for each dimension, store it
            for (t_width, t_height, t_type), t_method in thumbnails.items():
                # Generate the thumbnail
                if t_method == "crop":
                    t_byte_source = await defer_to_thread(
                        self.hs.get_reactor(),
                        thumbnailer.crop,
                        t_width,
                        t_height,
                        t_type,
                    )
                elif t_method == "scale":
                    t_byte_source = await defer_to_thread(
                        self.hs.get_reactor(),
                        thumbnailer.scale,
                        t_width,
                        t_height,
                        t_type,
                    )
                else:
                    logger.error("Unrecognized method: %r", t_method)
                    continue

                if not t_byte_source:
                    continue

                file_info = FileInfo(
                    server_name=server_name,
                    file_id=file_id,
                    url_cache=url_cache,
                    thumbnail=ThumbnailInfo(
                        width=t_width,
                        height=t_height,
                        method=t_method,
                        type=t_type,
                        length=t_byte_source.tell(),
                    ),
                )

                async with self.media_storage.store_into_file(file_info) as (f, fname):
                    try:
                        await self.media_storage.write_to_file(t_byte_source, f)
                    finally:
                        t_byte_source.close()

                    # We flush and close the file to ensure that the bytes have
                    # been written before getting the size.
                    f.flush()
                    f.close()

                    t_len = os.path.getsize(fname)

                    # Write to database
                    if server_name:
                        # Multiple remote media download requests can race (when
                        # using multiple media repos), so this may throw a violation
                        # constraint exception. If it does we'll delete the newly
                        # generated thumbnail from disk (as we're in the ctx
                        # manager).
                        #
                        # However: we've already called `finish()` so we may have
                        # also written to the storage providers. This is preferable
                        # to the alternative where we call `finish()` *after* this,
                        # where we could end up having an entry in the DB but fail
                        # to write the files to the storage providers.
                        try:
                            await self.store.store_remote_media_thumbnail(
                                server_name,
                                media_id,
                                file_id,
                                t_width,
                                t_height,
                                t_type,
                                t_method,
                                t_len,
                            )
                        except Exception as e:
                            thumbnail_exists = (
                                await self.store.get_remote_media_thumbnail(
                                    server_name,
                                    media_id,
                                    t_width,
                                    t_height,
                                    t_type,
                                )
                            )
                            if not thumbnail_exists:
                                raise e
                    else:
                        await self.store.store_local_thumbnail(
                            media_id, t_width, t_height, t_type, t_method, t_len
                        )

        return {"width": m_width, "height": m_height}

    async def _apply_media_retention_rules(self) -> None:
        """
        Purge old local and remote media according to the media retention rules
        defined in the homeserver config.
        """
        # Purge remote media
        if self._media_retention_remote_media_lifetime_ms is not None:
            # Calculate a threshold timestamp derived from the configured lifetime. Any
            # media that has not been accessed since this timestamp will be removed.
            remote_media_threshold_timestamp_ms = (
                self.clock.time_msec() - self._media_retention_remote_media_lifetime_ms
            )

            logger.info(
                "Purging remote media last accessed before"
                f" {remote_media_threshold_timestamp_ms}"
            )

            await self.delete_old_remote_media(
                before_ts=remote_media_threshold_timestamp_ms
            )

        # And now do the same for local media
        if self._media_retention_local_media_lifetime_ms is not None:
            # This works the same as the remote media threshold
            local_media_threshold_timestamp_ms = (
                self.clock.time_msec() - self._media_retention_local_media_lifetime_ms
            )

            logger.info(
                "Purging local media last accessed before"
                f" {local_media_threshold_timestamp_ms}"
            )

            await self.delete_old_local_media(
                before_ts=local_media_threshold_timestamp_ms,
                keep_profiles=True,
                delete_quarantined_media=False,
                delete_protected_media=False,
            )

    async def delete_old_remote_media(self, before_ts: int) -> Dict[str, int]:
        old_media = await self.store.get_remote_media_ids(
            before_ts, include_quarantined_media=False
        )

        deleted = 0

        for origin, media_id, file_id in old_media:
            key = (origin, media_id)

            logger.info("Deleting: %r", key)

            # TODO: Should we delete from the backup store

            async with self.remote_media_linearizer.queue(key):
                full_path = self.filepaths.remote_media_filepath(origin, file_id)
                try:
                    os.remove(full_path)
                except OSError as e:
                    logger.warning("Failed to remove file: %r", full_path)
                    if e.errno == errno.ENOENT:
                        pass
                    else:
                        continue

                thumbnail_dir = self.filepaths.remote_media_thumbnail_dir(
                    origin, file_id
                )
                shutil.rmtree(thumbnail_dir, ignore_errors=True)

                await self.store.delete_remote_media(origin, media_id)
                deleted += 1

        return {"deleted": deleted}

    async def delete_local_media_ids(
        self, media_ids: List[str]
    ) -> Tuple[List[str], int]:
        """
        Delete the given local or remote media ID from this server

        Args:
            media_id: The media ID to delete.
        Returns:
            A tuple of (list of deleted media IDs, total deleted media IDs).
        """
        return await self._remove_local_media_from_disk(media_ids)

    async def delete_old_local_media(
        self,
        before_ts: int,
        size_gt: int = 0,
        keep_profiles: bool = True,
        delete_quarantined_media: bool = False,
        delete_protected_media: bool = False,
    ) -> Tuple[List[str], int]:
        """
        Delete local or remote media from this server by size and timestamp. Removes
        media files, any thumbnails and cached URLs.

        Args:
            before_ts: Unix timestamp in ms.
                Files that were last used before this timestamp will be deleted.
            size_gt: Size of the media in bytes. Files that are larger will be deleted.
            keep_profiles: Switch to delete also files that are still used in image data
                (e.g user profile, room avatar). If false these files will be deleted.
            delete_quarantined_media: If True, media marked as quarantined will be deleted.
            delete_protected_media: If True, media marked as protected will be deleted.

        Returns:
            A tuple of (list of deleted media IDs, total deleted media IDs).
        """
        old_media = await self.store.get_local_media_ids(
            before_ts,
            size_gt,
            keep_profiles,
            include_quarantined_media=delete_quarantined_media,
            include_protected_media=delete_protected_media,
        )
        return await self._remove_local_media_from_disk(old_media)

    async def _remove_local_media_from_disk(
        self, media_ids: List[str]
    ) -> Tuple[List[str], int]:
        """
        Delete local or remote media from this server. Removes media files,
        any thumbnails and cached URLs.

        Args:
            media_ids: List of media_id to delete
        Returns:
            A tuple of (list of deleted media IDs, total deleted media IDs).
        """
        removed_media = []
        for media_id in media_ids:
            logger.info("Deleting media with ID '%s'", media_id)
            full_path = self.filepaths.local_media_filepath(media_id)
            try:
                os.remove(full_path)
            except OSError as e:
                logger.warning("Failed to remove file: %r: %s", full_path, e)
                if e.errno == errno.ENOENT:
                    pass
                else:
                    continue

            thumbnail_dir = self.filepaths.local_media_thumbnail_dir(media_id)
            shutil.rmtree(thumbnail_dir, ignore_errors=True)

            await self.store.delete_remote_media(self.server_name, media_id)

            await self.store.delete_url_cache((media_id,))
            await self.store.delete_url_cache_media((media_id,))

            removed_media.append(media_id)

        return removed_media, len(removed_media)