# mfer

Manifest file generator and checker.

# Problem Statement

Given a plain URL, there is no standard way to safely and programmatically download everything "under" that URL path.  `wget -r` can traverse directory listings if they're enabled, but every server has a different format, and this does not verify cryptographic integrity of the files, or enable them to be fetched using a different protocol other than HTTP/s.

Currently, the solution that people are using are sidecar files in the format of `SHASUMS` checksum files, as well as a `SHASUMS.asc` PGP detached signature.  This is not checksum-algorithm-agnostic and the sidecar file is not always consistently named.

Real issues I face:

* when I plug in an ExFAT hard drive, I don't know if any files on the filesystem are corrupted or missing
    * current ad-hoc solution are `SHASUMS`/`SHASUMS.asc` files
* when I want to mirror an HTTP archive, I have to use special tools like debmirror that understand the archive format
    * the debian repository metadata structure is hot garbage
* when I download a large file via HTTP, I have no way of knowing if the file content is what it's supposed to be

# Proposed Solution

A standard, a manifest file format, and a tool for generating same.

The manifest file would be called `index.mf`, and the tool for generating such would be called `mfer`.

The manifest file would do several important things:

* have a standard filename, so if given `https://example.com/downloadpackage/` one could fetch `https://example.com/downloadpackage/index.mf` to enumerate the full directory listing.
* contain a version field for extensibility
* contain structured data (protobuf, json, or cbor)
* provide an inner signed container, so that the manifest file itself can embed a signature and a public key alongside in a single file
* contain a list of files, each with a relative path to the manifest
* contain manifest timestamp
* contain ctime/mtime information for files so that file metadata can be preserved
* contain cryptographic checksums in several different algorithms for each file
    * probably encoded with multihash to indicate algo + hash
    * sha256 at the minimum
    * would be nice to include an IPFS/IPLD CIDv1 root hash for each file, which likely involves doing an ipfs file object chunking
    * maybe even including the complete IPFS/IPLD directory tree objects and chunklists?
        * this is because generating an `index.mf` does not imply publishing on ipfs at that time
    * maybe a bittorrent chunklist for torrent client compatibility? perhaps a top-level infohash for the whole manifest?

# Design Goals

* Replace SHASUMS/SHASUMS.asc files
* be easy to download/resume a whole directory tree published via HTTP
* be easy to use across protocols (given an HTTPS url, fetch manifest, then download file contents via bittorrent or ipfs)

# Non-Goals
* Manifest generation speed
    * likely involves IPFS chunking, bittorrent chunking, and several different cryptographic hash functions over the entirety of each and every file
* Small manifest file size (within reason)
    * 30MiB files are "small" these days, given modern storage/bandwidth
    * metadata size should not be used as an excuse to sacrifice utility (such as providing checksums over each chunk of a large file)

# Open Questions
* Should the manifest file include checksums of individual file chunks, or just for the whole assembled file?
    * If so, should the chunksize be fixed or dynamic?

# Tool Examples

* `mfer gen` / `mfer gen .`
    * recurses under current directory and writes out an `index.mf`
* `mfer check` / `mfer check .`
    * verifies checksums of all files in manifest, displaying error and exiting nonzero if any files are missing or corrupted
* `mfer fetch https://example.com/stuff/`
    * fetches `/stuff/index.mf` and downloads all files listed in manifest, optionally resuming any that already exist locally, and assures cryptographic integrity of downloaded files.

# Implementation Plan

## Phase One:

* golang module for reusability/embedding
* golang module client providing `mfer` CLI

## Phase Two:

* ES6 or TypeScript module for reusability/embedding
* ES6/TypeScript module client providing `mfer.js` CLI

# Hopes And Dreams

* `aria2c https://example.com/manifestdirectory/`
    * (fetches `https://example.com/manifestdirectory/index.mf`, downloads and checksums all files, resumes any that exist locally already)
* `mfer fetch https://example.com/manifestdirectory/`
* a command line option to zero/omit mtime/ctime, as well as manifest timestamp, and sort all directory listings so that manifest file generation is deterministic/reproducible
* URL format `mfer fetch https://exmaple.com/manifestdirectory/?key=5539AD00DE4C42F3AFE11575052443F4DF2A55C2` to assert in the URL which PGP signing key should be used in the manifest, so that shared URLs have a cryptographic trust root
* a "well-known" key in the manifest that maps well known keys (could reuse the http spec) to specific file paths in the manifest.
    * example: a `berlin.sneak.app.slideshow` key that maps to a json slideshow config listing what image paths to show, and for how long, and in what order

# Use Cases

## Web Images

I'd like to be able to put a bunch of images into a directory, generate a manifest, and then point a slideshow client (such as an ambient display, or a react app with the target directory in a query string arg) at that statically hosted directory, and have it discover the full list of images available at that URL.

## Software Distribution

I'd like to be able to download a whole tree of files available via HTTP resumably by either HTTP or IPFS/BitTorrent without a .torrent file.

## Filesystem Archive Integrity

I use filesystems that don't include data checksums, and I would like a cryptographically signed checksum file so that I can later verify that a set of archive files have not been modified, none are missing, and that the checksums have not been altered in storage by a second party.

## Filesystem-Independent Checksums

I would like to be able to plug in a hard drive or flash drive and, if there is an `index.mf` in the root, automatically detect missing/corrupted files, regardless of filesystem format.

# Collaboration
Please email [`sneak@sneak.berlin`](mailto:sneak@sneak.berlin) with your desired username for an account on this Gitea instance.

I am currently interested in hiring a contractor skilled with the Go standard library interfaces to specify this tool in full and develop a prototype implementation.