dehub/SPEC.md

# .dehub

The `.dehub` directory contains all meta information related to
decentralized repository management and access control.

## config.yml

The `.dehub/config.yml` file takes the following structure:

```yaml
# accounts defines all accounts which are known to the repo.
accounts:

    # Each account is an object with an id and at least one identifier. The id
    # must be unique for each account.
    - id: some_user_id:

      # signifiers describes different methods the account might use to
      # identify itself. Generally, these will be different public keys which
      # commits will be signed with. At least one is required.
      signifiers:
          - type: "pgp_public_key"
            body: "FULL PGP PUBLIC KEY STRING"

          - type: "pgp_public_key_file"
            path: ".dehub/some_user_id.asc"

          - type: "keybase"
            user: "some_keybase_user_id"

# access_controls defines under what conditions different files in the repo may
# be modified. For each file modified in a commit, all access control patterns
# are applied sequentially until one matches, and the associated access control
# conditions are checked. A commit is only allowed if the conditions of all
# modified files are met.
access_controls:

    # pattern is a glob pattern describing what files this access control
    # applies to. Single star matches all characters except path separators,
    # double star matches everything.
    - pattern: ".dehub/**"

      # signature conditions indicate that a commit must be signed by one or
      # more accounts to be allowed.
      condition:
        type: signature

        # account_ids lists all accounts whose signature will count towards
        # meeting the condition
        account_ids:
            - some_user_id

        # count describes how many signatures are required. It can be either a
        # contrete integer (e.g. 2, meaning any 2 accounts listed by
        # account_ids) or a percent.
        count: 100%

    # This catch-all pattern for the rest of the repo requires that changes to
    # any files not under `.dehub/` are signed by at least one of the
    # defined accounts.
    - pattern: "**"
      condition:
        type: signature
        any_account: true # indicates any account defined in accounts is valid
        count: 1
```

# Change Hash

When a change commit (see Commits section) is being signed by a signifier there
is an expected data format for the data to be signed. The format is a SHA-256
hash of the following pieces of data concatenated together (the change hash):

* A uvarint indicating the number of bytes in the commit message.
* The message.
* A uvarint indicating the number of files changed.
* For each file changed in the commit, ordered lexographically-ascending based
  on its full relative path within the repo, the following is then written:
  * A uvarint indicating the length of the full relative path of the file
    within the repo.
  * The full relative path of the file within the repo.
  * A little-endian uint32 representing the previous file mode of the file (or 0
    if the file is being inserted).
  * The 20-byte SHA1 hash of the previous version of the file's contents (or 20
    0 bytes if the file is being inserted).
  * A little-endian uint32 representing the new file mode of the file (or 0
    if the file is being deleted).
  * The 20-byte SHA1 hash of the new version of the file's contents (or 20
    0 bytes if the file is being deleted).

The raw output from the SHA-256 is then prepended with a `0` byte (for forward
compatibility). The result is the raw change hash.

# Credentials

All file changes need to have some kind of credential to be accepted into the
`trunk` branch (see Trunk Branch section). Each credential is encoded as a yaml
object with a `type` field.

All credentials contain enough information to correspond them to a specific
signifier in the `config.yml`, so as to be able to verify them.

## PGP Signature Credential

Currently there is only a single credential type, the `pgp_signature`, which
signs a raw change hash (which is communicated out-of-band of the object):

```
type: pgp_signature
account_id: some_user_id
pub_key_id: XXX
body: "base-64 signature body"
```

# Commits

All commit messages in dehub repositories are expected to follow the following
template (newlines included, yaml comments start with `#` and are only for
informational purposes):

```
Human readable message head

---
# Three dashes indicate the start of the yaml body. Everything after must be
# valid yaml.

type: type of the commit # Always required
fieldA: valueA
fieldB: valueB
```

## Change Commits

Commits of type `change` correspond to the standard git commit; they encompass a
set of file changes as well as a message describing the changes which occurred.
They extend the standard git commit with a few dehub specific features, such as
the change hash and credentials.

`change` commits are, currently, the _only_ commit type which are allowed to
have file changes.

Example change commit message:

```
This is the message head. It will be re-iterated within the message field

---
type: change
message: >
    This is the message head. It will be re-iterated within the message field

    The rest of this field is for the message body, which corresponds to the
    body of a normal commit message which might give a more long-form
    explanation of the commit's changes.

    Since the message is used in generating the signature it's necessary for it
    to be encoded here fully formed, even though the message head is then
    duplicated. Otherwise the exact bytes of the message would be ambiguous.
    This situation is ugly, but not unbearable.

# The change_hash is able to be computed from the commit's message and changed
# files, but is reproduced in the commit message for forward compatibility, e.g.
# if the algorithm to compute the hash changes.
change_hash: XXX

# Credentials are the set of credentials which indicate approval of the change
credentials:
    - type: pgp_signature
      account_id: some_user_id
      pub_key_id: XXX
      body: "base-64 signature body"
```

## Credential Commits

Commits of type `credential` contain one or more credentials for some set of
changes, and the change hash to which those credentials apply. The commit
message head is not spec'd, but should be a human-readable description of "who
is crediting what, and how".

Example credential commit message:

```
some_user_id pgp sig of commits AAA..BBB with key CCC

---
change_hash: XXX
credentials:
    - type: pgp_signature
      account_id: some_user_id
      pub_key_id: CCC
      body: "base-64 signature body"
```

# Branches

dehub branches correspond 1-to-1 with branches in the underlying git repo. All
commits in a dehub branch should contain an encoded message as specified in the
Commits section of this document, and possibly file changes as appropriate.

## Trunk Branch

The "primary" branch of a dehub repo is the `trunk` branch. All new commits
being appended to the HEAD of the `trunk` branch are subject to the following
requirements:

* Must be `change` commits.

* Must conform to all requirements defined by the `access_controls` section of
  the `config.yml`, as found in the current HEAD. If the commit is the initial
  commit of the branch then it instead uses the `config.yml` found in itself.

* Must be a "fast-forward" commit (this may be amended later, but at present it
  simplifies implementation).


## Thread Branches

Branches which are not the `trunk` branch are referred to as "threads", and have
much less stringent requirements than the `trunk` branch:

* They can contain commits of any type, as long as the commits come from those
  with an account defined in the `config.yml`.

* `change` commits are not subject `access_controls` requirements.

# TODO

* access control patterns related to who may push to MR branches, and what types
  of commits they can push.