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Add docs on symlink

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Tim Hockin 2024-08-12 10:23:57 -07:00
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README.md
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@ -25,6 +25,41 @@ git-sync can also be configured to make a webhook call or exec a command upon
successful git repo synchronization. The call is made after the symlink is successful git repo synchronization. The call is made after the symlink is
updated. updated.
## What it produces and why - the contract
git-sync has two required flags: `--repo`, which specifies which remote git
repo to sync, and `--root` which specifies a working directory for git-sync,
which presents an "API" of sorts.
The `--root` directory is _not_ the synced data.
Inside the `--root` directory git-sync stores the synced git state and other
things. That directory may or may not respond to git commands - it's an
implementation detail.
One of the things in that directory is a symlink (see the `--link` flag) to the
most recently synced data. This is how the data is expected to be consumed,
and is considered to be the "contract" between git-sync and consumers. The
exact target of that symlink is an implementation detail, but the leaf
component of the target (i.e. `basename "$(readlink <link>)"`) is the git hash
of the synced revision. This is also part of the contract.
git-sync looks for changes in the remote repo periodically (see the `--period`
flag) and will attempt to transfer as little data as possible and use as little
disk space as possible (see the `--depth` and `--git-gc` flags), but this is
not part of the contract.
### Why the symlink?
git checkouts are not "atomic" operations. If you look at the repository while
a checkout is happening, you might see data that is neither exactly the old
revision nor the new. git-sync "publishes" updates via the symlink to present
an atomic interface to consumers. When the remote repo has changed, git-sync
will fetch the data _without_ checking it out, then create a new worktree, then
change the symlink to point to that new worktree.
git-sync does not currently have a no-symlink mode.
## Major update: v3.x -> v4.x ## Major update: v3.x -> v4.x
git-sync has undergone many significant changes between v3.x and v4.x. [See git-sync has undergone many significant changes between v3.x and v4.x. [See
@ -139,6 +174,38 @@ DESCRIPTION
git-sync can also be configured to make a webhook call upon successful git git-sync can also be configured to make a webhook call upon successful git
repo synchronization. The call is made after the symlink is updated. repo synchronization. The call is made after the symlink is updated.
CONTRACT
git-sync has two required flags:
--repo: specifies which remote git repo to sync
--root: specifies a working directory for git-sync
The root directory is not the synced data.
Inside the root directory, git-sync stores the synced git state and other
things. That directory may or may not respond to git commands - it's an
implementation detail.
One of the things in that directory is a symlink (see the --link flag) to
the most recently synced data. This is how the data is expected to be
consumed, and is considered to be the "contract" between git-sync and
consumers. The exact target of that symlink is an implementation detail,
but the leaf component of the target (i.e. basename "$(readlink <link>)")
is the git hash of the synced revision. This is also part of the contract.
Why the symlink? git checkouts are not "atomic" operations. If you look
at the repository while a checkout is happening, you might see data that is
neither exactly the old revision nor the new. git-sync "publishes" updates
via the symlink to present an atomic interface to consumers. When the
remote repo has changed, git-sync will fetch the data _without_ checking it
out, then create a new worktree, then change the symlink to point to that
new worktree.
git-sync looks for changes in the remote repo periodically (see the
--period flag) and will attempt to transfer as little data as possible and
use as little disk space as possible (see the --depth and --git-gc flags),
but this is not part of the contract.
OPTIONS OPTIONS
Many options can be specified as either a commandline flag or an environment Many options can be specified as either a commandline flag or an environment

32
main.go
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@ -2169,6 +2169,38 @@ DESCRIPTION
git-sync can also be configured to make a webhook call upon successful git git-sync can also be configured to make a webhook call upon successful git
repo synchronization. The call is made after the symlink is updated. repo synchronization. The call is made after the symlink is updated.
CONTRACT
git-sync has two required flags:
--repo: specifies which remote git repo to sync
--root: specifies a working directory for git-sync
The root directory is not the synced data.
Inside the root directory, git-sync stores the synced git state and other
things. That directory may or may not respond to git commands - it's an
implementation detail.
One of the things in that directory is a symlink (see the --link flag) to
the most recently synced data. This is how the data is expected to be
consumed, and is considered to be the "contract" between git-sync and
consumers. The exact target of that symlink is an implementation detail,
but the leaf component of the target (i.e. basename "$(readlink <link>)")
is the git hash of the synced revision. This is also part of the contract.
Why the symlink? git checkouts are not "atomic" operations. If you look
at the repository while a checkout is happening, you might see data that is
neither exactly the old revision nor the new. git-sync "publishes" updates
via the symlink to present an atomic interface to consumers. When the
remote repo has changed, git-sync will fetch the data _without_ checking it
out, then create a new worktree, then change the symlink to point to that
new worktree.
git-sync looks for changes in the remote repo periodically (see the
--period flag) and will attempt to transfer as little data as possible and
use as little disk space as possible (see the --depth and --git-gc flags),
but this is not part of the contract.
OPTIONS OPTIONS
Many options can be specified as either a commandline flag or an environment Many options can be specified as either a commandline flag or an environment