# diff.sr.ht

A git compare/diff viewer for a self-hosted [SourceHut] instance. It compares
two refs (branches, tags, or commits) of any git.sr.ht repository — `base...head`
or `base..head` — and renders the diff with [`@pierre/diffs`] (Shiki-based
syntax-highlighted diffs) and a [`@pierre/trees`] file tree, plus a
single-commit view. Runs at `https://diff.srht.bigb.es`.

[SourceHut]: https://sourcehut.org
[`@pierre/diffs`]: https://www.npmjs.com/package/@pierre/diffs
[`@pierre/trees`]: https://www.npmjs.com/package/@pierre/trees

> **The service is `diff.sr.ht`; the repository is still `sr-ht-compare`.** The
> service was called `compare.sr.ht` until it was renamed, and what the rename
> moved is everything the instance sees: the `config.ini` section, the origin,
> the apk package, the container. What it deliberately did not move is anything
> with a cost and no benefit — the Go module path
> (`sourcecraft.dev/bigbes/sr-ht-compare`), the repository name, the binary
> (`comparesrht`) and the `/~owner/repo/compare/base...head` routes, which are
> the URLs people have in their history.

## Architecture

diff.sr.ht is a **stateless Go daemon**: it owns no database and no object
storage, so it needs neither Postgres nor Redis. It integrates into SourceHut
purely through configuration — no upstream sources are modified (the
[sourcehut-custom-service integration model]). Repository data is read directly
from the bare repos on disk (`{[git.sr.ht] repos}/~{owner}/{name}`) using
[go-git] in-process; no `git` binary is executed at runtime. Every request is
authorized against the git.sr.ht **internal GraphQL API** using core-go's
internal-auth client, acting as the cookie's logged-in user — or anonymously,
which git.sr.ht's own loader scopes to public/unlisted repositories, so private
repos are never leaked (an unauthorized or missing repo is always a 404, never a
403). Identity comes from decrypting the shared `sr.ht.unified-login.v1` cookie
with the instance network key; there is no login flow of our own. Pages are
server-rendered Go templates wrapped in the SourceHut chrome (nav,
service-switcher, login block, environment banner), which comes from the shared
[sr-ht-ecore] `chrome` package rather than from a copy of its own. The diff/tree UI is one
vendored [pierre-libs] esbuild bundle driven by a JSON blob embedded in the
page, so the browser does all diff rendering from a single request with no
second authorization round-trip. A short-TTL in-memory cache in front of the
authorizer spares git.sr.ht a GraphQL call on every page load.

[sourcehut-custom-service integration model]: https://man.sr.ht/
[go-git]: https://github.com/go-git/go-git
[pierre-libs]: https://www.npmjs.com/org/pierre
[sr-ht-ecore]: https://git.srht.bigb.es/~bigbes/sr-ht-ecore

## Layout

- `core/` — pure domain: owner/repo/ref validation, the compare-spec grammar,
  sentinel errors. No external dependencies.
- `gitx/` — bare-repo access over go-git: refs, ref-to-ref diffs, single-commit
  diffs, and commit logs, all bounded by context timeouts and output-size caps.
- `authz/` — the git.sr.ht GraphQL authorizer with a short TTL cache. Identity
  is not here any more: the unified-login cookie is decoded by [sr-ht-ecore]'s
  `login`, the instance's one copy of that decode, which — unlike the local one
  it replaced — refuses a name that could not be a username.
- `web/` — chi router, handlers, Go templates, embedded static assets. Most of
  the machinery around them is not here but in [sr-ht-ecore], wired up in
  `web/server.go`: `chrome` for the page frame, `pages` for template discovery
  and the shared error page, `assets` for the hashed artefacts and their cache
  policy, `csrf` and `middleware` for the router's guards, `chimw` for the
  GET+HEAD route pair, the rendered 404/405 and the request log record. What is
  left is this service's own: the routes, the handlers, and the templates they
  render.
- `frontend/` + `scss/` — build-time TypeScript diff bundle and the SCSS entry.
- `cmd/comparesrht/` — the daemon entry point and startup validation.
- `contrib/` — nginx server block, systemd unit, and a dev GraphQL stub.

The core-go dependency is pinned to a private fork
(`git.srht.bigb.es/~bigbes/core-go`) via a `replace` directive in `go.mod`; the
fork carries one production S3 patch on top of upstream.

## Build requirements

- **Go** 1.26+ (module `sourcecraft.dev/bigbes/sr-ht-compare`).
- **sassc** and **minify** — CSS pipeline (`make css`), building against the
  shared sourcehut scss partials installed at `/usr/share/sourcehut/scss` (from
  `core.sr.ht`'s `make install`). `dart-sass` also works for local builds; the
  production `css` target uses `sassc -I /usr/share/sourcehut/scss`.
- **Node.js** (build time only) — the frontend diff bundle (`make bundle`,
  esbuild). The vendored, content-hashed `web/static/bundle.<hash>.js` is
  committed (the hash busts the browser cache on deploy, like the stylesheet), so
  Node is not needed at runtime.

```sh
make build   # compile ./comparesrht
make test    # go test ./...
make cover   # the same suite plus ./cover.out (what CI uploads to cov.sr.ht)
make bench   # the diffing benchmarks as benchfmt (what CI uploads to bench.sr.ht)
make css     # build the hashed stylesheet (sassc + minify)
make bundle  # rebuild the vendored frontend bundle (esbuild)
```

> **Static assets are `//go:embed`-ed into the binary** (`web/templates.go`
> embeds `static`). `make css` / `make bundle` only update the files under
> `web/static/` — the running daemon serves the copy baked into `./comparesrht`,
> so **re-run `make build` after either** or the change won't appear. Rebuilding
> the CSS or bundle without a following `go build` is a common way to chase a
> stale asset.

## Configuration

See `config.example.ini`. On a real instance, append the `[diff.sr.ht]`
section to the shared `/etc/sr.ht/config.ini`; the service reads the instance's
existing shared keys (`[sr.ht]`, `[webhooks]`, `[meta.sr.ht]`, `[git.sr.ht]`) in
place. core-go's `LoadConfig()` searches, in order: `./config.ini`,
`../config.ini`, `/etc/sr.ht/config.ini`, `/etc/sr.ht/*.ini`.

At startup the daemon validates that all required keys are present — the
`[sr.ht] network-key`, `[webhooks] private-key`, `[git.sr.ht] repos`, a
git.sr.ht API origin candidate (`api-internal-origin` / `internal-origin` /
`api-origin` / `origin`), `[meta.sr.ht] origin`, and `[diff.sr.ht] origin` —
and exits with a single clear message listing anything missing.

## Development

Run the service locally against a directory of bare repositories and the
dev-stub GraphQL API (no real instance required).

1. **Write a local `config.ini`** in the repo root (git-ignored). Minimal
   template — the two crypto keys can be any dev values (see below):

   ```ini
   [sr.ht]
   network-key=<a fresh Fernet key>
   site-name=sourcehut
   environment=development

   [webhooks]
   private-key=<base64 of 32 random bytes>

   [diff.sr.ht]
   origin=http://localhost:5090

   [meta.sr.ht]
   origin=http://localhost:5100

   [git.sr.ht]
   origin=http://localhost:5101
   api-origin=http://localhost:5101   # dev-stub serves POST /query here
   repos=/path/to/local/bare/repos    # holds ~owner/name bare repos
   ```

   Generate the keys with a throwaway program (both use core-go's fernet
   dependency):

   ```go
   // go run ./gen-keys.go
   package main

   import (
       "crypto/rand"
       "encoding/base64"
       "fmt"

       "github.com/fernet/fernet-go"
   )

   func main() {
       var k fernet.Key
       _ = k.Generate()
       seed := make([]byte, 32)
       _, _ = rand.Read(seed)
       fmt.Println("network-key =", k.Encode())
       fmt.Println("private-key =", base64.StdEncoding.EncodeToString(seed))
   }
   ```

2. **Prepare a bare repo** for the stub to resolve. The dev-stub reports every
   repository as PUBLIC, so gitx just needs the on-disk repo to exist:

   ```sh
   mkdir -p /path/to/local/bare/repos/~alice
   git clone --bare /some/existing/repo /path/to/local/bare/repos/~alice/demo
   ```

3. **Start the dev-stub** (fake git.sr.ht GraphQL API):

   ```sh
   go run ./contrib/dev-stub -addr 127.0.0.1:5101
   ```

4. **Run the daemon:**

   ```sh
   make run-dev            # builds, then ./comparesrht -b localhost:5090
   ```

   Visit `http://localhost:5090/~alice/demo`, then a compare such as
   `http://localhost:5090/~alice/demo/compare/main...some-branch`, or a commit
   page at `/~alice/demo/commit/<sha>`. Append `.patch` to any compare/commit
   URL for the raw unified diff.

### Forging a dev login cookie

There is no dedicated helper. Identity is just the `sr.ht.unified-login.v1`
cookie: a Fernet token (sealed with `[sr.ht] network-key`) whose JSON payload's
only meaningful field is `name`. Mint one with a five-line program that reuses
the same config and crypto core-go uses at runtime:

```go
// go run ./mint-cookie.go   (run from the dir holding config.ini)
package main

import (
    "encoding/json"
    "fmt"

    "sourcecraft.dev/bigbes/sr-ht-core/config"
    "sourcecraft.dev/bigbes/sr-ht-core/crypto"
)

func main() {
    conf := config.LoadConfig()
    crypto.InitCrypto(conf)
    payload, _ := json.Marshal(map[string]string{"name": "bigbes"})
    fmt.Println(string(crypto.Encrypt(payload)))
}
```

Set the printed value as the `sr.ht.unified-login.v1` cookie for
`localhost:5090` (browser devtools → Application → Cookies), reload, and the nav
shows "Logged in as bigbes" with your repository list (from the stub's
`me.repositories`).

## Deployment

diff.sr.ht deploys like any other SourceHut web service. On the instance:

1. **Install** the binary and static assets:

   ```sh
   make install PREFIX=/usr/local
   # → /usr/local/bin/comparesrht
   # → /usr/share/sourcehut/diff.sr.ht/static/{bundle.<hash>.js,main.min.<hash>.css}
   ```

2. **Config.** Append the `[diff.sr.ht]` section (`origin=` and
   `static-dir=`) to the shared `/etc/sr.ht/config.ini`. To make diff.sr.ht
   appear in the shared nav/service-switcher of the *other* services, that same
   `[diff.sr.ht] origin=` line must be visible to their configs too (on a
   single shared `config.ini` this is automatic) — then **restart those
   services** (git.sr.ht, meta.sr.ht, …) so they pick up the new switcher entry.

3. **DNS.** Point `diff.srht.bigb.es` at the instance. It must be a subdomain
   of the shared cookie domain (`*.srht.bigb.es`) so the unified-login cookie is
   sent to us.

4. **internal-ipnet.** This host must fall inside the git.sr.ht API's
   `[sr.ht] internal-ipnet` CIDR, or the internal-auth GraphQL calls
   (including anonymous `AUTH_ANON_INTERNAL`) are rejected. If diff.sr.ht
   runs on the same box as git.sr.ht, the default loopback/private ranges
   already cover it.

5. **nginx.** Install `contrib/diff.sr.ht.conf` alongside the other
   `*.sr.ht.conf` files (adjust `server_name`), provide the TLS cert include it
   references (`diff-ssl.conf`), and reload nginx. It is a plain
   `proxy_pass http://127.0.0.1:5090`; static assets are served by the app from
   its embedded FS with immutable cache headers.

6. **systemd.** Install `contrib/diff-srht.service`, then
   `systemctl enable --now diff-srht`. The unit runs as **`User=git`** so it
   has read access to the bare repositories under `/var/lib/git`
   (`ReadOnlyPaths=/var/lib/git`, `ProtectSystem=strict` — the service only ever
   reads). It stops with `KillSignal=SIGINT` because core-go's `server.Run`
   performs its warm shutdown on SIGINT, not the systemd default SIGTERM.

7. **Verify.** `GET https://diff.srht.bigb.es/healthz` → `ok`. Logged in,
   the landing page lists your repos and a PUBLIC repo's `main...branch` compare
   renders with syntax highlighting, the tree sidebar, and the split/unified
   toggle; a PRIVATE repo is a 404 to anonymous viewers and 200 to its owner.

## Design notes

- **go-git, not `git` shell-out.** git.sr.ht itself shells out to the `git`
  binary, and the original plan did too. On the user's decision we read
  repositories in-process with go-git instead: no subprocess management, no
  `PATH`/argument-injection surface, and cleaner output-size bounding. The diff
  output was fidelity-verified against real `git` (see `gitx/fidelity_test.go`)
  so the patches `@pierre/diffs` parses carry standard `diff --git` headers and
  match git's rename/binary handling.
- **10 MB vendored bundle.** `web/static/bundle.<hash>.js` is a ~10 MB committed
  esbuild output. It is large because `@pierre/diffs` bundles Shiki with its
  grammars/themes for client-side syntax highlighting. We accept the size: it is
  built once, served with a long immutable cache lifetime, gzips/brotlis down
  substantially on the wire, and keeps the runtime a single static Go binary
  with zero Node dependency. Trimming Shiki's language set is the obvious future
  lever if the transfer size becomes a problem.
- **LICENSE pending.** No `LICENSE` file has been chosen yet. SourceHut's own
  services are typically AGPL/GPL; pick and add one before any public
  distribution.
