add human readme

+# My git viewer

+

+### Why I did this

+

+So, the premise behind this project was a few different things:

+

+- I wanted a git viewer stack that, while modular, remained light.

+- I liked the idea of having reusable "templates" rather than generating the HTML dynamically in the code. This is much closer to how things like Hugo operate.

+- It needs to be easy to extend (modularity!). A core is responsible for loading a git repo's context and other request state, but all "real" functionality is implemented via modules. I could add/remove things without needing to worry (too much...) about breaking unrelated things.

+- I wanted something that was modern, but didn't require javascript to operate. All features on this site work without javascript, though your experience is improved with it.

+- I wanted to have a way to view private git repositories using systems I already have.

+ - I don't want to/have the capability to SSH clone my repos to show something off.

+ - Could I have done this in cgit? Perhaps, but it wasn't built for it.

+- And, probably most visibly, this was a trial in "vibe coding". While the idea around the design of this software was mine, I wrote very little of the code. Especially the UI, and this is for the better. I am not a graphics designer and whatever slop the LLM pumps out (with my input here and there) will be leagues better than whatever I do; for better or worse.

+

+The name "gsg" doesn't mean much (I don't name things). It're pretty much "git static generator". It was the placeholder when I was thinking of a system that was "kind of a combination of cgit's lightness and hugo's composability and templating".

+

+### The design

+

+First and foremost, the AI writeup is in ./llm_readme.md. Read that if you want all of the verbose details.

+

+Also, as alluded to above, no javascript is strictly required. The few places it is used it is just used to make the experience nicer, and a fallback always exists. For example, the JSON/YAML codepath has a JS module that allows you to search for values/keys, perform folding, etc. This is a core design tenant: JS always hydrates what exists already.

+

+(Not) Broadly speaking, as stated above, this project is split up into:

+

+- The core

+ - gitx - the module that actually interfaces with git. This transforms a context into a re-usable struct (should I ever want to use a real implementation)

+ - access - Consolidated checks for whether someone can see/not see a repo

+ - session - Owns all privileged access logic. It generates/verifies tokens that are used across the site. Everything is stateless once authenticated.

+ - authn - Route owner that defines login/logout flows. Uses session internally

+ - httpx - Shared helpers used when generating responses/evaling a req

+ - notices - Logic for me to post notices to the site or repos

+ - share - Logic for authenticated users to mint links to private repos they are allowed to. Uses same auth logic as users under the hood.

+ - api - Exposes repo details as a JSON endpoint, will be used by my main site later on

+ - core/site - All the main things needed to make this tick. Build req context, define routes and where they live, define module registration structs.

+- The modules

+ - blob - Responsible for returning files (raw or templated)

+ - commit - Render a commit

+ - compare - Render a diff between two commits/refs

+ - graph - Render commit log graph

+ - image - Image preview, defines compatible file types and max size

+ - markdown - Render markdown

+ - readme - Inherits markdown to render a readme (what you see here!)

+ - notices - Handles cache invalidation for repos that need one rendered

+ - log - View the git log

+ - repos - Aggregates the repos you may view based on session

+ - structured - Whether a file is a YAML or JSON. If so, it prepares data for JS in the frontend to perform folding and suchA

+ - tree - the directory-structure viewer

+

+As time goes on, I am sure I will find more things to add to this. This is really meant to be a project for me, not necessarily building "the next git viewer for everyone".

+

+I figured I would upload this here in case my tokens are useful for others. Enjoy!

+# gsg — a modular git browser

+

+cgit's weight, Hugo's composability, served dynamically. A **module**

+computes one piece of a view; a **route** binds a renderer to a URL pattern.

+Adding a feature means adding a module and calling it from a template —

+`internal/core` never changes.

+

+One dependency (`goldmark`, which itself has none) plus the `git` binary. Go 1.22+ (uses `net/http`

+pattern wildcards, so there is no router dependency either).

+

+```

+go build -o gsg .

+./gsg -root /srv/git -addr :8080 -name "rschanz.org"

+./gsg -root /srv/git -templates ./templates # re-parse the theme per request

+./gsg -root /srv/git -notices /etc/gsg/notices.yaml -admin-addr 127.0.0.1:8081

+```

+

+## The idea

+

+```go

+type Module func(c *Ctx, args ...string) (any, error)

+```

+

+Templates reach modules through one funcmap entry:

+

+```gotmpl

+{{ with mod "meta" }}<h1>{{ .Title }}</h1>{{ end }}

+{{ $d := mod "diff" }}

+{{ with modOr "readme" }}{{ .HTML }}{{ end }}

+```

+

+- **Lazy.** A template that calls `mod "authors"` is what *causes* authors to

+ be computed. Views that don't ask don't pay.

+- **Memoized twice.** Once per request (`Ctx.cache`), and once process-wide

+ against the resolved commit SHA (`core.LRU`).

+- **No manifest.** Dependencies are declared by use. There is no module list

+ to keep in sync with the templates.

+

+`internal/modules/example_authors.go` is a live demonstration: 30 lines, an

+`init()`, and one `{{ with mod "authors" }}` block. Nothing else moved.

+

+## Pages and endpoints are the same mechanism

+

+A route is `{pattern, renderer}`. `core.View` renders a template,

+`core.JSON` serializes an endpoint. Both take a `*Ctx`, both call modules.

+

+```go

+{Name: "commit", Immutable: true,

+ Pattern: "GET /{repo}/commit/{rev}",

+ Render: core.View{Template: "commit.html"}},

+

+{Name: "api-commit", Immutable: true,

+ Pattern: "GET /{repo}/api/commit/{rev}",

+ Render: core.JSON{Build: api.CommitEndpoint}},

+```

+

+### Endpoints use DTOs, not module values

+

+`internal/api` defines explicit structs and never marshals a module's return

+value. Go marshals every exported field by default, so serializing a module

+type means the day someone adds `Body` to `gitx.Commit`, commit messages are

+public. The allowlist is one readable file.

+

+```

+GET /api/repos.json site index

+GET /{repo}/api/repo.json slug, title, description, owner, section,

+ clone_url, default_branch, last_commit

+GET /{repo}/api/commit/{sha} sha, short, authored, parents, and

+ file/line counts — no subject, no body

+```

+

+## Routes

+

+| Route | URL |

+|---|---|

+| index | `/` |

+| repo | `/{repo}/` — default branch, last update, latest commit, README |

+| files | `/{repo}/tree/{ref}/{path}` |

+| file | `/{repo}/blob/{ref}/{path}` |

+| **raw bytes** | `/{repo}/raw/{ref}/{path}` |

+| log | `/{repo}/log/{ref}` |

+| refs | `/{repo}/refs/` |

+| commit | `/{repo}/commit/{sha}` |

+| **compare** | `/{repo}/compare/{base}..{head}` or `{base}...{head}` |

+| **branch graph** | `/{repo}/graph/` |

+

+### Compare

+

+`a..b` is the literal endpoint difference. `a...b` diffs from the merge

+base, which is what you want when reviewing a branch — it excludes changes

+that landed on the base since the branch forked. Verified against

+`git merge-base` on a diverged fixture: `topic..main` lists `topic.txt` as

+removed, `topic...main` does not.

+

+### Raw files

+

+A repository can contain an `.html` file with a `<script>` tag. Serving that

+as `text/html` on your own origin turns any push into stored XSS against the

+whole site — which is why GitHub puts raw content on

+`raw.githubusercontent.com`, a separate origin. Same-host serving is only

+safe if the response cannot be interpreted as a document, so `/raw/` sends

+`text/plain` (or `application/octet-stream` for binaries, plus

+`Content-Disposition: attachment`), with `X-Content-Type-Options: nosniff`

+and `Content-Security-Policy: default-src \'none\'; sandbox` as a backstop.

+

+The exception is a validated raster image (PNG, JPEG, GIF, WebP, BMP, ICO,

+AVIF): when the extension and the magic bytes agree, `/raw/` declares the

+real `image/*` type inline so the blob page can preview it. An extension by

+itself is not enough — an `.png` whose contents are HTML still downloads as

+`application/octet-stream`. SVG is deliberately excluded: it is an XML

+document that can execute script, so it stays `text/plain`.

+

+If you would rather have real isolation, serve `/raw/` from a second

+hostname and the CSP becomes belt-and-braces rather than the only line.

+

+### Images and structured config files

+

+An image blob shows an inline preview with a `download` link to the same

+`/raw/` URL; images over 10 MiB skip the preview and offer the download only.

+

+JSON and YAML blobs get per-level indent guides, fold controls, key/value

+search, and YAML anchor/alias links. The search box also accepts a value

+path: typing `obj1.property3.items[4].val` resolves it against the parsed

+document and highlights that line and, for a container, its subtree. A

+query containing `.` or `[` is tried as a path first and falls back to

+plain substring search when it does not resolve, so dotted text stays

+searchable. Paths quote keys that need it (`obj1["a.b"]`) and attach indices

+directly; SVG is never previewed, and files past 512 KiB skip the parsing

+tooling entirely.

+

+### Branch graph

+

+`modules/graph.go` lays out the DAG in lanes in one pass over

+`git log --all --topo-order`, which guarantees a child is emitted before its

+parents. `active` holds, per lane, the SHA that lane is waiting to draw; a

+commit claims the lane expecting it (or a fresh one), hands that lane to its

+first parent, and opens a new lane per additional parent — which is what

+makes a merge fork visually.

+

+The module emits the per-row SVG because the geometry *is* the data, but

+every stroke refers to a CSS custom property (`--lane-0` … `--lane-5`), so

+the theme still owns the palette. Row height in the SVG must stay in sync

+with `table.graph td { height }` in the stylesheet.

+

+## Caching, which is the whole reason this works dynamically

+

+Every module result is a pure function of `(repo, commit SHA, path, args)`.

+Refs move; SHAs do not. So the process-wide cache is keyed on the resolved

+SHA and needs **no invalidation logic at all** — a stale entry is impossible

+by construction.

+

+`Ctx.Vars` are part of the cache key, not just the commit. They were not

+originally, and the bug was exactly the kind this cache should be immune to:

+`/compare/a..b` and `/compare/a...b` resolve to the same head commit, so the

+second request was served the first one\'s diff. Anything that changes what a

+module computes has to be in the key.

+

+ETags are derived from the resolved SHA plus a digest of every template

+file, *not* from the response body. A conditional request costs one ref

+lookup instead of a render, and restyling the theme invalidates every ETag

+at once (without the template digest, a restyled page keeps serving 304s).

+

+Two URL classes, two policies:

+

+| URL shape | Example | Cache-Control |

+|---|---|---|

+| SHA-addressed | `/demo/commit/64b90fff…` | `max-age=31536000, immutable` |

+| ref-addressed | `/demo/tree/main` | `no-cache` (revalidate via ETag) |

+

+## Ref-vs-path ambiguity

+

+`/{repo}/tree/{rest...}` fuses them, and `gitx.SplitRefPath` separates them

+by **longest matching prefix against the repo's actual ref list**, so

+`feature/x/src/main.go` resolves correctly. Splitting at the first `/` is

+wrong because branch names contain slashes; cgit dodges this with `?h=`

+query params, GitHub does what this does.

+

+## Serving is an attack surface; static generation was not

+

+- **Ref input never reaches `git rev-parse`.** rev-parse accepts an

+ expression language — `:/regex` searches history, `@{...}` reads the

+ reflog — and git subcommands treat a leading `-` as an option.

+ `gitx.Resolve` accepts either a hex SHA that already exists or an exact

+ match against the repo's own ref list. Verified: `--upload-pack=…`,

+ `:/secret`, `HEAD@{0}` and `-n` all return 404 with no side effects.

+- **Every git call is `exec.CommandContext`** with a per-request deadline

+ (`-timeout`, default 10s) and a scrubbed environment

+ (`GIT_CONFIG_NOSYSTEM=1`, no `HOME`, no terminal prompt).

+- **Output is capped** at `MaxGit` (8 MiB) per command; a diff that exceeds

+ it renders truncated rather than eating the heap.

+

+## Layout

+

+```

+main.go flags, repo discovery, embedded assets

+internal/gitx/ the ONLY package that knows git exists

+internal/core/core.go Ctx, RepoInfo, module registry, Store

+internal/core/route.go Route, View, JSON, route request parsing

+internal/core/server.go request -> Ctx, ETags, cache policy

+internal/core/cache.go LRU keyed on commit SHAs

+internal/core/funcs.go template funcmap (mod, modOr, dict, date, bytes)

+internal/access/ visibility and share-grant policy (imports no core)

+internal/authn/ login/logout endpoints

+internal/httpx/ shared admin/share HTTP security helpers

+internal/modules/ meta refs log tree readme repos commit diff blob notices

+internal/notices/ notices YAML store + admin UI (imports no core)

+internal/api/ JSON DTOs — the serialization allowlist

+internal/site/routes.go the route table (the file you edit most)

+internal/site/request.go route-specific path parsers (compare ranges)

+templates/ layouts/ + views/

+```

+

+`gitx` shells out to plumbing, one process per query, `git log` in a single

+pass. Swapping in go-git means rewriting that one package.

+

+## Sections

+

+`gsg.section` groups repositories on the index. The `sections` module builds

+on `repos` rather than re-walking the repo set, so the index pays for its log

+lookups once. When no repo sets a section, it returns a single unnamed group

+and the template renders a flat list — no config, no headings.

+

+```sh

+git --git-dir=/srv/git/demo.git config gsg.section "Infrastructure"

+```

+

+## Notices

+

+Operator-authored banners at the top of every page, site-wide and per

+repository. They live in one YAML file that is watched for changes, so

+editing it never needs a restart or a rebuild:

+

+```yaml

+global:

+ - type: critical # critical | warning | info | fix

+ title: Maintenance window

+ body: |

+ Saturday 02:00-04:00 UTC.

+ The site is read-only during the window.

+ link: https://status.example.org

+ link_text: status page

+repos:

+ demo:

+ - type: warning

+ title: Migrating to a new remote

+```

+

+```sh

+./gsg -root /srv/git -notices /etc/gsg/notices.yaml

+```

+

+Global notices render above every repository's; on the site index only the

+global list appears. The file is re-read on write (atomic-rename saves from

+an editor included); a parse error keeps the last good content rather than

+blanking the banners.

+

+### Editing from the web

+

+`-admin-addr` starts a second listener with a small HTML form to add, edit,

+and delete notices. It is deliberately separate from the read-only server:

+the admin routes are not reachable on the public port even if the reverse

+proxy is misconfigured.

+

+```sh

+./gsg -root /srv/git -notices /etc/gsg/notices.yaml -admin-addr 127.0.0.1:8081

+```

+

+Protect it with Caddy `forward_auth` and proxy it to the admin listener. gsg

+trusts the network in front of it, so the admin port must not be published

+directly. In Compose, put 8081 on the internal network only and pass

+`-admin-allow-remote`, because a container address is not loopback. Note

+that gsg performs no authentication itself -- the `forward_auth` block below

+is the only thing between the internet and the admin form.

+

+```caddyfile

+example.com {

+ # Admin: authenticate first, then proxy to the separate admin listener.

+ # handle, not handle_path: the admin mux matches the full /admin/...

+ # path, so stripping the prefix would 404 every request.

+ handle /admin/* {

+ forward_auth authentik:9000 {

+ uri /outpost.goauthentik.io/auth/caddy

+ copy_headers X-Authentik-Username

+ }

+ reverse_proxy gsg:8081

+ }

+

+ # Public, read-only.

+ handle {

+ reverse_proxy gsg:8080

+ }

+}

+```

+

+The `X-Authentik-Username` header is used only to attribute the mutation in

+the log; it is never consulted for authorization. By default Authentik

+decides who may reach the handler at all -- anyone forward_auth lets through

+`/admin/*` can edit notices.

+

+Mutations are POST-only, CSRF-protected (double-submit cookie plus

+`Origin`/`Sec-Fetch-Site`), and logged with the `X-Authentik-Username`

+header, which is used for audit only, never for authorization.

+

+### Gating notices editing to a group

+

+`/admin/*` is also where [Login](#login) mints the `gsg_user` cookie, so

+forward_auth for the whole prefix is usually left open to everyone you want

+able to log in (for share links, hidden-repo visibility, etc). To let more

+people log in without also handing them notices editing, add `-admin-group`:

+

+```sh

+./gsg -root /srv/git -notices /etc/gsg/notices.yaml \

+ -admin-addr 127.0.0.1:8081 -admin-group gsg-admins

+```

+

+This checks the `X-Authentik-Groups` header (override with

+`-admin-group-header`) for `gsg-admins` among its `|`-delimited entries,

+Authentik's own format for that header, and answers `403` to any request

+under `/admin/notices` from a caller that isn't a member -- before the

+handler does anything else, including setting the CSRF cookie. Add the group

+header to the same `forward_auth` block used above:

+

+```caddyfile

+ forward_auth authentik:9000 {

+ uri /outpost.goauthentik.io/auth/caddy

+ copy_headers X-Authentik-Username X-Authentik-Groups

+ }

+```

+

+Leaving `-admin-group` unset keeps today's behavior: anyone forward_auth

+admits to `/admin/*` can edit notices.

+

+**Immutable commit pages carry no notices.** `/{repo}/commit/{rev}` is

+served `Cache-Control: public, max-age=31536000, immutable`, so a banner

+rendered into it would stay frozen in the reader's browser. Notices are

+suppressed there by design; every other page picks them up on the next

+request.

+

+## Login

+

+Logging in reveals hidden repos whose `gsg.visible-to` list includes your

+username; everyone else, logged in or not, sees exactly what an anonymous

+visitor sees. It reuses the same Authentik `forward_auth` setup as the

+notices admin UI above, and needs nothing extra beyond `-admin-addr`

+(notices editing is not required — `-admin-addr` alone is enough to enable

+login).

+

+```sh

+./gsg -root /srv/git -admin-addr 127.0.0.1:8081

+```

+

+```caddyfile

+example.com {

+ # Login: same trust boundary as /admin/*, one hop mints the cookie

+ # and redirects back. This must be the exact path, not /auth/*: gsg

+ # also serves /auth/logout, but on the *public* listener, since

+ # logging out only clears gsg's own cookie and needs no Authentik

+ # round trip at all. Routing /auth/* here would send logout to the

+ # admin listener too, where no such handler exists, and gate it

+ # behind an Authentik check it doesn't need.

+ handle /auth/login {

+ forward_auth authentik:9000 {

+ uri /outpost.goauthentik.io/auth/caddy

+ copy_headers X-Authentik-Username

+ }

+ reverse_proxy gsg:8081

+ }

+

+ # Public, read-only (also handles /auth/logout, /share/new, /share/view/*).

+ handle {

+ reverse_proxy gsg:8080

+ }

+}

+```

+

+Visiting `/auth/login` (through Caddy, so `X-Authentik-Username` is set and

+trustworthy by the time gsg sees the request) mints a signed, stateless

+`gsg_user` cookie and redirects back to `/`. The cookie is verified on the

+public listener with an in-memory key — nothing is written to disk, and a

+process restart signs everyone out. `/auth/logout` clears it and needs no

+round trip through Authentik, since it only has to forget gsg's own cookie.

+

+**There is no "log in" link anywhere in the UI.** `/auth/login` is not

+discoverable from the site; people who need it are told the URL out of

+band. Once logged in, the nav bar shows who you are and a log-out link.

+

+## Share links

+

+Once logged in, `/share/new` lets you pick from your own hidden repos and

+mint a link that grants view access to exactly those repos to anyone who

+has it — no login, no Authentik involvement. It's entirely stateless: the

+link is a signed, self-contained token, and gsg keeps no record of what's

+been shared. An optional password can gate it.

+

+```

+git --git-dir=/srv/git/demo.git config gsg.share-max-age "720h"

+```

+

+`gsg.share-max-age` (Go duration syntax, default 30 days if unset) is both

+the ceiling no link's expiry may exceed and the default when the minting

+form doesn't specify one — you can always ask for less, never more. Sharing

+several repos at once uses the smallest ceiling among them.

+

+**Passwords are never stored, not even hashed.** The password is folded

+directly into the link's signature instead of being embedded in it: nobody

+holding just the URL has anything to brute-force offline, and checking a

+guess requires asking the server, which rate-limits attempts. This is a

+soft gate appropriate for a small self-hosted tool, not a cryptographic

+secret protecting high-value data.

+

+**Revocation.** A stateless token can't be individually revoked — there's

+no list of what's been issued. The one lever:

+

+```

+git --git-dir=/srv/git/demo.git config gsg.share-revoked-after "$(date +%s)"

+```

+

+Any share grant for that repo issued at or before this timestamp stops

+working immediately, including in a browser that already redeemed the

+link — not just future redemptions. Two things worth knowing before you

+rely on this:

+

+- There's no per-recipient state, so revoking means invalidating *every*

+ outstanding share of that repo, then re-sharing with whoever should still

+ have it.

+- Removing a username from `gsg.visible-to` does **not** revoke a share

+ link that user already minted for that repo. The two mechanisms are

+ independent; only `gsg.share-revoked-after` invalidates outstanding

+ shares.

+

+## README rendering

+

+`modules/markdown.go` uses goldmark with GFM, Typographer, and automatic

+heading IDs — Hugo\'s own goldmark defaults, so a README renders identically

+to the same file on your blog.

+

+`WithUnsafe` is deliberately not set, which is also Hugo\'s default. Anyone

+who can push can write a README, so raw HTML in markdown is untrusted input;

+goldmark drops it. A `<script>` committed to a README comes out as

+`<!-- raw HTML omitted -->`.

+

+Relative links are rewritten against the file\'s own directory: links become

+the blob view, images become `/raw/` (an `<img>` needs bytes, not an HTML

+page). Absolute URLs, site-absolute paths, fragments and `mailto:` are left

+alone, and anything resolving above the repo root is not rewritten.

+

+## Per-repository config

+

+Read from each repo's own git config, cgit-style, with `gitweb.*` and the

+legacy `description` file as fallbacks, so an existing cgit tree works as-is:

+

+```sh

+git --git-dir=/srv/git/demo.git config gsg.title "Demo Project"

+git --git-dir=/srv/git/demo.git config gsg.description "A demo repository"

+git --git-dir=/srv/git/demo.git config gsg.clone "git://rschanz.org/demo"

+git --git-dir=/srv/git/demo.git config gsg.hide true

+git --git-dir=/srv/git/demo.git config gsg.visible-to "alice,bob"

+git --git-dir=/srv/git/demo.git config gsg.share-max-age "720h"

+git --git-dir=/srv/git/demo.git config gsg.share-revoked-after "$(date +%s)"

+```

+

+Add a key by adding a field to `core.RepoInfo` and a line in `LoadRepoInfo`.

+

+A repo's slug is its directory name (minus `.git`), and slugs share the

+public listener's URL namespace with a few reserved top-level paths:

+`static`, `auth`, and `share`. A repo named e.g. `share.git` would collide

+with the share-link endpoints below and is not supported.

+

+`gsg.visible-to` is a comma-separated allowlist of usernames (matched

+case-insensitively against a logged-in session, see "Login" below) who may

+see this repo even though `gsg.hide` is set. It's a separate key from

+`gsg.owner` on purpose: `Owner` is a free-text display field that falls

+back to `gitweb.owner` for cgit-migrated repos, so treating it as an access

+list could silently grant visibility nobody intended.

+

+## Theme

+

+Monospace-first: every value on these pages is an identifier, hash, path or

+count, so the interface type is the same face as the code, and the sans face

+appears only inside rendered README prose. A cool slate ramp, one indigo

+accent, and a six-colour lane ramp shared by the commit graph and its branch

+chips. Light and dark both defined via `prefers-color-scheme`.

+

+Diffs mark the gutter rather than flooding whole rows with green and red —

+the signal stays readable when a hunk is mostly additions.

+

+No webfonts; system stacks only, so there is no third-party request. All

+colour lives in `:root` custom properties in `static/style.css`.

+

+## Known gaps

+

+- **No syntax highlighting.** `blob` returns numbered plain lines; Chroma

+ drops into the same module.

+- **No pagination on `log` or `graph`.** They cap at 200 and 150 commits.

+- **The graph loads all refs into memory** before laying out. Fine to a few

+ thousand commits; beyond that it needs windowing.

+- **The LRU is bounded by entry count, not bytes.** A giant diff and a ref

+ list cost the same slot. The `Store` interface is the only thing a

+ size-aware replacement has to satisfy.

+- **Repo discovery is one level deep** and happens once at startup; a repo

+ created later needs a restart.

+- **Module errors surface at render time**, not load time. Add a CI pass

+ that renders every view against a fixture repo.