2026-10-24 17:21:05 +11:00
11 changed files with 762 additions and 4 deletions
@@ -41,6 +41,7 @@ Each type's paths, Terraform examples and local/virtual behaviour are in `docs/<
 - `pypi`: [remote](docs/pypi/remote.md)
 - `rpm`: [remote](docs/rpm/remote.md), [remote-github](docs/rpm/remote-github.md)
 - `terraform`: [remote](docs/terraform/remote.md), [local](docs/terraform/local.md)
+- `vcs`: [remote](docs/vcs/remote.md)

 ### GitHub authentication

@@ -98,4 +98,4 @@ Each type's page lists its auto-detected mutable and immutable paths:
 [docker](../docker/remote.md), [generic](../generic/remote.md), [gems](../gems/remote.md), [goproxy](../goproxy/remote.md),
 [helm](../helm/remote.md), [npm](../npm/remote.md), [nuget](../nuget/remote.md),
 [puppet](../puppet/remote.md), [pypi](../pypi/remote.md), [rpm](../rpm/remote.md),
-[rpm github](../rpm/remote-github.md), [terraform](../terraform/remote.md).
+[rpm github](../rpm/remote-github.md), [terraform](../terraform/remote.md), [vcs](../vcs/remote.md).
@@ -0,0 +1,29 @@
+# `vcs` remote
+
+Shared classification, TTL and eviction rules: [caching](../common/caching.md).
+
+Caches source archives and release assets from GitHub (`base_url = "https://github.com"`) or Gitea (any other `base_url`). GitHub Enterprise is not supported: a non-github.com host is treated as Gitea. Only the paths below are served; anything else is a 404.
+
+| Path | Behaviour |
+|---|---|
+| `<owner>/<repo>/archive/refs/tags/<tag>.(tar.gz\|zip)` | immutable |
+| `<owner>/<repo>/archive/<40-char sha>.(tar.gz\|zip)` | immutable |
+| `<owner>/<repo>/releases/download/<tag>/<asset>` | immutable |
+| `<owner>/<repo>/releases/latest/download/<asset>` | mutable |
+| `<owner>/<repo>/archive/refs/heads/<branch>.(tar.gz\|zip)` | `302` to the archive of the branch's current commit, resolved via the provider's branch API and reused for `mutable_ttl` |
+
+Branch archives redirect, so `curl` needs `-L`; pip and npm follow redirects. The archive is the host's commit archive (GitHub names its top-level directory `<repo>-<sha>`). `patterns` and `blocklist` match both the branch path and the commit path it redirects to, so allowlist repos by prefix (`^cli/cli/`); a branch whose commit path is denied is a `403`. A missing branch is a `404`, cached for `mutable_ttl` (at least 60s). An API rate limit (`429`, or `403` with rate-limit headers) is a `503` with `Retry-After`, unless `stale_on_error` serves the last known commit. Each remote caches up to 4096 branch lookups. GitHub API calls use the [server GitHub credential](../../README.md#github-authentication); Gitea API calls use the remote's `username`/`password`.
+
+```hcl
+resource "artifactapi_remote_vcs" "github" {
+  name        = "github-vcs"
+  base_url    = "https://github.com"
+  mutable_ttl = 600
+  patterns    = ["^cli/cli/", "^psf/requests/"]
+}
+```
+
+```bash
+curl -fsSLO https://artifactapi.example/api/v1/remote/github-vcs/cli/cli/archive/refs/tags/v2.60.0.tar.gz
+pip install https://artifactapi.example/api/v1/remote/github-vcs/psf/requests/archive/refs/tags/v2.32.3.tar.gz
+```
@@ -0,0 +1,7 @@
+//go:build dockere2e
+
+package e2edocker
+
+func init() {
+	cachingCases = append(cachingCases, cachingCase{"vcs", "octo/repo/archive/refs/tags/v1.0.0.tar.gz", "octo/repo/archive/refs/tags/v1.0.0.tar.gz"})
+}
@@ -0,0 +1,3 @@
+package all
+
+import _ "git.unkin.net/unkin/artifactapi/internal/provider/vcs"
@@ -71,7 +71,7 @@ func (p *Provider) AuthHeaders(ctx context.Context, remote models.Remote) (http.
 		h.Set("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(remote.Username+":"+remote.Password)))
 		return h, nil
 	}
-	if isGitHubHost(remote.BaseURL) {
+	if IsGitHubHost(remote.BaseURL) {
 		if c := githubauth.Server(); c != nil {
 			tok, err := c.Token(ctx)
 			if err != nil {
@@ -85,11 +85,11 @@ func (p *Provider) AuthHeaders(ctx context.Context, remote models.Remote) (http.
 	return h, nil
 }

-// isGitHubHost reports whether rawURL targets a GitHub API/download host that
+// IsGitHubHost reports whether rawURL targets a GitHub API/download host that
 // accepts the server credential. objects.githubusercontent.com is deliberately
 // excluded: release-asset downloads 302-redirect there with a pre-signed URL
 // that must not carry an Authorization header.
-func isGitHubHost(rawURL string) bool {
+func IsGitHubHost(rawURL string) bool {
 	u, err := url.Parse(rawURL)
 	if err != nil {
 		return false
@@ -0,0 +1,309 @@
+// Package vcs caches source archives and release assets from GitHub or Gitea,
+// keyed by ref: tags, commits and release assets are immutable, and branch
+// archives redirect to the archive of the commit the branch currently points at.
+package vcs
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/sync/singleflight"
+
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+	"git.unkin.net/unkin/artifactapi/internal/provider/generic"
+	"git.unkin.net/unkin/artifactapi/internal/proxy"
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+func init() {
+	provider.Register(New())
+}
+
+type kind int
+
+const (
+	tagArchive kind = iota + 1
+	branchArchive
+	commitArchive
+	releaseAsset
+	latestReleaseAsset
+)
+
+// target is a parsed vcs request path.
+type target struct {
+	Kind        kind
+	Owner, Repo string
+	Name        string // tag, branch, commit or asset
+	Ext         string
+}
+
+var (
+	segmentRe = regexp.MustCompile(`^[A-Za-z0-9._+-]+$`)
+	commitRe  = regexp.MustCompile(`^[0-9a-f]{40}$`)
+)
+
+var errNotFound = errors.New("ref not found")
+
+const (
+	maxRefs     = 4096
+	negativeTTL = time.Minute
+)
+
+// Provider embeds generic for upstream URLs, content types and GitHub/Basic auth.
+type Provider struct {
+	generic.Provider
+
+	client    *http.Client
+	githubAPI string
+
+	group singleflight.Group
+	mu    sync.Mutex
+	refs  map[string]map[string]resolved
+}
+
+// resolved is a branch lookup; an empty commit records a missing branch.
+type resolved struct {
+	commit string
+	at     time.Time
+}
+
+func New() *Provider {
+	return &Provider{
+		client:    &http.Client{Timeout: 30 * time.Second},
+		githubAPI: "https://api.github.com",
+		refs:      map[string]map[string]resolved{},
+	}
+}
+
+func (p *Provider) Type() models.PackageType { return models.PackageVCS }
+
+func (p *Provider) Classify(path string) provider.Mutability {
+	if ref, ok := parsePath(path); ok && (ref.Kind == branchArchive || ref.Kind == latestReleaseAsset) {
+		return provider.Mutable
+	}
+	return provider.Immutable
+}
+
+// parsePath accepts only the archive and release-download shapes, rejecting
+// any segment that could escape owner/repo or a ref.
+func parsePath(path string) (target, bool) {
+	parts := strings.SplitN(strings.TrimPrefix(path, "/"), "/", 3)
+	if len(parts) != 3 || !validSegment(parts[0]) || !validSegment(parts[1]) {
+		return target{}, false
+	}
+	ref := target{Owner: parts[0], Repo: parts[1]}
+	rest := parts[2]
+	switch {
+	case strings.HasPrefix(rest, "archive/"):
+		name, ext, ok := archiveName(strings.TrimPrefix(rest, "archive/"))
+		if !ok {
+			return target{}, false
+		}
+		ref.Ext = ext
+		switch {
+		case strings.HasPrefix(name, "refs/tags/"):
+			ref.Kind, ref.Name = tagArchive, strings.TrimPrefix(name, "refs/tags/")
+		case strings.HasPrefix(name, "refs/heads/"):
+			ref.Kind, ref.Name = branchArchive, strings.TrimPrefix(name, "refs/heads/")
+		case commitRe.MatchString(name):
+			return target{Kind: commitArchive, Owner: ref.Owner, Repo: ref.Repo, Name: name, Ext: ext}, true
+		default:
+			return target{}, false
+		}
+		return ref, validRefName(ref.Name)
+	case strings.HasPrefix(rest, "releases/latest/download/"):
+		ref.Kind, ref.Name = latestReleaseAsset, strings.TrimPrefix(rest, "releases/latest/download/")
+		return ref, validSegment(ref.Name)
+	case strings.HasPrefix(rest, "releases/download/"):
+		tagAsset := strings.TrimPrefix(rest, "releases/download/")
+		i := strings.LastIndex(tagAsset, "/")
+		if i < 0 {
+			return target{}, false
+		}
+		ref.Kind, ref.Name = releaseAsset, tagAsset[i+1:]
+		return ref, validRefName(tagAsset[:i]) && validSegment(ref.Name)
+	}
+	return target{}, false
+}
+
+func archiveName(s string) (string, string, bool) {
+	for _, ext := range []string{".tar.gz", ".zip"} {
+		if name, ok := strings.CutSuffix(s, ext); ok && name != "" {
+			return name, ext, true
+		}
+	}
+	return "", "", false
+}
+
+func validSegment(s string) bool {
+	return segmentRe.MatchString(s) && s != "." && s != ".." && !strings.Contains(s, "..")
+}
+
+func validRefName(s string) bool {
+	for _, seg := range strings.Split(s, "/") {
+		if !validSegment(seg) || strings.HasPrefix(seg, ".") {
+			return false
+		}
+	}
+	return true
+}
+
+// ServeRemote rejects unsupported paths and redirects branch archives to the
+// immutable archive of the branch's current commit; everything else is proxied.
+func (p *Provider) ServeRemote(w http.ResponseWriter, r *http.Request, remote models.Remote, path, proxyBaseURL string, _ provider.RemoteMetadataStore) bool {
+	ref, ok := parsePath(path)
+	if !ok {
+		http.Error(w, "unsupported vcs path", http.StatusNotFound)
+		return true
+	}
+	if ref.Kind != branchArchive {
+		return false
+	}
+	classifier := proxy.NewClassifier(p)
+	if classifier.Classify(remote, path) == proxy.ClassDenied {
+		http.Error(w, "access denied", http.StatusForbidden)
+		return true
+	}
+	commit, err := p.resolve(r.Context(), remote, ref)
+	var se *provider.UpstreamStatusError
+	switch {
+	case errors.Is(err, errNotFound):
+		http.Error(w, "branch not found", http.StatusNotFound)
+		return true
+	case errors.As(err, &se) && (se.Status == http.StatusTooManyRequests || se.Status == http.StatusForbidden && !se.RetryAt.IsZero()):
+		secs := 60
+		if !se.RetryAt.IsZero() {
+			secs = max(1, int(time.Until(se.RetryAt).Seconds()+1))
+		}
+		w.Header().Set("Retry-After", strconv.Itoa(secs))
+		http.Error(w, "upstream rate limited", http.StatusServiceUnavailable)
+		return true
+	case err != nil:
+		http.Error(w, "bad gateway", http.StatusBadGateway)
+		return true
+	}
+	target := ref.Owner + "/" + ref.Repo + "/archive/" + commit + ref.Ext
+	if classifier.Classify(remote, target) == proxy.ClassDenied {
+		http.Error(w, "access denied", http.StatusForbidden)
+		return true
+	}
+	http.Redirect(w, r, strings.TrimRight(proxyBaseURL, "/")+provider.RemoteMountPath+remote.Name+"/"+target, http.StatusFound)
+	return true
+}
+
+// resolve maps a branch to its commit, reusing the answer for mutable_ttl (a
+// missing branch for at least negativeTTL) and, with stale_on_error, past an
+// upstream failure. Concurrent lookups of one branch share a single API call.
+func (p *Provider) resolve(ctx context.Context, remote models.Remote, ref target) (string, error) {
+	key := ref.Owner + "/" + ref.Repo + "\x00" + ref.Name
+	ttl := time.Duration(remote.MutableTTL) * time.Second
+	p.mu.Lock()
+	prev, ok := p.refs[remote.Name][key]
+	p.mu.Unlock()
+	if ok && prev.commit != "" && time.Since(prev.at) < ttl {
+		return prev.commit, nil
+	}
+	if ok && prev.commit == "" && time.Since(prev.at) < max(ttl, negativeTTL) {
+		return "", errNotFound
+	}
+	v, err, _ := p.group.Do(remote.Name+"\x00"+key, func() (any, error) {
+		commit, err := p.lookup(context.WithoutCancel(ctx), remote, ref)
+		if err == nil || errors.Is(err, errNotFound) {
+			p.store(remote.Name, key, commit)
+		}
+		return commit, err
+	})
+	if err != nil {
+		if ok && prev.commit != "" && remote.StaleOnError && !errors.Is(err, errNotFound) {
+			return prev.commit, nil
+		}
+		return "", err
+	}
+	return v.(string), nil
+}
+
+// store records a lookup, evicting the remote's oldest entry once it holds maxRefs.
+func (p *Provider) store(remote, key, commit string) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	m := p.refs[remote]
+	if m == nil {
+		m = map[string]resolved{}
+		p.refs[remote] = m
+	}
+	if _, ok := m[key]; !ok && len(m) >= maxRefs {
+		var oldest string
+		for k, e := range m {
+			if oldest == "" || e.at.Before(m[oldest].at) {
+				oldest = k
+			}
+		}
+		delete(m, oldest)
+	}
+	m[key] = resolved{commit: commit, at: time.Now()}
+}
+
+func (p *Provider) lookup(ctx context.Context, remote models.Remote, ref target) (string, error) {
+	segs := strings.Split(ref.Name, "/")
+	for i, s := range segs {
+		segs[i] = url.PathEscape(s)
+	}
+	branch := strings.Join(segs, "/")
+	github := generic.IsGitHubHost(remote.BaseURL)
+	api := strings.TrimRight(remote.BaseURL, "/") + "/api/v1/repos/" + ref.Owner + "/" + ref.Repo + "/branches/" + branch
+	if github {
+		api = p.githubAPI + "/repos/" + ref.Owner + "/" + ref.Repo + "/git/ref/heads/" + branch
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, api, nil)
+	if err != nil {
+		return "", err
+	}
+	h, err := p.AuthHeaders(ctx, remote)
+	if err != nil {
+		return "", err
+	}
+	req.Header = h
+	if github {
+		req.Header.Set("Accept", "application/vnd.github+json")
+	}
+	resp, err := p.client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode == http.StatusNotFound || resp.StatusCode == http.StatusUnprocessableEntity {
+		return "", errNotFound
+	}
+	if resp.StatusCode != http.StatusOK {
+		return "", provider.NewUpstreamStatusError(api, resp)
+	}
+	var b struct {
+		Commit struct {
+			ID string `json:"id"`
+		} `json:"commit"`
+		Object struct {
+			SHA string `json:"sha"`
+		} `json:"object"`
+	}
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&b); err != nil {
+		return "", err
+	}
+	commit := b.Commit.ID
+	if github {
+		commit = b.Object.SHA
+	}
+	if !commitRe.MatchString(commit) {
+		return "", fmt.Errorf("branch lookup %s: unexpected commit %q", api, commit)
+	}
+	return commit, nil
+}
@@ -0,0 +1,378 @@
+package vcs
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"git.unkin.net/unkin/artifactapi/internal/githubauth"
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+const (
+	shaA = "4f2cfe92e3499f8581bf39db77e0a1431fa7b55c"
+	shaB = "7fa5434dbc083c853eef435d1915020345219d2f"
+)
+
+func TestParsePath(t *testing.T) {
+	tests := []struct {
+		path string
+		ok   bool
+		kind kind
+		name string
+	}{
+		{"cli/cli/archive/refs/tags/v2.60.0.tar.gz", true, tagArchive, "v2.60.0"},
+		{"/cli/cli/archive/refs/tags/v2.60.0.zip", true, tagArchive, "v2.60.0"},
+		{"o/r/archive/refs/tags/release/1.0.tar.gz", true, tagArchive, "release/1.0"},
+		{"o/r/archive/refs/heads/feature/x.tar.gz", true, branchArchive, "feature/x"},
+		{"o/r/archive/" + shaA + ".tar.gz", true, commitArchive, shaA},
+		{"o/r/releases/download/v1.0/tool_linux_amd64.tar.gz", true, releaseAsset, "tool_linux_amd64.tar.gz"},
+		{"o/r/releases/latest/download/tool.zip", true, latestReleaseAsset, "tool.zip"},
+		{"o/r/archive/main.tar.gz", false, 0, ""},
+		{"o/r/archive/" + shaA[:7] + ".tar.gz", false, 0, ""},
+		{"o/r/archive/refs/tags/v1.tar.bz2", false, 0, ""},
+		{"o/r/archive/refs/tags/.tar.gz", false, 0, ""},
+		{"../r/archive/refs/tags/v1.tar.gz", false, 0, ""},
+		{"o/../archive/refs/tags/v1.tar.gz", false, 0, ""},
+		{"o/r/archive/refs/tags/../../../etc/passwd.tar.gz", false, 0, ""},
+		{"o/r/archive/refs/heads/a//b.tar.gz", false, 0, ""},
+		{"o/r/archive/refs/heads/.hidden.tar.gz", false, 0, ""},
+		{"o/r/archive/refs/heads/a..b.tar.gz", false, 0, ""},
+		{"o/r/archive/refs/tags/v1%2f.tar.gz", false, 0, ""},
+		{"o/r/releases/download/v1/../x", false, 0, ""},
+		{"o/r/releases/download/asset", false, 0, ""},
+		{"o/r/raw/main/README.md", false, 0, ""},
+		{"o/r", false, 0, ""},
+	}
+	for _, tt := range tests {
+		ref, ok := parsePath(tt.path)
+		if ok != tt.ok || (ok && (ref.Kind != tt.kind || ref.Name != tt.name)) {
+			t.Errorf("parsePath(%q) = %+v, %v; want kind %v name %q ok %v", tt.path, ref, ok, tt.kind, tt.name, tt.ok)
+		}
+	}
+}
+
+func TestClassify(t *testing.T) {
+	p := New()
+	for path, want := range map[string]provider.Mutability{
+		"o/r/archive/refs/tags/v1.tar.gz":        provider.Immutable,
+		"o/r/archive/" + shaA + ".zip":           provider.Immutable,
+		"o/r/releases/download/v1/a.bin":         provider.Immutable,
+		"o/r/archive/refs/heads/main.tar.gz":     provider.Mutable,
+		"o/r/releases/latest/download/webui.zip": provider.Mutable,
+	} {
+		if got := p.Classify(path); got != want {
+			t.Errorf("Classify(%q) = %v, want %v", path, got, want)
+		}
+	}
+}
+
+type upstream struct {
+	srv    *httptest.Server
+	hits   atomic.Int32
+	commit atomic.Value
+	status atomic.Int32
+	header atomic.Value
+	accept atomic.Value
+	auth   atomic.Value
+	path   atomic.Value
+	gate   chan struct{}
+}
+
+func newUpstream(t *testing.T, gitea bool) *upstream {
+	u := &upstream{}
+	u.commit.Store(shaA)
+	u.status.Store(http.StatusOK)
+	u.header.Store(http.Header{})
+	u.srv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		u.hits.Add(1)
+		if u.gate != nil {
+			<-u.gate
+		}
+		u.accept.Store(r.Header.Get("Accept"))
+		u.auth.Store(r.Header.Get("Authorization"))
+		u.path.Store(r.URL.EscapedPath())
+		for k, v := range u.header.Load().(http.Header) {
+			w.Header()[k] = v
+		}
+		if s := int(u.status.Load()); s != http.StatusOK {
+			w.WriteHeader(s)
+			return
+		}
+		if gitea {
+			_, _ = w.Write([]byte(`{"name":"main","commit":{"id":"` + u.commit.Load().(string) + `"}}`))
+			return
+		}
+		_, _ = w.Write([]byte(`{"ref":"refs/heads/main","object":{"sha":"` + u.commit.Load().(string) + `","type":"commit"}}`))
+	}))
+	t.Cleanup(u.srv.Close)
+	return u
+}
+
+func serve(p *Provider, remote models.Remote, path string) (*httptest.ResponseRecorder, bool) {
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest(http.MethodGet, "/api/v1/remote/"+remote.Name+"/"+path, nil)
+	return w, p.ServeRemote(w, r, remote, path, "http://proxy", nil)
+}
+
+// age backdates every cached lookup of a remote by d.
+func age(p *Provider, remote string, d time.Duration) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	for k, e := range p.refs[remote] {
+		e.at = e.at.Add(-d)
+		p.refs[remote][k] = e
+	}
+}
+
+type staticCred string
+
+func (s staticCred) Token(context.Context) (string, error) { return string(s), nil }
+
+func TestServeRemoteGiteaBranchRedirectsToCommit(t *testing.T) {
+	u := newUpstream(t, true)
+	p := New()
+	remote := models.Remote{Name: "gitea", BaseURL: u.srv.URL, MutableTTL: 3600, Username: "bot", Password: "pw"}
+
+	w, handled := serve(p, remote, "unkin/app/archive/refs/heads/feature/x.zip")
+	if !handled || w.Code != http.StatusFound {
+		t.Fatalf("handled=%v code=%d", handled, w.Code)
+	}
+	if got, want := w.Header().Get("Location"), "http://proxy/api/v1/remote/gitea/unkin/app/archive/"+shaA+".zip"; got != want {
+		t.Errorf("Location = %q, want %q", got, want)
+	}
+	if got := u.path.Load(); got != "/api/v1/repos/unkin/app/branches/feature/x" {
+		t.Errorf("api path = %q", got)
+	}
+	if got := u.auth.Load(); got != "Basic Ym90OnB3" {
+		t.Errorf("Authorization = %q, want remote basic auth", got)
+	}
+}
+
+func TestServeRemoteGitHubBranchUsesAPI(t *testing.T) {
+	githubauth.SetServer(staticCred("ghs_server"))
+	t.Cleanup(func() { githubauth.SetServer(nil) })
+	u := newUpstream(t, false)
+	p := New()
+	p.githubAPI = u.srv.URL
+
+	for _, base := range []string{"https://github.com", "https://www.github.com/", "https://api.github.com"} {
+		remote := models.Remote{Name: base, BaseURL: base, MutableTTL: 3600}
+		w, _ := serve(p, remote, "cli/cli/archive/refs/heads/feature/x.tar.gz")
+		if !strings.HasSuffix(w.Header().Get("Location"), "/cli/cli/archive/"+shaA+".tar.gz") {
+			t.Fatalf("%s: Location = %q", base, w.Header().Get("Location"))
+		}
+		if u.path.Load() != "/repos/cli/cli/git/ref/heads/feature/x" || u.accept.Load() != "application/vnd.github+json" {
+			t.Errorf("%s: api path %q accept %q", base, u.path.Load(), u.accept.Load())
+		}
+		if got := u.auth.Load(); got != "Bearer ghs_server" {
+			t.Errorf("%s: Authorization = %q, want server credential", base, got)
+		}
+	}
+}
+
+func TestServeRemoteBranchResolutionHonoursMutableTTL(t *testing.T) {
+	u := newUpstream(t, true)
+	p := New()
+	remote := models.Remote{Name: "g", BaseURL: u.srv.URL, MutableTTL: 600}
+	path := "o/r/archive/refs/heads/main.tar.gz"
+
+	serve(p, remote, path)
+	u.commit.Store(shaB)
+	age(p, remote.Name, 599*time.Second)
+	w, _ := serve(p, remote, path)
+	if u.hits.Load() != 1 || !strings.Contains(w.Header().Get("Location"), shaA) {
+		t.Fatalf("within ttl: hits=%d location=%q", u.hits.Load(), w.Header().Get("Location"))
+	}
+
+	age(p, remote.Name, 2*time.Second)
+	w, _ = serve(p, remote, path)
+	if u.hits.Load() != 2 || !strings.Contains(w.Header().Get("Location"), shaB) {
+		t.Fatalf("past ttl: hits=%d location=%q", u.hits.Load(), w.Header().Get("Location"))
+	}
+}
+
+func TestServeRemoteBranchUpstreamFailure(t *testing.T) {
+	path := "o/r/archive/refs/heads/main.tar.gz"
+	for _, tc := range []struct {
+		name  string
+		stale bool
+		want  int
+	}{
+		{"stale", true, http.StatusFound},
+		{"strict", false, http.StatusBadGateway},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			u := newUpstream(t, true)
+			p := New()
+			remote := models.Remote{Name: tc.name, BaseURL: u.srv.URL, StaleOnError: tc.stale}
+			serve(p, remote, path)
+			u.status.Store(http.StatusInternalServerError)
+			if w, _ := serve(p, remote, path); w.Code != tc.want {
+				t.Fatalf("code = %d, want %d", w.Code, tc.want)
+			}
+		})
+	}
+}
+
+func TestServeRemoteBranchRateLimited(t *testing.T) {
+	reset := strconv.FormatInt(time.Now().Add(120*time.Second).Unix(), 10)
+	for _, tc := range []struct {
+		name   string
+		status int
+		header http.Header
+		want   int
+		retry  [2]int
+	}{
+		{"primary 403", http.StatusForbidden, http.Header{"X-Ratelimit-Remaining": {"0"}, "X-Ratelimit-Reset": {reset}}, http.StatusServiceUnavailable, [2]int{100, 122}},
+		{"secondary 403", http.StatusForbidden, http.Header{"Retry-After": {"30"}}, http.StatusServiceUnavailable, [2]int{30, 31}},
+		{"429", http.StatusTooManyRequests, http.Header{"Retry-After": {"5"}}, http.StatusServiceUnavailable, [2]int{5, 6}},
+		{"429 no hint", http.StatusTooManyRequests, http.Header{}, http.StatusServiceUnavailable, [2]int{60, 60}},
+		{"plain 403", http.StatusForbidden, http.Header{}, http.StatusBadGateway, [2]int{}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			u := newUpstream(t, false)
+			u.status.Store(int32(tc.status))
+			u.header.Store(tc.header)
+			p := New()
+			p.githubAPI = u.srv.URL
+			w, _ := serve(p, models.Remote{Name: "gh", BaseURL: "https://github.com"}, "o/r/archive/refs/heads/main.tar.gz")
+			if w.Code != tc.want {
+				t.Fatalf("code = %d, want %d", w.Code, tc.want)
+			}
+			ra := w.Header().Get("Retry-After")
+			if tc.want != http.StatusServiceUnavailable {
+				if ra != "" {
+					t.Fatalf("Retry-After = %q on %d", ra, w.Code)
+				}
+				return
+			}
+			if n, err := strconv.Atoi(ra); err != nil || n < tc.retry[0] || n > tc.retry[1] {
+				t.Fatalf("Retry-After = %q, want %d..%d", ra, tc.retry[0], tc.retry[1])
+			}
+		})
+	}
+}
+
+func TestServeRemoteBranchNotFoundIsCached(t *testing.T) {
+	u := newUpstream(t, false)
+	u.status.Store(http.StatusNotFound)
+	p := New()
+	p.githubAPI = u.srv.URL
+	remote := models.Remote{Name: "gh", BaseURL: "https://github.com"}
+	path := "o/r/archive/refs/heads/nope.tar.gz"
+
+	for range 3 {
+		if w, _ := serve(p, remote, path); w.Code != http.StatusNotFound {
+			t.Fatalf("code = %d, want 404", w.Code)
+		}
+	}
+	if u.hits.Load() != 1 {
+		t.Fatalf("hits = %d, want 1 within negative ttl", u.hits.Load())
+	}
+	u.status.Store(http.StatusOK)
+	age(p, remote.Name, negativeTTL)
+	if w, _ := serve(p, remote, path); w.Code != http.StatusFound || u.hits.Load() != 2 {
+		t.Fatalf("after negative ttl: code=%d hits=%d", w.Code, u.hits.Load())
+	}
+}
+
+func TestServeRemoteConcurrentLookupsShareOneCall(t *testing.T) {
+	u := newUpstream(t, true)
+	u.gate = make(chan struct{})
+	p := New()
+	remote := models.Remote{Name: "g", BaseURL: u.srv.URL, MutableTTL: 600}
+
+	var wg sync.WaitGroup
+	codes := make([]int, 20)
+	for i := range codes {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			w, _ := serve(p, remote, "o/r/archive/refs/heads/main.tar.gz")
+			codes[i] = w.Code
+		}()
+	}
+	for u.hits.Load() == 0 {
+		time.Sleep(time.Millisecond)
+	}
+	time.Sleep(50 * time.Millisecond)
+	close(u.gate)
+	wg.Wait()
+	if u.hits.Load() != 1 {
+		t.Fatalf("hits = %d, want 1", u.hits.Load())
+	}
+	for i, c := range codes {
+		if c != http.StatusFound {
+			t.Fatalf("request %d: code %d", i, c)
+		}
+	}
+}
+
+func TestStoreBoundsEntriesPerRemote(t *testing.T) {
+	p := New()
+	for i := range maxRefs + 10 {
+		p.store("a", fmt.Sprint(i), "")
+	}
+	p.store("b", "x", shaA)
+	if n := len(p.refs["a"]); n != maxRefs {
+		t.Fatalf("remote a holds %d entries, want %d", n, maxRefs)
+	}
+	if len(p.refs["b"]) != 1 {
+		t.Fatalf("remote b must keep its own budget")
+	}
+	if _, ok := p.refs["a"][fmt.Sprint(maxRefs+9)]; !ok {
+		t.Fatalf("newest entry evicted")
+	}
+}
+
+func TestServeRemoteRejectsBadCommit(t *testing.T) {
+	u := newUpstream(t, true)
+	u.commit.Store("../../etc")
+	w, _ := serve(New(), models.Remote{Name: "g", BaseURL: u.srv.URL}, "o/r/archive/refs/heads/main.tar.gz")
+	if w.Code != http.StatusBadGateway {
+		t.Fatalf("code = %d, want 502", w.Code)
+	}
+}
+
+func TestServeRemoteAllowlist(t *testing.T) {
+	u := newUpstream(t, true)
+	remote := models.Remote{Name: "g", BaseURL: u.srv.URL, Patterns: []string{"^allowed/repo/"}}
+	if w, _ := serve(New(), remote, "other/repo/archive/refs/heads/main.tar.gz"); w.Code != http.StatusForbidden {
+		t.Fatalf("code = %d, want 403", w.Code)
+	}
+	if u.hits.Load() != 0 {
+		t.Fatalf("denied branch must not hit the API")
+	}
+}
+
+func TestServeRemoteBlockedRedirectTarget(t *testing.T) {
+	u := newUpstream(t, true)
+	remote := models.Remote{Name: "g", BaseURL: u.srv.URL, Blocklist: []string{"/archive/" + shaA}}
+	w, _ := serve(New(), remote, "o/r/archive/refs/heads/main.tar.gz")
+	if w.Code != http.StatusForbidden || w.Header().Get("Location") != "" {
+		t.Fatalf("code = %d location %q, want 403 without redirect", w.Code, w.Header().Get("Location"))
+	}
+}
+
+func TestServeRemotePassesThroughAndRejects(t *testing.T) {
+	p := New()
+	remote := models.Remote{Name: "g", BaseURL: "https://github.com"}
+	if _, handled := serve(p, remote, "o/r/archive/refs/tags/v1.tar.gz"); handled {
+		t.Error("tag archives must go through the proxy engine")
+	}
+	if _, handled := serve(p, remote, "o/r/releases/download/v1/a.bin"); handled {
+		t.Error("release assets must go through the proxy engine")
+	}
+	if w, handled := serve(p, remote, "o/r/raw/main/x"); !handled || w.Code != http.StatusNotFound {
+		t.Errorf("unsupported path: handled=%v code=%d", handled, w.Code)
+	}
+}
@@ -0,0 +1,5 @@
+package models
+
+const PackageVCS PackageType = "vcs"
+
+func init() { registerPackageType(PackageVCS) }
@@ -0,0 +1,26 @@
+import type { PackageTypeUI } from '../types';
+
+const def: PackageTypeUI = {
+  color: 'default',
+  snippets: ({ proxy }) => {
+    return [
+      {
+        title: 'Download a tag archive',
+        language: 'bash',
+        code: `curl -fsSLO ${proxy}/<owner>/<repo>/archive/refs/tags/<tag>.tar.gz`,
+      },
+      {
+        title: 'Download a branch archive (redirects to its current commit)',
+        language: 'bash',
+        code: `curl -fsSL -o src.tar.gz ${proxy}/<owner>/<repo>/archive/refs/heads/<branch>.tar.gz`,
+      },
+      {
+        title: 'Download a release asset',
+        language: 'bash',
+        code: `curl -fsSLO ${proxy}/<owner>/<repo>/releases/download/<tag>/<asset>`,
+      },
+    ];
+  },
+};
+
+export default def;