Add gems virtual repositories (#154)

Bundler needs one source for internal and public gems, but gems virtuals have no merger, so a local gems repo and rubygems.org cannot be served together.

- merge `info/<gem>` across members (member order wins a duplicate version-platform); pass a single-member gem through verbatim
- regenerate `versions` lines and md5s for gems several members list; union `names`
- 302 `gems/*.gem` and `quick/Marshal.4.8/*` to the member owning that version, via the shared member-path validation
- return 502 on a member error; cache merges in the shared virtual cache; route HEAD on virtuals
- add `docs/gems/virtual.md` and a stock `ruby:3.3` bundler e2e-docker case

Reviewed-on: #154
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

e2e-docker/README.md

@@ -33,7 +33,9 @@ already-running stack.
   `gem install`, `bundle install` + `require`, republish rejected, `gem yank`).
 - **Virtual repositories** — pypi simple-index merge and helm `index.yaml` merge
   across two members; npm packument merge over two locals via a stock `node:22`
-  client (merged versions, install through the member redirect).
+  client (merged versions, install through the member redirect); gems compact
+  index merge over two locals via stock `ruby:3.3` bundler (member order wins,
+  downloads 302 to the owning member).
 - **Mirrorlist** — an rpm remote with a `mirrorlist` of extra upstream mirrors
   (pool = `base_url` + `mirrorlist`): round-robin distribution across both mirrors
   (constant-body `mockupstreama` / `mockupstreamb`), failover past a dead primary,

e2e-docker/gems_virtual_test.go

@@ -0,0 +1,69 @@
+//go:build dockere2e
+
+package e2edocker
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+	"time"
+)
+
+// TestVirtualGemsInstall pushes to two local gems repos and drives stock
+// bundler through a virtual over both: merged versions, member order winning a
+// duplicate version, and downloads redirected to the owning member.
+func TestVirtualGemsInstall(t *testing.T) {
+	network := os.Getenv("COMPOSE_NETWORK")
+	internal := os.Getenv("ARTIFACTAPI_INTERNAL")
+	if network == "" || internal == "" {
+		t.Skip("COMPOSE_NETWORK/ARTIFACTAPI_INTERNAL not set; run via scripts/docker-e2e.sh")
+	}
+	if _, err := exec.LookPath("docker"); err != nil {
+		t.Skip("docker not available on the test host")
+	}
+
+	id := time.Now().UnixNano()
+	a, b, virt := fmt.Sprintf("e2e-gems-a-%d", id), fmt.Sprintf("e2e-gems-b-%d", id), fmt.Sprintf("e2e-gems-v-%d", id)
+	for _, name := range []string{a, b} {
+		createRepo(t, fmt.Sprintf(`{"name":%q,"package_type":"gems","repo_type":"local"}`, name))
+		defer deleteRepo(t, name)
+	}
+	createVirtual(t, fmt.Sprintf(`{"name":%q,"package_type":"gems","members":[%q,%q]}`, virt, a, b))
+	defer deleteVirtual(t, virt)
+
+	base := strings.TrimRight(internal, "/")
+	script := `set -euo pipefail
+export GEM_HOST_API_KEY=unused
+pub() { d=/w/src-$1-$2; mkdir -p $d/lib; cd $d
+  echo "module UnkinE2eHello; VERSION = '$1:$2'; end" > lib/unkin-e2e-hello.rb
+  printf 'Gem::Specification.new { |s| s.name = "unkin-e2e-hello"; s.version = "%s"; s.summary = "e2e"; s.authors = ["e2e"]; s.files = ["lib/unkin-e2e-hello.rb"] }' "$2" > g.gemspec
+  gem build g.gemspec >/dev/null 2>&1; gem push --host "$BASE/api/v1/local/$1" unkin-e2e-hello-$2.gem; }
+pub "$A" 0.1.0
+pub "$B" 0.1.0
+pub "$B" 0.2.0
+V="$BASE/api/v1/virtual/$V"
+echo "VERSIONS $(curl -s "$V/versions" | grep '^unkin-e2e-hello ' | cut -d' ' -f2)"
+mkdir -p /w/app && cd /w/app
+printf 'source "%s/"\ngem "unkin-e2e-hello", "0.1.0"\n' "$V" > Gemfile
+bundle install
+bundle exec ruby -e 'require "unkin-e2e-hello"; puts "REQ #{UnkinE2eHello::VERSION}"'
+echo "REDIRECT $(curl -s -o /dev/null -w '%{redirect_url}' "$V/gems/unkin-e2e-hello-0.2.0.gem")"`
+
+	out, err := exec.Command("docker", "run", "--rm", "--network", network,
+		"-e", "BASE="+base, "-e", "A="+a, "-e", "B="+b, "-e", "V="+virt,
+		"ruby:3.3", "bash", "-c", script).CombinedOutput()
+	if err != nil {
+		t.Fatalf("bundler run failed: %v\n%s", err, out)
+	}
+	for _, want := range []string{
+		"VERSIONS 0.1.0,0.2.0",
+		"REQ " + a + ":0.1.0",
+		"REDIRECT " + base + "/api/v1/local/" + b + "/gems/unkin-e2e-hello-0.2.0.gem",
+	} {
+		if !strings.Contains(string(out), want) {
+			t.Fatalf("missing %q in bundler output:\n%s", want, out)
+		}
+	}
+}