all: librarify golink and make importable

Export LastSnapshot var so that snapshots can be stored in separate repo
from the golink code.

.gitignore

@@ -1,3 +1,2 @@
 node_modules
 package-lock.json
-golink

build.sh

@@ -8,7 +8,7 @@ export PATH=$(readlink -f $(dirname $0)/../../tool):$PATH
 go run github.com/tailscale/mkctr \
   --target="flyio" \
   --base="alpine:3.15" \
-  --gopaths="tailscale.io/cmd/golink:/tsgo" \
+  --gopaths="github.com/tailscale/golink/cmd/golink:/tsgo" \
   --tags="latest" \
   --repos="registry.fly.io/tsgo" \
   --push \

cmd/golink/main.go

@@ -0,0 +1,19 @@
+// The golink server runs http://go/, a private shortlink service for tailnets.
+package main
+
+import (
+	_ "embed"
+	"log"
+
+	"github.com/tailscale/golink"
+)
+
+//go:embed link-snapshot.json
+var lastSnapshot []byte
+
+func main() {
+	golink.LastSnapshot = lastSnapshot
+	if err := golink.Run(); err != nil {
+		log.Fatal(err)
+	}
+}

db.go

@@ -1,4 +1,4 @@
-package main
+package golink
 
 import (
 	"context"

db_test.go

@@ -1,4 +1,4 @@
-package main
+package golink
 
 import (
 	"path"

golink.go

@@ -1,5 +1,5 @@
 // The golink server runs http://go/, a private shortlink service for tailnets.
-package main
+package golink
 
 import (
 	"bufio"
@@ -43,8 +43,9 @@ var stats struct {
 	dirty ClickStats
 }
 
-//go:embed link-snapshot.json
-var lastSnapshot []byte
+// LastSnapshot is the data snapshot (as returned by the /.export handler)
+// that will be loaded on startup.
+var LastSnapshot []byte
 
 //go:embed static tmpl/*.html
 var embeddedFS embed.FS
@@ -54,25 +55,25 @@ var db *SQLiteDB
 
 var localClient *tailscale.LocalClient
 
-func main() {
+func Run() error {
 	flag.Parse()
 
 	if *sqlitefile == "" {
 		if devMode() {
 			tmpdir, err := ioutil.TempDir("", "golink_dev_*")
 			if err != nil {
-				log.Fatal(err)
+				return err
 			}
 			*sqlitefile = filepath.Join(tmpdir, "golink.db")
 			log.Printf("Dev mode temp db: %s", *sqlitefile)
 		} else {
-			log.Fatalf("--sqlitedb is required")
+			return errors.New("--sqlitedb is required")
 		}
 	}
 
 	var err error
 	if db, err = NewSQLiteDB(*sqlitefile); err != nil {
-		log.Fatalf("NewSQLiteDB(%q): %v", *sqlitefile, err)
+		return fmt.Errorf("NewSQLiteDB(%q): %w", *sqlitefile, err)
 	}
 
 	if err := restoreLastSnapshot(); err != nil {
@@ -105,19 +106,20 @@ func main() {
 		srv.Logf = log.Printf
 	}
 	if err := srv.Start(); err != nil {
-		log.Fatal(err)
+		return err
 	}
 	localClient, _ = srv.LocalClient()
 
 	l80, err := srv.Listen("tcp", ":80")
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 
 	log.Printf("Serving http://go/ ...")
 	if err := http.Serve(l80, nil); err != nil {
-		log.Fatal(err)
+		return err
 	}
+	return nil
 }
 
 var (
@@ -520,7 +522,7 @@ func serveExport(w http.ResponseWriter, r *http.Request) {
 }
 
 func restoreLastSnapshot() error {
-	bs := bufio.NewScanner(bytes.NewReader(lastSnapshot))
+	bs := bufio.NewScanner(bytes.NewReader(LastSnapshot))
 	var restored int
 	for bs.Scan() {
 		link := new(Link)

golink_test.go

@@ -1,4 +1,4 @@
-package main
+package golink
 
 import (
 	"testing"