add support for resolving links locally

Specify a command line argument to resolve a link locally and exit.

Also add a new flag, -resolve-from-backup, which loads a snapshot into
an in-memory database and resolves the specified link.

Author: willnorris

README.md

@@ -120,3 +120,7 @@ Only links that don't already exist in the database will be added.
     golink -snapshot links.json
 
 [JSON lines]: https://jsonlines.org/
+
+You can also resolve links locally using a snapshot file:
+
+    golink -resolve-from-backup links.json go/link

golink.go

@@ -36,11 +36,12 @@ import (
 const defaultHostname = "go"
 
 var (
-	verbose    = flag.Bool("verbose", false, "be verbose")
-	sqlitefile = flag.String("sqlitedb", "", "path of SQLite database to store links")
-	dev        = flag.String("dev-listen", "", "if non-empty, listen on this addr and run in dev mode; auto-set sqlitedb if empty and don't use tsnet")
-	snapshot   = flag.String("snapshot", "", "file path of snapshot file")
-	hostname   = flag.String("hostname", defaultHostname, "service name")
+	verbose           = flag.Bool("verbose", false, "be verbose")
+	sqlitefile        = flag.String("sqlitedb", "", "path of SQLite database to store links")
+	dev               = flag.String("dev-listen", "", "if non-empty, listen on this addr and run in dev mode; auto-set sqlitedb if empty and don't use tsnet")
+	snapshot          = flag.String("snapshot", "", "file path of snapshot file")
+	hostname          = flag.String("hostname", defaultHostname, "service name")
+	resolveFromBackup = flag.String("resolve-from-backup", "", "resolve a link from snapshot file and exit")
 )
 
 var stats struct {
@@ -66,6 +67,16 @@ var localClient *tailscale.LocalClient
 func Run() error {
 	flag.Parse()
 
+	// if resolving from backup, set sqlitefile and snapshot flags to
+	// restore links into an in-memory sqlite database.
+	if *resolveFromBackup != "" {
+		*sqlitefile = ":memory:"
+		snapshot = resolveFromBackup
+		if flag.NArg() != 1 {
+			log.Fatal("--resolve-from-backup also requires a link to be resolved")
+		}
+	}
+
 	if *sqlitefile == "" {
 		if devMode() {
 			tmpdir, err := ioutil.TempDir("", "golink_dev_*")
@@ -102,6 +113,16 @@ func Run() error {
 		log.Printf("initializing stats: %v", err)
 	}
 
+	// if link specified on command line, resolve and exit
+	if flag.NArg() > 0 {
+		destination, err := resolveLink(flag.Arg(0))
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println(destination)
+		os.Exit(0)
+	}
+
 	// flush stats periodically
 	go flushStatsLoop()
 
@@ -588,3 +609,19 @@ func restoreLastSnapshot() error {
 	}
 	return bs.Err()
 }
+
+func resolveLink(link string) (string, error) {
+	// if link specified as "go/name", trim "go" prefix.
+	// Remainder will parse as URL with no scheme or host
+	link = strings.TrimPrefix(link, *hostname)
+	u, err := url.Parse(link)
+	if err != nil {
+		return "", err
+	}
+	short, remainder, _ := strings.Cut(strings.TrimPrefix(u.RequestURI(), "/"), "/")
+	l, err := db.Load(short)
+	if err != nil {
+		return "", err
+	}
+	return expandLink(l.Long, expandEnv{Now: time.Now().UTC(), Path: remainder})
+}

golink_test.go

@@ -87,3 +87,60 @@ func TestExpandLink(t *testing.T) {
 		})
 	}
 }
+
+func TestResolveLink(t *testing.T) {
+	var err error
+	db, err = NewSQLiteDB(":memory:")
+	if err != nil {
+		t.Fatal(err)
+	}
+	db.Save(&Link{Short: "meet", Long: "https://meet.google.com/lookup/"})
+	db.Save(&Link{Short: "cs", Long: "http://codesearch/{{with .Path}}search?q={{.}}{{end}}"})
+
+	tests := []struct {
+		link string
+		want string
+	}{
+		{
+			link: "meet",
+			want: "https://meet.google.com/lookup/",
+		},
+		{
+			link: "meet/foo",
+			want: "https://meet.google.com/lookup/foo",
+		},
+		{
+			link: "go/meet/foo",
+			want: "https://meet.google.com/lookup/foo",
+		},
+		{
+			link: "http://go/meet/foo",
+			want: "https://meet.google.com/lookup/foo",
+		},
+		{
+			// if absolute URL provided, host doesn't actually matter
+			link: "http://mygo/meet/foo",
+			want: "https://meet.google.com/lookup/foo",
+		},
+		{
+			link: "cs",
+			want: "http://codesearch/",
+		},
+		{
+			link: "cs/term",
+			want: "http://codesearch/search?q=term",
+		},
+	}
+	for _, tt := range tests {
+		name := "golink " + tt.link
+		t.Run(name, func(t *testing.T) {
+			got, err := resolveLink(tt.link)
+			if err != nil {
+				t.Error(err)
+			}
+			if got != tt.want {
+				t.Errorf("ResolveLink(%q) = %q; want %q", tt.link, got, tt.want)
+			}
+		})
+	}
+}