Add support for systemd socket activation

cmd/gitsign-credential-cache/README.md

@@ -43,6 +43,36 @@ that is used is output by `gitsign-credential-cache` when it is spawned. See
 [os.UserCacheDir](https://pkg.go.dev/os#UserCacheDir) for details on how the
 cache directory is selected.
 
+### Systemd service
+
+There are systemd user units in contrib
+
+Change path to gitsign-credential-cache in service unit
+
+```sh
+${EDITOR:-vi} ./contrib/gitsign-credential-cache.service
+```
+
+Install units in home directory for specific user
+
+```sh
+install -m 0660 -D -t $HOME/.config/systemd/user/ ./contrib/gitsign-credential-cache.{socket,service}
+systemctl --user daemon-reload
+```
+
+OR install them for all users
+
+```sh
+sudo install -m 0660 -D -t /etc/systemd/user/ ./contrib/gitsign-credential-cache.{socket,service}
+sudo systemctl daemon-reload
+```
+
+After that you can enable and start socket service
+
+```sh
+systemctl --user enable --now gitsign-credential-cache.socket
+```
+
 ### Forwarding cache over SSH
 
 (Requires gitsign >= v0.5)

cmd/gitsign-credential-cache/main.go

@@ -23,6 +23,7 @@ import (
 	"path/filepath"
 	"syscall"
 
+	"github.com/coreos/go-systemd/v22/activation"
 	"github.com/pborman/getopt/v2"
 
 	"github.com/sigstore/gitsign/internal/cache/service"
@@ -32,6 +33,7 @@ import (
 var (
 	// Action flags
 	versionFlag = getopt.BoolLong("version", 'v', "print the version number")
+	systemdFlag = getopt.BoolLong("systemd-socket-activation", 's', "use systemd socket activation")
 )
 
 func main() {
@@ -47,31 +49,67 @@ func main() {
 		os.Exit(0)
 	}
 
-	user, err := os.UserCacheDir()
-	if err != nil {
-		log.Fatalf("error getting user cache directory: %v", err)
-	}
+	var connChan = make(chan net.Conn)
+	if *systemdFlag {
+		// Stop if we're not running under systemd.
+		if os.Getenv("LISTEN_PID") == "" {
+			log.Fatalf("systemd socket activation requested but not running under systemd")
+		}
 
-	dir := filepath.Join(user, "sigstore", "gitsign")
-	if err := os.MkdirAll(dir, 0700); err != nil {
-		log.Fatalf("error creating %s: %v", dir, err)
-	}
+		listeners, err := activation.Listeners()
+		if err != nil {
+			log.Fatalf("error getting systemd listeners: %v", err)
+		}
+		var validCount int
+		for _, l := range listeners {
+			if l == nil {
+				continue
+			}
+			fmt.Println(l.Addr().String())
+			go connToChan(l, connChan)
+			validCount++
+		}
+		if validCount == 0 {
+			log.Fatalf("no valid systemd listeners found")
+		}
+	} else {
+		user, err := os.UserCacheDir()
+		if err != nil {
+			log.Fatalf("error getting user cache directory: %v", err)
+		}
 
-	path := filepath.Join(dir, "cache.sock")
-	if _, err := os.Stat(path); err == nil {
-		os.Remove(path)
-	}
-	fmt.Println(path)
+		dir := filepath.Join(user, "sigstore", "gitsign")
+		if err := os.MkdirAll(dir, 0700); err != nil {
+			log.Fatalf("error creating %s: %v", dir, err)
+		}
+
+		path := filepath.Join(dir, "cache.sock")
+		if _, err := os.Stat(path); err == nil {
+			os.Remove(path)
+		}
+		fmt.Println(path)
 
-	l, err := net.Listen("unix", path)
-	if err != nil {
-		log.Fatalf("error opening socket: %v", err)
+		l, err := net.Listen("unix", path)
+		if err != nil {
+			log.Fatalf("error opening socket: %v", err)
+		}
+		go connToChan(l, connChan)
 	}
 	srv := rpc.NewServer()
 	if err := srv.Register(service.NewService()); err != nil {
 		log.Fatalf("error registering RPC service: %v", err)
 	}
+	for conn := range connChan {
+		go srv.ServeConn(conn)
+	}
+}
+
+func connToChan(l net.Listener, connChan chan net.Conn) {
 	for {
-		srv.Accept(l)
+		conn, err := l.Accept()
+		if err != nil {
+			log.Fatalf("error accepting connection: %v", err)
+		}
+		connChan <- conn
 	}
 }

contrib/systemd/gitsign-credential-cache.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=GitSign credential cache
+
+[Service]
+Type=simple
+ExecStart=%h/.local/bin/gitsign-credential-cache
+
+[Install]
+WantedBy=default.target

contrib/systemd/gitsign-credential-cache.socket

@@ -0,0 +1,9 @@
+[Unit]
+Description=GitSign credential cache socket
+
+[Socket]
+ListenStream=%C/sigstore/gitsign/cache.sock
+DirectoryMode=0700
+
+[Install]
+WantedBy=default.target

go.mod

@@ -4,6 +4,7 @@ go 1.19
 
 require (
 	github.com/coreos/go-oidc/v3 v3.5.0
+	github.com/coreos/go-systemd/v22 v22.5.0
 	github.com/github/smimesign v0.2.0
 	github.com/go-git/go-billy/v5 v5.4.0
 	github.com/go-git/go-git/v5 v5.5.2
@@ -86,7 +87,6 @@ require (
 	github.com/common-nighthawk/go-figure v0.0.0-20210622060536-734e95fb86be // indirect
 	github.com/containerd/stargz-snapshotter/estargz v0.12.0 // indirect
 	github.com/coreos/go-semver v0.3.0 // indirect
-	github.com/coreos/go-systemd/v22 v22.3.2 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
 	github.com/cyberphone/json-canonicalization v0.0.0-20210823021906-dc406ceaf94b // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect

go.sum

@@ -395,8 +395,9 @@ github.com/coreos/go-systemd v0.0.0-20180511133405-39ca1b05acc7/go.mod h1:F5haX7
 github.com/coreos/go-systemd v0.0.0-20190321100706-95778dfbb74e/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/coreos/go-systemd v0.0.0-20190620071333-e64a0ec8b42a/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/coreos/go-systemd/v22 v22.1.0/go.mod h1:xO0FLkIi5MaZafQlIrOotqXZ90ih+1atmu1JpKERPPk=
-github.com/coreos/go-systemd/v22 v22.3.2 h1:D9/bQk5vlXQFZ6Kwuu6zaiXJ9oTPe68++AzAJc1DzSI=
 github.com/coreos/go-systemd/v22 v22.3.2/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
+github.com/coreos/go-systemd/v22 v22.5.0 h1:RrqgGjYQKalulkV8NGVIfkXQf6YYmOyiJKk8iXXhfZs=
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/coreos/pkg v0.0.0-20160727233714-3ac0863d7acf/go.mod h1:E3G3o1h8I7cfcXa63jLwjI0eiQQMgzzUDFVpN/nH/eA=
 github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f/go.mod h1:E3G3o1h8I7cfcXa63jLwjI0eiQQMgzzUDFVpN/nH/eA=
 github.com/cpuguy83/go-md2man v1.0.10/go.mod h1:SmD6nW6nTyfqj6ABTjUi3V3JVMnlJmwcJI5acqYI6dE=