Stamp shared build metadata into banger binaries

Treat `banger`, `bangerd`, and `banger-vsock-agent` as one release by
stamping the same version, commit SHA, and build timestamp into every
binary through a shared ldflag-backed `internal/buildinfo` package.

Add `banger version`, extend daemon ping/status to report the running
daemon's build tuple, and keep the guest helper linked to the same build
metadata without adding a new public version surface for it.

Validate with `GOCACHE=/tmp/banger-gocache go test ./...`, `make build`,
`./build/bin/banger version`, and `./build/bin/banger daemon status`
after the daemon restarts onto the new binary.

Makefile

@@ -20,6 +20,10 @@ VOID_VM_NAME ?= void-dev
 ALPINE_RELEASE ?= 3.23.3
 ALPINE_IMAGE_NAME ?= alpine
 ALPINE_VM_NAME ?= alpine-dev
+VERSION ?= $(shell git describe --tags --exact-match 2>/dev/null || echo dev)
+COMMIT ?= $(shell git rev-parse --verify HEAD 2>/dev/null || echo unknown)
+BUILT_AT ?= $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
+GO_LDFLAGS := -X banger/internal/buildinfo.Version=$(VERSION) -X banger/internal/buildinfo.Commit=$(COMMIT) -X banger/internal/buildinfo.BuiltAt=$(BUILT_AT)
 
 .DEFAULT_GOAL := help
 
@@ -51,15 +55,15 @@ build: $(BINARIES)
 
 $(BANGER_BIN): $(GO_SOURCES) go.mod go.sum
 	mkdir -p "$(BUILD_BIN_DIR)"
-	$(GO) build -o "$(BANGER_BIN)" ./cmd/banger
+	$(GO) build -ldflags '$(GO_LDFLAGS)' -o "$(BANGER_BIN)" ./cmd/banger
 
 $(BANGERD_BIN): $(GO_SOURCES) go.mod go.sum
 	mkdir -p "$(BUILD_BIN_DIR)"
-	$(GO) build -o "$(BANGERD_BIN)" ./cmd/bangerd
+	$(GO) build -ldflags '$(GO_LDFLAGS)' -o "$(BANGERD_BIN)" ./cmd/bangerd
 
 $(VSOCK_AGENT_BIN): $(GO_SOURCES) go.mod go.sum
 	mkdir -p "$(BUILD_BIN_DIR)"
-	CGO_ENABLED=0 GOOS=linux GOARCH=amd64 $(GO) build -o "$(VSOCK_AGENT_BIN)" ./cmd/banger-vsock-agent
+	CGO_ENABLED=0 GOOS=linux GOARCH=amd64 $(GO) build -ldflags '$(GO_LDFLAGS)' -o "$(VSOCK_AGENT_BIN)" ./cmd/banger-vsock-agent
 
 test:
 	$(GO) test ./...

cmd/banger-vsock-agent/main.go

@@ -11,12 +11,15 @@ import (
 	"syscall"
 	"time"
 
+	"banger/internal/buildinfo"
 	sdkvsock "github.com/firecracker-microvm/firecracker-go-sdk/vsock"
 	"github.com/sirupsen/logrus"
 
 	"banger/internal/vsockagent"
 )
 
+var _, _, _ = buildinfo.Version, buildinfo.Commit, buildinfo.BuiltAt
+
 func main() {
 	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer cancel()

internal/api/types.go

@@ -12,6 +12,9 @@ type PingResult struct {
 	Status  string `json:"status"`
 	PID     int    `json:"pid"`
 	WebURL  string `json:"web_url,omitempty"`
+	Version string `json:"version,omitempty"`
+	Commit  string `json:"commit,omitempty"`
+	BuiltAt string `json:"built_at,omitempty"`
 }
 
 type ShutdownResult struct {

internal/buildinfo/buildinfo.go

@@ -0,0 +1,34 @@
+package buildinfo
+
+import "strings"
+
+var (
+	Version = "dev"
+	Commit  = "unknown"
+	BuiltAt = "unknown"
+)
+
+type Info struct {
+	Version string
+	Commit  string
+	BuiltAt string
+}
+
+func Current() Info {
+	return Normalize(Version, Commit, BuiltAt)
+}
+
+func Normalize(version, commit, builtAt string) Info {
+	return Info{
+		Version: normalizedValue(version, "dev"),
+		Commit:  normalizedValue(commit, "unknown"),
+		BuiltAt: normalizedValue(builtAt, "unknown"),
+	}
+}
+
+func normalizedValue(value, fallback string) string {
+	if trimmed := strings.TrimSpace(value); trimmed != "" {
+		return trimmed
+	}
+	return fallback
+}

internal/buildinfo/buildinfo_test.go

@@ -0,0 +1,33 @@
+package buildinfo
+
+import "testing"
+
+func TestNormalizeUsesFallbacks(t *testing.T) {
+	t.Parallel()
+
+	info := Normalize("", "  ", "\t")
+	if info.Version != "dev" {
+		t.Fatalf("Version = %q, want dev", info.Version)
+	}
+	if info.Commit != "unknown" {
+		t.Fatalf("Commit = %q, want unknown", info.Commit)
+	}
+	if info.BuiltAt != "unknown" {
+		t.Fatalf("BuiltAt = %q, want unknown", info.BuiltAt)
+	}
+}
+
+func TestNormalizeTrimsValues(t *testing.T) {
+	t.Parallel()
+
+	info := Normalize(" v1.2.3 ", " abc123 ", " 2026-03-22T12:00:00Z ")
+	if info.Version != "v1.2.3" {
+		t.Fatalf("Version = %q, want v1.2.3", info.Version)
+	}
+	if info.Commit != "abc123" {
+		t.Fatalf("Commit = %q, want abc123", info.Commit)
+	}
+	if info.BuiltAt != "2026-03-22T12:00:00Z" {
+		t.Fatalf("BuiltAt = %q, want 2026-03-22T12:00:00Z", info.BuiltAt)
+	}
+}

internal/cli/banger.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"banger/internal/api"
+	"banger/internal/buildinfo"
 	"banger/internal/config"
 	"banger/internal/daemon"
 	"banger/internal/guest"
@@ -70,6 +71,9 @@ var (
 	vmHealthFunc = func(ctx context.Context, socketPath, idOrName string) (api.VMHealthResult, error) {
 		return rpc.Call[api.VMHealthResult](ctx, socketPath, "vm.health", api.VMRefParams{IDOrName: idOrName})
 	}
+	daemonPingFunc = func(ctx context.Context, socketPath string) (api.PingResult, error) {
+		return rpc.Call[api.PingResult](ctx, socketPath, "ping", api.Empty{})
+	}
 	vmCreateBeginFunc = func(ctx context.Context, socketPath string, params api.VMCreateParams) (api.VMCreateBeginResult, error) {
 		return rpc.Call[api.VMCreateBeginResult](ctx, socketPath, "vm.create.begin", params)
 	}
@@ -121,7 +125,7 @@ func NewBangerCommand() *cobra.Command {
 		RunE:          helpNoArgs,
 	}
 	root.CompletionOptions.DisableDefaultCmd = true
-	root.AddCommand(newDaemonCommand(), newDoctorCommand(), newVMCommand(), newImageCommand(), newInternalCommand())
+	root.AddCommand(newDaemonCommand(), newDoctorCommand(), newImageCommand(), newInternalCommand(), newVersionCommand(), newVMCommand())
 	return root
 }
 
@@ -146,6 +150,18 @@ func newDoctorCommand() *cobra.Command {
 	}
 }
 
+func newVersionCommand() *cobra.Command {
+	return &cobra.Command{
+		Use:   "version",
+		Short: "Show banger build information",
+		Args:  noArgsUsage("usage: banger version"),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			_, err := fmt.Fprint(cmd.OutOrStdout(), formatBuildInfoBlock(buildinfo.Current()))
+			return err
+		},
+	}
+}
+
 func newInternalCommand() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:    "internal",
@@ -342,7 +358,7 @@ func newDaemonCommand() *cobra.Command {
 				if err != nil {
 					return err
 				}
-				ping, pingErr := rpc.Call[api.PingResult](cmd.Context(), layout.SocketPath, "ping", api.Empty{})
+				ping, pingErr := daemonPingFunc(cmd.Context(), layout.SocketPath)
 				if pingErr != nil {
 					if strings.TrimSpace(cfg.WebListenAddr) != "" {
 						_, err = fmt.Fprintf(cmd.OutOrStdout(), "stopped\nsocket: %s\nlog: %s\ndns: %s\nweb: http://%s\n", layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr, cfg.WebListenAddr)
@@ -351,11 +367,12 @@ func newDaemonCommand() *cobra.Command {
 					_, err = fmt.Fprintf(cmd.OutOrStdout(), "stopped\nsocket: %s\nlog: %s\ndns: %s\n", layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr)
 					return err
 				}
+				info := buildinfo.Normalize(ping.Version, ping.Commit, ping.BuiltAt)
 				if strings.TrimSpace(ping.WebURL) != "" {
-					_, err = fmt.Fprintf(cmd.OutOrStdout(), "running\npid: %d\nsocket: %s\nlog: %s\ndns: %s\nweb: %s\n", ping.PID, layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr, ping.WebURL)
+					_, err = fmt.Fprintf(cmd.OutOrStdout(), "running\npid: %d\n%ssocket: %s\nlog: %s\ndns: %s\nweb: %s\n", ping.PID, formatBuildInfoBlock(info), layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr, ping.WebURL)
 					return err
 				}
-				_, err = fmt.Fprintf(cmd.OutOrStdout(), "running\npid: %d\nsocket: %s\nlog: %s\ndns: %s\n", ping.PID, layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr)
+				_, err = fmt.Fprintf(cmd.OutOrStdout(), "running\npid: %d\n%ssocket: %s\nlog: %s\ndns: %s\n", ping.PID, formatBuildInfoBlock(info), layout.SocketPath, layout.DaemonLog, vmdns.DefaultListenAddr)
 				return err
 			},
 		},
@@ -1141,7 +1158,7 @@ func ensureDaemon(ctx context.Context) (paths.Layout, model.DaemonConfig, error)
 	if err != nil {
 		return paths.Layout{}, model.DaemonConfig{}, err
 	}
-	if ping, err := rpc.Call[api.PingResult](ctx, layout.SocketPath, "ping", api.Empty{}); err == nil {
+	if ping, err := daemonPingFunc(ctx, layout.SocketPath); err == nil {
 		if daemonOutdated(ping.PID) {
 			if err := restartDaemon(ctx, layout, ping.PID); err != nil {
 				return paths.Layout{}, model.DaemonConfig{}, err
@@ -2067,3 +2084,7 @@ func relativeTime(t time.Time) string {
 		return fmt.Sprintf("%d weeks ago", int(delta.Hours()/(24*7)))
 	}
 }
+
+func formatBuildInfoBlock(info buildinfo.Info) string {
+	return fmt.Sprintf("version: %s\ncommit: %s\nbuilt_at: %s\n", info.Version, info.Commit, info.BuiltAt)
+}

internal/cli/cli_test.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	"banger/internal/api"
+	"banger/internal/buildinfo"
 	"banger/internal/model"
 	"banger/internal/system"
 )
@@ -25,12 +26,36 @@ func TestNewBangerCommandHasExpectedSubcommands(t *testing.T) {
 	for _, sub := range cmd.Commands() {
 		names = append(names, sub.Name())
 	}
-	want := []string{"daemon", "doctor", "image", "internal", "vm"}
+	want := []string{"daemon", "doctor", "image", "internal", "version", "vm"}
 	if !reflect.DeepEqual(names, want) {
 		t.Fatalf("subcommands = %v, want %v", names, want)
 	}
 }
 
+func TestVersionCommandPrintsBuildInfo(t *testing.T) {
+	cmd := NewBangerCommand()
+	var stdout bytes.Buffer
+	cmd.SetOut(&stdout)
+	cmd.SetErr(&stdout)
+	cmd.SetArgs([]string{"version"})
+
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+
+	info := buildinfo.Current()
+	output := stdout.String()
+	for _, want := range []string{
+		"version: " + info.Version,
+		"commit: " + info.Commit,
+		"built_at: " + info.BuiltAt,
+	} {
+		if !strings.Contains(output, want) {
+			t.Fatalf("output = %q, want %q", output, want)
+		}
+	}
+}
+
 func TestLegacyRemovedCommandIsRejected(t *testing.T) {
 	cmd := NewBangerCommand()
 	cmd.SetArgs([]string{"tui"})
@@ -1222,6 +1247,55 @@ func TestDaemonStatusIncludesLogPathWhenStopped(t *testing.T) {
 	}
 }
 
+func TestDaemonStatusIncludesDaemonBuildInfoWhenRunning(t *testing.T) {
+	origDaemonPing := daemonPingFunc
+	t.Cleanup(func() {
+		daemonPingFunc = origDaemonPing
+	})
+
+	configHome := filepath.Join(t.TempDir(), "config")
+	stateHome := filepath.Join(t.TempDir(), "state")
+	runtimeHome := filepath.Join(t.TempDir(), "runtime")
+	t.Setenv("XDG_CONFIG_HOME", configHome)
+	t.Setenv("XDG_STATE_HOME", stateHome)
+	t.Setenv("XDG_RUNTIME_DIR", runtimeHome)
+
+	daemonPingFunc = func(context.Context, string) (api.PingResult, error) {
+		return api.PingResult{
+			Status:  "ok",
+			PID:     42,
+			WebURL:  "http://127.0.0.1:7777",
+			Version: "v1.2.3",
+			Commit:  "abc123",
+			BuiltAt: "2026-03-22T12:00:00Z",
+		}, nil
+	}
+
+	cmd := NewBangerCommand()
+	var stdout bytes.Buffer
+	cmd.SetOut(&stdout)
+	cmd.SetErr(&stdout)
+	cmd.SetArgs([]string{"daemon", "status"})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+
+	output := stdout.String()
+	for _, want := range []string{
+		"running\n",
+		"pid: 42",
+		"version: v1.2.3",
+		"commit: abc123",
+		"built_at: 2026-03-22T12:00:00Z",
+		"log: " + filepath.Join(stateHome, "banger", "bangerd.log"),
+		"web: http://127.0.0.1:7777",
+	} {
+		if !strings.Contains(output, want) {
+			t.Fatalf("output = %q, want %q", output, want)
+		}
+	}
+}
+
 func TestBuildDaemonCommandIsDetachedFromCallerContext(t *testing.T) {
 	cmd := buildDaemonCommand("/tmp/bangerd")
 

internal/daemon/daemon.go

@@ -16,6 +16,7 @@ import (
 	"time"
 
 	"banger/internal/api"
+	"banger/internal/buildinfo"
 	"banger/internal/config"
 	"banger/internal/model"
 	"banger/internal/paths"
@@ -250,7 +251,15 @@ func (d *Daemon) dispatch(ctx context.Context, req rpc.Request) rpc.Response {
 	}
 	switch req.Method {
 	case "ping":
-		result, _ := rpc.NewResult(api.PingResult{Status: "ok", PID: d.pid, WebURL: d.webURL})
+		info := buildinfo.Current()
+		result, _ := rpc.NewResult(api.PingResult{
+			Status:  "ok",
+			PID:     d.pid,
+			WebURL:  d.webURL,
+			Version: info.Version,
+			Commit:  info.Commit,
+			BuiltAt: info.BuiltAt,
+		})
 		return result
 	case "shutdown":
 		go d.Close()

internal/daemon/daemon_test.go

@@ -2,14 +2,17 @@ package daemon
 
 import (
 	"context"
+	"encoding/json"
 	"os"
 	"path/filepath"
 	"strings"
 	"testing"
 
 	"banger/internal/api"
+	"banger/internal/buildinfo"
 	"banger/internal/model"
 	"banger/internal/paths"
+	"banger/internal/rpc"
 	"banger/internal/system"
 )
 
@@ -42,6 +45,28 @@ func TestRegisterImageRequiresKernel(t *testing.T) {
 	}
 }
 
+func TestDispatchPingIncludesBuildInfo(t *testing.T) {
+	d := &Daemon{pid: 42, webURL: "http://127.0.0.1:7777"}
+
+	resp := d.dispatch(context.Background(), rpc.Request{Version: rpc.Version, Method: "ping"})
+	if !resp.OK {
+		t.Fatalf("dispatch(ping) = %+v, want ok", resp)
+	}
+
+	var got api.PingResult
+	if err := json.Unmarshal(resp.Result, &got); err != nil {
+		t.Fatalf("Unmarshal(PingResult): %v", err)
+	}
+
+	info := buildinfo.Current()
+	if got.Status != "ok" || got.PID != 42 || got.WebURL != "http://127.0.0.1:7777" {
+		t.Fatalf("PingResult = %+v, want status/pid/weburl populated", got)
+	}
+	if got.Version != info.Version || got.Commit != info.Commit || got.BuiltAt != info.BuiltAt {
+		t.Fatalf("PingResult build info = %+v, want %+v", got, info)
+	}
+}
+
 func TestPromoteImageCopiesBootArtifactsIntoArtifactDir(t *testing.T) {
 	dir := t.TempDir()
 	rootfs := filepath.Join(dir, "rootfs.ext4")