model: redirect mappings (RedirectTo, RedirectPermanent, RedirectKeepPath)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Formatting
+        run: |
+          unformatted=$(gofmt -l .)
+          if [ -n "$unformatted" ]; then
+            echo "These files need gofmt:"
+            echo "$unformatted"
+            exit 1
+          fi
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test ./...
+
+      # Reef has platform-specific files (Windows named pipes for Docker), so make
+      # sure it builds everywhere the programs that import it do.
+      - name: Builds on every platform
+        run: |
+          for t in linux/amd64 linux/arm64 linux/arm windows/amd64 darwin/amd64 darwin/arm64; do
+            echo "building for $t"
+            GOOS=${t%/*} GOARCH=${t#*/} GOARM=7 CGO_ENABLED=0 go build ./...
+          done

README.md

@@ -1,6 +1,6 @@
 # Reef
 
-A shared library for Hammerhead, Blacktip, and Bamboo
+A shared library for Hammerhead, Blacktip, Bamboo and Sandbar
 
 Shared types and building blocks for the sharks stack: [Hammerhead](https://git.veillax.com/Veillax/hammerhead) (control plane), [Blacktip](https://git.veillax.com/Veillax/blacktip) (edge) and [Bamboo](https://git.veillax.com/Veillax/bamboo) (site agent).
 
@@ -15,6 +15,7 @@ Reef holds the code all three programs agree on, so each can be built and releas
 | `netguard` | Refuses internal addresses for anything that connects out on a user's behalf (webhooks, mail delivery), and dials the address it checked |
 | `docker` | Lists running containers through the Docker Engine API, with no SDK |
 | `dotenv` | Loads a `.env` file into the environment without overriding real variables |
+| `secretbox` | AES-256-GCM sealing of small secrets (`enc1:` values) before they are written to a database |
 
 ## Using it
 

model/model.go

@@ -1,7 +1,10 @@
 // Package model holds the types shared by hammerhead, blacktip and bamboo.
 package model
 
-import "time"
+import (
+	"strings"
+	"time"
+)
 
 const (
 	ProtoTCP   = "tcp"   // raw TCP on ip:port
@@ -19,6 +22,21 @@ func (m Mapping) LastPort() int {
 	return m.Port
 }
 
+// IsRedirect reports whether the mapping answers with a redirect instead of forwarding to a target.
+func (m Mapping) IsRedirect() bool { return m.RedirectTo != "" }
+
+// RedirectLocation is where a request for requestURI (path and query) is sent. With KeepPath the
+// request's path and query follow the destination, so example.com/a?b=1 goes to to/a?b=1.
+func (m Mapping) RedirectLocation(requestURI string) string {
+	if !m.RedirectKeepPath {
+		return m.RedirectTo
+	}
+	if requestURI == "" || requestURI[0] != '/' {
+		requestURI = "/" + requestURI
+	}
+	return strings.TrimRight(m.RedirectTo, "/") + requestURI
+}
+
 // HostBased reports whether mappings of this protocol are routed by hostname.
 func HostBased(proto string) bool {
 	return proto == ProtoHTTP || proto == ProtoHTTPS || proto == ProtoTLS
@@ -39,6 +57,13 @@ type Edge struct {
 	OrgIDs     []string  `json:"orgIds"`            // orgs allowed to use this edge; empty = all
 	IPs        []string  `json:"ips"`               // addresses the edge reported it can bind
 	LastSeen   time.Time `json:"lastSeen"`
+
+	// Version is the release the program reports (e.g. v0.1.5). AutoUpdate says whether it may update
+	// itself; only then will it act on an update request (UpdateID). UpdateMsg is the outcome of the last requested update.
+	Version    string `json:"version,omitempty"`
+	AutoUpdate bool   `json:"autoUpdate,omitempty"`
+	UpdateID   string `json:"updateId,omitempty"` // set while an update requested by an administrator is pending
+	UpdateMsg  string `json:"updateMsg,omitempty"`
 }
 
 // Site is a bamboo agent: a private network that holds the real services.
@@ -54,8 +79,17 @@ type Site struct {
 	Local  bool   `json:"local"`
 	EdgeID string `json:"edgeId,omitempty"` // the edge a local site belongs to
 
+	Tags []string `json:"tags,omitempty"` // labels for grouping and filtering in the dashboard
+
 	TunnelIP  string `json:"tunnelIp,omitempty"`  // the site's address inside the tunnel network
 	PublicKey string `json:"publicKey,omitempty"` // WireGuard public key, reported by the agent
+
+	// Version is the release the program reports (e.g. v0.1.5). AutoUpdate says whether it may update
+	// itself; only then will it act on an update request (UpdateID). UpdateMsg is the outcome of the last requested update.
+	Version    string `json:"version,omitempty"`
+	AutoUpdate bool   `json:"autoUpdate,omitempty"`
+	UpdateID   string `json:"updateId,omitempty"` // set while an update requested by an administrator is pending
+	UpdateMsg  string `json:"updateMsg,omitempty"`
 }
 
 // Domain is a base domain an org owns. Hostnames of web/tls mappings must sit under one.
@@ -111,10 +145,17 @@ type Mapping struct {
 	Hostname string   `json:"hostname,omitempty"` // web/tls only; "*.example.com" allowed
 	Targets  []Target `json:"targets"`            // udp uses only the first
 	Enabled  bool     `json:"enabled"`
+	Tags     []string `json:"tags,omitempty"` // labels for grouping and filtering in the dashboard
 	// ProxyProtocol ("v1" or "v2") makes the edge start each tcp/tls connection to the
 	// target with a PROXY protocol header carrying the real client address.
 	ProxyProtocol string `json:"proxyProtocol,omitempty"`
 
+	// A web mapping with RedirectTo set sends visitors there instead of to a target (so it has no
+	// targets, login or health checks). It answers 301 when RedirectPermanent, otherwise 302.
+	RedirectTo        string `json:"redirectTo,omitempty"`
+	RedirectPermanent bool   `json:"redirectPermanent,omitempty"`
+	RedirectKeepPath  bool   `json:"redirectKeepPath,omitempty"`
+
 	// web (http/https) options
 	Auth          Auth   `json:"auth"`
 	AuthEpoch     int64  `json:"authEpoch"` // bumped to sign every visitor out; set by hammerhead only
@@ -216,6 +257,7 @@ type EdgeConfig struct {
 	Local      []string  `json:"local"`    // site IDs the edge dials directly on its own machine
 	AcmeEmail  string    `json:"acmeEmail"`
 	AcmeStages bool      `json:"acmeStaging"`
+	UpdateID   string    `json:"updateId,omitempty"` // an administrator asked this edge to update itself now; echoed back in its report
 
 	MailEgress []MailPolicy `json:"mailEgress"`
 }
@@ -289,6 +331,14 @@ type EdgeReport struct {
 	Stats      map[string]Stat          `json:"stats"` // deltas since last report
 	Containers []Container              `json:"containers"`
 	MailChecks map[string]MailCheck     `json:"mailChecks"` // by mail-egress ID
+	Version    string                   `json:"version,omitempty"`
+	AutoUpdate bool                     `json:"autoUpdate,omitempty"`
+	UpdateMsg  string                   `json:"updateMsg,omitempty"` // outcome of the update asked for by UpdateID
+	UpdateID   string                   `json:"updateId,omitempty"`
+	// progress of that update, for the dashboard's progress bar and log
+	UpdateStage string   `json:"updateStage,omitempty"`
+	UpdatePct   int      `json:"updatePct,omitempty"`
+	UpdateLog   []string `json:"updateLog,omitempty"`
 }
 
 // EdgeRef tells a site where to dial.
@@ -306,6 +356,7 @@ type SiteConfig struct {
 	SiteID   string    `json:"siteId"`
 	TunnelIP string    `json:"tunnelIp"` // this site's WireGuard address
 	Edges    []EdgeRef `json:"edges"`
+	UpdateID string    `json:"updateId,omitempty"` // an administrator asked this agent to update itself now; echoed back in its report
 
 	MailEgress []MailSpec `json:"mailEgress"`
 }
@@ -316,6 +367,14 @@ type SiteReport struct {
 	MailEgress map[string]string `json:"mailEgress"` // egress ID -> "" (listening) or an error
 	Connected  []string          `json:"connected"`
 	Containers []Container       `json:"containers"`
+	Version    string            `json:"version,omitempty"`
+	AutoUpdate bool              `json:"autoUpdate,omitempty"`
+	UpdateMsg  string            `json:"updateMsg,omitempty"`
+	UpdateID   string            `json:"updateId,omitempty"`
+	// progress of that update, for the dashboard's progress bar and log
+	UpdateStage string   `json:"updateStage,omitempty"`
+	UpdatePct   int      `json:"updatePct,omitempty"`
+	UpdateLog   []string `json:"updateLog,omitempty"`
 }
 
 // HostMatches reports whether host matches an exact name or a "*.example.com" pattern.

model/model_test.go

@@ -0,0 +1,25 @@
+package model
+
+import "testing"
+
+func TestRedirectLocation(t *testing.T) {
+	cases := []struct {
+		m    Mapping
+		uri  string
+		want string
+	}{
+		{Mapping{RedirectTo: "https://new.example.com"}, "/a?b=1", "https://new.example.com"},
+		{Mapping{RedirectTo: "https://new.example.com", RedirectKeepPath: true}, "/a?b=1", "https://new.example.com/a?b=1"},
+		{Mapping{RedirectTo: "https://new.example.com/", RedirectKeepPath: true}, "/", "https://new.example.com/"},
+		{Mapping{RedirectTo: "https://new.example.com/base", RedirectKeepPath: true}, "/x/y", "https://new.example.com/base/x/y"},
+		{Mapping{RedirectTo: "https://new.example.com", RedirectKeepPath: true}, "", "https://new.example.com/"},
+	}
+	for _, c := range cases {
+		if got := c.m.RedirectLocation(c.uri); got != c.want {
+			t.Errorf("%+v %q: got %q, want %q", c.m, c.uri, got, c.want)
+		}
+	}
+	if (Mapping{}).IsRedirect() || !(Mapping{RedirectTo: "https://x"}).IsRedirect() {
+		t.Error("IsRedirect is wrong")
+	}
+}

secretbox/secretbox.go

@@ -0,0 +1,87 @@
+// Package secretbox encrypts small secrets (tokens, passwords, private keys)
+// before they are written to the database, using AES-256-GCM.
+//
+// Sealed values look like "enc1:<base64>". Opening a value that isn't sealed
+// returns it unchanged, so data written before encryption was turned on is
+// still readable and gets sealed the next time it is saved.
+package secretbox
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+	"errors"
+	"strings"
+)
+
+const prefix = "enc1:"
+
+type Box struct{ aead cipher.AEAD }
+
+// GenerateKey returns a new random key in the form New accepts.
+func GenerateKey() string {
+	b := make([]byte, 32)
+	rand.Read(b)
+	return base64.StdEncoding.EncodeToString(b)
+}
+
+// New builds a Box from a key given as base64 or hex of 32 bytes. Any other
+// text is treated as a passphrase and stretched with SHA-256.
+func New(key string) (*Box, error) {
+	key = strings.TrimSpace(key)
+	if key == "" {
+		return nil, errors.New("empty key")
+	}
+	raw := decodeKey(key)
+	block, err := aes.NewCipher(raw)
+	if err != nil {
+		return nil, err
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	return &Box{aead: aead}, nil
+}
+
+func decodeKey(key string) []byte {
+	if b, err := base64.StdEncoding.DecodeString(key); err == nil && len(b) == 32 {
+		return b
+	}
+	if b, err := hex.DecodeString(key); err == nil && len(b) == 32 {
+		return b
+	}
+	sum := sha256.Sum256([]byte(key))
+	return sum[:]
+}
+
+// Seal encrypts s. The empty string stays empty so unset secrets stay visibly unset.
+func (b *Box) Seal(s string) string {
+	if s == "" || strings.HasPrefix(s, prefix) {
+		return s
+	}
+	nonce := make([]byte, b.aead.NonceSize())
+	rand.Read(nonce)
+	return prefix + base64.StdEncoding.EncodeToString(b.aead.Seal(nonce, nonce, []byte(s), nil))
+}
+
+// Open decrypts a sealed value. A wrong key or damaged data is an error, so a
+// bad key can never silently turn secrets into garbage.
+func (b *Box) Open(s string) (string, error) {
+	if !strings.HasPrefix(s, prefix) {
+		return s, nil
+	}
+	raw, err := base64.StdEncoding.DecodeString(s[len(prefix):])
+	if err != nil || len(raw) < b.aead.NonceSize() {
+		return "", errors.New("damaged secret")
+	}
+	n := b.aead.NonceSize()
+	plain, err := b.aead.Open(nil, raw[:n], raw[n:], nil)
+	if err != nil {
+		return "", errors.New("can't decrypt a stored secret: is HAMMERHEAD_MASTER_KEY the key it was saved with?")
+	}
+	return string(plain), nil
+}

secretbox/secretbox_test.go

@@ -0,0 +1,51 @@
+package secretbox
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSealOpenRoundTripAndKeys(t *testing.T) {
+	key := GenerateKey()
+	b, err := New(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sealed := b.Seal("hunter2")
+	if !strings.HasPrefix(sealed, "enc1:") || strings.Contains(sealed, "hunter2") {
+		t.Fatalf("not sealed: %q", sealed)
+	}
+	if again := b.Seal("hunter2"); again == sealed {
+		t.Error("two seals of the same value must differ (random nonce)")
+	}
+	if b.Seal(sealed) != sealed {
+		t.Error("sealing an already sealed value must not double-encrypt")
+	}
+	if got, err := b.Open(sealed); err != nil || got != "hunter2" {
+		t.Errorf("Open = %q, %v", got, err)
+	}
+	if got, _ := b.Open("legacy plaintext"); got != "legacy plaintext" {
+		t.Errorf("unsealed legacy data should pass through, got %q", got)
+	}
+	if b.Seal("") != "" {
+		t.Error("empty stays empty")
+	}
+
+	other, _ := New(GenerateKey())
+	if _, err := other.Open(sealed); err == nil {
+		t.Error("the wrong key must fail loudly, not return garbage")
+	}
+	if _, err := b.Open(sealed[:len(sealed)-4] + "AAAA"); err == nil {
+		t.Error("tampered data must fail")
+	}
+
+	// a passphrase works as a key, and is stable
+	p1, _ := New("correct horse battery staple")
+	p2, _ := New("correct horse battery staple")
+	if got, err := p2.Open(p1.Seal("x")); err != nil || got != "x" {
+		t.Errorf("passphrase keys must be reproducible: %q %v", got, err)
+	}
+	if _, err := New("  "); err == nil {
+		t.Error("an empty key must be rejected")
+	}
+}

selfupdate/restart_unix.go

@@ -0,0 +1,13 @@
+//go:build !windows
+
+package selfupdate
+
+import (
+	"os"
+	"syscall"
+)
+
+// Restart replaces this process with the new binary, with the same arguments and environment.
+func Restart(exe string) error {
+	return syscall.Exec(exe, os.Args, os.Environ())
+}

selfupdate/restart_windows.go

@@ -0,0 +1,7 @@
+package selfupdate
+
+import "errors"
+
+func Restart(string) error {
+	return errors.New("restarting in place is not supported on Windows")
+}

selfupdate/selfupdate.go

@@ -0,0 +1,388 @@
+// Package selfupdate lets a program replace itself with the newest release published on a
+// Gitea server: it checks the latest release, downloads the archive for this platform,
+// verifies it against the release's SHA256SUMS, checks that the new binary runs, swaps it
+// in and restarts into it.
+package selfupdate
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"math/rand"
+	"net/http"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const maxArchive = 300 << 20
+
+// Event is one step of an update, for showing progress: the stage ("checking", "downloading",
+// "verifying", "installing", "restarting", "done" or "failed"), how far along it is (0-100, or -1 to
+// leave the bar where it was) and, when there is something worth showing in a log, a line of text.
+type Event struct {
+	Stage string
+	Pct   int
+	Line  string
+}
+
+// Config says what to update and where from.
+type Config struct {
+	Server  string // e.g. https://git.veillax.com
+	Repo    string // owner/name, e.g. Veillax/blacktip
+	App     string // binary and archive prefix, e.g. blacktip
+	Current string // the running version, e.g. v0.1.2; anything that isn't vX.Y.Z is never updated
+	// Interval between checks (default 6 hours).
+	Interval time.Duration
+	Logf     func(format string, args ...any)
+	// Progress, if set, is told about every step of an update (it is called from the updating goroutine).
+	Progress func(Event)
+
+	// The fields below exist for tests and unusual setups.
+	HTTP    *http.Client
+	GOOS    string
+	GOARCH  string
+	ExePath string // binary to replace (default: the running one)
+	// Verify runs on the downloaded binary before it replaces the old one. The default
+	// runs it with -version and checks that it reports the new tag.
+	Verify func(path, tag string) error
+	// Restart is called after the swap (default: re-exec the new binary in place, keeping the
+	// process ID and environment).
+	Restart func(exe string) error
+}
+
+func (c *Config) defaults() {
+	if c.Interval <= 0 {
+		c.Interval = 6 * time.Hour
+	}
+	if c.Logf == nil {
+		c.Logf = func(string, ...any) {}
+	}
+	if c.HTTP == nil {
+		c.HTTP = &http.Client{Timeout: 5 * time.Minute}
+	}
+	if c.GOOS == "" {
+		c.GOOS = runtime.GOOS
+	}
+	if c.GOARCH == "" {
+		c.GOARCH = runtime.GOARCH
+	}
+	if c.Verify == nil {
+		c.Verify = verifyRuns(c.App)
+	}
+	if c.Restart == nil {
+		c.Restart = Restart
+	}
+	c.Server = strings.TrimRight(c.Server, "/")
+}
+
+// Run checks shortly after start and then every Interval until ctx ends. When an update
+// is installed, Restart takes over and Run normally does not return.
+func Run(ctx context.Context, cfg Config) {
+	cfg.defaults()
+	if _, ok := parseVersion(cfg.Current); !ok {
+		cfg.Logf("auto-update: this is a development build (%q), so it will not update itself", cfg.Current)
+		return
+	}
+	if cfg.GOOS == "windows" {
+		cfg.Logf("auto-update: not supported on Windows, because a running program can't be replaced; update it by hand")
+		return
+	}
+	wait := time.Duration(30+rand.Intn(240)) * time.Second // spread a fleet's first checks out
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(wait):
+		}
+		if _, err := CheckOnce(ctx, cfg); err != nil {
+			cfg.Logf("auto-update: %v", err)
+		}
+		wait = cfg.Interval + time.Duration(rand.Int63n(int64(cfg.Interval/10)+1))
+	}
+}
+
+func (c Config) say(stage string, pct int, line string) {
+	if c.Progress != nil {
+		c.Progress(Event{Stage: stage, Pct: pct, Line: line})
+	}
+}
+
+// CheckOnce looks for a newer release and installs it. It returns the new tag when it
+// installed one (and Restart returned, which only happens in tests or on failure).
+func CheckOnce(ctx context.Context, cfg Config) (string, error) {
+	cfg.defaults()
+	tag, err := checkOnce(ctx, cfg)
+	if err != nil {
+		cfg.say("failed", -1, "Failed: "+err.Error())
+	}
+	return tag, err
+}
+
+func checkOnce(ctx context.Context, cfg Config) (string, error) {
+	cur, ok := parseVersion(cfg.Current)
+	if !ok {
+		return "", fmt.Errorf("%q is not a release version", cfg.Current)
+	}
+	cfg.say("checking", 2, "Checking "+cfg.Server+" for the newest release of "+cfg.App)
+	rel, err := latestRelease(ctx, cfg)
+	if err != nil {
+		return "", err
+	}
+	if rel.Prerelease || rel.Draft {
+		cfg.say("done", 100, "Already on the newest release ("+cfg.Current+")")
+		return "", nil
+	}
+	latest, ok := parseVersion(rel.Tag)
+	if !ok || !latest.newerThan(cur) {
+		cfg.say("done", 100, "Already on the newest release ("+cfg.Current+")")
+		return "", nil // up to date, or something we don't understand: never downgrade
+	}
+
+	if cfg.GOOS == "windows" {
+		return "", errors.New("auto-update is not supported on Windows")
+	}
+	archive := fmt.Sprintf("%s_%s_%s_%s.tar.gz", cfg.App, rel.Tag, cfg.GOOS, cfg.GOARCH)
+	var archiveURL, sumsURL string
+	for _, a := range rel.Assets {
+		switch a.Name {
+		case archive:
+			archiveURL = a.URL
+		case "SHA256SUMS":
+			sumsURL = a.URL
+		}
+	}
+	if archiveURL == "" || sumsURL == "" {
+		return "", fmt.Errorf("release %s has no %s with SHA256SUMS yet (it may still be building); will retry", rel.Tag, archive)
+	}
+	cfg.Logf("auto-update: %s is available (running %s); downloading %s", rel.Tag, cfg.Current, archive)
+	cfg.say("checking", 5, rel.Tag+" is available (running "+cfg.Current+")")
+
+	sums, err := get(ctx, cfg.HTTP, sumsURL, 1<<20, nil)
+	if err != nil {
+		return "", err
+	}
+	want := ""
+	for _, line := range strings.Split(string(sums), "\n") {
+		f := strings.Fields(line)
+		if len(f) == 2 && strings.TrimPrefix(f[1], "*") == archive {
+			want = strings.ToLower(f[0])
+		}
+	}
+	if want == "" {
+		return "", fmt.Errorf("SHA256SUMS does not list %s", archive)
+	}
+	cfg.say("downloading", 6, "Downloading "+archive)
+	lastQuarter := 0
+	data, err := get(ctx, cfg.HTTP, archiveURL, maxArchive, func(done, total int64) {
+		if total <= 0 {
+			cfg.say("downloading", -1, "")
+			return
+		}
+		pct := 6 + int(80*done/total)
+		line := ""
+		if q := int(100 * done / total / 25); q > lastQuarter {
+			lastQuarter = q
+			line = fmt.Sprintf("Downloaded %.1f of %.1f MB (%d%%)", float64(done)/1e6, float64(total)/1e6, 100*done/total)
+		}
+		cfg.say("downloading", pct, line)
+	})
+	if err != nil {
+		return "", err
+	}
+	cfg.say("verifying", 88, "Verifying the checksum")
+	got := sha256.Sum256(data)
+	if hex.EncodeToString(got[:]) != want {
+		return "", fmt.Errorf("checksum mismatch for %s: not installing", archive)
+	}
+	cfg.say("verifying", 90, "The checksum matches")
+	cfg.say("installing", 92, "Unpacking the new binary")
+	bin, err := extract(data, cfg.App)
+	if err != nil {
+		return "", err
+	}
+
+	exe := cfg.ExePath
+	if exe == "" {
+		if exe, err = os.Executable(); err != nil {
+			return "", err
+		}
+		if exe, err = filepath.EvalSymlinks(exe); err != nil {
+			return "", err
+		}
+	}
+	tmp := filepath.Join(filepath.Dir(exe), "."+filepath.Base(exe)+".new")
+	if err := os.WriteFile(tmp, bin, 0o755); err != nil {
+		return "", fmt.Errorf("can't write next to %s (is its folder writable by this user?): %w", exe, err)
+	}
+	cfg.say("installing", 94, "Checking that the new binary starts")
+	if err := cfg.Verify(tmp, rel.Tag); err != nil {
+		os.Remove(tmp)
+		return "", fmt.Errorf("the new binary failed its check, keeping the old one: %w", err)
+	}
+	cfg.say("installing", 97, "Replacing "+exe)
+	if err := os.Rename(tmp, exe); err != nil { // atomic; the running process keeps its old file
+		os.Remove(tmp)
+		return "", fmt.Errorf("replacing %s: %w", exe, err)
+	}
+	cfg.Logf("auto-update: installed %s, restarting", rel.Tag)
+	cfg.say("restarting", 100, "Installed "+rel.Tag+"; restarting into it")
+	if err := cfg.Restart(exe); err != nil {
+		return rel.Tag, fmt.Errorf("installed %s but could not restart into it (it will start with the next restart): %w", rel.Tag, err)
+	}
+	return rel.Tag, nil
+}
+
+type release struct {
+	Tag        string `json:"tag_name"`
+	Prerelease bool   `json:"prerelease"`
+	Draft      bool   `json:"draft"`
+	Assets     []struct {
+		Name string `json:"name"`
+		URL  string `json:"browser_download_url"`
+	} `json:"assets"`
+}
+
+func latestRelease(ctx context.Context, cfg Config) (release, error) {
+	var rel release
+	body, err := get(ctx, cfg.HTTP, cfg.Server+"/api/v1/repos/"+cfg.Repo+"/releases/latest", 1<<20, nil)
+	if err != nil {
+		return rel, fmt.Errorf("checking for a new release: %w", err)
+	}
+	if err := json.Unmarshal(body, &rel); err != nil {
+		return rel, fmt.Errorf("reading the latest release: %w", err)
+	}
+	return rel, nil
+}
+
+// Check reports the newest full release and whether it is newer than cfg.Current, without
+// installing anything. A development build (a Current that isn't vX.Y.Z) is never "newer".
+func Check(ctx context.Context, cfg Config) (latest string, newer bool, err error) {
+	cfg.defaults()
+	rel, err := latestRelease(ctx, cfg)
+	if err != nil {
+		return "", false, err
+	}
+	if rel.Prerelease || rel.Draft {
+		return "", false, nil
+	}
+	l, ok := parseVersion(rel.Tag)
+	if !ok {
+		return rel.Tag, false, nil
+	}
+	cur, ok := parseVersion(cfg.Current)
+	return rel.Tag, ok && l.newerThan(cur), nil
+}
+
+func get(ctx context.Context, c *http.Client, url string, max int64, onProgress func(done, total int64)) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("User-Agent", "sharks-selfupdate")
+	resp, err := c.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("%s: %s", url, resp.Status)
+	}
+	var b []byte
+	buf := make([]byte, 64<<10)
+	for {
+		n, err := resp.Body.Read(buf)
+		b = append(b, buf[:n]...)
+		if int64(len(b)) > max {
+			return nil, fmt.Errorf("%s is larger than %d bytes", url, max)
+		}
+		if onProgress != nil && n > 0 {
+			onProgress(int64(len(b)), resp.ContentLength)
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	return b, nil
+}
+
+// extract finds the program inside a release archive (<pkg>/<app>).
+func extract(data []byte, app string) ([]byte, error) {
+	zr, err := gzip.NewReader(bytes.NewReader(data))
+	if err != nil {
+		return nil, err
+	}
+	tr := tar.NewReader(zr)
+	for {
+		h, err := tr.Next()
+		if err == io.EOF {
+			return nil, fmt.Errorf("no %s inside the archive", app)
+		}
+		if err != nil {
+			return nil, err
+		}
+		if h.Typeflag == tar.TypeReg && path.Base(h.Name) == app && strings.Count(h.Name, "/") == 1 {
+			return io.ReadAll(io.LimitReader(tr, maxArchive))
+		}
+	}
+}
+
+func verifyRuns(app string) func(path, tag string) error {
+	return func(p, tag string) error {
+		ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+		defer cancel()
+		out, err := exec.CommandContext(ctx, p, "-version").Output()
+		if err != nil {
+			return err
+		}
+		if want := app + " " + tag; strings.TrimSpace(string(out)) != want {
+			return fmt.Errorf("it reports %q, expected %q", strings.TrimSpace(string(out)), want)
+		}
+		return nil
+	}
+}
+
+type version [3]int
+
+func parseVersion(s string) (version, bool) {
+	var v version
+	if !strings.HasPrefix(s, "v") || strings.ContainsAny(s, "-+") {
+		return v, false // pre-releases and local builds are never part of auto-update
+	}
+	parts := strings.Split(s[1:], ".")
+	if len(parts) != 3 {
+		return v, false
+	}
+	for i, p := range parts {
+		n, err := strconv.Atoi(p)
+		if err != nil || n < 0 {
+			return v, false
+		}
+		v[i] = n
+	}
+	return v, true
+}
+
+func (a version) newerThan(b version) bool {
+	for i := range a {
+		if a[i] != b[i] {
+			return a[i] > b[i]
+		}
+	}
+	return false
+}

selfupdate/selfupdate_test.go

@@ -0,0 +1,197 @@
+package selfupdate
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func makeArchive(t *testing.T, pkg, app, content string) []byte {
+	t.Helper()
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gz)
+	for name, body := range map[string]string{pkg + "/README.md": "hi", pkg + "/" + app: content} {
+		if err := tw.WriteHeader(&tar.Header{Name: name, Mode: 0o755, Size: int64(len(body)), Typeflag: tar.TypeReg}); err != nil {
+			t.Fatal(err)
+		}
+		tw.Write([]byte(body))
+	}
+	tw.Close()
+	gz.Close()
+	return buf.Bytes()
+}
+
+// fakeGitea serves one release with the given tag.
+func fakeGitea(t *testing.T, tag string, prerelease bool, corrupt bool) *httptest.Server {
+	archive := fmt.Sprintf("demo_%s_linux_amd64.tar.gz", tag)
+	data := makeArchive(t, strings.TrimSuffix(archive, ".tar.gz"), "demo", "NEW-BINARY "+tag)
+	sum := sha256.Sum256(data)
+	sums := hex.EncodeToString(sum[:]) + "  " + archive + "\n"
+	if corrupt {
+		sums = strings.Repeat("0", 64) + "  " + archive + "\n"
+	}
+	var srv *httptest.Server
+	mux := http.NewServeMux()
+	mux.HandleFunc("/api/v1/repos/Veillax/demo/releases/latest", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, `{"tag_name":%q,"prerelease":%v,"assets":[{"name":%q,"browser_download_url":"%s/dl/%s"},{"name":"SHA256SUMS","browser_download_url":"%s/dl/SHA256SUMS"}]}`,
+			tag, prerelease, archive, srv.URL, archive, srv.URL)
+	})
+	mux.HandleFunc("/dl/SHA256SUMS", func(w http.ResponseWriter, r *http.Request) { fmt.Fprint(w, sums) })
+	mux.HandleFunc("/dl/"+archive, func(w http.ResponseWriter, r *http.Request) { w.Write(data) })
+	srv = httptest.NewServer(mux)
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+func setup(t *testing.T, srv *httptest.Server, current string) (Config, string, *string) {
+	exe := filepath.Join(t.TempDir(), "demo")
+	os.WriteFile(exe, []byte("OLD-BINARY"), 0o755)
+	restarted := new(string)
+	return Config{Server: srv.URL, Repo: "Veillax/demo", App: "demo", Current: current, GOOS: "linux", GOARCH: "amd64", ExePath: exe,
+		Verify:  func(p, tag string) error { return nil },
+		Restart: func(e string) error { *restarted = e; return nil }}, exe, restarted
+}
+
+func TestInstallsANewerRelease(t *testing.T) {
+	cfg, exe, restarted := setup(t, fakeGitea(t, "v0.2.0", false, false), "v0.1.5")
+	tag, err := CheckOnce(context.Background(), cfg)
+	if err != nil || tag != "v0.2.0" {
+		t.Fatalf("tag=%q err=%v", tag, err)
+	}
+	if b, _ := os.ReadFile(exe); string(b) != "NEW-BINARY v0.2.0" {
+		t.Fatalf("binary is %q", b)
+	}
+	if *restarted != exe {
+		t.Fatalf("restart called with %q", *restarted)
+	}
+	if _, err := os.Stat(filepath.Join(filepath.Dir(exe), ".demo.new")); err == nil {
+		t.Fatal("temporary file left behind")
+	}
+}
+
+func TestLeavesThingsAloneWhenItShould(t *testing.T) {
+	for _, c := range []struct {
+		name, current, tag string
+		pre                bool
+	}{
+		{"same version", "v0.2.0", "v0.2.0", false},
+		{"never downgrades", "v0.3.0", "v0.2.0", false},
+		{"pre-release is skipped", "v0.1.0", "v0.2.0", true},
+		{"dev build", "dev", "v0.2.0", false},
+		{"local build", "v0.2.0-local", "v0.9.0", false},
+	} {
+		cfg, exe, restarted := setup(t, fakeGitea(t, c.tag, c.pre, false), c.current)
+		tag, _ := CheckOnce(context.Background(), cfg)
+		if b, _ := os.ReadFile(exe); tag != "" || string(b) != "OLD-BINARY" || *restarted != "" {
+			t.Errorf("%s: changed things (tag=%q binary=%q)", c.name, tag, b)
+		}
+	}
+}
+
+func TestRefusesABadChecksum(t *testing.T) {
+	cfg, exe, restarted := setup(t, fakeGitea(t, "v0.2.0", false, true), "v0.1.0")
+	if _, err := CheckOnce(context.Background(), cfg); err == nil || !strings.Contains(err.Error(), "checksum") {
+		t.Fatalf("err=%v", err)
+	}
+	if b, _ := os.ReadFile(exe); string(b) != "OLD-BINARY" || *restarted != "" {
+		t.Fatal("installed a binary that failed its checksum")
+	}
+}
+
+func TestKeepsTheOldBinaryWhenTheNewOneFailsItsCheck(t *testing.T) {
+	cfg, exe, restarted := setup(t, fakeGitea(t, "v0.2.0", false, false), "v0.1.0")
+	cfg.Verify = func(p, tag string) error { return fmt.Errorf("segfault") }
+	if _, err := CheckOnce(context.Background(), cfg); err == nil {
+		t.Fatal("expected an error")
+	}
+	if b, _ := os.ReadFile(exe); string(b) != "OLD-BINARY" || *restarted != "" {
+		t.Fatal("replaced the binary despite a failed check")
+	}
+	if _, err := os.Stat(filepath.Join(filepath.Dir(exe), ".demo.new")); err == nil {
+		t.Fatal("temporary file left behind")
+	}
+}
+
+func TestVersionOrdering(t *testing.T) {
+	for _, c := range []struct {
+		a, b string
+		want bool
+	}{{"v0.1.10", "v0.1.9", true}, {"v1.0.0", "v0.99.99", true}, {"v0.1.2", "v0.1.2", false}, {"v0.1.1", "v0.2.0", false}} {
+		a, _ := parseVersion(c.a)
+		b, _ := parseVersion(c.b)
+		if a.newerThan(b) != c.want {
+			t.Errorf("%s newer than %s: want %v", c.a, c.b, c.want)
+		}
+	}
+}
+
+func TestCheckReportsWithoutInstalling(t *testing.T) {
+	srv := fakeGitea(t, "v0.2.0", false, false)
+	for _, c := range []struct {
+		current string
+		newer   bool
+	}{{"v0.1.0", true}, {"v0.2.0", false}, {"v0.3.0", false}, {"dev", false}, {"v0.1.0-local", false}} {
+		cfg, exe, restarted := setup(t, srv, c.current)
+		tag, newer, err := Check(context.Background(), cfg)
+		if err != nil || tag != "v0.2.0" || newer != c.newer {
+			t.Errorf("%s: tag=%q newer=%v err=%v", c.current, tag, newer, err)
+		}
+		if b, _ := os.ReadFile(exe); string(b) != "OLD-BINARY" || *restarted != "" {
+			t.Errorf("%s: Check changed things", c.current)
+		}
+	}
+}
+
+func TestReportsProgressThroughTheWholeUpdate(t *testing.T) {
+	cfg, _, _ := setup(t, fakeGitea(t, "v0.2.0", false, false), "v0.1.0")
+	var events []Event
+	cfg.Progress = func(e Event) { events = append(events, e) }
+	if _, err := CheckOnce(context.Background(), cfg); err != nil {
+		t.Fatal(err)
+	}
+	var stages []string
+	last, lines := 0, ""
+	for _, e := range events {
+		if len(stages) == 0 || stages[len(stages)-1] != e.Stage {
+			stages = append(stages, e.Stage)
+		}
+		if e.Pct >= 0 {
+			if e.Pct < last {
+				t.Errorf("progress went backwards: %d after %d (%+v)", e.Pct, last, e)
+			}
+			last = e.Pct
+		}
+		lines += e.Line + "\n"
+	}
+	if got := strings.Join(stages, ","); got != "checking,downloading,verifying,installing,restarting" {
+		t.Errorf("stages: %s", got)
+	}
+	if last != 100 || !strings.Contains(lines, "v0.2.0 is available") || !strings.Contains(lines, "checksum matches") {
+		t.Errorf("progress ended at %d with log:\n%s", last, lines)
+	}
+}
+
+func TestProgressReportsFailureAndNothingToDo(t *testing.T) {
+	cfg, _, _ := setup(t, fakeGitea(t, "v0.2.0", false, true), "v0.1.0")
+	var last Event
+	cfg.Progress = func(e Event) { last = e }
+	if _, err := CheckOnce(context.Background(), cfg); err == nil || last.Stage != "failed" || !strings.Contains(last.Line, "checksum") {
+		t.Errorf("err=%v last=%+v", err, last)
+	}
+	cfg, _, _ = setup(t, fakeGitea(t, "v0.2.0", false, false), "v0.2.0")
+	cfg.Progress = func(e Event) { last = e }
+	if tag, err := CheckOnce(context.Background(), cfg); err != nil || tag != "" || last.Stage != "done" || last.Pct != 100 {
+		t.Errorf("tag=%q err=%v last=%+v", tag, err, last)
+	}
+}