pulse/internal/api/unified_agent.go

package api

import (
	"archive/tar"
	"archive/zip"
	"bytes"
	"compress/gzip"
	"context"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/rcourtman/pulse-go-rewrite/internal/updates"
	"github.com/rs/zerolog/log"
)

const (
	canonicalUnifiedAgentReportPath = "/api/agents/agent/report"
	legacyUnifiedAgentReportPath    = "/api/agents/host/report"
	defaultInstallScriptReleaseRepo = "rcourtman/Pulse"
	checksumHeaderName              = "X-Checksum-Sha256"
	signatureHeaderName             = "X-Signature-Ed25519"
	sshSignatureHeaderName          = "X-Signature-SSHSIG"
)

func installScriptReleaseRepo() string {
	repo := strings.TrimSpace(os.Getenv("PULSE_GITHUB_REPO"))
	if repo == "" {
		return defaultInstallScriptReleaseRepo
	}
	return repo
}

func githubReleaseAssetURL(tag, assetName string) string {
	return fmt.Sprintf("https://github.com/%s/releases/download/%s/%s", installScriptReleaseRepo(), strings.TrimSpace(tag), assetName)
}

func (r *Router) handleDownloadUnifiedInstallScript(w http.ResponseWriter, req *http.Request) {
	handleDownloadInstallScriptCommon(w, req, r.serverVersion, "/opt/pulse/scripts/install.sh", filepath.Join(r.projectRoot, "scripts", "install.sh"), "install.sh", "text/x-shellscript")
}

func (r *Router) handleDownloadUnifiedInstallScriptPS(w http.ResponseWriter, req *http.Request) {
	handleDownloadInstallScriptCommon(w, req, r.serverVersion, "/opt/pulse/scripts/install.ps1", filepath.Join(r.projectRoot, "scripts", "install.ps1"), "install.ps1", "text/plain")
}

// handleDownloadInstallScriptCommon serves the locally bundled AGENT installer
// (install.sh / install.ps1). It deliberately has no GitHub fallback: the agent
// installer is a per-build artifact bundled into every release tarball and Docker
// image, NOT a release asset. The top-level GitHub install.sh asset is the SERVER
// installer, so proxying it here would hand the agent wizard a script that rejects
// --url/--token-file (issue #1470). If the local script is genuinely missing the
// install is broken; fail closed rather than serving a wrong-identity script.
func handleDownloadInstallScriptCommon(w http.ResponseWriter, req *http.Request, serverVersion, prodPath, fallbackPath, scriptName, contentType string) {
	if req.Method != http.MethodGet && req.Method != http.MethodHead {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}

	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.Header().Set("Expires", "0")

	scriptPath := prodPath
	if _, err := os.Stat(scriptPath); os.IsNotExist(err) {
		scriptPath = fallbackPath
		if _, err := os.Stat(scriptPath); os.IsNotExist(err) {
			log.Error().Str("script", scriptName).Msg("Bundled install script not found; the Pulse install is incomplete")
			http.Error(w, "Install script unavailable: the bundled agent installer is missing from this Pulse install", http.StatusServiceUnavailable)
			return
		}
	}

	signature, sigErr := readReleaseAssetSignature(scriptPath)
	sshSignature, sshSigErr := readReleaseAssetSSHSignature(scriptPath)
	if (sigErr != nil || sshSigErr != nil) && isPublishedReleaseAssetVersion(serverVersion) {
		// The local agent installer is present but its detached signatures are not
		// (e.g. an install from before the installer deployed the sidecars). Serve
		// the local AGENT installer anyway; do NOT proxy the GitHub install.sh
		// release asset, which is the SERVER installer (rejects the wizard's
		// --url/--token-file). The served /install.sh endpoint must only ever hand
		// out the agent installer. Nothing on the agent install path verifies these
		// headers (the wizard is `curl ... | bash`), so omitting them is safe; new
		// installs ship the sidecars and are served signed. See issue #1470.
		log.Warn().Err(errors.Join(sigErr, sshSigErr)).Str("path", scriptPath).Msg("Serving local install script without release signatures; sidecars not deployed")
	}

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Disposition", "inline; filename=\""+scriptName+"\"")
	if signature != "" {
		w.Header().Set(signatureHeaderName, signature)
	}
	if sshSignature != "" {
		w.Header().Set(sshSignatureHeaderName, sshSignature)
	}
	http.ServeFile(w, req, scriptPath)
}

// normalizeUnifiedAgentArch normalizes architecture strings for the unified agent.
func normalizeUnifiedAgentArch(arch string) string {
	arch = strings.ToLower(strings.TrimSpace(arch))
	switch arch {
	case "linux-amd64", "amd64", "x86_64":
		return "linux-amd64"
	case "linux-arm64", "arm64", "aarch64":
		return "linux-arm64"
	case "linux-armv7", "armv7", "armv7l", "armhf":
		return "linux-armv7"
	case "linux-armv6", "armv6":
		return "linux-armv6"
	case "linux-386", "386", "i386", "i686":
		return "linux-386"
	case "darwin-amd64", "macos-amd64":
		return "darwin-amd64"
	case "darwin-arm64", "macos-arm64":
		return "darwin-arm64"
	case "freebsd-amd64":
		return "freebsd-amd64"
	case "freebsd-arm64":
		return "freebsd-arm64"
	case "windows-amd64":
		return "windows-amd64"
	case "windows-arm64":
		return "windows-arm64"
	case "windows-386":
		return "windows-386"
	default:
		return ""
	}
}

func unifiedAgentLocalBuildCommand(normalized string) string {
	goos, goarch, ok := strings.Cut(strings.TrimSpace(normalized), "-")
	if !ok || goos == "" || goarch == "" {
		goos = "linux"
		goarch = "amd64"
		normalized = "linux-amd64"
	}

	env := []string{"CGO_ENABLED=0", "GOOS=" + goos}
	switch goarch {
	case "armv7":
		env = append(env, "GOARCH=arm", "GOARM=7")
	case "armv6":
		env = append(env, "GOARCH=arm", "GOARM=6")
	default:
		env = append(env, "GOARCH="+goarch)
	}

	return fmt.Sprintf("%s go build -o bin/pulse-agent-%s ./cmd/pulse-agent", strings.Join(env, " "), normalized)
}

// handleDownloadUnifiedAgent serves the pulse-agent binary
func (r *Router) handleDownloadUnifiedAgent(w http.ResponseWriter, req *http.Request) {
	if req.Method != http.MethodGet && req.Method != http.MethodHead {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}

	// Prevent caching - always serve the latest version
	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.Header().Set("Expires", "0")

	archParam := strings.TrimSpace(req.URL.Query().Get("arch"))

	// Validate architecture if provided
	if archParam != "" && normalizeUnifiedAgentArch(archParam) == "" {
		http.Error(w, "Invalid architecture specified", http.StatusBadRequest)
		return
	}

	searchPaths := make([]string, 0, 6)

	// If a specific architecture is requested, only look for that architecture
	// Do NOT fall back to generic binary - that could serve the wrong architecture
	normalized := normalizeUnifiedAgentArch(archParam)
	if normalized != "" {
		searchPaths = append(searchPaths,
			filepath.Join(pulseBinDir(), "pulse-agent-"+normalized),
			filepath.Join("/opt/pulse", "pulse-agent-"+normalized),
			filepath.Join("/app", "pulse-agent-"+normalized),
			filepath.Join(r.projectRoot, "bin", "pulse-agent-"+normalized),
		)
	} else {
		// No specific architecture requested - allow fallback to generic binary
		searchPaths = append(searchPaths,
			filepath.Join(pulseBinDir(), "pulse-agent"),
			"/opt/pulse/pulse-agent",
			filepath.Join("/app", "pulse-agent"),
			filepath.Join(r.projectRoot, "bin", "pulse-agent"),
		)
	}

	expectedAgentVersion := expectedAgentBinaryVersion(r.resolveAgentBinaryVersionSource())
	invalidCandidates := make([]string, 0, len(searchPaths))

	for _, candidate := range searchPaths {
		if candidate == "" {
			continue
		}

		info, err := os.Stat(candidate)
		if err != nil || info.IsDir() {
			continue
		}

		if err := validateUnifiedAgentBinary(candidate, expectedAgentVersion); err != nil {
			log.Warn().Err(err).Str("path", candidate).Msg("Skipping incompatible local unified agent binary")
			invalidCandidates = append(invalidCandidates, fmt.Sprintf("%s (%v)", candidate, err))
			continue
		}

		checksum, err := r.cachedSHA256(candidate, info)
		if err != nil {
			log.Error().Err(err).Str("path", candidate).Msg("Failed to compute unified agent checksum")
			continue
		}

		file, err := os.Open(candidate)
		if err != nil {
			log.Error().Err(err).Str("path", candidate).Msg("Failed to open unified agent binary for download")
			continue
		}
		defer file.Close()

		signature, sigErr := readReleaseAssetSignature(candidate)
		sshSignature, sshSigErr := readReleaseAssetSSHSignature(candidate)
		if (sigErr != nil || sshSigErr != nil) && isPublishedReleaseAssetVersion(r.serverVersion) {
			log.Warn().Err(errors.Join(sigErr, sshSigErr)).Str("path", candidate).Msg("Skipping unsigned local unified agent binary")
			invalidCandidates = append(invalidCandidates, fmt.Sprintf("%s (%v)", candidate, errors.Join(sigErr, sshSigErr)))
			continue
		}

		w.Header().Set(checksumHeaderName, checksum)
		if signature != "" {
			w.Header().Set(signatureHeaderName, signature)
		}
		if sshSignature != "" {
			w.Header().Set(sshSignatureHeaderName, sshSignature)
		}
		http.ServeContent(w, req, filepath.Base(candidate), info.ModTime(), file)
		return
	}

	if len(invalidCandidates) > 0 {
		log.Warn().Strs("paths", invalidCandidates).Msg("Ignoring stale local unified agent binaries")
	}

	// Fallback: proxy from GitHub releases for the binary
	// This handles LXC/barebone installations that don't have agent binaries locally.
	// We proxy instead of redirecting because agents require the X-Checksum-Sha256 header,
	// which GitHub doesn't provide.
	if normalized != "" {
		// Outside published release builds, never fall through to GitHub releases —
		// that would silently fetch the wrong channel. Return a clear 404 with build
		// instructions instead.
		if !isPublishedReleaseAssetVersion(r.serverVersion) {
			reason := fmt.Sprintf("Agent binary not found for %q in dev mode.", normalized)
			if len(invalidCandidates) > 0 {
				reason = fmt.Sprintf("Local agent binary for %q is stale or incompatible in dev mode:\n  %s",
					normalized,
					strings.Join(invalidCandidates, "\n  "),
				)
			}
			http.Error(w, reason+"\nBuild with:\n  "+unifiedAgentLocalBuildCommand(normalized), http.StatusNotFound)
			return
		}
		r.proxyAgentBinaryFromGitHub(w, req, normalized)
		return
	}

	// No architecture specified and no local binary - can't redirect without knowing arch
	if len(invalidCandidates) > 0 {
		http.Error(w, "Local agent binary is stale or incompatible. Specify ?arch=linux-amd64 (or your architecture) after rebuilding the local agent artifact.", http.StatusNotFound)
		return
	}
	http.Error(w, "Agent binary not found. Specify ?arch=linux-amd64 (or your architecture)", http.StatusNotFound)
}

// validateUnifiedAgentBinary rejects a local agent binary that this server must
// not hand out. The endpoint checks catch a binary built against a superseded
// report contract; the version check catches one that is merely old.
//
// Staleness is not cosmetic. The installer generates its wrapper from this
// server's current template, so a binary predating a flag that template now
// passes fails to start and crash-loops under the watchdog. `bin/` is a
// gitignored build output that nothing refreshes on its own, so it goes stale
// silently. Refusing here turns that into a loud failure at the point of
// download: a dev server answers 404 with the build command, and a published
// release falls through to the GitHub proxy and fetches the correct version.
func validateUnifiedAgentBinary(path string, expectedVersion string) error {
	file, err := os.Open(path)
	if err != nil {
		return fmt.Errorf("open binary: %w", err)
	}
	defer file.Close()

	hasCanonical, hasLegacy, hasVersion, err := scanUnifiedAgentBinaryContract(file, expectedVersion)
	if err != nil {
		return fmt.Errorf("scan binary contract: %w", err)
	}
	if hasLegacy {
		return fmt.Errorf("references deprecated host endpoint %s", legacyUnifiedAgentReportPath)
	}
	if !hasCanonical {
		return fmt.Errorf("missing canonical host endpoint %s", canonicalUnifiedAgentReportPath)
	}
	if !hasVersion {
		return fmt.Errorf("stale build: does not carry this server's agent version %s", expectedVersion)
	}
	return nil
}

// resolveAgentBinaryVersionSource picks the version this server should expect
// its agent binaries to carry.
//
// It deliberately prefers updates.GetCurrentVersion over the compiled-in
// serverVersion. A development server is exactly where agent binaries go stale,
// and there the compiled-in value is a placeholder ("dev", "dev-pro") that no
// version parser accepts, which would silently disable the freshness check on
// the only builds that need it. GetCurrentVersion resolves the VERSION file,
// the same source `make build-agents` stamps into the agent, so dev and release
// builds compare against one identity. IsDevelopment is intentionally not
// consulted: a dev build still knows which agent it expects.
func (r *Router) resolveAgentBinaryVersionSource() string {
	if versionInfo, err := updates.GetCurrentVersion(); err == nil && versionInfo != nil {
		if resolved := strings.TrimSpace(versionInfo.Version); resolved != "" {
			return resolved
		}
	}
	return r.serverVersion
}

// expectedAgentBinaryVersion reduces a server version to the release-identity
// string that `make build-agents` stamps into the agent through
// -X main.Version, i.e. "v6.2.0-rc.8" for a server reporting
// "6.2.0-rc.8+git.44.gdd72bd149.dirty". Build metadata is dropped because it
// records how the server itself was built and never appears in the agent.
// Returns "" when the version cannot be parsed, which disables the freshness
// check rather than rejecting every candidate.
func expectedAgentBinaryVersion(rawVersion string) string {
	rawVersion = strings.TrimSpace(rawVersion)
	if rawVersion == "" || strings.EqualFold(rawVersion, "dev") {
		return ""
	}
	version, err := updates.ParseVersion(rawVersion)
	if err != nil {
		return ""
	}
	identity := fmt.Sprintf("v%d.%d.%d", version.Major, version.Minor, version.Patch)
	if prerelease := strings.TrimSpace(version.Prerelease); prerelease != "" {
		identity += "-" + prerelease
	}
	return identity
}

func scanUnifiedAgentBinaryContract(r io.Reader, versionNeedle string) (hasCanonical bool, hasLegacy bool, hasVersion bool, err error) {
	canonicalNeedle := []byte(canonicalUnifiedAgentReportPath)
	legacyNeedle := []byte(legacyUnifiedAgentReportPath)
	versionBytes := []byte(versionNeedle)
	// An empty needle would match everything, so treat "no expected version"
	// as "already satisfied" and skip the comparison entirely.
	hasVersion = len(versionBytes) == 0
	maxNeedleLen := len(canonicalNeedle)
	if len(legacyNeedle) > maxNeedleLen {
		maxNeedleLen = len(legacyNeedle)
	}
	if len(versionBytes) > maxNeedleLen {
		maxNeedleLen = len(versionBytes)
	}
	overlap := maxNeedleLen - 1
	if overlap < 0 {
		overlap = 0
	}

	buf := make([]byte, 64*1024)
	window := make([]byte, 0, len(buf)+overlap)
	for {
		n, readErr := r.Read(buf)
		if n > 0 {
			window = append(window, buf[:n]...)
			if bytes.Contains(window, canonicalNeedle) {
				hasCanonical = true
			}
			if bytes.Contains(window, legacyNeedle) {
				hasLegacy = true
			}
			if !hasVersion && bytes.Contains(window, versionBytes) {
				hasVersion = true
			}
			if hasCanonical && hasLegacy && hasVersion {
				return true, true, true, nil
			}
			if len(window) > overlap {
				window = append(window[:0], window[len(window)-overlap:]...)
			}
		}
		if readErr == io.EOF {
			break
		}
		if readErr != nil {
			return false, false, false, readErr
		}
	}
	return hasCanonical, hasLegacy, hasVersion, nil
}

// proxyAgentBinaryFromGitHub downloads an agent binary from GitHub releases and serves
// it to the requesting agent with the X-Checksum-Sha256 header. This is used when the
// binary isn't available locally (e.g., LXC/bare-metal installations updated via web UI).
// We must proxy instead of redirecting because the agent requires the checksum header
// for security verification, and GitHub doesn't provide it.
func (r *Router) proxyAgentBinaryFromGitHub(w http.ResponseWriter, req *http.Request, normalized string) {
	githubURL, err := r.agentBinaryReleaseAssetURL(normalized)
	if err != nil {
		log.Error().Err(err).Str("server_version", strings.TrimSpace(r.serverVersion)).Str("arch", normalized).Msg("Agent binary fallback unavailable for current server build")
		http.Error(w, "Agent binary unavailable for current server build", http.StatusServiceUnavailable)
		return
	}
	signatureURL := githubURL + ".sig"
	sshSignatureURL := githubURL + ".sshsig"

	log.Info().Str("arch", normalized).Str("url", githubURL).Msg("Local agent binary not found, proxying from GitHub releases")

	client := r.installScriptClient
	if client == nil {
		client = &http.Client{
			Timeout: 5 * time.Minute,
		}
	}

	resp, err := client.Get(githubURL)
	if err != nil {
		log.Error().Err(err).Str("url", githubURL).Msg("Failed to fetch agent binary from GitHub")
		http.Error(w, "Failed to fetch agent binary", http.StatusServiceUnavailable)
		return
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusOK {
		content, checksum, readErr := readBinaryWithChecksum(resp.Body)
		if readErr != nil {
			log.Error().Err(readErr).Msg("Failed to read agent binary from GitHub")
			http.Error(w, "Failed to read agent binary", http.StatusInternalServerError)
			return
		}
		signature, sigErr := fetchReleaseAssetContent(req.Context(), client, signatureURL, 16*1024)
		if sigErr != nil {
			log.Error().Err(sigErr).Str("url", signatureURL).Msg("Failed to fetch agent binary signature from GitHub")
			http.Error(w, "Failed to fetch agent binary signature", http.StatusServiceUnavailable)
			return
		}
		sshSignature, sshSigErr := fetchReleaseAssetContent(req.Context(), client, sshSignatureURL, 64*1024)
		if sshSigErr != nil {
			log.Error().Err(sshSigErr).Str("url", sshSignatureURL).Msg("Failed to fetch agent binary SSH signature from GitHub")
			http.Error(w, "Failed to fetch agent binary SSH signature", http.StatusServiceUnavailable)
			return
		}
		serveProxiedAgentBinaryWithSignatures(w, content, checksum, strings.TrimSpace(string(signature)), encodeSSHSignatureForHeader(sshSignature), "github-proxy")
		return
	}

	if resp.StatusCode != http.StatusNotFound {
		log.Error().Int("status", resp.StatusCode).Str("url", githubURL).Msg("GitHub returned non-200 status for agent binary")
		http.Error(w, "Agent binary not found on GitHub", http.StatusNotFound)
		return
	}

	archiveContent, checksum, archiveErr := r.fetchAgentBinaryFromReleaseArchive(client, normalized)
	if archiveErr != nil {
		log.Error().Err(archiveErr).Str("arch", normalized).Msg("Failed archive fallback for agent binary")
		http.Error(w, "Agent binary not found on GitHub", http.StatusNotFound)
		return
	}
	signature, sigErr := fetchReleaseAssetContent(req.Context(), client, signatureURL, 16*1024)
	if sigErr != nil {
		log.Error().Err(sigErr).Str("url", signatureURL).Msg("Failed to fetch agent binary signature from GitHub")
		http.Error(w, "Failed to fetch agent binary signature", http.StatusServiceUnavailable)
		return
	}
	sshSignature, sshSigErr := fetchReleaseAssetContent(req.Context(), client, sshSignatureURL, 64*1024)
	if sshSigErr != nil {
		log.Error().Err(sshSigErr).Str("url", sshSignatureURL).Msg("Failed to fetch agent binary SSH signature from GitHub")
		http.Error(w, "Failed to fetch agent binary SSH signature", http.StatusServiceUnavailable)
		return
	}
	serveProxiedAgentBinaryWithSignatures(w, archiveContent, checksum, strings.TrimSpace(string(signature)), encodeSSHSignatureForHeader(sshSignature), "github-proxy-archive")
}

const maxAgentBinarySize = 100 * 1024 * 1024

func readBinaryWithChecksum(body io.Reader) ([]byte, string, error) {
	limitedReader := io.LimitReader(body, maxAgentBinarySize+1)
	hasher := sha256.New()
	content, err := io.ReadAll(io.TeeReader(limitedReader, hasher))
	if err != nil {
		return nil, "", err
	}
	if int64(len(content)) > maxAgentBinarySize {
		return nil, "", fmt.Errorf("binary exceeds size limit")
	}
	return content, hex.EncodeToString(hasher.Sum(nil)), nil
}

func serveProxiedAgentBinaryWithSignatures(w http.ResponseWriter, content []byte, checksum, signature, sshSignature, servedFrom string) {
	w.Header().Set(checksumHeaderName, checksum)
	if strings.TrimSpace(signature) != "" {
		w.Header().Set(signatureHeaderName, strings.TrimSpace(signature))
	}
	if strings.TrimSpace(sshSignature) != "" {
		w.Header().Set(sshSignatureHeaderName, strings.TrimSpace(sshSignature))
	}
	w.Header().Set("X-Served-From", servedFrom)
	w.Header().Set("Content-Type", "application/octet-stream")
	w.Write(content)
}

func (r *Router) fetchAgentBinaryFromReleaseArchive(client *http.Client, normalized string) ([]byte, string, error) {
	tag, err := r.releaseAssetTag()
	if err != nil {
		return nil, "", err
	}
	version := strings.TrimPrefix(tag, "v")

	archiveName := fmt.Sprintf("pulse-agent-v%s-%s.tar.gz", version, normalized)
	entryName := "pulse-agent-" + normalized
	isWindows := strings.HasPrefix(normalized, "windows-")
	if isWindows {
		archiveName = fmt.Sprintf("pulse-agent-v%s-%s.zip", version, normalized)
		entryName += ".exe"
	}

	archiveURL := githubReleaseAssetURL(tag, archiveName)
	resp, err := client.Get(archiveURL)
	if err != nil {
		return nil, "", fmt.Errorf("failed to fetch release archive: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, "", fmt.Errorf("release archive returned status %d", resp.StatusCode)
	}

	archiveReader := io.LimitReader(resp.Body, maxAgentBinarySize+1)
	archiveBytes, err := io.ReadAll(archiveReader)
	if err != nil {
		return nil, "", fmt.Errorf("failed reading release archive: %w", err)
	}
	if int64(len(archiveBytes)) > maxAgentBinarySize {
		return nil, "", fmt.Errorf("release archive exceeded size limit")
	}

	var binary []byte
	if isWindows {
		binary, err = extractFromZip(archiveBytes, entryName)
	} else {
		binary, err = extractFromTarGz(archiveBytes, entryName)
	}
	if err != nil {
		return nil, "", err
	}
	if int64(len(binary)) > maxAgentBinarySize {
		return nil, "", fmt.Errorf("extracted binary exceeded size limit")
	}
	sum := sha256.Sum256(binary)
	return binary, hex.EncodeToString(sum[:]), nil
}

func isPublishedReleaseAssetVersion(rawVersion string) bool {
	rawVersion = strings.TrimSpace(rawVersion)
	if rawVersion == "" || strings.EqualFold(rawVersion, "dev") {
		return false
	}
	version, err := updates.ParseVersion(rawVersion)
	if err != nil {
		return false
	}
	return version.IsPublishedReleaseAssetVersion()
}

func readReleaseAssetSignature(path string) (string, error) {
	signaturePath := path + ".sig"
	data, err := os.ReadFile(signaturePath)
	if err != nil {
		return "", fmt.Errorf("read release signature %s: %w", signaturePath, err)
	}
	signature := strings.TrimSpace(string(data))
	if signature == "" {
		return "", fmt.Errorf("release signature %s is empty", signaturePath)
	}
	return signature, nil
}

func readReleaseAssetSSHSignature(path string) (string, error) {
	signaturePath := path + ".sshsig"
	data, err := os.ReadFile(signaturePath)
	if err != nil {
		return "", fmt.Errorf("read release ssh signature %s: %w", signaturePath, err)
	}
	if len(bytes.TrimSpace(data)) == 0 {
		return "", fmt.Errorf("release ssh signature %s is empty", signaturePath)
	}
	return encodeSSHSignatureForHeader(data), nil
}

func encodeSSHSignatureForHeader(data []byte) string {
	return base64.StdEncoding.EncodeToString(data)
}

func fetchReleaseAssetContent(ctx context.Context, client *http.Client, url string, limit int64) ([]byte, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, fmt.Errorf("create release asset request: %w", err)
	}
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("release asset returned status %d", resp.StatusCode)
	}
	content, err := io.ReadAll(io.LimitReader(resp.Body, limit+1))
	if err != nil {
		return nil, err
	}
	if int64(len(content)) > limit {
		return nil, fmt.Errorf("release asset exceeded size limit")
	}
	return content, nil
}

func extractFromTarGz(archive []byte, entryName string) ([]byte, error) {
	gzReader, err := gzip.NewReader(bytes.NewReader(archive))
	if err != nil {
		return nil, fmt.Errorf("failed to open tar.gz: %w", err)
	}
	defer gzReader.Close()

	tr := tar.NewReader(gzReader)
	for {
		header, err := tr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("failed reading tar entry: %w", err)
		}
		if filepath.Base(header.Name) != entryName {
			continue
		}
		content, err := io.ReadAll(io.LimitReader(tr, maxAgentBinarySize+1))
		if err != nil {
			return nil, fmt.Errorf("failed reading binary from tar.gz: %w", err)
		}
		if int64(len(content)) > maxAgentBinarySize {
			return nil, fmt.Errorf("binary from tar.gz exceeded size limit")
		}
		return content, nil
	}
	return nil, fmt.Errorf("binary %q not found in tar.gz", entryName)
}

func extractFromZip(archive []byte, entryName string) ([]byte, error) {
	zr, err := zip.NewReader(bytes.NewReader(archive), int64(len(archive)))
	if err != nil {
		return nil, fmt.Errorf("failed to open zip: %w", err)
	}
	for _, file := range zr.File {
		if filepath.Base(file.Name) != entryName {
			continue
		}
		rc, err := file.Open()
		if err != nil {
			return nil, fmt.Errorf("failed opening binary in zip: %w", err)
		}
		content, readErr := io.ReadAll(io.LimitReader(rc, maxAgentBinarySize+1))
		rc.Close()
		if readErr != nil {
			return nil, fmt.Errorf("failed reading binary from zip: %w", readErr)
		}
		if int64(len(content)) > maxAgentBinarySize {
			return nil, fmt.Errorf("binary from zip exceeded size limit")
		}
		return content, nil
	}
	return nil, fmt.Errorf("binary %q not found in zip", entryName)
}

func (r *Router) releaseAssetTag() (string, error) {
	rawVersion := strings.TrimSpace(r.serverVersion)
	if rawVersion == "" {
		return "", fmt.Errorf("server version is unavailable")
	}
	if strings.EqualFold(rawVersion, "dev") {
		return "", fmt.Errorf("development builds must serve local assets")
	}

	version, err := updates.ParseVersion(rawVersion)
	if err != nil {
		return "", fmt.Errorf("server version %q is not a published release version", rawVersion)
	}
	if !version.IsPublishedReleaseAssetVersion() {
		return "", fmt.Errorf("server version %q is not a published release asset version", rawVersion)
	}

	return "v" + version.String(), nil
}

func (r *Router) releaseAssetURL(assetName string) (string, error) {
	tag, err := r.releaseAssetTag()
	if err != nil {
		return "", err
	}
	return githubReleaseAssetURL(tag, assetName), nil
}

func (r *Router) agentBinaryReleaseAssetURL(normalized string) (string, error) {
	binaryName := "pulse-agent-" + normalized
	if strings.HasPrefix(normalized, "windows-") {
		binaryName += ".exe"
	}
	return r.releaseAssetURL(binaryName)
}