coder · deansheather · Jan 17, 2023 · Jan 17, 2023 · Jan 17, 2023 · Jan 17, 2023
diff --git a/coderd/coderd.go b/coderd/coderd.go
@@ -197,7 +197,7 @@ func New(options *Options) *API {
 	if siteCacheDir != "" {
 		siteCacheDir = filepath.Join(siteCacheDir, "site")
 	}
-	binFS, err := site.ExtractOrReadBinFS(siteCacheDir, site.FS())
+	binFS, binHashes, err := site.ExtractOrReadBinFS(siteCacheDir, site.FS())
 	if err != nil {
 		panic(xerrors.Errorf("read site bin failed: %w", err))
 	}
@@ -213,7 +213,7 @@ func New(options *Options) *API {
 		ID:          uuid.New(),
 		Options:     options,
 		RootHandler: r,
-		siteHandler: site.Handler(site.FS(), binFS),
+		siteHandler: site.Handler(site.FS(), binFS, binHashes),
 		HTTPAuth: &HTTPAuthorizer{
 			Authorizer: options.Authorizer,
 			Logger:     options.Logger,

diff --git a/site/site.go b/site/site.go
@@ -16,6 +16,7 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+	"sync"
 	"text/template" // html/template escapes some nonces
 	"time"
 
@@ -24,6 +25,7 @@ import (
 	"github.com/unrolled/secure"
 	"golang.org/x/exp/slices"
 	"golang.org/x/sync/errgroup"
+	"golang.org/x/sync/singleflight"
 	"golang.org/x/xerrors"
 
 	"github.com/coder/coder/coderd/httpapi"
@@ -48,7 +50,7 @@ func init() {
 }
 
 // Handler returns an HTTP handler for serving the static site.
-func Handler(siteFS fs.FS, binFS http.FileSystem) http.Handler {
+func Handler(siteFS fs.FS, binFS http.FileSystem, binHashes map[string]string) http.Handler {
 	// html files are handled by a text/template. Non-html files
 	// are served by the default file server.
 	//
@@ -59,13 +61,36 @@ func Handler(siteFS fs.FS, binFS http.FileSystem) http.Handler {
 		panic(xerrors.Errorf("Failed to return handler for static files. Html files failed to load: %w", err))
 	}
 
+	binHashCache := newBinHashCache(binFS, binHashes)
+
 	mux := http.NewServeMux()
 	mux.Handle("/bin/", http.StripPrefix("/bin", http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 		// Convert underscores in the filename to hyphens. We eventually want to
 		// change our hyphen-based filenames to underscores, but we need to
 		// support both for now.
 		r.URL.Path = strings.ReplaceAll(r.URL.Path, "_", "-")
 
+		// Set ETag header to the SHA1 hash of the file contents.
+		name := filePath(r.URL.Path)
+		if name == "" || strings.Contains(name, "/") {
+			http.NotFound(rw, r)
+			return
+		}
+		hash, err := binHashCache.getHash(name)
+		if xerrors.Is(err, os.ErrNotExist) {
+			http.NotFound(rw, r)
+			return
+		}
+		if err != nil {
+			http.Error(rw, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// ETag header needs to be quoted.
+		rw.Header().Set("ETag", fmt.Sprintf(`%q`, hash))
+
+		// http.FileServer will see the ETag header and automatically handle
+		// If-Match and If-None-Match headers on the request properly.
 		http.FileServer(binFS).ServeHTTP(rw, r)
 	})))
 	mux.Handle("/", http.FileServer(http.FS(siteFS))) // All other non-html static files.
@@ -409,20 +434,23 @@ func htmlFiles(files fs.FS) (*htmlTemplates, error) {
 	}, nil
 }
 
-// ExtractOrReadBinFS checks the provided fs for compressed coder
-// binaries and extracts them into dest/bin if found. As a fallback,
-// the provided FS is checked for a /bin directory, if it is non-empty
-// it is returned. Finally dest/bin is returned as a fallback allowing
-// binaries to be manually placed in dest (usually
-// ${CODER_CACHE_DIRECTORY}/site/bin).
-func ExtractOrReadBinFS(dest string, siteFS fs.FS) (http.FileSystem, error) {
+// ExtractOrReadBinFS checks the provided fs for compressed coder binaries and
+// extracts them into dest/bin if found. As a fallback, the provided FS is
+// checked for a /bin directory, if it is non-empty it is returned. Finally
+// dest/bin is returned as a fallback allowing binaries to be manually placed in
+// dest (usually ${CODER_CACHE_DIRECTORY}/site/bin).
+//
+// Returns a http.FileSystem that serves unpacked binaries, and a map of binary
+// name to SHA1 hash. The returned hash map may be incomplete or contain hashes
+// for missing files.
+func ExtractOrReadBinFS(dest string, siteFS fs.FS) (http.FileSystem, map[string]string, error) {
 	if dest == "" {
 		// No destination on fs, embedded fs is the only option.
 		binFS, err := fs.Sub(siteFS, "bin")
 		if err != nil {
-			return nil, xerrors.Errorf("cache path is empty and embedded fs does not have /bin: %w", err)
+			return nil, nil, xerrors.Errorf("cache path is empty and embedded fs does not have /bin: %w", err)
 		}
-		return http.FS(binFS), nil
+		return http.FS(binFS), nil, nil
 	}
 
 	dest = filepath.Join(dest, "bin")
@@ -440,51 +468,63 @@ func ExtractOrReadBinFS(dest string, siteFS fs.FS) (http.FileSystem, error) {
 			files, err := fs.ReadDir(siteFS, "bin")
 			if err != nil {
 				if xerrors.Is(err, fs.ErrNotExist) {
-					// Given fs does not have a bin directory,
-					// serve from cache directory.
-					return mkdest()
+					// Given fs does not have a bin directory, serve from cache
+					// directory without extracting anything.
+					binFS, err := mkdest()
+					if err != nil {
+						return nil, nil, xerrors.Errorf("mkdest failed: %w", err)
+					}
+					return binFS, map[string]string{}, nil
 				}
-				return nil, xerrors.Errorf("site fs read dir failed: %w", err)
+				return nil, nil, xerrors.Errorf("site fs read dir failed: %w", err)
 			}
 
 			if len(filterFiles(files, "GITKEEP")) > 0 {
-				// If there are other files than bin/GITKEEP,
-				// serve the files.
+				// If there are other files than bin/GITKEEP, serve the files.
 				binFS, err := fs.Sub(siteFS, "bin")
 				if err != nil {
-					return nil, xerrors.Errorf("site fs sub dir failed: %w", err)
+					return nil, nil, xerrors.Errorf("site fs sub dir failed: %w", err)
 				}
-				return http.FS(binFS), nil
+				return http.FS(binFS), nil, nil
 			}
 
-			// Nothing we can do, serve the cache directory,
-			// thus allowing binaries to be places there.
-			return mkdest()
+			// Nothing we can do, serve the cache directory, thus allowing
+			// binaries to be places there.
+			binFS, err := mkdest()
+			if err != nil {
+				return nil, nil, xerrors.Errorf("mkdest failed: %w", err)
+			}
+			return binFS, map[string]string{}, nil
 		}
-		return nil, xerrors.Errorf("open coder binary archive failed: %w", err)
+		return nil, nil, xerrors.Errorf("open coder binary archive failed: %w", err)
 	}
 	defer archive.Close()
 
-	dir, err := mkdest()
+	binFS, err := mkdest()
 	if err != nil {
-		return nil, err
+		return nil, nil, err
+	}
+
+	shaFiles, err := parseSHA1(siteFS)
+	if err != nil {
+		return nil, nil, xerrors.Errorf("parse sha1 file failed: %w", err)
 	}
 
-	ok, err := verifyBinSha1IsCurrent(dest, siteFS)
+	ok, err := verifyBinSha1IsCurrent(dest, siteFS, shaFiles)
 	if err != nil {
-		return nil, xerrors.Errorf("verify coder binaries sha1 failed: %w", err)
+		return nil, nil, xerrors.Errorf("verify coder binaries sha1 failed: %w", err)
 	}
 	if !ok {
 		n, err := extractBin(dest, archive)
 		if err != nil {
-			return nil, xerrors.Errorf("extract coder binaries failed: %w", err)
+			return nil, nil, xerrors.Errorf("extract coder binaries failed: %w", err)
 		}
 		if n == 0 {
-			return nil, xerrors.New("no files were extracted from coder binaries archive")
+			return nil, nil, xerrors.New("no files were extracted from coder binaries archive")
 		}
 	}
 
-	return dir, nil
+	return binFS, shaFiles, nil
 }
 
 func filterFiles(files []fs.DirEntry, names ...string) []fs.DirEntry {
@@ -501,24 +541,32 @@ func filterFiles(files []fs.DirEntry, names ...string) []fs.DirEntry {
 // errHashMismatch is a sentinel error used in verifyBinSha1IsCurrent.
 var errHashMismatch = xerrors.New("hash mismatch")
 
-func verifyBinSha1IsCurrent(dest string, siteFS fs.FS) (ok bool, err error) {
-	b1, err := fs.ReadFile(siteFS, "bin/coder.sha1")
+func parseSHA1(siteFS fs.FS) (map[string]string, error) {
+	b, err := fs.ReadFile(siteFS, "bin/coder.sha1")
 	if err != nil {
-		return false, xerrors.Errorf("read coder sha1 from embedded fs failed: %w", err)
+		return nil, xerrors.Errorf("read coder sha1 from embedded fs failed: %w", err)
 	}
-	// Parse sha1 file.
-	shaFiles := make(map[string][]byte)
-	for _, line := range bytes.Split(bytes.TrimSpace(b1), []byte{'\n'}) {
+
+	shaFiles := make(map[string]string)
+	for _, line := range bytes.Split(bytes.TrimSpace(b), []byte{'\n'}) {
 		parts := bytes.Split(line, []byte{' ', '*'})
 		if len(parts) != 2 {
-			return false, xerrors.Errorf("malformed sha1 file: %w", err)
+			return nil, xerrors.Errorf("malformed sha1 file: %w", err)
 		}
-		shaFiles[string(parts[1])] = parts[0]
+		shaFiles[string(parts[1])] = strings.ToLower(string(parts[0]))
 	}
 	if len(shaFiles) == 0 {
-		return false, xerrors.Errorf("empty sha1 file: %w", err)
+		return nil, xerrors.Errorf("empty sha1 file: %w", err)
 	}
 
+	return shaFiles, nil
+}
+
+func verifyBinSha1IsCurrent(dest string, siteFS fs.FS, shaFiles map[string]string) (ok bool, err error) {
+	b1, err := fs.ReadFile(siteFS, "bin/coder.sha1")
+	if err != nil {
+		return false, xerrors.Errorf("read coder sha1 from embedded fs failed: %w", err)
+	}
 	b2, err := os.ReadFile(filepath.Join(dest, "coder.sha1"))
 	if err != nil {
 		if xerrors.Is(err, fs.ErrNotExist) {
@@ -551,7 +599,7 @@ func verifyBinSha1IsCurrent(dest string, siteFS fs.FS) (ok bool, err error) {
 				}
 				return xerrors.Errorf("hash file failed: %w", err)
 			}
-			if !bytes.Equal(hash1, hash2) {
+			if !strings.EqualFold(hash1, hash2) {
 				return errHashMismatch
 			}
 			return nil
@@ -570,24 +618,24 @@ func verifyBinSha1IsCurrent(dest string, siteFS fs.FS) (ok bool, err error) {
 
 // sha1HashFile computes a SHA1 hash of the file, returning the hex
 // representation.
-func sha1HashFile(name string) ([]byte, error) {
+func sha1HashFile(name string) (string, error) {
 	//#nosec // Not used for cryptography.
 	hash := sha1.New()
 	f, err := os.Open(name)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 	defer f.Close()
 
 	_, err = io.Copy(hash, f)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
 	b := make([]byte, hash.Size())
 	hash.Sum(b[:0])
 
-	return []byte(hex.EncodeToString(b)), nil
+	return hex.EncodeToString(b), nil
 }
 
 func extractBin(dest string, r io.Reader) (numExtracted int, err error) {
@@ -672,3 +720,67 @@ func RenderStaticErrorPage(rw http.ResponseWriter, r *http.Request, data ErrorPa
 		return
 	}
 }
+
+type binHashCache struct {
+	binFS http.FileSystem
+
+	hashes map[string]string
+	mut    *sync.RWMutex
+	sf     *singleflight.Group
+	sem    chan struct{}
+}
+
+func newBinHashCache(binFS http.FileSystem, binHashes map[string]string) *binHashCache {
+	b := &binHashCache{
+		binFS:  binFS,
+		hashes: make(map[string]string, len(binHashes)),
+		mut:    &sync.RWMutex{},
+		sf:     &singleflight.Group{},
+		sem:    make(chan struct{}, 4),
+	}
+	// Make a copy since we're gonna be mutating it.
+	for k, v := range binHashes {
+		b.hashes[k] = v
+	}
+
+	return b
+}
+
+func (b *binHashCache) getHash(name string) (string, error) {
+	b.mut.RLock()
+	hash, ok := b.hashes[name]
+	b.mut.RUnlock()
+	if ok {
+		return hash, nil
+	}
+
+	// Avoid DOS by using a pool, and only doing work once per file.
+	v, err, _ := b.sf.Do(name, func() (interface{}, error) {
+		b.sem <- struct{}{}
+		defer func() { <-b.sem }()
+
+		f, err := b.binFS.Open(name)
+		if err != nil {
+			return "", err
+		}
+		defer f.Close()
+
+		h := sha1.New() //#nosec // Not used for cryptography.
+		_, err = io.Copy(h, f)
+		if err != nil {
+			return "", err
+		}
+
+		hash := hex.EncodeToString(h.Sum(nil))
+		b.mut.Lock()
+		b.hashes[name] = hash
+		b.mut.Unlock()
+		return hash, nil
+	})
+	if err != nil {
+		return "", err
+	}
+
+	//nolint:forcetypeassert
+	return strings.ToLower(v.(string)), nil
+}