Implement HTTP early hint support for static files

internal/app/load_config.go → internal/app/setup.go

@@ -305,6 +305,27 @@ func getRequestUrl(r *http.Request) string {
 	}
 }
 
+func (a *App) earlyHints(w http.ResponseWriter, r *http.Request) {
+	sendHint := false
+	a.Info().Msgf("Sending early hints for %s", a.sourceFS.StaticFiles())
+	for _, f := range a.sourceFS.StaticFiles() {
+		if strings.HasSuffix(f, ".css") {
+			sendHint = true
+			w.Header().Add("Link", fmt.Sprintf("<%s>; rel=preload; as=style",
+				path.Join(a.Path, a.sourceFS.HashName(f))))
+		} else if strings.HasSuffix(f, ".js") {
+			sendHint = true
+			w.Header().Add("Link", fmt.Sprintf("<%s>; rel=preload; as=script",
+				path.Join(a.Path, a.sourceFS.HashName(f))))
+		}
+	}
+
+	if sendHint {
+		a.Trace().Msg("Sending early hints for static files")
+		w.WriteHeader(http.StatusEarlyHints)
+	}
+}
+
 func (a *App) createHandlerFunc(html, block string, handler starlark.Callable, rtype string) http.HandlerFunc {
 	goHandler := func(w http.ResponseWriter, r *http.Request) {
 		thread := &starlark.Thread{
@@ -313,6 +334,13 @@ func (a *App) createHandlerFunc(html, block string, handler starlark.Callable, r
 		}
 
 		isHtmxRequest := r.Header.Get("HX-Request") == "true" && !(r.Header.Get("HX-Boosted") == "true")
+
+		if !a.IsDev && r.Method == http.MethodGet && r.Header.Get("sec-fetch-mode") == "navigate" &&
+			!(strings.ToLower(rtype) == "json") && !(isHtmxRequest && block != "") {
+			// Prod mode, for a GET request from newer browsers on a top level HTML page, send http early hints
+			a.earlyHints(w, r)
+		}
+
 		appPath := a.Path
 		if appPath == "/" {
 			appPath = ""

internal/app/testhelper.go

@@ -34,10 +34,13 @@ func CreateTestAppInt(logger *utils.Logger, path string, fileData map[string]str
 	} else {
 		fs = &TestReadFS{fileData: fileData}
 	}
-	sourceFS := util.NewSourceFs("", fs, isDev)
+	sourceFS, err := util.NewSourceFs("", fs, isDev)
+	if err != nil {
+		return nil, nil, err
+	}
 	workFS := util.NewWorkFs("", &TestWriteFS{TestReadFS: &TestReadFS{fileData: map[string]string{}}})
 	a := NewApp(sourceFS, workFS, logger, createTestAppEntry(path, isDev), &systemConfig)
-	err := a.Initialize()
+	err = a.Initialize()
 	return a, workFS, err
 }
 
@@ -157,6 +160,10 @@ func (f *TestReadFS) Stat(name string) (fs.FileInfo, error) {
 	return &TestFileInfo{file}, nil
 }
 
+func (d *TestReadFS) StaticFiles() []string {
+	return []string{} // Not implemented for disk fs, used only in prod mode
+}
+
 func (f *TestReadFS) Reset() {
 	// do nothing
 }

internal/app/util/disk_fs.go

@@ -81,6 +81,10 @@ func (d *DiskReadFS) Glob(pattern string) (matches []string, err error) {
 	return fs.Glob(d.fs, pattern)
 }
 
+func (d *DiskReadFS) StaticFiles() []string {
+	return []string{} // Not implemented for disk fs, used only in prod mode
+}
+
 func (d *DiskReadFS) Reset() {
 	// do nothing
 }

internal/app/util/source_fs.go

@@ -29,9 +29,10 @@ type SourceFs struct {
 	Root  string
 	isDev bool
 
-	mu         sync.RWMutex
-	nameToHash map[string]string    // lookup (path to hash path)
-	hashToName map[string][2]string // reverse lookup (hash path to path)
+	staticFiles []string
+	mu          sync.RWMutex
+	nameToHash  map[string]string    // lookup (path to hash path)
+	hashToName  map[string][2]string // reverse lookup (hash path to path)
 }
 
 var _ utils.ReadableFS = (*SourceFs)(nil)
@@ -64,16 +65,27 @@ func (w *WritableSourceFs) Remove(name string) error {
 	return wfs.Remove(name)
 }
 
-func NewSourceFs(dir string, fs utils.ReadableFS, isDev bool) *SourceFs {
+func NewSourceFs(dir string, fs utils.ReadableFS, isDev bool) (*SourceFs, error) {
+	var staticFiles []string
+	if !isDev {
+		// For prod mode, get the list of static files for early hints
+		staticFiles = fs.StaticFiles()
+	}
+
 	return &SourceFs{
-		Root:       dir,
-		ReadableFS: fs,
-		isDev:      isDev,
+		Root:        dir,
+		ReadableFS:  fs,
+		isDev:       isDev,
+		staticFiles: staticFiles,
 
 		// File hashing code based on https://github.com/benbjohnson/hashfs/blob/main/hashfs.go
 		// Copyright (c) 2020 Ben Johnson. MIT License
 		nameToHash: make(map[string]string),
-		hashToName: make(map[string][2]string)}
+		hashToName: make(map[string][2]string)}, nil
+}
+
+func (f *SourceFs) StaticFiles() []string {
+	return f.staticFiles
 }
 
 func (f *SourceFs) ClearCache() {

internal/metadata/dbfs.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"io/fs"
 	"path"
+	"strings"
 	"time"
 
 	"github.com/andybalholm/brotli"
@@ -214,6 +215,16 @@ func (d *DbFs) Glob(pattern string) (matches []string, err error) {
 	return matchedFiles, nil
 }
 
+func (d *DbFs) StaticFiles() []string {
+	staticFiles := []string{}
+	for name := range d.fileInfo {
+		if strings.HasPrefix(name, "static/") {
+			staticFiles = append(staticFiles, name)
+		}
+	}
+	return staticFiles
+}
+
 func (d *DbFs) Reset() {
 	d.fileStore.Reset()
 }

internal/server/app_apis.go

@@ -198,12 +198,19 @@ func (s *Server) setupApp(appEntry *utils.AppEntry, tx metadata.Transaction) (*a
 		if err != nil {
 			return nil, err
 		}
-		sourceFS = util.NewSourceFs("", dbFs, false)
+		sourceFS, err = util.NewSourceFs("", dbFs, false)
+		if err != nil {
+			return nil, err
+		}
 	} else {
 		// Dev mode, use local disk as source
-		sourceFS = util.NewSourceFs(appEntry.SourceUrl,
+		var err error
+		sourceFS, err = util.NewSourceFs(appEntry.SourceUrl,
 			&util.DiskWriteFS{DiskReadFS: util.NewDiskReadFS(&appLogger, appEntry.SourceUrl)},
 			appEntry.IsDev)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	appPath := fmt.Sprintf(os.ExpandEnv("$CL_HOME/run/app/%s"), appEntry.Id)

internal/utils/types.go

@@ -213,7 +213,8 @@ type ReadableFS interface {
 	fs.GlobFS
 	// Stat returns the stats for the named file.
 	Stat(name string) (fs.FileInfo, error)
-	Reset() // Used to reset the file system transaction for the DbFs, no-op for others
+	Reset()                // Used to reset the file system transaction for the DbFs, no-op for others
+	StaticFiles() []string // Return list of static files
 }
 
 type CompressedReader interface {

tests/test_basics.yaml

@@ -80,6 +80,10 @@ tests:
       exactly: "1" # X-Clace-Compressed is not set, encoding is not set
     exit-code: 0
 
+  basic164: ## Check HTTP early hints
+    command: 'curl -kv -H "sec-fetch-mode: navigate" —http2 https://localhost:9155/test2?aaaa'
+    stderr: "HTTP/2 103"
+
   basic170: # check curl works with password
     command: curl -sS -u "admin:abcd" localhost:9154/test2
     stdout: "Test app body"