Add HTTP file-server helper

pkg/http/file_server.go

@@ -0,0 +1,145 @@
+package http
+
+import (
+	"io/fs"
+	"net/http"
+	"path"
+	"strings"
+
+	"github.com/go-chi/chi/v5"
+	"go.uber.org/zap"
+)
+
+type (
+	// special file-server meant to be used for serving single page applications
+	// or anything that needs a bit of extra attention like fallback handling
+	// 404 handler, error handler and URL prefixing
+	fileServer struct {
+		// fileServer files
+		files http.FileSystem
+
+		urlPrefix string
+
+		fallbacks []string
+
+		// Final not-found handler
+		notFound http.HandlerFunc
+
+		// how errors are handled
+		errHandler func(w http.ResponseWriter, error string, code int)
+
+		logger *zap.Logger
+	}
+
+	configurator func(*fileServer) error
+)
+
+// MountSPA helper function, preconfigures FileServer for SPA serving
+// and mounts it to chi Router
+func MountSPA(r chi.Router, path string, root fs.FS, cc ...configurator) error {
+	path = "/" + strings.Trim(strings.TrimRight(path, "*"), "/") + "/"
+	handler, err := FileServer(root, append(cc, UrlPrefix(path), Fallbacks("index.html"))...)
+	if err != nil {
+		return err
+	}
+
+	r.Handle(
+		strings.TrimRight(path, "/"),
+		http.RedirectHandler("."+path, http.StatusTemporaryRedirect),
+	)
+
+	r.Handle(path+"*", handler)
+	return nil
+}
+
+func FileServer(files fs.FS, cc ...configurator) (h *fileServer, err error) {
+	h = &fileServer{
+		files:      http.FS(files),
+		notFound:   http.NotFound,
+		errHandler: http.Error,
+		logger:     zap.NewNop(),
+	}
+
+	for _, configure := range cc {
+		if err = configure(h); err != nil {
+			return
+		}
+	}
+
+	return
+}
+
+func UrlPrefix(prefix string) configurator {
+	return func(s *fileServer) error {
+		s.urlPrefix = prefix
+		return nil
+	}
+}
+
+func Fallbacks(ff ...string) configurator {
+	return func(s *fileServer) error {
+		s.fallbacks = ff
+		return nil
+	}
+}
+
+func NotFound(h http.HandlerFunc) configurator {
+	return func(s *fileServer) error {
+		s.notFound = h
+		return nil
+	}
+}
+
+func Logger(l *zap.Logger) configurator {
+	return func(s *fileServer) error {
+		s.logger = l
+		return nil
+	}
+}
+
+// Serves the single-page-application
+//
+// This is file-server with some special logic for handling missing
+// files (404s) and directories.
+// In both cases we serve index file directly
+func (h *fileServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// catch requests for non-existing files and redirect to index.html
+	if h.files == nil {
+		h.errHandler(w, "configured without files", http.StatusInternalServerError)
+		return
+	}
+
+	trimmed := path.Clean(strings.TrimPrefix(r.URL.Path, h.urlPrefix))
+	h.logger.Debug(r.URL.Path, zap.String("trimmed", trimmed), zap.String("urlPrefix", h.urlPrefix))
+	r.URL.Path = trimmed
+
+	var (
+		err error
+		fh  http.File
+		st  fs.FileInfo
+	)
+
+	for _, candidate := range append([]string{r.URL.Path}, h.fallbacks...) {
+		if len(candidate) == 0 {
+			continue
+		}
+
+		if fh, err = h.files.Open(candidate); err != nil {
+			continue
+		} else if st, err = fh.Stat(); err != nil {
+			continue
+		} else if st.IsDir() {
+			// index
+			continue
+		}
+
+		break
+	}
+
+	if fh == nil || st == nil {
+		h.notFound(w, r)
+		return
+	}
+
+	http.ServeContent(w, r, st.Name(), st.ModTime(), fh)
+}

pkg/http/file_server_test.go

@@ -0,0 +1,133 @@
+package http
+
+import (
+	"embed"
+	"io/fs"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	//go:embed test_data/file_server
+	testAssets embed.FS
+)
+
+func TestSPA(t *testing.T) {
+	testAssetsSub, err := fs.Sub(testAssets, "test_data/file_server")
+	if err != nil {
+		t.Errorf("failed to dive into subdirectory: %w", err)
+	}
+
+	testDirectAssets := os.DirFS("test_data/file_server")
+
+	var (
+		cases = []struct {
+			name string
+			fs   fs.FS
+			cc   []configurator
+			url  string
+			rsp  string
+		}{
+			{
+				name: "no special config",
+				fs:   testAssetsSub,
+				url:  "index.html",
+				rsp:  "index html\n",
+			},
+
+			{
+				name: "empty path",
+				fs:   testAssetsSub,
+				cc:   []configurator{Fallbacks("index.html")},
+				url:  "",
+				rsp:  "index html\n",
+			},
+			{
+				name: "slash",
+				fs:   testAssetsSub,
+				cc:   []configurator{Fallbacks("index.html")},
+				url:  "/",
+				rsp:  "index html\n",
+			},
+
+			{
+				name: "prefix, no slash",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/my-spa",
+				rsp:  "index html\n",
+			},
+
+			{
+				name: "sub dir with url prefix",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/my-spa/index.html",
+				rsp:  "index html\n",
+			},
+			{
+				name: "sub dir with url prefix, none existing file",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/not-here",
+				rsp:  "index html\n",
+			},
+			{
+				name: "sub dir with url prefix, dir",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/my-spa/sub",
+				rsp:  "index html\n",
+			},
+			{
+				name: "sub dir with url prefix, sub index",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/my-spa/sub/index.html",
+				rsp:  "sub index html\n",
+			},
+			{
+				name: "sub dir with url prefix, sub file",
+				fs:   testAssetsSub,
+				cc:   []configurator{UrlPrefix("/my-spa"), Fallbacks("index.html")},
+				url:  "/my-spa/sub/test.html",
+				rsp:  "sub test html\n",
+			},
+		}
+	)
+
+	// another set of test cases for direct fs
+	total := len(cases)
+	for c := 0; c < total; c++ {
+		direct := cases[c]
+		cases[c].name += "; embedded"
+		direct.name += "; direct"
+		direct.fs = testDirectAssets
+
+		cases = append(cases, direct)
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			var (
+				handler http.Handler
+				req     = require.New(t)
+				w       = httptest.NewRecorder()
+				r, err  = http.NewRequest(http.MethodGet, c.url, nil)
+			)
+
+			handler, err = FileServer(c.fs, c.cc...)
+
+			req.NoError(err)
+			handler.ServeHTTP(w, r)
+
+			req.Equal(c.rsp, w.Body.String())
+			req.Equal(http.StatusOK, w.Result().StatusCode)
+		})
+	}
+
+}

pkg/http/test_data/file_server/index.html

@@ -0,0 +1 @@
+index html

pkg/http/test_data/file_server/sub/index.html

@@ -0,0 +1 @@
+sub index html

pkg/http/test_data/file_server/sub/test.html

@@ -0,0 +1 @@
+sub test html

pkg/http/test_data/file_server/test.html

@@ -0,0 +1 @@
+ test html