make server & router reusable outside asynqmon package

static.go

@@ -0,0 +1,68 @@
+package asynqmon
+
+import (
+	"embed"
+	"errors"
+	"io/fs"
+	"net/http"
+	"path/filepath"
+
+	"github.com/ajatprabha/asynqmon/internal"
+)
+
+func NewStaticContentHandler() http.Handler {
+	return &staticContentHandler{
+		contents:      internal.StaticContents,
+		staticDirPath: "assets",
+		indexFileName: "index.html",
+	}
+}
+
+// staticFileServer implements the http.Handler interface, so we can use it
+// to respond to HTTP requests. The path to the static directory and
+// path to the index file within that static directory are used to
+// serve the SPA in the given static directory.
+type staticContentHandler struct {
+	contents      embed.FS
+	staticDirPath string
+	indexFileName string
+}
+
+// ServeHTTP inspects the URL path to locate a file within the static dir
+// on the SPA handler.
+// If path '/' is requested, it will serve the index file, otherwise it will
+// serve the file specified by the URL path.
+func (h *staticContentHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Get the absolute path to prevent directory traversal.
+	path, err := filepath.Abs(r.URL.Path)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	if path == "/" {
+		path = h.indexFilePath()
+	} else {
+		path = filepath.Join(h.staticDirPath, path)
+	}
+
+	bytes, err := h.contents.ReadFile(path)
+	// If path is error (e.g. file not exist, path is a directory), serve index file.
+	var pathErr *fs.PathError
+	if errors.As(err, &pathErr) {
+		bytes, err = h.contents.ReadFile(h.indexFilePath())
+	}
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	if _, err := w.Write(bytes); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+func (h *staticContentHandler) indexFilePath() string {
+	return filepath.Join(h.staticDirPath, h.indexFileName)
+}