🔥 Add PathPrefix parameter to filesystem middleware (#1326)

See #1308

This adds a parameter called `PathPrefix` to `filesystem.Config`
that is prepended to any filepath being read from
`filesystem.Root`.

Intended to be used with Go 1.16's `embed.FS` type.

Signed-off-by: Tom <tom@tdpain.net>

middleware/filesystem/README.md

@@ -92,11 +92,11 @@ func main() {
 	}))
 
 	// Access file "image.png" under `static/` directory via URL: `http://<server>/static/image.png`.
-	// With `http.FS(embedDirStatic)`, you have to access it via URL:
+	// Without `PathPrefix`, you have to access it via URL:
 	// `http://<server>/static/static/image.png`.
-	subFS, _ := fs.Sub(embedDirStatic, "static")
 	app.Use("/static", filesystem.New(filesystem.Config{
-		Root: http.FS(subFS),
+		Root: http.FS(embedDirStatic),
+		PathPrefix: "static"
 		Browse: true,
 	}))
 
@@ -251,6 +251,14 @@ type Config struct {
 	// Required. Default: nil
 	Root http.FileSystem `json:"-"`
 
+	// PathPrefix defines a prefix to be added to a filepath when
+	// reading a file from the FileSystem.
+	//
+	// Use when using Go 1.16 embed.FS
+	//
+	// Optional. Default ""
+	PathPrefix string `json:"path_prefix"`
+
 	// Enable directory browsing.
 	//
 	// Optional. Default: false
@@ -278,10 +286,11 @@ type Config struct {
 
 ```go
 var ConfigDefault = Config{
-	Next:   nil,
-	Root:   nil,
-	Browse: false,
-	Index:  "/index.html",
-	MaxAge: 0,
+	Next:       nil,
+	Root:       nil,
+	PathPrefix: "",
+	Browse:     false,
+	Index:      "/index.html",
+	MaxAge:     0,
 }
 ```

middleware/filesystem/filesystem.go

@@ -23,6 +23,14 @@ type Config struct {
 	// Required. Default: nil
 	Root http.FileSystem `json:"-"`
 
+	// PathPrefix defines a prefix to be added to a filepath when
+	// reading a file from the FileSystem.
+	//
+	// Use when using Go 1.16 embed.FS
+	//
+	// Optional. Default ""
+	PathPrefix string `json:"path_prefix"`
+
 	// Enable directory browsing.
 	//
 	// Optional. Default: false
@@ -47,11 +55,12 @@ type Config struct {
 
 // ConfigDefault is the default config
 var ConfigDefault = Config{
-	Next:   nil,
-	Root:   nil,
-	Browse: false,
-	Index:  "/index.html",
-	MaxAge: 0,
+	Next:       nil,
+	Root:       nil,
+	PathPrefix: "",
+	Browse:     false,
+	Index:      "/index.html",
+	MaxAge:     0,
 }
 
 // New creates a new middleware handler
@@ -79,6 +88,10 @@ func New(config ...Config) fiber.Handler {
 		panic("filesystem: Root cannot be nil")
 	}
 
+	if cfg.PathPrefix != "" && !strings.HasPrefix(cfg.PathPrefix, "/") {
+		cfg.PathPrefix = "/" + cfg.PathPrefix
+	}
+
 	var once sync.Once
 	var prefix string
 	var cacheControlStr = "public, max-age=" + strconv.Itoa(cfg.MaxAge)
@@ -107,6 +120,11 @@ func New(config ...Config) fiber.Handler {
 		if !strings.HasPrefix(path, "/") {
 			path = "/" + path
 		}
+		// Add PathPrefix
+		if cfg.PathPrefix != "" {
+			// PathPrefix already has a "/" prefix
+			path = cfg.PathPrefix + path
+		}
 
 		var (
 			file http.File

middleware/filesystem/filesystem_test.go

@@ -32,6 +32,11 @@ func Test_FileSystem(t *testing.T) {
 		NotFoundFile: "index.html",
 	}))
 
+	app.Use("/prefix", New(Config{
+		Root: http.Dir("../../.github/testdata/fs"),
+		PathPrefix: "img",
+	}))
+
 	tests := []struct {
 		name         string
 		url          string
@@ -96,6 +101,12 @@ func Test_FileSystem(t *testing.T) {
 			statusCode:  200,
 			contentType: "text/html",
 		},
+		{
+			name: "PathPrefix should be applied",
+			url: "/prefix/fiber.png",
+			statusCode: 200,
+			contentType: "image/png",
+		},
 	}
 
 	for _, tt := range tests {