Update dependencies (#1784)

vendor/github.com/labstack/echo/v4/echo_fs_go1.16.go

@@ -10,6 +10,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 )
 
@@ -94,10 +95,12 @@ func StaticFileHandler(file string, filesystem fs.FS) HandlerFunc {
 	}
 }
 
-// defaultFS emulates os.Open behaviour with filesystem opened by `os.DirFs`. Difference between `os.Open` and `fs.Open`
-// is that FS does not allow to open path that start with `..` or `/` etc. For example previously you could have `../images`
-// in your application but `fs := os.DirFS("./")` would not allow you to use `fs.Open("../images")` and this would break
-// all old applications that rely on being able to traverse up from current executable run path.
+// defaultFS exists to preserve pre v4.7.0 behaviour where files were open by `os.Open`.
+// v4.7 introduced `echo.Filesystem` field which is Go1.16+ `fs.Fs` interface.
+// Difference between `os.Open` and `fs.Open` is that FS does not allow opening path that start with `.`, `..` or `/`
+// etc. For example previously you could have `../images` in your application but `fs := os.DirFS("./")` would not
+// allow you to use `fs.Open("../images")` and this would break all old applications that rely on being able to
+// traverse up from current executable run path.
 // NB: private because you really should use fs.FS implementation instances
 type defaultFS struct {
 	prefix string
@@ -108,20 +111,26 @@ func newDefaultFS() *defaultFS {
 	dir, _ := os.Getwd()
 	return &defaultFS{
 		prefix: dir,
-		fs:     os.DirFS(dir),
+		fs:     nil,
 	}
 }
 
 func (fs defaultFS) Open(name string) (fs.File, error) {
+	if fs.fs == nil {
+		return os.Open(name)
+	}
 	return fs.fs.Open(name)
 }
 
 func subFS(currentFs fs.FS, root string) (fs.FS, error) {
 	root = filepath.ToSlash(filepath.Clean(root)) // note: fs.FS operates only with slashes. `ToSlash` is necessary for Windows
 	if dFS, ok := currentFs.(*defaultFS); ok {
-		// we need to make exception for `defaultFS` instances as it interprets root prefix differently from fs.FS to
-		// allow cases when root is given as `../somepath` which is not valid for fs.FS
-		root = filepath.Join(dFS.prefix, root)
+		// we need to make exception for `defaultFS` instances as it interprets root prefix differently from fs.FS.
+		// fs.Fs.Open does not like relative paths ("./", "../") and absolute paths at all but prior echo.Filesystem we
+		// were able to use paths like `./myfile.log`, `/etc/hosts` and these would work fine with `os.Open` but not with fs.Fs
+		if isRelativePath(root) {
+			root = filepath.Join(dFS.prefix, root)
+		}
 		return &defaultFS{
 			prefix: root,
 			fs:     os.DirFS(root),
@@ -130,6 +139,21 @@ func subFS(currentFs fs.FS, root string) (fs.FS, error) {
 	return fs.Sub(currentFs, root)
 }
 
+func isRelativePath(path string) bool {
+	if path == "" {
+		return true
+	}
+	if path[0] == '/' {
+		return false
+	}
+	if runtime.GOOS == "windows" && strings.IndexByte(path, ':') != -1 {
+		// https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file?redirectedfrom=MSDN#file_and_directory_names
+		// https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats
+		return false
+	}
+	return true
+}
+
 // MustSubFS creates sub FS from current filesystem or panic on failure.
 // Panic happens when `fsRoot` contains invalid path according to `fs.ValidPath` rules.
 //