url_windows.go

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package web
     6  
     7  import (
     8  	"errors"
     9  	"path/filepath"
    10  	"strings"
    11  )
    12  
    13  func convertFileURLPath(host, path string) (string, error) {
    14  	if len(path) == 0 || path[0] != '/' {
    15  		return "", errNotAbsolute
    16  	}
    17  
    18  	path = filepath.FromSlash(path)
    19  
    20  	// We interpret Windows file URLs per the description in
    21  	// https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/.
    22  
    23  	// The host part of a file URL (if any) is the UNC volume name,
    24  	// but RFC 8089 reserves the authority "localhost" for the local machine.
    25  	if host != "" && host != "localhost" {
    26  		// A common "legacy" format omits the leading slash before a drive letter,
    27  		// encoding the drive letter as the host instead of part of the path.
    28  		// (See https://blogs.msdn.microsoft.com/freeassociations/2005/05/19/the-bizarre-and-unhappy-story-of-file-urls/.)
    29  		// We do not support that format, but we should at least emit a more
    30  		// helpful error message for it.
    31  		if filepath.VolumeName(host) != "" {
    32  			return "", errors.New("file URL encodes volume in host field: too few slashes?")
    33  		}
    34  		return `\\` + host + path, nil
    35  	}
    36  
    37  	// If host is empty, path must contain an initial slash followed by a
    38  	// drive letter and path. Remove the slash and verify that the path is valid.
    39  	if vol := filepath.VolumeName(path[1:]); vol == "" || strings.HasPrefix(vol, `\\`) {
    40  		return "", errors.New("file URL missing drive letter")
    41  	}
    42  	return path[1:], nil
    43  }
    44
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