add file to url utility

Signed-off-by: Pablo Chacin <[email protected]>

pkg/util/url.go

@@ -0,0 +1,138 @@
+// Package util implements utility functions
+package util
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+// Adapted from https://go-review.googlesource.com/c/vuln/+/438175/7/internal/web/url.go
+
+// URLFromFilePath converts the given absolute path to a URL.
+func URLFromFilePath(path string) (*url.URL, error) {
+	if !filepath.IsAbs(path) {
+		return nil, fmt.Errorf("path is not absolute %q", path)
+	}
+
+	// If path has a Windows volume name, convert the volume to a host and prefix
+	// per https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/.
+	if vol := filepath.VolumeName(path); vol != "" {
+		if strings.HasPrefix(vol, `\\`) {
+			path = filepath.ToSlash(path[2:])
+			i := strings.IndexByte(path, '/')
+
+			if i < 0 {
+				// A degenerate case.
+				// \\host.example.com (without a share name)
+				// becomes
+				// file://host.example.com/
+				return &url.URL{
+					Scheme: "file",
+					Host:   path,
+					Path:   "/",
+				}, nil
+			}
+
+			// \\host.example.com\Share\path\to\file
+			// becomes
+			// file://host.example.com/Share/path/to/file
+			return &url.URL{
+				Scheme: "file",
+				Host:   path[:i],
+				Path:   filepath.ToSlash(path[i:]),
+			}, nil
+		}
+
+		// C:\path\to\file
+		// becomes
+		// file:///C:/path/to/file
+		return &url.URL{
+			Scheme: "file",
+			Path:   "/" + filepath.ToSlash(path),
+		}, nil
+	}
+
+	// /path/to/file
+	// becomes
+	// file:///path/to/file
+	return &url.URL{
+		Scheme: "file",
+		Path:   filepath.ToSlash(path),
+	}, nil
+}
+
+
+// URLToFilePath converts a file-scheme url to a file path.
+func URLToFilePath(u *url.URL) (string, error) {
+	if u.Scheme != "file" {
+		return "", errors.New("non-file URL")
+	}
+
+	checkAbs := func(path string) (string, error) {
+		if !filepath.IsAbs(path) {
+			return "", fmt.Errorf("path is not absolute %q", path)
+		}
+		return path, nil
+	}
+
+	if u.Path == "" {
+		if u.Host != "" || u.Opaque == "" {
+			return "", errors.New("file URL missing path")
+		}
+		return checkAbs(filepath.FromSlash(u.Opaque))
+	}
+
+	path, err := convertFileURLPath(u.Host, u.Path)
+	if err != nil {
+		return path, err
+	}
+	return checkAbs(path)
+}
+
+func convertFileURLPath(host, path string) (string, error) {
+	if runtime.GOOS == "windows" {
+		return convertFileURLPathWindows(host, path)
+	}
+	switch host {
+	case "", "localhost":
+	default:
+		return "", errors.New("file URL specifies non-local host")
+	}
+	return filepath.FromSlash(path), nil
+}
+
+func convertFileURLPathWindows(host, path string) (string, error) {
+	if len(path) == 0 || path[0] != '/' {
+		return "", fmt.Errorf("path is not absolute %q", path)
+	}
+
+	path = filepath.FromSlash(path)
+
+	// We interpret Windows file URLs per the description in
+	// https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/.
+
+	// The host part of a file URL (if any) is the UNC volume name,
+	// but RFC 8089 reserves the authority "localhost" for the local machine.
+	if host != "" && host != "localhost" {
+		// A common "legacy" format omits the leading slash before a drive letter,
+		// encoding the drive letter as the host instead of part of the path.
+		// (See https://blogs.msdn.microsoft.com/freeassociations/2005/05/19/the-bizarre-and-unhappy-story-of-file-urls/.)
+		// We do not support that format, but we should at least emit a more
+		// helpful error message for it.
+		if filepath.VolumeName(host) != "" {
+			return "", errors.New("file URL encodes volume in host field: too few slashes?")
+		}
+		return `\\` + host + path, nil
+	}
+
+	// If host is empty, path must contain an initial slash followed by a
+	// drive letter and path. Remove the slash and verify that the path is valid.
+	if vol := filepath.VolumeName(path[1:]); vol == "" || strings.HasPrefix(vol, `\\`) {
+		return "", errors.New("file URL missing drive letter")
+	}
+	return path[1:], nil
+}

pkg/util/url_test.go

@@ -0,0 +1,176 @@
+
+package util
+import (
+	"net/url"
+	"runtime"
+	"testing"
+)
+func TestURLToFilePath(t *testing.T) {
+	for _, tc := range urlTests() {
+		if tc.url == "" {
+			continue
+		}
+		tc := tc
+		t.Run(tc.url, func(t *testing.T) {
+			u, err := url.Parse(tc.url)
+			if err != nil {
+				t.Fatalf("url.Parse(%q): %v", tc.url, err)
+			}
+			path, err := URLToFilePath(u)
+			if err != nil {
+				if err.Error() == tc.wantErr {
+					return
+				}
+				if tc.wantErr == "" {
+					t.Fatalf("urlToFilePath(%v): %v; want <nil>", u, err)
+				} else {
+					t.Fatalf("urlToFilePath(%v): %v; want %s", u, err, tc.wantErr)
+				}
+			}
+			if path != tc.filePath || tc.wantErr != "" {
+				t.Fatalf("urlToFilePath(%v) = %q, <nil>; want %q, %s", u, path, tc.filePath, tc.wantErr)
+			}
+		})
+	}
+}
+func TestURLFromFilePath(t *testing.T) {
+	for _, tc := range urlTests() {
+		if tc.filePath == "" {
+			continue
+		}
+		tc := tc
+		t.Run(tc.filePath, func(t *testing.T) {
+			u, err := URLFromFilePath(tc.filePath)
+			if err != nil {
+				if err.Error() == tc.wantErr {
+					return
+				}
+				if tc.wantErr == "" {
+					t.Fatalf("urlFromFilePath(%v): %v; want <nil>", tc.filePath, err)
+				} else {
+					t.Fatalf("urlFromFilePath(%v): %v; want %s", tc.filePath, err, tc.wantErr)
+				}
+			}
+			if tc.wantErr != "" {
+				t.Fatalf("urlFromFilePath(%v) = <nil>; want error: %s", tc.filePath, tc.wantErr)
+			}
+			wantURL := tc.url
+			if tc.canonicalURL != "" {
+				wantURL = tc.canonicalURL
+			}
+			if u.String() != wantURL {
+				t.Errorf("urlFromFilePath(%v) = %v; want %s", tc.filePath, u, wantURL)
+			}
+		})
+	}
+}
+func urlTests() []urlTest {
+	if runtime.GOOS == "windows" {
+		return urlTestsWindows
+	}
+	return urlTestsOthers
+}
+type urlTest struct {
+	url          string
+	filePath     string
+	canonicalURL string // If empty, assume equal to url.
+	wantErr      string
+}
+var urlTestsOthers = []urlTest{
+	// Examples from RFC 8089:
+	{
+		url:      `file:///path/to/file`,
+		filePath: `/path/to/file`,
+	},
+	{
+		url:          `file:/path/to/file`,
+		filePath:     `/path/to/file`,
+		canonicalURL: `file:///path/to/file`,
+	},
+	{
+		url:          `file://localhost/path/to/file`,
+		filePath:     `/path/to/file`,
+		canonicalURL: `file:///path/to/file`,
+	},
+	// We reject non-local files.
+	{
+		url:     `file://host.example.com/path/to/file`,
+		wantErr: "file URL specifies non-local host",
+	},
+}
+var urlTestsWindows = []urlTest{
+	// Examples from https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/:
+	{
+		url:      `file://laptop/My%20Documents/FileSchemeURIs.doc`,
+		filePath: `\\laptop\My Documents\FileSchemeURIs.doc`,
+	},
+	{
+		url:      `file:///C:/Documents%20and%20Settings/davris/FileSchemeURIs.doc`,
+		filePath: `C:\Documents and Settings\davris\FileSchemeURIs.doc`,
+	},
+	{
+		url:      `file:///D:/Program%20Files/Viewer/startup.htm`,
+		filePath: `D:\Program Files\Viewer\startup.htm`,
+	},
+	{
+		url:          `file:///C:/Program%20Files/Music/Web%20Sys/main.html?REQUEST=RADIO`,
+		filePath:     `C:\Program Files\Music\Web Sys\main.html`,
+		canonicalURL: `file:///C:/Program%20Files/Music/Web%20Sys/main.html`,
+	},
+	{
+		url:      `file://applib/products/a-b/abc_9/4148.920a/media/start.swf`,
+		filePath: `\\applib\products\a-b\abc_9\4148.920a\media\start.swf`,
+	},
+	{
+		url:     `file:////applib/products/a%2Db/abc%5F9/4148.920a/media/start.swf`,
+		wantErr: "file URL missing drive letter",
+	},
+	{
+		url:     `C:\Program Files\Music\Web Sys\main.html?REQUEST=RADIO`,
+		wantErr: "non-file URL",
+	},
+	// The example "file://D:\Program Files\Viewer\startup.htm" errors out in
+	// url.Parse, so we substitute a slash-based path for testing instead.
+	{
+		url:     `file://D:/Program Files/Viewer/startup.htm`,
+		wantErr: "file URL encodes volume in host field: too few slashes?",
+	},
+	// The blog post discourages the use of non-ASCII characters because they
+	// depend on the user's current codepage. However, when we are working with Go
+	// strings we assume UTF-8 encoding, and our url package refuses to encode
+	// URLs to non-ASCII strings.
+	{
+		url:          `file:///C:/exampleㄓ.txt`,
+		filePath:     `C:\exampleㄓ.txt`,
+		canonicalURL: `file:///C:/example%E3%84%93.txt`,
+	},
+	{
+		url:      `file:///C:/example%E3%84%93.txt`,
+		filePath: `C:\exampleㄓ.txt`,
+	},
+	// Examples from RFC 8089:
+	// We allow the drive-letter variation from section E.2, because it is
+	// simpler to support than not to. However, we do not generate the shorter
+	// form in the reverse direction.
+	{
+		url:          `file:c:/path/to/file`,
+		filePath:     `c:\path\to\file`,
+		canonicalURL: `file:///c:/path/to/file`,
+	},
+	// We encode the UNC share name as the authority following section E.3.1,
+	// because that is what the Microsoft blog post explicitly recommends.
+	{
+		url:      `file://host.example.com/Share/path/to/file.txt`,
+		filePath: `\\host.example.com\Share\path\to\file.txt`,
+	},
+	// We decline the four- and five-slash variations from section E.3.2.
+	// The paths in these URLs would change meaning under path.Clean.
+	{
+		url:     `file:////host.example.com/path/to/file`,
+		wantErr: "file URL missing drive letter",
+	},
+	{
+		url:     `file://///host.example.com/path/to/file`,
+		wantErr: "file URL missing drive letter",
+	},
+}