drive: move normalizeShareName into pkg drive and make func public (#11638)

This change makes the normalizeShareName function public, so it can be
used for validation in control.

Updates tailscale/corp#16827

Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>

drive/remote.go

@@ -7,14 +7,22 @@ package drive
 
 import (
 	"bytes"
+	"errors"
 	"net/http"
+	"regexp"
 	"strings"
 )
 
 var (
 	// DisallowShareAs forcibly disables sharing as a specific user, only used
 	// for testing.
-	DisallowShareAs = false
+	DisallowShareAs     = false
+	ErrDriveNotEnabled  = errors.New("Taildrive not enabled")
+	ErrInvalidShareName = errors.New("Share names may only contain the letters a-z, underscore _, parentheses (), or spaces")
+)
+
+var (
+	shareNameRegex = regexp.MustCompile(`^[a-z0-9_\(\) ]+$`)
 )
 
 // AllowShareAs reports whether sharing files as a specific user is allowed.
@@ -103,3 +111,20 @@ type FileSystemForRemote interface {
 	// Close() stops serving the WebDAV content
 	Close() error
 }
+
+// NormalizeShareName normalizes the given share name and returns an error if
+// it contains any disallowed characters.
+func NormalizeShareName(name string) (string, error) {
+	// Force all share names to lowercase to avoid potential incompatibilities
+	// with clients that don't support case-sensitive filenames.
+	name = strings.ToLower(name)
+
+	// Trim whitespace
+	name = strings.TrimSpace(name)
+
+	if !shareNameRegex.MatchString(name) {
+		return "", ErrInvalidShareName
+	}
+
+	return name, nil
+}

drive/remote_test.go

@@ -0,0 +1,40 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package drive
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestNormalizeShareName(t *testing.T) {
+	tests := []struct {
+		name string
+		want string
+		err  error
+	}{
+		{
+			name: "  (_this is A 5 nAme )_ ",
+			want: "(_this is a 5 name )_",
+		},
+		{
+			name: "",
+			err:  ErrInvalidShareName,
+		},
+		{
+			name: "generally good except for .",
+			err:  ErrInvalidShareName,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("name %q", tt.name), func(t *testing.T) {
+			got, err := NormalizeShareName(tt.name)
+			if tt.err != nil && err != tt.err {
+				t.Errorf("wanted error %v, got %v", tt.err, err)
+			} else if got != tt.want {
+				t.Errorf("wanted %q, got %q", tt.want, got)
+			}
+		})
+	}
+}