config: check config names more carefully and report errors - fixes #3506

Before this change it was possible to make a remote with an invalid
name in the config file, either manually or with `rclone config
create` (but not with `rclone config`).

When this remote was used, because it was invalid, rclone would
presume this remote name was a local directory for a very suprising
user experience!

This change checks remote names more carefully and returns errors
- when the user tries to use an invalid remote name on the command line
- when an invalid remote name is used in `rclone config create/update/password`
- when the user tries to enter an invalid remote name in `rclone config`

This does not prevent the user entering a remote name with invalid
characters in the config manually, but such a remote will fail
immediately when it is used on the command line.

fs/fspath/path.go

@@ -2,6 +2,7 @@
 package fspath
 
 import (
+	"errors"
 	"path"
 	"path/filepath"
 	"regexp"
@@ -10,8 +11,40 @@ import (
 	"github.com/rclone/rclone/fs/driveletter"
 )
 
-// Matcher is a pattern to match an rclone URL
-var Matcher = regexp.MustCompile(`^(:?[\w_ -]+):(.*)$`)
+const (
+	configNameRe = `[\w_ -]+`
+	remoteNameRe = `^(:?` + configNameRe + `):`
+)
+
+var (
+	errInvalidCharacters = errors.New("config name contains invalid characters - may only contain 0-9, A-Z ,a-z ,_ , - and space ")
+
+	// urlMatcher is a pattern to match an rclone URL
+	// note that this matches invalid remoteNames
+	urlMatcher = regexp.MustCompile(`^(:?[^\\/:]*):(.*)$`)
+
+	// configNameMatcher is a pattern to match an rclone config name
+	configNameMatcher = regexp.MustCompile(`^` + configNameRe + `$`)
+
+	// remoteNameMatcher is a pattern to match an rclone remote name
+	remoteNameMatcher = regexp.MustCompile(remoteNameRe + `$`)
+)
+
+// CheckConfigName returns an error if configName is invalid
+func CheckConfigName(configName string) error {
+	if !configNameMatcher.MatchString(configName) {
+		return errInvalidCharacters
+	}
+	return nil
+}
+
+// CheckRemoteName returns an error if remoteName is invalid
+func CheckRemoteName(remoteName string) error {
+	if !remoteNameMatcher.MatchString(remoteName) {
+		return errInvalidCharacters
+	}
+	return nil
+}
 
 // Parse deconstructs a remote path into configName and fsPath
 //
@@ -21,15 +54,21 @@ var Matcher = regexp.MustCompile(`^(:?[\w_ -]+):(.*)$`)
 // and "/path/to/local" will return ("", "/path/to/local")
 //
 // Note that this will turn \ into / in the fsPath on Windows
-func Parse(path string) (configName, fsPath string) {
-	parts := Matcher.FindStringSubmatch(path)
+//
+// An error may be returned if the remote name has invalid characters in it.
+func Parse(path string) (configName, fsPath string, err error) {
+	parts := urlMatcher.FindStringSubmatch(path)
 	configName, fsPath = "", path
 	if parts != nil && !driveletter.IsDriveLetter(parts[1]) {
 		configName, fsPath = parts[1], parts[2]
+		err = CheckRemoteName(configName + ":")
+		if err != nil {
+			return configName, fsPath, errInvalidCharacters
+		}
 	}
 	// change native directory separators to / if there are any
 	fsPath = filepath.ToSlash(fsPath)
-	return configName, fsPath
+	return configName, fsPath, nil
 }
 
 // Split splits a remote into a parent and a leaf
@@ -40,14 +79,17 @@ func Parse(path string) (configName, fsPath string) {
 //
 // The returned values have the property that parent + leaf == remote
 // (except under Windows where \ will be translated into /)
-func Split(remote string) (parent string, leaf string) {
-	remoteName, remotePath := Parse(remote)
+func Split(remote string) (parent string, leaf string, err error) {
+	remoteName, remotePath, err := Parse(remote)
+	if err != nil {
+		return "", "", err
+	}
 	if remoteName != "" {
 		remoteName += ":"
 	}
 	// Construct new remote name without last segment
 	parent, leaf = path.Split(remotePath)
-	return remoteName + parent, leaf
+	return remoteName + parent, leaf, nil
 }
 
 // JoinRootPath joins any number of path elements into a single path, adding a