Added error message if user tries to mount to occupied drive.

Fixes #1888

src/main/java/org/cryptomator/common/mountpoint/CustomDriveLetterChooser.java

@@ -5,6 +5,9 @@ import org.cryptomator.common.settings.VaultSettings;
 import org.cryptomator.common.vaults.Volume;
 
 import javax.inject.Inject;
+import java.nio.file.FileAlreadyExistsException;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.Optional;
@@ -27,4 +30,13 @@ class CustomDriveLetterChooser implements MountPointChooser {
 	public Optional<Path> chooseMountPoint(Volume caller) {
 		return this.vaultSettings.getWinDriveLetter().map(letter -> letter.charAt(0) + ":\\").map(Paths::get);
 	}
+
+	@Override
+	public boolean prepare(Volume caller, Path driveLetter) throws InvalidMountPointException {
+		if (!Files.notExists(driveLetter, LinkOption.NOFOLLOW_LINKS)) {
+			//Drive already exists OR can't be determined
+			throw new InvalidMountPointException(new FileAlreadyExistsException(driveLetter.toString()));
+		}
+		return false;
+	}
 }

src/main/java/org/cryptomator/common/mountpoint/CustomMountPointChooser.java

@@ -56,7 +56,7 @@ class CustomMountPointChooser implements MountPointChooser {
 				throw new InvalidMountPointException(new IllegalStateException("Illegal MountPointRequirement"));
 			}
 			default -> {
-				//Currently the case for "PARENT_OPT_MOUNT_POINT"
+				//Currently the case for "NO_PARENT_NO_MOUNT_POINT, PARENT_OPT_MOUNT_POINT"
 				throw new InvalidMountPointException(new IllegalStateException("Not implemented"));
 			}
 		}

src/main/java/org/cryptomator/common/mountpoint/TemporaryMountPointChooser.java

@@ -65,7 +65,7 @@ class TemporaryMountPointChooser implements MountPointChooser {
 					throw new InvalidMountPointException(new IllegalStateException("Illegal MountPointRequirement"));
 				}
 				default -> {
-					//Currently the case for "PARENT_OPT_MOUNT_POINT"
+					//Currently the case for "NO_PARENT_NO_MOUNT_POINT, PARENT_OPT_MOUNT_POINT"
 					throw new InvalidMountPointException(new IllegalStateException("Not implemented"));
 				}
 			}

src/main/java/org/cryptomator/common/vaults/DokanyVolume.java

@@ -86,7 +86,7 @@ public class DokanyVolume extends AbstractVolume {
 
 	@Override
 	public MountPointRequirement getMountPointRequirement() {
-		return MountPointRequirement.EMPTY_MOUNT_POINT;
+		return this.vaultSettings.getWinDriveLetter().isPresent() ? MountPointRequirement.NO_PARENT_NO_MOUNT_POINT : MountPointRequirement.EMPTY_MOUNT_POINT;
 	}
 
 	public static boolean isSupportedStatic() {

src/main/java/org/cryptomator/common/vaults/FuseVolume.java

@@ -4,6 +4,7 @@ import com.google.common.collect.Iterators;
 import org.apache.commons.lang3.SystemUtils;
 import org.cryptomator.common.mountpoint.InvalidMountPointException;
 import org.cryptomator.common.mountpoint.MountPointChooser;
+import org.cryptomator.common.settings.VaultSettings;
 import org.cryptomator.common.settings.VolumeImpl;
 import org.cryptomator.cryptofs.CryptoFileSystem;
 import org.cryptomator.frontend.fuse.mount.EnvironmentVariables;
@@ -28,11 +29,14 @@ public class FuseVolume extends AbstractVolume {
 	private static final Logger LOG = LoggerFactory.getLogger(FuseVolume.class);
 	private static final Pattern NON_WHITESPACE_OR_QUOTED = Pattern.compile("[^\\s\"']+|\"([^\"]*)\"|'([^']*)'"); // Thanks to https://stackoverflow.com/a/366532
 
+	private final VaultSettings vaultSettings;
+
 	private Mount mount;
 
 	@Inject
-	public FuseVolume(@Named("orderedMountPointChoosers") Iterable<MountPointChooser> choosers) {
+	public FuseVolume(VaultSettings vaultSettings, @Named("orderedMountPointChoosers") Iterable<MountPointChooser> choosers) {
 		super(choosers);
+		this.vaultSettings = vaultSettings;
 	}
 
 	@Override
@@ -50,7 +54,7 @@ public class FuseVolume extends AbstractVolume {
 					.withFileNameTranscoder(mounter.defaultFileNameTranscoder()) //
 					.build();
 			this.mount = mounter.mount(root, envVars, onExitAction);
-		} catch ( FuseMountException | FuseNotSupportedException e) {
+		} catch (FuseMountException | FuseNotSupportedException e) {
 			throw new VolumeException("Unable to mount Filesystem", e);
 		}
 	}
@@ -119,7 +123,10 @@ public class FuseVolume extends AbstractVolume {
 
 	@Override
 	public MountPointRequirement getMountPointRequirement() {
-		return SystemUtils.IS_OS_WINDOWS ? MountPointRequirement.PARENT_NO_MOUNT_POINT : MountPointRequirement.EMPTY_MOUNT_POINT;
+		if (!SystemUtils.IS_OS_WINDOWS) {
+			return MountPointRequirement.EMPTY_MOUNT_POINT;
+		}
+		return this.vaultSettings.getWinDriveLetter().isPresent() ? MountPointRequirement.NO_PARENT_NO_MOUNT_POINT : MountPointRequirement.PARENT_NO_MOUNT_POINT;
 	}
 
 	public static boolean isSupportedStatic() {

src/main/java/org/cryptomator/common/vaults/MountPointRequirement.java

@@ -6,6 +6,11 @@ package org.cryptomator.common.vaults;
  */
 public enum MountPointRequirement {
 
+	/**
+	 * There must not be a parent folder and the actual Mountpoint must not exist.
+	 */
+	NO_PARENT_NO_MOUNT_POINT,
+
 	/**
 	 * No Mountpoint on the local filesystem required. (e.g. WebDAV)
 	 */

src/main/java/org/cryptomator/ui/unlock/UnlockInvalidMountPointController.java

@@ -1,5 +1,6 @@
 package org.cryptomator.ui.unlock;
 
+import org.apache.commons.lang3.SystemUtils;
 import org.cryptomator.common.vaults.MountPointRequirement;
 import org.cryptomator.common.vaults.Vault;
 import org.cryptomator.ui.common.FxController;
@@ -32,12 +33,24 @@ public class UnlockInvalidMountPointController implements FxController {
 		return vault.getVaultSettings().getCustomMountPath().orElse("AUTO");
 	}
 
-	public boolean getMustExist() {
-		MountPointRequirement requirement = vault.getVolume().orElseThrow(() -> new IllegalStateException("Invalid Mountpoint without a Volume?!")).getMountPointRequirement();
+	public boolean getNotExisting() {
+		return getMountPointRequirement() == MountPointRequirement.EMPTY_MOUNT_POINT;
+	}
+
+	public boolean getExisting() {
+		return getMountPointRequirement() == MountPointRequirement.PARENT_NO_MOUNT_POINT;
+	}
+
+	public boolean getDriveLetterOccupied() {
+		return getMountPointRequirement() == MountPointRequirement.NO_PARENT_NO_MOUNT_POINT;
+	}
+
+	private MountPointRequirement getMountPointRequirement() {
+		var requirement = vault.getVolume().orElseThrow(() -> new IllegalStateException("Invalid Mountpoint without a Volume?!")).getMountPointRequirement();
 		assert requirement != MountPointRequirement.NONE; //An invalid MountPoint with no required MountPoint doesn't seem sensible
 		assert requirement != MountPointRequirement.PARENT_OPT_MOUNT_POINT; //Not implemented anywhere (yet)
+		assert requirement != MountPointRequirement.NO_PARENT_NO_MOUNT_POINT || SystemUtils.IS_OS_WINDOWS; //Not implemented anywhere, but on Windows
 
-		return requirement == MountPointRequirement.EMPTY_MOUNT_POINT;
+		return requirement;
 	}
-
-}
+}

src/main/java/org/cryptomator/ui/unlock/UnlockWorkflow.java

@@ -2,6 +2,7 @@ package org.cryptomator.ui.unlock;
 
 import com.google.common.base.Throwables;
 import dagger.Lazy;
+import org.apache.commons.lang3.SystemUtils;
 import org.cryptomator.common.mountpoint.InvalidMountPointException;
 import org.cryptomator.common.vaults.MountPointRequirement;
 import org.cryptomator.common.vaults.Vault;
@@ -79,9 +80,10 @@ public class UnlockWorkflow extends Task<Boolean> {
 	}
 
 	private void handleInvalidMountPoint(InvalidMountPointException impExc) {
-		MountPointRequirement requirement = vault.getVolume().orElseThrow(() -> new IllegalStateException("Invalid Mountpoint without a Volume?!", impExc)).getMountPointRequirement();
+		var requirement = vault.getVolume().orElseThrow(() -> new IllegalStateException("Invalid Mountpoint without a Volume?!", impExc)).getMountPointRequirement();
 		assert requirement != MountPointRequirement.NONE; //An invalid MountPoint with no required MountPoint doesn't seem sensible
 		assert requirement != MountPointRequirement.PARENT_OPT_MOUNT_POINT; //Not implemented anywhere (yet)
+		assert requirement != MountPointRequirement.NO_PARENT_NO_MOUNT_POINT || SystemUtils.IS_OS_WINDOWS; //Not implemented anywhere, but on Windows
 
 		Throwable cause = impExc.getCause();
 		// TODO: apply https://openjdk.java.net/jeps/8213076 in future JDK versions
@@ -93,7 +95,11 @@ public class UnlockWorkflow extends Task<Boolean> {
 			}
 			showInvalidMountPointScene();
 		} else if (cause instanceof FileAlreadyExistsException) {
-			LOG.error("Unlock failed. Mountpoint already exists: {}", cause.getMessage());
+			if (requirement == MountPointRequirement.NO_PARENT_NO_MOUNT_POINT) {
+				LOG.error("Unlock failed. Drive Letter already occupied: {}", cause.getMessage());
+			} else {
+				LOG.error("Unlock failed. Mountpoint already exists: {}", cause.getMessage());
+			}
 			showInvalidMountPointScene();
 		} else if (cause instanceof DirectoryNotEmptyException) {
 			LOG.error("Unlock failed. Mountpoint not an empty directory: {}", cause.getMessage());

src/main/resources/fxml/unlock_invalid_mount_point.fxml

@@ -29,8 +29,9 @@
 			</StackPane>
 			<VBox spacing="6" HBox.hgrow="ALWAYS">
 				<Text text="%unlock.error.heading" styleClass="label-large"/>
-				<FormattedLabel visible="${controller.mustExist}" managed="${controller.mustExist}" format="%unlock.error.invalidMountPoint.notExisting" arg1="${controller.mountPoint}" wrapText="true"/>
-				<FormattedLabel visible="${!controller.mustExist}" managed="${!controller.mustExist}" format="%unlock.error.invalidMountPoint.existing" arg1="${controller.mountPoint}" wrapText="true"/>
+				<FormattedLabel visible="${controller.notExisting}" managed="${controller.notExisting}" format="%unlock.error.invalidMountPoint.notExisting" arg1="${controller.mountPoint}" wrapText="true"/>
+				<FormattedLabel visible="${controller.existing}" managed="${controller.existing}" format="%unlock.error.invalidMountPoint.existing" arg1="${controller.mountPoint}" wrapText="true"/>
+				<FormattedLabel visible="${controller.driveLetterOccupied}" managed="${controller.driveLetterOccupied}" format="%unlock.error.invalidMountPoint.driveLetterOccupied" arg1="${controller.mountPoint}" wrapText="true"/>
 			</VBox>
 		</HBox>
 

src/main/resources/i18n/strings.properties

@@ -115,6 +115,7 @@ unlock.error.heading=Unable to unlock vault
 ### Invalid Mount Point
 unlock.error.invalidMountPoint.notExisting=Mount point "%s" is not a directory, not empty or does not exist.
 unlock.error.invalidMountPoint.existing=Mount point "%s" already exists or parent folder is missing.
+unlock.error.invalidMountPoint.driveLetterOccupied=Drive Letter "%s" is already occupied.
 
 # Lock
 ## Force