fix(fs): better errors for unresolved selectors

Adds an appropriate error at a couple different levels. The first is in
FilesystemService. Callers of FilesystemService.node are expected to
provide either an absolute path or an instance of a filesystem node
selector, but there wasn't an explicit check for this so instead an
arbitrary error (read property of undefined) would be thrown. The second
is a higher-level APIError in the batch executor that's a bit more
helpful than a 500 Internal Server Error.

src/backend/src/api/APIError.js

@@ -283,6 +283,11 @@ module.exports = class APIError {
             status: 400,
             message: 'Invalid file metadata.',
         },
+        'unresolved_relative_path': {
+            status: 400,
+            message: ({ path }) => `Unresolved relative path: ${quot(path)}. ` +
+                    "You may need to specify a full path starting with '/'.",
+        },
 
         // Open
         'no_suitable_app': {

src/backend/src/filesystem/FilesystemService.js

@@ -19,7 +19,7 @@
 // TODO: database access can be a service
 const { RESOURCE_STATUS_PENDING_CREATE } = require('../modules/puterfs/ResourceService.js');
 const { TraceService } = require('../services/TraceService.js');
-const { NodePathSelector, NodeUIDSelector, NodeInternalIDSelector } = require('./node/selectors.js');
+const { NodePathSelector, NodeUIDSelector, NodeInternalIDSelector, NodeSelector } = require('./node/selectors.js');
 const FSNodeContext = require('./FSNodeContext.js');
 const { Context } = require('../util/context.js');
 const APIError = require('../api/APIError.js');
@@ -29,6 +29,8 @@ const { UserActorType } = require('../services/auth/Actor');
 const { get_user } = require('../helpers');
 const BaseService = require('../services/BaseService');
 const { MANAGE_PERM_PREFIX } = require('../services/auth/permissionConts.mjs');
+const { PuterFSProvider } = require('../modules/puterfs/lib/PuterFSProvider.js');
+const { quot } = require('@heyputer/putility/src/libs/string.js');
 
 class FilesystemService extends BaseService {
     static MODULES = {
@@ -329,6 +331,14 @@ class FilesystemService extends BaseService {
                 selector = new NodeInternalIDSelector('mysql', selector.mysql_id);
             }
         }
+        
+        if ( ! (selector instanceof NodeSelector) ) {
+            throw new Error(
+                'FileSystemService could not resolve the specified node value ' +
+                quot(''+selector) + ` (type: ${typeof selector}) ` +
+                'to a filesystem node selector',
+            );
+        }
 
         system_dir_check: {
             if ( ! (selector instanceof NodePathSelector) ) break system_dir_check;

src/backend/src/filesystem/node/selectors.js

@@ -19,8 +19,22 @@
 const _path = require('path');
 const { PuterPath } = require('../lib/PuterPath');
 
-class NodePathSelector {
+/**
+ * The base class doesn't add any functionality, but it's useful for
+ * `instanceof` checks.
+ */
+class NodeSelector {
+    constructor () {
+        if ( this.constructor === NodeSelector ) {
+            throw new Error('cannot instantiate NodeSelector directly; ' +
+                'that would be like using this: https://devmeme.puter.site/plug.webp');
+        }
+    }
+}
+
+class NodePathSelector extends NodeSelector {
     constructor (path) {
+        super();
         this.value = path;
     }
 
@@ -34,8 +48,9 @@ class NodePathSelector {
     }
 }
 
-class NodeUIDSelector {
+class NodeUIDSelector extends NodeSelector {
     constructor (uid) {
+        super();
         this.value = uid;
     }
 
@@ -58,8 +73,9 @@ class NodeUIDSelector {
     }
 }
 
-class NodeInternalIDSelector {
+class NodeInternalIDSelector extends NodeSelector {
     constructor (service, id, debugInfo) {
+    super();
         this.service = service;
         this.id = id;
         this.debugInfo = debugInfo;
@@ -81,8 +97,9 @@ class NodeInternalIDSelector {
     }
 }
 
-class NodeChildSelector {
+class NodeChildSelector extends NodeSelector {
     constructor (parent, name) {
+        super();
         this.parent = parent;
         this.name = name;
     }
@@ -101,7 +118,7 @@ class NodeChildSelector {
     }
 }
 
-class RootNodeSelector {
+class RootNodeSelector extends NodeSelector {
     static entry = {
         is_dir: true,
         is_root: true,
@@ -114,6 +131,7 @@ class RootNodeSelector {
         node.uid = PuterPath.NULL_UUID;
     }
     constructor () {
+        super();
         this.entry = this.constructor.entry;
     }
 
@@ -122,8 +140,9 @@ class RootNodeSelector {
     }
 }
 
-class NodeRawEntrySelector {
+class NodeRawEntrySelector extends NodeSelector {
     constructor (entry) {
+        super();
         // Fix entries from get_descendants
         if ( ! entry.uuid && entry.uid ) {
             entry.uuid = entry.uid;
@@ -190,6 +209,7 @@ const relativeSelector = (parent, path) => {
 }
 
 module.exports = {
+    NodeSelector,
     NodePathSelector,
     NodeUIDSelector,
     NodeInternalIDSelector,

src/backend/src/routers/filesystem_api/batch/PathResolver.js

@@ -96,6 +96,9 @@ module.exports = class PathResolver {
         if ( inputPath === '~' ) {
             return `/${username}`;
         }
+        if ( inputPath.startsWith('.') ) {
+            throw APIError.create('unresolved_relative_path', null, { path: inputPath });
+        }
         const refName = this.getReferenceUsed(inputPath);
         if ( refName === null ) return inputPath;