Handle CHANNEL_EOF messages explicitly

There is an open PR in the upstream / ssh2 library related to properly
closing SFTP channels when a `CHANNEL_EOF` message is received[1].
Unfortunately that PR has not yet been merged.

Until that happens we need to handle the signal ourselves.
Unfortunately this requires us to access "private" attributes
(JavaScript doesn't support the concept of private attributes, so we are
able to do this...). This is, of course a terrible and horrible idea and
all of our tooling gets very upset about it.  As a result I had to
disable the tooling for the relevant line.

Once the PR is merged in upstream we should upgrade to it and delete the
contents of this commit.

Issue #45 rclone hangs after completion

[1] mscdex/ssh2#1111

src/classes/SshConnectionHandler.ts

@@ -105,9 +105,13 @@ export class SshConnectionHandler {
   ): void => {
     logger.verbose('SSH request for a new session');
     const session = accept();
-    const sessionHandler = new SshSessionHandler(this.authSession?.authToken ?? '');
+    const sessionHandler = new SshSessionHandler(
+      session,
+      this.authSession?.authToken ?? '',
+    );
     session.on('sftp', sessionHandler.onSftp);
     session.on('close', sessionHandler.onClose);
+    session.on('eof', sessionHandler.onEof);
   };
 
   /**

src/classes/SshSessionHandler.ts

@@ -1,11 +1,20 @@
 import { logger } from '../logger';
 import { SftpSessionHandler } from './SftpSessionHandler';
-import type { SFTPWrapper } from 'ssh2';
+import type {
+  Session,
+  SFTPWrapper,
+} from 'ssh2';
 
 export class SshSessionHandler {
   private readonly authToken: string;
 
-  public constructor(authToken: string) {
+  private readonly session: Session;
+
+  public constructor(
+    session: Session,
+    authToken: string,
+  ) {
+    this.session = session;
     this.authToken = authToken;
   }
 
@@ -50,4 +59,20 @@ export class SshSessionHandler {
   public onClose = (): void => {
     logger.verbose('SSH session closed');
   };
+
+  public onEof = (): void => {
+    // This addresses a bug in the ssh2 library where EOF is not properly
+    // handled for sftp connections.
+    // An upstream PR that would fix the behavior: https://github.com/mscdex/ssh2/pull/1111
+    // And some context from our own debugging: https://github.com/PermanentOrg/sftp-service/issues/45
+    //
+    // The solution here is not ideal, as it is accessing an undocumented attribute that
+    // doesn't exist in TypeScript.  As a result I need to disable typescript checks.
+    //
+    // Once upstream makes that patch this entire handler should become completely unnecessary
+    //
+    // !!BEWARE: THERE BE DRAGONS HERE!!
+    // @ts-expect-error because `_channel` is private / isn't actually documented.
+    this.session._channel.end(); // eslint-disable-line max-len, no-underscore-dangle, @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-member-access
+  };
 }