fix - ECONNRESET in datasocket unnecessarily closes the controlsocket

package.json

@@ -15,6 +15,7 @@
     "lint-fix": "eslint --fix \"./src/**/*.ts\"",
     "dev": "npm run clean && tsc --watch",
     "tdd": "mocha --watch",
+    "prepare": "tsc",
     "buildOnly": "tsc"
   },
   "repository": {

src/FtpContext.ts

@@ -1,7 +1,7 @@
 import { Socket } from "net"
 import { ConnectionOptions as TLSConnectionOptions, TLSSocket } from "tls"
-import { parseControlResponse } from "./parseControlResponse"
 import { StringEncoding } from "./StringEncoding"
+import { parseControlResponse } from "./parseControlResponse"
 
 interface Task {
     /** Handles a response for a task. */
@@ -361,16 +361,33 @@ export class FTPContext {
     protected _setupDefaultErrorHandlers(socket: Socket, identifier: string) {
         socket.once("error", error => {
             error.message += ` (${identifier})`
-            this.closeWithError(error)
+            if(identifier == "control socket") {
+                this.closeWithError(error)
+            } else {
+                //only close data socket, not the control socket as well
+                this._closeSocket(socket)
+                this._passToHandler(error)
+            }
         })
         socket.once("close", hadError => {
             if (hadError) {
-                this.closeWithError(new Error(`Socket closed due to transmission error (${identifier})`))
+                if(identifier == "control socket") {
+                    this.closeWithError(new Error(`Socket closed due to transmission error (${identifier})`))
+                } else {
+                    //only close data socket, not the control socket as well
+                    this._closeSocket(socket)
+                    this._passToHandler(new Error(`Socket closed due to transmission error (${identifier})`))
+                }
             }
         })
         socket.once("timeout", () => {
             socket.destroy()
-            this.closeWithError(new Error(`Timeout (${identifier})`))
+            if(identifier == "control socket") {
+                this.closeWithError(new Error(`Timeout (${identifier})`)) 
+            } else {
+                this._closeSocket(socket)
+                this._passToHandler(new Error(`Timeout (${identifier})`))
+            }
         })
     }
 

test/MockFtpServer.js

@@ -39,6 +39,15 @@ module.exports = class MockFtpServer {
         })
         this.dataConn = undefined
         this.dataServer = net.createServer(conn => {
+            if(!conn.resetAndDestroy) {
+                conn.resetAndDestroy = () => {
+                    conn._handle.reset(() => {
+                        this.conn.emit("close")
+                    })
+                    conn._handle.onread = () =>{};
+                    conn._handle = null;
+                }
+            }
             this.dataConn = conn
             this.connections.push(conn)
             this.didOpenDataConn()

test/downloadSpec.js

@@ -4,6 +4,7 @@ const { StringWriter } = require("../dist/StringWriter");
 const MockFtpServer = require("./MockFtpServer");
 const { Writable } = require("stream")
 const fs = require("fs");
+const { Socket } = require("net");
 
 const FILENAME = "file.txt"
 const TIMEOUT = 1000
@@ -146,6 +147,28 @@ describe("Download to stream", function() {
         await this.client.downloadTo(buf, FILENAME)
         dataSocket.destroy(new Error("Error that should be ignored because task has completed successfully"))
     })
+    it("handles early data socket closure", async () => {
+        /**
+         * type of this.client
+         * @type {Client}
+         */
+        this.client;
+
+        this.server.addHandlers({
+            "pasv": () => `227 Entering Passive Mode (${this.server.dataAddressForPasvResponse})`,
+            "retr": ({arg})  => {
+                //close data connection such that client receives ECONNRESET
+                this.server.dataConn.resetAndDestroy()
+
+                return `550 ${arg}: No such file or directory.`
+            }
+        })
+
+        const buf = new StringWriter()
+        await this.client.downloadTo(buf, FILENAME).catch(err => {})
+        //control socket should still be open
+        assert(this.client.ftp.socket?.writable)
+    })
 
     it("stops tracking timeout after failure")
     it("can get a directory listing")