From cb485f49285f7bcf857d02e343b4823adaa9b350 Mon Sep 17 00:00:00 2001
From: Alexander Vega <alxvj2@gmail.com>
Date: Sun, 20 Nov 2022 20:06:32 +0000
Subject: [PATCH 1/2] copyFilesSync from one file system to another

---
 src/__tests__/union.test.ts | 18 ++++++++++++++++++
 src/fs.ts                   |  1 +
 src/union.ts                | 31 +++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/src/__tests__/union.test.ts b/src/__tests__/union.test.ts
index dd8efa84..06f3c265 100644
--- a/src/__tests__/union.test.ts
+++ b/src/__tests__/union.test.ts
@@ -183,6 +183,24 @@ describe('union', () => {
           expect(() => ufs.readdirSync('/bar')).toThrow();
         });
       });
+
+      describe('copyFileSync()', () => {
+        it('can copy from one filesystem to another', async () => {
+          const vol1 = Volume.fromJSON({
+            '/foo/bar': 'bar',
+          });
+          const vol2 = Volume.fromJSON({
+            '/bar/baz': 'baz',
+          });
+
+          const ufs = new Union();
+          ufs.use(vol1 as any).use(vol2 as any);
+
+          ufs.copyFileSync('/foo/bar', '/bar/barCopy');
+          expect(vol2.readFileSync('/bar/barCopy').toString()).toEqual('bar');
+          expect(vol1.existsSync('/bar/barCopy')).toBeFalsy();
+        });
+      });
     });
     describe('async methods', () => {
       it('Basic one file system', done => {
diff --git a/src/fs.ts b/src/fs.ts
index efd71f3f..62e0c390 100644
--- a/src/fs.ts
+++ b/src/fs.ts
@@ -32,6 +32,7 @@ type FSMethods =
   | 'readFileSync'
   | 'writeFileSync'
   | 'appendFileSync'
+  | 'copyFileSync'
   | 'existsSync'
   | 'accessSync'
   | 'createReadStream'
diff --git a/src/union.ts b/src/union.ts
index 94183001..ab730acc 100644
--- a/src/union.ts
+++ b/src/union.ts
@@ -1,6 +1,8 @@
 import { FSWatcher, Dirent } from 'fs';
 import { IFS } from './fs';
 import { Readable, Writable } from 'stream';
+import { dirname } from 'path';
+import { ENOENT } from 'constants';
 const { fsAsyncMethods, fsSyncMethods } = require('fs-monkey/lib/util/lists');
 
 export interface IUnionFsError extends Error {
@@ -13,6 +15,7 @@ const SPECIAL_METHODS = new Set([
   'existsSync',
   'readdir',
   'readdirSync',
+  'copyFileSync',
   'createReadStream',
   'createWriteStream',
   'watch',
@@ -245,6 +248,34 @@ export class Union {
     return this.sortedArrayFromReaddirResult(result);
   };
 
+  public copyFileSync(src: string, dest: string, flags?: number) {
+    const destDir = dirname(dest);
+
+    // CASE 1: dest is a filename. Don't treat, standard copy (opinionated)
+    if (destDir.length == 0) {
+      return this.syncMethod('copyFileSync', [src, dest, flags]);
+    }
+
+    // CASE 2: src doesn't exist in any fs.
+    const srcFS = this.fss.find(fs => fs.existsSync(src));
+    if (!srcFS) {
+      const error = new Error(`no such source file: ${src}`) as NodeJS.ErrnoException;
+      error.errno = ENOENT;
+      throw error;
+    }
+
+    // CASE 3: dest dir does not exist or is in the same fs.
+    // To protect ourselves, simply launch standard copy, whatever the policies
+    // about destination dir doesn't exist.
+    const destFS = this.fss.find(fs => fs.existsSync(destDir));
+    if (!destFS || srcFS == destFS) {
+      return this.syncMethod('copyFileSync', [src, dest, flags]);
+    }
+
+    // CASE 4: different FS. Workaround: read src, write dest.
+    destFS.writeFileSync(dest, srcFS.readFileSync(src));
+  }
+
   public readdirPromise = async (...args): Promise<Array<readdirEntry>> => {
     let lastError: IUnionFsError | null = null;
     let result = new Map<string, readdirEntry>();

From 52b6e5d23fb8db5a2880078bb2e652208161abc5 Mon Sep 17 00:00:00 2001
From: Alexander Vega <alxvj2@gmail.com>
Date: Mon, 21 Nov 2022 16:29:39 +0000
Subject: [PATCH 2/2] Added try-catch to copyFileSync fs finding

---
 src/union.ts | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/union.ts b/src/union.ts
index ab730acc..32d57e16 100644
--- a/src/union.ts
+++ b/src/union.ts
@@ -257,7 +257,11 @@ export class Union {
     }
 
     // CASE 2: src doesn't exist in any fs.
-    const srcFS = this.fss.find(fs => fs.existsSync(src));
+    const srcFS = this.fss.find(fs => {
+      try { return fs.existsSync(src) }
+      catch (error) { return false }; 
+    })
+
     if (!srcFS) {
       const error = new Error(`no such source file: ${src}`) as NodeJS.ErrnoException;
       error.errno = ENOENT;
@@ -267,7 +271,11 @@ export class Union {
     // CASE 3: dest dir does not exist or is in the same fs.
     // To protect ourselves, simply launch standard copy, whatever the policies
     // about destination dir doesn't exist.
-    const destFS = this.fss.find(fs => fs.existsSync(destDir));
+    const destFS = this.fss.find(fs => {
+      try { return fs.existsSync(destDir) }
+      catch (error) { return false };
+    });
+    
     if (!destFS || srcFS == destFS) {
       return this.syncMethod('copyFileSync', [src, dest, flags]);
     }