lib: add UNC support to url.pathToFileURL()

Fixes: https://github.com/nodejs/node/issues/34736

PR-URL: https://github.com/nodejs/node/pull/34743
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/internal/url.js

@@ -27,6 +27,7 @@ const { getConstructorOf, removeColors } = require('internal/util');
 const {
   ERR_ARG_NOT_ITERABLE,
   ERR_INVALID_ARG_TYPE,
+  ERR_INVALID_ARG_VALUE,
   ERR_INVALID_CALLBACK,
   ERR_INVALID_FILE_URL_HOST,
   ERR_INVALID_FILE_URL_PATH,
@@ -1365,27 +1366,54 @@ const backslashRegEx = /\\/g;
 const newlineRegEx = /\n/g;
 const carriageReturnRegEx = /\r/g;
 const tabRegEx = /\t/g;
+
+function encodePathChars(filepath) {
+  if (filepath.includes('%'))
+    filepath = filepath.replace(percentRegEx, '%25');
+  // In posix, backslash is a valid character in paths:
+  if (!isWindows && filepath.includes('\\'))
+    filepath = filepath.replace(backslashRegEx, '%5C');
+  if (filepath.includes('\n'))
+    filepath = filepath.replace(newlineRegEx, '%0A');
+  if (filepath.includes('\r'))
+    filepath = filepath.replace(carriageReturnRegEx, '%0D');
+  if (filepath.includes('\t'))
+    filepath = filepath.replace(tabRegEx, '%09');
+  return filepath;
+}
+
 function pathToFileURL(filepath) {
-  let resolved = path.resolve(filepath);
-  // path.resolve strips trailing slashes so we must add them back
-  const filePathLast = filepath.charCodeAt(filepath.length - 1);
-  if ((filePathLast === CHAR_FORWARD_SLASH ||
-       (isWindows && filePathLast === CHAR_BACKWARD_SLASH)) &&
-      resolved[resolved.length - 1] !== path.sep)
-    resolved += '/';
   const outURL = new URL('file://');
-  if (resolved.includes('%'))
-    resolved = resolved.replace(percentRegEx, '%25');
-  // In posix, "/" is a valid character in paths
-  if (!isWindows && resolved.includes('\\'))
-    resolved = resolved.replace(backslashRegEx, '%5C');
-  if (resolved.includes('\n'))
-    resolved = resolved.replace(newlineRegEx, '%0A');
-  if (resolved.includes('\r'))
-    resolved = resolved.replace(carriageReturnRegEx, '%0D');
-  if (resolved.includes('\t'))
-    resolved = resolved.replace(tabRegEx, '%09');
-  outURL.pathname = resolved;
+  if (isWindows && filepath.startsWith('\\\\')) {
+    // UNC path format: \\server\share\resource
+    const paths = filepath.split('\\');
+    if (paths.length <= 3) {
+      throw new ERR_INVALID_ARG_VALUE(
+        'filepath',
+        filepath,
+        'Missing UNC resource path'
+      );
+    }
+    const hostname = paths[2];
+    if (hostname.length === 0) {
+      throw new ERR_INVALID_ARG_VALUE(
+        'filepath',
+        filepath,
+        'Empty UNC servername'
+      );
+    }
+    outURL.hostname = domainToASCII(hostname);
+    outURL.pathname = encodePathChars(paths.slice(3).join('/'));
+  } else {
+    let resolved = path.resolve(filepath);
+    // path.resolve strips trailing slashes so we must add them back
+    const filePathLast = filepath.charCodeAt(filepath.length - 1);
+    if ((filePathLast === CHAR_FORWARD_SLASH ||
+         (isWindows && filePathLast === CHAR_BACKWARD_SLASH)) &&
+        resolved[resolved.length - 1] !== path.sep)
+      resolved += '/';
+    outURL.pathname = encodePathChars(resolved);
+  }
   return outURL;
 }
 

test/parallel/test-url-fileurltopath.js

@@ -94,7 +94,9 @@ assert.throws(() => url.fileURLToPath('https://a/b/c'), {
       // Euro sign (BMP code point)
       { path: 'C:\\€', fileURL: 'file:///C:/%E2%82%AC' },
       // Rocket emoji (non-BMP code point)
-      { path: 'C:\\🚀', fileURL: 'file:///C:/%F0%9F%9A%80' }
+      { path: 'C:\\🚀', fileURL: 'file:///C:/%F0%9F%9A%80' },
+      // UNC path (see https://docs.microsoft.com/en-us/archive/blogs/ie/file-uris-in-windows)
+      { path: '\\\\nas\\My Docs\\File.doc', fileURL: 'file://nas/My%20Docs/File.doc' },
     ];
   } else {
     testCases = [

test/parallel/test-url-pathtofileurl.js

@@ -23,6 +23,26 @@ const url = require('url');
   assert.ok(fileURL.includes('%25'));
 }
 
+{
+  if (isWindows) {
+    // UNC path: \\server\share\resource
+
+    // Missing server:
+    assert.throws(() => url.pathToFileURL('\\\\\\no-server'), {
+      code: 'ERR_INVALID_ARG_VALUE'
+    });
+
+    // Missing share or resource:
+    assert.throws(() => url.pathToFileURL('\\\\host'), {
+      code: 'ERR_INVALID_ARG_VALUE'
+    });
+  } else {
+    // UNC paths on posix are considered a single path that has backslashes:
+    const fileURL = url.pathToFileURL('\\\\nas\\share\\path.txt').href;
+    assert.match(fileURL, /file:\/\/.+%5C%5Cnas%5Cshare%5Cpath\.txt$/);
+  }
+}
+
 {
   let testCases;
   if (isWindows) {
@@ -68,7 +88,9 @@ const url = require('url');
       // Euro sign (BMP code point)
       { path: 'C:\\€', expected: 'file:///C:/%E2%82%AC' },
       // Rocket emoji (non-BMP code point)
-      { path: 'C:\\🚀', expected: 'file:///C:/%F0%9F%9A%80' }
+      { path: 'C:\\🚀', expected: 'file:///C:/%F0%9F%9A%80' },
+      // UNC path (see https://docs.microsoft.com/en-us/archive/blogs/ie/file-uris-in-windows)
+      { path: '\\\\nas\\My Docs\\File.doc', expected: 'file://nas/My%20Docs/File.doc' }
     ];
   } else {
     testCases = [