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path: strip extended-length path prefix in C++ PathResolve and JS win32.resolve #2

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Merged
jazelly merged 1 commit into from
Apr 1, 2026
Merged

path: strip extended-length path prefix in C++ PathResolve and JS win32.resolve #2

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68 changes: 0 additions & 68 deletions lib/fs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -132,14 +132,6 @@ const {
const {
CHAR_FORWARD_SLASH,
CHAR_BACKWARD_SLASH,
CHAR_COLON,
CHAR_QUESTION_MARK,
CHAR_UPPERCASE_A,
CHAR_UPPERCASE_C,
CHAR_UPPERCASE_Z,
CHAR_LOWERCASE_A,
CHAR_LOWERCASE_N,
CHAR_LOWERCASE_Z,
} = require('internal/constants');
const {
isInt32,
Expand Down Expand Up @@ -2636,43 +2628,6 @@ function unwatchFile(filename, listener) {
}


// Strips the Windows extended-length path prefix (\\?\) from a resolved path.
// Extended-length paths (\\?\C:\... or \\?\UNC\...) are a Win32 API mechanism
// to bypass MAX_PATH limits. Node.js should handle them transparently by
// converting to standard paths for internal processing. The \\?\ prefix is
// re-added when needed via path.toNamespacedPath() before system calls.
// See: https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file
function stripExtendedPathPrefix(p) {
// Check for \\?\ prefix
if (p.length >= 4 &&
StringPrototypeCharCodeAt(p, 0) === CHAR_BACKWARD_SLASH &&
StringPrototypeCharCodeAt(p, 1) === CHAR_BACKWARD_SLASH &&
StringPrototypeCharCodeAt(p, 2) === CHAR_QUESTION_MARK &&
StringPrototypeCharCodeAt(p, 3) === CHAR_BACKWARD_SLASH) {
// \\?\C:\ -> C:\ (extended drive path)
if (p.length >= 6) {
const drive = StringPrototypeCharCodeAt(p, 4);
if (((drive >= CHAR_UPPERCASE_A && drive <= CHAR_UPPERCASE_Z) ||
(drive >= CHAR_LOWERCASE_A && drive <= CHAR_LOWERCASE_Z)) &&
StringPrototypeCharCodeAt(p, 5) === CHAR_COLON) {
return StringPrototypeSlice(p, 4);
}
}
// \\?\UNC\server\share -> \\server\share (extended UNC path)
if (p.length >= 8 &&
(StringPrototypeCharCodeAt(p, 4) === 85 /* U */ ||
StringPrototypeCharCodeAt(p, 4) === 117 /* u */) &&
(StringPrototypeCharCodeAt(p, 5) === 78 /* N */ ||
StringPrototypeCharCodeAt(p, 5) === CHAR_LOWERCASE_N) &&
(StringPrototypeCharCodeAt(p, 6) === CHAR_UPPERCASE_C ||
StringPrototypeCharCodeAt(p, 6) === 99 /* c */) &&
StringPrototypeCharCodeAt(p, 7) === CHAR_BACKWARD_SLASH) {
return '\\\\' + StringPrototypeSlice(p, 8);
}
}
return p;
}

let splitRoot;
if (isWindows) {
// Regex to find the device root on Windows (e.g. 'c:\\'), including trailing
Expand Down Expand Up @@ -2735,12 +2690,6 @@ function realpathSync(p, options) {
validatePath(p);
p = pathModule.resolve(p);

// On Windows, strip the extended-length path prefix (\\?\) so that the
// path walking logic below works with standard drive-letter or UNC roots.
if (isWindows) {
p = stripExtendedPathPrefix(p);
}

const cache = options[realpathCacheKey];
const maybeCachedResult = cache?.get(p);
if (maybeCachedResult) {
Expand Down Expand Up @@ -2844,11 +2793,6 @@ function realpathSync(p, options) {
// Resolve the link, then start over
p = pathModule.resolve(resolvedLink, StringPrototypeSlice(p, pos));

// Strip extended path prefix again in case pathModule.resolve re-added it
if (isWindows) {
p = stripExtendedPathPrefix(p);
}

// Skip over roots
current = base = splitRoot(p);
pos = current.length;
Expand Down Expand Up @@ -2907,12 +2851,6 @@ function realpath(p, options, callback) {
validatePath(p);
p = pathModule.resolve(p);

// On Windows, strip the extended-length path prefix (\\?\) so that the
// path walking logic below works with standard drive-letter or UNC roots.
if (isWindows) {
p = stripExtendedPathPrefix(p);
}

const seenLinks = new SafeMap();
const knownHard = new SafeSet();

Expand Down Expand Up @@ -3013,12 +2951,6 @@ function realpath(p, options, callback) {
function gotResolvedLink(resolvedLink) {
// Resolve the link, then start over
p = pathModule.resolve(resolvedLink, StringPrototypeSlice(p, pos));

// Strip extended path prefix again in case pathModule.resolve re-added it
if (isWindows) {
p = stripExtendedPathPrefix(p);
}

current = base = splitRoot(p);
pos = current.length;

Expand Down
28 changes: 27 additions & 1 deletion lib/path.js
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Original file line number Diff line number Diff line change
Expand Up @@ -230,10 +230,36 @@ const win32 = {
}
}

const len = path.length;
let rootEnd = 0;
let device = '';
let isAbsolute = false;

// Strip extended-length path prefix (\\?\C:\... -> C:\...,
// \\?\UNC\... -> \\...) before processing.
if (path.length >= 6 &&
StringPrototypeCharCodeAt(path, 0) === CHAR_BACKWARD_SLASH &&
StringPrototypeCharCodeAt(path, 1) === CHAR_BACKWARD_SLASH &&
StringPrototypeCharCodeAt(path, 2) === CHAR_QUESTION_MARK &&
StringPrototypeCharCodeAt(path, 3) === CHAR_BACKWARD_SLASH) {
const drive = StringPrototypeCharCodeAt(path, 4);
if (isWindowsDeviceRoot(drive) &&
StringPrototypeCharCodeAt(path, 5) === CHAR_COLON) {
// \\?\C:\ -> C:\
path = StringPrototypeSlice(path, 4);
} else if (path.length >= 8 &&
(drive === 85 || drive === 117) && // U/u
(StringPrototypeCharCodeAt(path, 5) === 78 ||
StringPrototypeCharCodeAt(path, 5) === 110) && // N/n
(StringPrototypeCharCodeAt(path, 6) === 67 ||
StringPrototypeCharCodeAt(path, 6) === 99) && // C/c
StringPrototypeCharCodeAt(path, 7) ===
CHAR_BACKWARD_SLASH) {
// \\?\UNC\server\share -> \\server\share
path = `\\\\${StringPrototypeSlice(path, 8)}`;
}
}

const len = path.length;
const code = StringPrototypeCharCodeAt(path, 0);

// Try to match a root
Expand Down
26 changes: 26 additions & 0 deletions src/path.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,28 @@ constexpr bool IsWindowsDeviceRoot(const char c) noexcept {
return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

// Strip Windows extended-length path prefix (\\?\) only when it wraps a
// drive letter path (\\?\C:\...) or a UNC path (\\?\UNC\...).
// Device paths like \\?\PHYSICALDRIVE0 are left unchanged.
// See: https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file
static void StripExtendedPathPrefix(std::string& path) {
if (path.size() >= 4 && path[0] == '\\' && path[1] == '\\' &&
path[2] == '?' && path[3] == '\\') {
// \\?\C:\ -> C:\ (extended drive path)
if (path.size() >= 6 && IsWindowsDeviceRoot(path[4]) && path[5] == ':') {
path = path.substr(4);
return;
}
// \\?\UNC\server\share -> \\server\share (extended UNC path)
if (path.size() >= 8 && ToLower(path[4]) == 'u' &&
ToLower(path[5]) == 'n' && ToLower(path[6]) == 'c' &&
path[7] == '\\') {
path = "\\\\" + path.substr(8);
return;
}
}
}

std::string PathResolve(Environment* env,
const std::vector<std::string_view>& paths) {
std::string resolvedDevice = "";
Expand Down Expand Up @@ -132,6 +154,10 @@ std::string PathResolve(Environment* env,
}
}

// Strip extended-length path prefix (\\?\C:\... -> C:\...,
// \\?\UNC\... -> \\...) before processing.
StripExtendedPathPrefix(path);

const size_t len = path.length();
int rootEnd = 0;
std::string device = "";
Expand Down
8 changes: 8 additions & 0 deletions test/cctest/test_path.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,14 @@ TEST_F(PathTest, PathResolve) {
"\\\\.\\PHYSICALDRIVE0");
EXPECT_EQ(PathResolve(*env, {"\\\\?\\PHYSICALDRIVE0"}),
"\\\\?\\PHYSICALDRIVE0");
// Extended-length path prefix (\\?\) should be stripped for drive paths
EXPECT_EQ(PathResolve(*env, {"\\\\?\\C:\\foo"}), "C:\\foo");
EXPECT_EQ(PathResolve(*env, {"\\\\?\\C:\\"}), "C:\\");
// Extended-length UNC path prefix (\\?\UNC\) should be stripped
EXPECT_EQ(PathResolve(*env, {"\\\\?\\UNC\\server\\share"}),
"\\\\server\\share\\");
EXPECT_EQ(PathResolve(*env, {"\\\\?\\UNC\\server\\share\\dir"}),
"\\\\server\\share\\dir");
#else
EXPECT_EQ(PathResolve(*env, {"/var/lib", "../", "file/"}), "/var/file");
EXPECT_EQ(PathResolve(*env, {"/var/lib", "/../", "file/"}), "/file");
Expand Down
55 changes: 0 additions & 55 deletions test/parallel/test-fs-realpath-extended-windows-path.js
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6 changes: 6 additions & 0 deletions test/parallel/test-path-resolve.js
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,12 @@ const resolveTests = [
'C:\\foo\\tmp.3\\cycles\\root.js'],
[['\\\\.\\PHYSICALDRIVE0'], '\\\\.\\PHYSICALDRIVE0'],
[['\\\\?\\PHYSICALDRIVE0'], '\\\\?\\PHYSICALDRIVE0'],
// Extended-length path prefix (\\?\) should be stripped for drive paths
[['\\\\?\\C:\\foo'], 'C:\\foo'],
[['\\\\?\\C:\\'], 'C:\\'],
// Extended-length UNC path prefix (\\?\UNC\) should be stripped
[['\\\\?\\UNC\\server\\share'], '\\\\server\\share\\'],
[['\\\\?\\UNC\\server\\share\\dir'], '\\\\server\\share\\dir'],
],
],
[ path.posix.resolve,
Expand Down
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